PCB board rigid circuit board
Rigid circuit board
PCB (Printed Circuit Board), the Chinese name for printed circuit boards, also known as printed circuit boards, is an important electronic component, a support for electronic components, and a carrier for electrical connection of electronic components. Because it is made by electronic printing, it is called a "printing" circuit board.
table of Contents
1 raw materials
2 polychlorinated biphenyls
3 printed circuit boards
4 industry trends
From the beginning of the 20th century to the end of the 1940s, it was the burgeoning stage of the development of the PCB substrate material industry. Its development characteristics are mainly manifested in: the resin, reinforcing materials and insulating substrates used for the substrate materials in this period have emerged in large quantities, and the technology has been initially explored. These have created the necessary conditions for the advent and development of the most typical substrate material for printed circuit boards, the copper clad laminate. On the other hand, the PCB manufacturing technology in which the circuit is the mainstream by the metal foil etching method (reduction method) has been initially established and developed. It plays a decisive role in determining the structural composition and characteristic conditions of the copper clad laminate.
PCB polychlorinated biphenyl is a synthetic organic compound used commercially in North America from 1929 until the late 1970s. Although it has not been processed in Canada, it has been widely used in electrical equipment insulation, heat exchangers, Water system and other special applications.
After decades, people realized the pollution of PCBs to the global environment. It is a mixture of various chlorinated biphenyls, which is extremely harmful to the human body. The Canadian government has taken steps to eliminate PCBs, but illegally imported, processed and sold PCBs in Canada in 1977, and illegally released PCBs into the natural environment in 1985, while the Canadian Constitution allowed PCB equipment owners to continue to use them. PCB until the life of the device. Since 1988, provincial governments in Canada have begun to regulate the storage, transportation and destruction of PCBs.
PCBs are not easily decomposed in the natural environment, and they travel very far. PCBs enter the air, soil and rivers and oceans during production, processing, use, transportation and waste disposal. Small marine organisms and fish inhale PCBs into the body. They become food for large marine life, so that the PCB enters the body of all marine life, including mammalian marine life. The accumulation of PCB in marine organisms far exceeds its content in water, almost a few thousand times the number.
Printed circuit board
After the electronic equipment adopts the printed board, due to the consistency of the same printed board, the manual wiring is avoided, and the electronic components can be automatically inserted or mounted, automatically soldered, and automatically detected to ensure the quality of the electronic equipment. Increase labor productivity, reduce costs, and facilitate maintenance.
Printed boards have evolved from single layers to double-sided, multi-layer and flexible, and still maintain their respective trends. Due to the continuous development of high precision, high density and high reliability, the volume is reduced, the cost is reduced, and the performance is improved, so that the printed board still maintains a strong vitality in the development of electronic equipment in the future.
The domestic and international discussion on the future development trend of printed board manufacturing technology is basically the same, that is, high density, high precision, fine aperture, fine wire, fine pitch, high reliability, multi-layer, high-speed transmission, lightweight, The development of thin-type direction, in the production at the same time to improve productivity, reduce costs, reduce pollution, adapt to the development of multi-variety, small-volume production. The technical development level of printed circuits is generally represented by the line width, aperture, and plate thickness/aperture ratio on the printed board.
The creator of the printed circuit board was the Austrian Paul Eisler. In 1936, he first used a printed circuit board on the radio. In 1943, Americans used the technology for military radio. In 1948, the United States officially recognized the invention for commercial use. Since the mid-1950s, printed circuit boards have been widely used.
Prior to the advent of the PCB, the interconnection between the electronic components was done by direct connection of the wires. Today, circuit boards exist only in laboratory applications; printed circuit boards are definitely in an absolute control position in the electronics industry.
1. The overall development of China's PCB industry is rapid
Since the reform and opening up, China has attracted large-scale transfer of manufacturing industries in Europe and the United States due to preferential policies in labor resources, markets, and investment. A large number of electronic products and manufacturers have set up factories in China, and this has led to the inclusion of PCBs. The development of related industries within. According to China's CPCA statistics, in 2006 China's actual PCB production reached 130 million square meters, with an output value of US$12.1 billion, accounting for 24.90% of the global PCB output value, surpassing Japan to become the world's number one. From 2000 to 2006, China's PCB market grew at an average annual rate of 20%, far exceeding the global average. The global financial crisis in 2008 caused a huge impact on the PCB industry, but it did not cause a catastrophic impact on China's PCB industry. Under the stimulus of national economic policies, China's PCB industry experienced a full recovery in 2010. In 2010, China's PCB output value reached US$19.071 billion. . Prismark predicts that China will maintain a compound annual growth rate of 8.10% between 2010 and 2015, which is higher than the global average growth rate of 5.40%.
2. Uneven distribution of industrial areas
China's PCB industry is mainly distributed in South China and East China, and the two add up to 90% of the country, and the industrial clustering effect is obvious. This phenomenon is mainly related to the main production bases of China's electronics industry, which are concentrated in the Pearl River Delta and the Yangtze River Delta.
3. Distribution of downstream applications in China's PCB industry
The downstream application distribution of China's PCB industry is shown in the following figure. Consumer electronics accounted for the highest proportion, reaching 39%; followed by computers, accounting for 22%; communications accounting for 14%; industrial control/medical instruments accounting for 14%; automotive electronics accounting for 6%; and defense and aerospace accounting for 5%.
4. Technology development lags behind the world's advanced level
Although China is already the world's number one in terms of industry scale, it still lags behind the world's advanced level in terms of the overall technical level of the PCB industry. In terms of product structure, multi-layer boards occupy most of the output value ratio, but most of them are medium- and low-end products with less than 8 layers. HDI, flexible boards, etc. have a certain scale but are technically superior to foreign products such as Japan. The gap, the most technologically advanced IC carrier board, is rarely produced in China.
According to the design of the PCB board, the price will be due to the material of the PCB, the number of layers of the PCB, the size of the PCB, the quantity of each production, the process of production, the minimum line width, the minimum aperture and the number of holes, special The process and other requirements are determined. There are several ways to calculate the price in the current industry:
1, the price is calculated by size (for small batches of samples)
The manufacturer will give the unit price per square centimeter according to different PCB layers and different processes. The customer only needs to change the PCB size to centimeter and multiply the unit price per square centimeter to get the unit price of the PCB to be produced. The calculation method is very suitable for common process PCB, which is convenient for both manufacturers and buyers. The following are examples:
For example, a manufacturer's pricing single panel, FR-4 material, 10-20 square meters of order, unit price is 0.04 yuan / square centimeter, then if the buyer's PCB size is 10 * 10CM, the production quantity is 1000-2000 Just meet this standard, the unit price is equal to 10*10*0.04=4 yuan.
2, the price is refined according to the cost (for large quantities)
Because the raw material of the PCB circuit board is copper clad laminate, the factory that produces the copper clad laminate has some fixed sizes for sale in the market. The common ones are 915MM*1220MM (36"*48"); 940MM*1245MM (37"*49"). ;1020MM*1220MM (40"*48"); 1067mm*1220mm (42"*48"); 1042MM*1245MM (41"49"); 1093MM*1245MM (43"*49"); the manufacturer will produce according to the The material, the number of layers, the process, the quantity and other parameters of the circuit board calculate the utilization ratio of the copper-clad board of the batch of boards, thereby calculating the material cost. For example, if you produce a 100*100MM circuit board, the factory needs to improve the production efficiency. He may be able to make a large plate of 100*4 and 100*5 to produce.
3, PCB online meter
Since the price of PCB is affected by many factors, ordinary buyers do not understand the supplier's quotation process. It often takes a long time to get a price, a lot of manpower and material resources are wasted, and because they want to know about a PCB. The price, the personal contact information was handed over to the factory, bringing follow-up harassment. Many companies have started to build a PCB pricing program on their website, through some rules, let customers freely calculate the price. PCB people can also easily calculate the price of the PCB.
The following is an example of a company's PCB online meter
From the picture can be seen at a glance, divided into simple version and professional version, only need the user to input and select the corresponding specifications, you can get the price, very convenient and simple.
4.PCB online ordering steps
As mentioned above, the traditional order mode, the customer quotation by email, production contract, fax return confirmation, bank payment, receipt
This traditional mode has slow response to email quotation, making production contracts time-consuming and laborious, inconvenient for public payment, low efficiency, customers can not know the production situation, missing can not be found in time, etc.
In order to solve these problems, a group of companies' PCB model factories invested heavily in the successful development of PCB online ERP system, which can realize online quotation, offline ordering, online payment, online inquiry of order process progress, online printing contract, online download Bills, etc., make PCB trading efficient, intelligent and paperless, and the production process can be mastered at any time.
This designed PCB requires the following steps from ordering to receiving the PCB.
1. Calculate the price: fill in the order quantity, size, process requirements, calculate the price
2. Online order: fill in the order quantity, size, process requirements, upload PCB file
3. Audit confirmation: PCB factory audit process, delivery, price, etc.
4. Online payment: If the PCB board is approved, it can be paid for production.
5. Progress inquiry: PCB production requires a lot of processes, such as: cutting, drilling, copper sinking, wiring, plating, etching, solder mask, text, surface treatment, testing, molding, etc. It takes a long time, so When we place an order, we can clearly see which process our order is in. We can plan other work arrangements for the next step very well. When the factory misses the order or other problems cause the PCB production to be blocked, we can follow up and adjust in time.
6. Receipt evaluation: When you get the PCB, you can check the process quality, quantity and customer service, etc., and give an objective evaluation, which is convenient for other customers to refer to, so that the suppliers with good service, good quality and fast delivery will be pushed to everyone. Conducive to the overall level of the industry as a whole
Classified according to the number of circuit layers: divided into single-panel, double-panel and multi-layer boards. Common multi-layer boards are generally 4-layer boards or 6-layer boards, and complex multi-layer boards can reach dozens of layers.
PCB boards have the following three main types of division:
Single-Sided Boards On the most basic PCB, the parts are concentrated on one side, and the wires are concentrated on the other side (when the chip components are on the same side as the wires, the plug-in devices are on the other side). Since the wire only appears on one side, this PCB is called a single-sided. Because single-panel has many strict restrictions on the design line (because there is only one side, the wiring can not cross and must be around the path), so only the early circuit used this type of board.
Double-Sided Boards These boards have wiring on both sides, but to use the two-sided wires, you must have proper circuit connections between the two sides. The "bridge" between such circuits is called a via. The via hole is a small hole filled or coated with metal on the PCB, which can be connected to the wires on both sides. Because the area of the double panel is twice as large as that of the single panel, the double panel solves the difficulty of wiring interleaving in a single panel (which can be conducted through the hole to the other side), which is more suitable for circuits that are more complicated than single panels.
Multi-Layer Boards To increase the area that can be routed, multi-layer boards use more single or double-sided wiring boards. Using a double-sided inner layer, two single-sided outer layers or two double-sided inner layers, two single-sided outer printed circuit boards, alternating between the positioning system and the insulating bonding material and conductive patterns Printed circuit boards that are interconnected according to design requirements become four-layer, six-layer printed circuit boards, also known as multilayer printed wiring boards. The number of layers of the board does not mean that there are several layers of independent wiring layers. In special cases, empty layers are added to control the thickness of the board. Usually the number of layers is even and the outermost two layers are included. Most of the motherboards are 4 to 8 layers of structure, but technically they can achieve nearly 100 layers of PCB. Large supercomputers mostly use quite a few multi-layer motherboards, but because such computers can already be replaced by clusters of many common computers, super-multilayer boards have gradually disappeared. Because the layers in the PCB are tightly coupled, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.
PCBs are becoming more widely used because they have many unique advantages, as outlined below.
Can be high density. For decades, the high density of printed boards has grown with the increased integration of integrated circuits and advances in mounting technology.
High reliability. Through a series of inspections, tests and aging tests, the PCB can be reliably operated for a long period of time (usually 20 years).
Designability. For the various performances of PCB (electrical, physical, chemical, mechanical, etc.), the design of printed boards can be realized through design standardization and standardization, with short time and high efficiency.
Productivity. With modern management, it can carry out standardization, scale (quantity), automation and other production to ensure product quality consistency.
Testability. Established relatively complete test methods, test standards, various test equipment and instruments to detect and identify PCB product qualification and service life.
Assemblyability. PCB products not only facilitate the standardized assembly of various components, but also can be automated, large-scale mass production. At the same time, the PCB and various component assembly components can be assembled to form larger components and systems up to the complete machine.
Maintainability. Since PCB products and various component assembly components are produced in a standardized design and scale, these components are also standardized. Therefore, once the system fails, it can be replaced quickly, conveniently and flexibly, and the system can be quickly restored. Of course, you can say more about it. Such as miniaturization and weight reduction of the system, high-speed signal transmission, and the like.
Soft and hard classification
Divided into rigid circuit board and flexible circuit board, soft and hard board. The PCB shown in the first figure below is generally referred to as a rigid (Rigid) PCB, and the yellow connection line in the second figure is referred to as a flexible (or permeable) PCB. The intuitive difference between a rigid PCB and a flexible PCB is that the flexible PCB can be bent. Common thicknesses of rigid PCBs are 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.6 mm, 2.0 mm, and the like. The common thickness of a flexible PCB is 0.2 mm. The place where the part is to be welded will be thickened with a thick layer of 0.2 mm and 0.4 mm. The purpose of understanding these is to provide them with a spatial reference when designing the structural engineer. Common materials for rigid PCBs include: phenolic paper laminates, epoxy paper laminates, polyester glass mat laminates, and epoxy glass cloth laminates; flexible PCB materials commonly include: polyester film, polyamide Amine film, fluorinated ethylene propylene film.
A copper clad laminate is a substrate material for making a printed circuit board. It is used to support various components and to achieve electrical or electrical insulation between them.
PCB aluminum substrate (metal-based heat sink including aluminum substrate, copper substrate, iron substrate) is a low-alloyed Al-Mg-Si high-plastic alloy plate (see the figure below), which has good thermal conductivity and electrical insulation properties. And machining performance, now the mainstream aluminum substrate Fosslet.
The solder mask green paint covers most of the copper surface of the circuit and only exposes the terminal contacts for soldering, electrical testing and board insertion. This endpoint requires an additional protective layer to avoid oxides at the terminals of the anode (+) that are connected during long-term use, affecting circuit stability and creating safety concerns.
[Electroplating hard gold] On the plug-in end of the board (commonly known as gold finger) is coated with a layer of nickel and a highly chemically blunt gold layer to protect the end points and provide good connection performance, which contains an appropriate amount of cobalt, which is excellent. Wear characteristics.
[Spray tin] Covers a layer of tin-lead alloy on the soldering end of the board with a hot air leveling to protect the board ends and provide good soldering performance.
[Pre-welding] Overlay the upper layer of anti-oxidation pre-weld film on the soldering end of the board, temporarily protect the soldering end point and provide a flat soldering surface before soldering, so as to have good soldering performance.
[Carbon ink] A layer of carbon ink is printed on the contact end of the board to protect the end points and provide good connection performance.
Cut the board into a CNC molding machine (or die press) to the customer's desired size. When cutting, the plug is fixed on the bed (or mold) through the previously drilled positioning hole. After the cutting, the gold finger portion is further processed by the bevel angle to facilitate the plugging of the circuit board. For the multi-chip forming circuit board, it is necessary to add an X-shaped broken line (known in the industry as V-Cut) to facilitate the customer to split and disassemble after the plug-in. Finally, the dust on the board and the surface ionic contaminants are washed.
Final inspection package
The final electrical conduction, impedance test, and solderability and thermal shock resistance tests were performed on the board prior to packaging. And with appropriate baking to eliminate the moisture and accumulated thermal stress of the board during the process, and finally packaged in a vacuum bag.
PCB manufacturing methods for electronic enthusiasts mainly include thermal transfer method, photosensitive wet film method, and photosensitive dry film method. The etchant is environmentally friendly ferric chloride (FeCl3) with fast hydrochloric acid + hydrogen peroxide (HCl + H2O2). Common PCB plotting software includes Protel series software such as Protel99se. Photosensitive dry film + ferric chloride is the best choice for amateurs.
Image (forming / wire making)
The first step in production is to create wiring that connects the parts. We use a subtractive transfer method to present the working film on a metal conductor. The trick is to lay a thin layer of copper on the entire surface and remove the excess. Additive Pattern Transfer is another way of using less people. This is a way to apply copper wire only where it is needed, but we won't talk about it here.
If you are making a double-panel, the PCB will be covered with copper foil on both sides of the substrate. If you are making a multi-layer board, the next step will stick the boards together.
Positive photoresist is made of sensitizer, which dissolves under illumination (negative photoresist is decomposed if not illuminated). There are many ways to handle photoresist on copper surfaces, but the most common way is to heat it and roll it on the surface containing the photoresist (called a dry film photoresist). It can also be sprayed on the head in a liquid state, but the dry film type provides a higher resolution and can also make a thinner wire.
The hood is just a template for the PCB layer in the manufacturing process. Before the photoresist on the PCB is exposed to UV light, the hood overlying it prevents some areas of the photoresist from being exposed (assuming a positive photoresist). These places covered by photoresist will become wiring.
Other bare copper portions to be etched after photoresist development. The etching process can immerse the board in an etching solvent or spray the solvent onto the board. Generally used as an etching solvent, ferric chloride (Ferric Chloride), alkaline ammonia (Alkaline Ammonia), sulfuric acid plus hydrogen peroxide (Sulfuric Acid + Hydrogen Peroxide), and copper chloride (Cupric Chloride), etc. It is oxidized (eg Cu+2FeCl3=CuCl2+2FeCl2). The remaining photoresist is removed after the etching is completed. This is called a stripping process.
Drilling and plating
If you are making a multi-layer PCB board and have buried or blind holes in it, each layer must be drilled and plated before bonding. If you don't go through this step, there is no way to connect to each other.
After drilling the machine equipment according to the drilling requirements, the hole must be plated (Plated-Through-Hole technology, PTH). After metal treatment inside the hole, the internal layers can be connected to each other. Before starting the plating, the debris in the hole must be removed. This is because the resin epoxy will have some chemical changes after heating, and it will cover the inner PCB layer, so it must be removed first. Both the removal and plating operations are done in a chemical process.
Multilayer PCB press
Each monolithic layer must be laminated to produce a multilayer board. The pressing action includes adding an insulating layer between the layers, and sticking each other. If there are several layers of vias, then each layer must be processed repeatedly. The wiring on the outer sides of the multilayer board is usually processed after the multilayer board is pressed.
Treatment of solder mask, screen printing surface and gold finger plating
Next, the solder resist is overlaid on the outermost wiring so that the wiring does not touch the plating part. The screen printing surface is printed on it to indicate the position of each part. It cannot cover any wiring or gold fingers, otherwise it may reduce the solderability or the stability of the current connection. The gold finger portion is usually plated with gold so that a high quality current connection is ensured when inserted into the expansion slot.
Test the PCB for shorts or open circuits and test it optically or electronically. Optical scanning is used to find defects in each layer, and electronic testing is usually done with a Flying-Probe to check all connections. Electronic tests are more accurate in finding short circuits or open circuits, but optical tests can more easily detect problems with incorrect gaps between conductors.
Parts mounting and welding
The last step is to install and solder the parts. Both THT and SMT parts are machined to be placed on the PCB.
THT parts are usually soldered in a way called Wave Soldering. This allows all parts to be soldered to the PCB at a time. First cut the pin close to the board and bend it slightly to allow the part to be fixed. The PCB is then moved to the water flux of the co-solvent and the bottom is contacted with a co-solvent so that the oxide on the bottom metal can be removed. After heating the PCB, this time it is moved to the molten solder and the soldering is completed after contact with the bottom.
The way to automatically weld SMT parts is called Over Reflow Soldering. The paste solder containing the solvent and the solder is processed once after the parts are mounted on the PCB, and then processed after being heated by the PCB. After the PCB is cooled, the soldering is completed, and the next step is to prepare for the final testing of the PCB.
The Chinese name of the PCB is a printed circuit board, also known as a printed circuit board. The printed circuit board is an important electronic component that is a support for electronic components. It is a provider of electrical connections for electronic components. Because it is made by electronic printing, it is called a "printing" circuit board.
PCB proofing refers to the trial production of printed circuit boards before mass production. The main application is for PCB engineers to design a good circuit and complete the PCB Layout and then perform small-scale trial production to the factory. The production quantity of PCB proofing generally has no specific boundary. Generally, engineers call it PCB proofing before the product design is completed and confirmed.
During the PCB layout process, after the system layout is completed, the PCB diagram should be reviewed to see if the layout of the system is reasonable and whether the optimal effect can be achieved. It can usually be examined from several aspects:
1. Does the system layout ensure that the wiring is reasonable or optimal, whether the wiring can be reliably carried out, and whether the reliability of the circuit operation can be guaranteed. In the layout, you need to have an overall understanding and planning of the direction of the signal and the power and ground network.
2. Whether the size of the printed board is consistent with the size of the processed paper, whether it meets the requirements of the PCB manufacturing process, and whether there is a mark of behavior. This point requires special attention. Many PCB layouts and layouts are beautifully designed and reasonable, but neglecting the precise positioning of the positioning connectors prevents the designed circuit from interfacing with other circuits.
3. Whether the component has conflicts in two-dimensional or three-dimensional space. Note the actual size of the device, especially the height of the device. In the case of solder-free layout, the height should generally not exceed 3mm.
4. Whether the component layout is dense and orderly, neatly arranged, and whether it is completely finished. In the layout of components, not only the direction of the signal and the type of signal, the place that needs attention or protection, but also the overall density of the device layout should be considered, so that the density is uniform.
5. Whether the components that need to be replaced frequently can be easily replaced, and whether the plug-in board is inserted into the device is convenient. It should be convenient and reliable to replace and plug in frequently replaced components.
7. The RF part should pay special attention to the layout. To avoid radio frequency interference with other components, it must be isolated.
Whether it is single-panel, double-panel, multi-layer board design, it was previously designed with protel, and the existing PADS, Allegro and other designs.
The design of the printed circuit board is based on the circuit schematic diagram to achieve the functions required by the circuit designer. The design of the printed circuit board mainly refers to the layout design, which needs to consider the layout of the external connection, the optimized layout of the internal electronic components, the optimized layout of the metal wiring and the through hole, the electromagnetic protection, the heat dissipation and the like. Excellent layout design can save production costs and achieve good circuit performance and heat dissipation. Simple layout designs can be implemented manually, and complex layout designs need to be implemented with computer-aided design (CAD).
The purpose of this document is to illustrate the process and some considerations for the printed board design using the PADS printed board design software PowerPCB, to provide design specifications for designers of a working group to facilitate communication and mutual inspection between designers.
2 design process
The PCB design flow is divided into six steps: netlist input, rule setting, component layout, wiring, inspection, review, and output.
2.1 Netlist input
There are two ways to input the netlist. One is to use PowerLogic's OLE PowerPCB Connection function, select Send Netlist, and apply OLE function, you can keep the schematic and PCB diagram consistent at all times, and minimize the possibility of error. Another method is to load the netlist directly in the PowerPCB, select File->Import, and enter the netlist generated by the schematic.
2.2 Rule settings
If you have already set the PCB design rules in the schematic design stage, you don't need to set these rules anymore, because when you enter the netlist, the design rules have been entered into the PowerPCB with the netlist. If the design rules are modified, the schematic must be synchronized to ensure that the schematic and PCB are consistent. In addition to design rules and layer definitions, there are some rules that need to be set, such as Pad Stacks, which need to modify the size of standard vias. If the designer has created a new pad or via, be sure to add Layer 25.
PCB design rules, layer definitions, via settings, and CAM output settings have been created as default startup files. The name is Default.stp. After the netlist is entered, the power network and ground are assigned to the power and ground layers according to the actual design conditions. And set other advanced rules. After all the rules are set, in PowerLogic, use the Rules From PCB function of OLE PowerPCB Connection to update the rule settings in the schematic to ensure that the rules of the schematic and the PCB are consistent.
2.3 Component layout
After the netlist is input, all the components will be placed at the zero point of the work area and overlapped. The next step is to separate the components and arrange them neatly according to some rules, that is, the layout of the components. PowerPCB offers two methods, manual layout and automatic layout.
2.3.1 Manual layout
1. The structural dimensions of the tool printed board are drawn with the board outline.
2. Disperse the components and arrange the components around the edge of the board.
3. Move the components one by one, rotate them, and place them inside the edge of the board. Place them neatly according to certain rules.
2.3.2 Automatic layout
PowerPCB provides automatic layout and automatic local cluster layout, but for most designs, the effect is not ideal and is not recommended.
a. The first principle of the layout is to ensure the routing rate of the wiring. Pay attention to the connection of the flying wires when moving the device, and put together the devices with the connection relationship.
b. Digital devices and analog devices should be separated and kept as far as possible
c. Decoupling capacitors as close as possible to the VCC of the device
d. Consider the future soldering when placing the device, not too dense
e. Increase the efficiency of the layout by using the Array and Union functions provided by the software.
There are also two ways to route, manual routing and automatic routing. The power wiring provided by PowerPCB is very powerful, including automatic push, online design rule checking (DRC), and automatic routing is performed by Specctra's routing engine. Usually these two methods are used together. The common steps are manual-automatic-manual.
2.4.1 Manual wiring
1. Before auto-routing, first manually lay some important networks, such as high-frequency clocks, main power supplies, etc. These networks often have special requirements for trace distance, line width, line spacing, shielding, etc. Other special packages, Like BGA,
Automatic routing is difficult to lay out with rules, and manual wiring is also required.
2. After the automatic wiring, the wiring of the PCB should be adjusted by manual wiring.
2.4.2 Automatic wiring
After the manual routing is over, the remaining network is handed over to the autorouter. Select Tools->SPECCTRA, start the interface of the Specctra router, set the DO file, press Continue to start the automatic routing of the Specctra router. If the routing rate is 100% after the end, you can manually adjust the wiring; if not To 100%, there is a problem with the layout or manual wiring, and the layout or manual wiring needs to be adjusted until all the connections are made.
a. Power cord and ground wire should be as thick as possible
b. Decoupling capacitors should be directly connected to VCC
c. When setting the DO file of Specctra, first add the Protect all wires command to protect the line of the manual cloth from being redeployed by the autorouter.
d. If there is a hybrid power layer, the layer should be defined as Split/mixed Plane, split before wiring, and after the wire is finished, use Pour Manager's Plane Connect for copper cladding.
e. Set all device pins to the thermal pad mode by setting Filter to Pins and selecting all pins.
Modify the properties and tick the Thermal option
f. Open the DRC option during manual routing, using Dynamic Route (Dynamic Route)
Items to be checked include Clearance, Connectivity, High Speed, and Plane. These items can be selected by Tools->Verify Design. If a high speed rule is set, it must be checked, otherwise this item can be skipped. Check for errors and you must modify the layout and routing.
Some errors can be ignored. For example, some of the connectors' outlines are placed outside the board frame, and errors are detected when checking the spacing. In addition, each time the traces and vias are modified, the copper is re-copied once.
Review according to the "PCB checklist", including design rules, layer definition, line width, spacing, pad, via settings; also focus on reviewing the rationality of device layout, power, ground network routing, high-speed clock network The wiring and shielding, the placement and connection of decoupling capacitors, etc. If the review fails, the designer must modify the layout and wiring. After passing the test, the reviewer and the designer separately sign.
2.7 Design output
The PCB design can be output to a printer or output illuminating file. The printer can print the PCB layer by layer, which is convenient for designers and reviewers to check; the lithography file is handed over to the board manufacturer to produce the printed board. The output of the light painting file is very important, which is related to the success or failure of this design. The following will focus on the precautions for outputting the light painting file.
a. The layers that need to be output are wiring layers (including top layer, bottom layer, intermediate wiring layer), power layer (including VCC layer and GND layer), silk screen layer (including top screen printing, bottom screen printing), solder mask (including top solder mask) And underlying solder mask), in addition to generate drilling files (NC Drill)
b. If the power layer is set to Split/Mixed, select Routing in the Document item of the Add Document window, and use the Pour Manager's Plane Connect to laminate the PCB before each output of the illuminating file; if set to CAM Plane, choose Plane. When setting the Layer item, add Layer25 and select Pads and Vias in the Layer 25 layer.
c. In the Device Settings window (press Device Setup), change the value of Aperture to 199.
d. Select the Board Outline when setting the Layer for each layer.
e. When setting the layer of the silkscreen layer, do not select Part Type, select the top (bottom) and silkscreen layers of Outline, Text, Line
f. When setting the layer of the solder mask, selecting the via hole means that no solder mask is added on the via hole, and the via hole is not selected to indicate the home solder mask, which is determined according to the specific situation.
g. When generating the drilling file, use the default settings of PowerPCB, do not make any changes.
h. After all the lithography files are output, open and print with CAM350, and the designer and reviewer will check according to the “PCB checklist”.
According to the upstream and downstream of the industry chain, it can be divided into raw materials - copper clad plate - printed circuit board - electronic product application, the relationship is simply expressed as: fiberglass cloth: fiberglass cloth is one of the raw materials of copper clad laminate, textile fiberglass yarn It is about 40% (thick plate) and 25% (thin plate) of CCL. The glass fiber yarn is calcined into a liquid state by a raw material such as silica sand in a kiln, and is drawn into a very fine glass fiber through a very fine alloy nozzle, and then several hundred glass fibers are twisted into a glass fiber yarn. The construction investment of the kiln is huge, generally it needs hundreds of millions of funds, and once the ignition has to be produced 24 hours a day, the cost of entry and exit is huge. Fiberglass fabric manufacturing is similar to weaving companies. It can control the production capacity and quality by controlling the speed. The specifications are relatively simple and stable. There has been almost no change in specifications since World War II. Unlike CCL, the price of fiberglass cloth is most affected by the supply and demand relationship. In recent years, the price fluctuated between 0.50-1.00 USD/m. Taiwan and China's production capacity accounts for about 70% of the world's total.
Copper foil: Copper foil is the largest raw material in the cost of copper clad, accounting for about 30% (thick plate) and 50% (thin plate) of CCL cost. Therefore, the price increase of copper foil is the main driving force for the price increase of CCL. The price of copper foil is closely reflected in the price change of copper, but the bargaining power is weak. Recently, with the high price of copper, the copper foil manufacturers are in a difficult situation. Many companies are forced to close down or be merged, even if the CCL manufacturers accept copper foil. The price rise of various copper foil manufacturers is still in a state of general loss. Due to the price gap, there is a high probability that another wave of price increases will occur in the first quarter of 2006, which may drive CCL prices up.
CCL: CCL is a product of pressing glass fiber and copper foil together with epoxy resin as a fusion agent. It is a direct raw material for PCB. It is made into a printed circuit after being etched, plated, and laminated. board. The demand for funds in the CCL industry is not high, about 30-40 million yuan, and can be discontinued or converted at any time. In the upstream and downstream industrial chain structure, CCL has the strongest bargaining power, not only can have a strong voice in the procurement of raw materials such as fiberglass cloth and copper foil, but also can pass the pressure of rising costs as long as the downstream demand is acceptable. Downstream PCB manufacturers. In the third quarter, CCL began to raise prices, and the price increase was around 5-8%. The main driving force is to reflect the price increase of copper foil, and the strong downstream demand can digest the price pressure of CCL manufacturers. South Asia, the world's second-largest CCL supplier, also raised its product prices on December 15, 2006, indicating that PCB demand was in good shape in at least the first quarter of 2006.
The output value of the global PCB industry accounts for more than a quarter of the total output value of the electronic components industry. It is the largest proportion of the various electronic component industry, with an industry scale of 40 billion US dollars. At the same time, due to its unique position in the electronic infrastructure industry, it has become the most active industry in the contemporary electronic components industry. In 2003 and 2004, global PCB production value was US$34.4 billion and US$40.1 billion, respectively, with a year-on-year growth rate of 5.27%. And 16.47%. Domestic PCB industry development status
China's PCB development work began in 1956, and gradually expanded to form the PCB industry from 1963 to 1978. More than 20 years after the reform and opening up, due to the introduction of foreign advanced technology and equipment, single-panel, double-panel and multi-layer boards have achieved rapid development, and the domestic PCB industry has gradually developed from small to large. Due to the concentration of downstream industries and relatively low labor land costs, China has become the region with the strongest development momentum. In 2002, it became the third largest PCB producer. In 2003, PCB output value and import and export volume exceeded US$6 billion, surpassing the United States for the first time, becoming the world's second largest PCB producer. The proportion of output value also increased from 8.54% in 2000 to 15.30%, nearly doubled. In 2006, China has replaced Japan as the world's largest PCB production base and the most active technology development country. China's PCB industry maintains a high growth rate of around 20%, far higher than the growth rate of the global PCB industry.
From the perspective of production composition, the main products of China's PCB industry have been turned from single-panel and double-panel to multi-layer boards, and are being upgraded from 4 to 6 layers to 6 to 8 layers. With the rapid growth of multi-layer boards, HDI boards and flexible boards, China's PCB industry structure is gradually being optimized and improved.
However, although China's PCB industry has made great progress, it still has a big gap compared with advanced countries, and there is still much room for improvement and improvement in the future. First of all, China has entered the PCB industry late, there is no special PCB R&D institution, and there is a big gap between it and some foreign manufacturers in some new technology research and development capabilities. Secondly, from the perspective of product structure, the production of medium and low-layer boards is still the mainstay. Although FPC and HDI are growing rapidly, the proportion is still low due to the small base. Thirdly, most of China's PCB production equipment relies on imports, and some core raw materials can only rely on imports. The incompleteness of the industrial chain has also hindered the development of domestic PCB series enterprises.
Folding industry general review
As the most versatile electronic component product, PCB has a strong vitality. Regardless of whether it is from the relationship between supply and demand or from the historical cycle, the beginning of 2006 is the stage of the industry's entry into the climate, and the continued strong downstream demand has driven the shipments of various manufacturers in the PCB industry chain at a level, forming at least in 2006. In the first quarter of the year, the "low season is not weak" situation. Upgrade the industry rating from “avoidance” to “good”.
Folding industry status
Thanks to the support of new products in the terminal and new markets, the global PCB market has successfully achieved recovery and growth. Hong Kong Circuit Board Association (HKPCA) statistics show that the global PCB market will grow steadily in 2011 and is expected to grow by 6-9%, while China is expected to grow by 9-12%. The Taiwan Industrial Technology Research Institute (IEK) analysis report predicts that global PCB production will increase by 10.36% in 2011, with a scale of US$41.615 billion. According to the analysis data of Prismark and the report issued by Industrial Securities R&D Center, the changes in PCB application structure and product structure reflect the future development trend of the industry. With the decrease in the output value of single/double-panel and multi-layer boards, the increase in the output value of HDI boards, package carriers, and soft boards indicates that the growth in the fields of computer motherboards, communication backplanes, and automotive boards is slow. HDI boards, packaging boards and flexible boards for "light and thin" electronic products such as high-end mobile phones and notebook computers will continue to grow rapidly.
The American Printed Circuit Board Association (IPC) announced that in February 2011, the overall printed circuit board manufacturer's book-to-bill ratio in North America was 0.95, meaning that for every $100 shipped in the month, only Received a new order worth $95. The B/B value was lower than the fifth consecutive month, and the industry sentiment in North America did not rebound substantially.
· Japan's earthquake short-term impact part of PCB raw material supply, medium and long-term is conducive to the transfer of production capacity to Taiwan and the mainland
· High-end PCB manufacturers accelerate the expansion of production in the mainland, and the transfer of technology, capacity and orders to the mainland is the trend of the times.
· Taiwan Zhongshi News reported that Japan's supply chain is broken, China and South Korea PCB board factory will become a big winner
· Institute of Industrial Technology (IEK) analysts pointed out that benefiting from the global economic recovery and consumption support of emerging countries, Taiwan's PCB industry is expected to grow by 29% in 2011. Global production capacity will be further transferred to China. China Investment Consulting Analysis Report pointed out that China's printed circuit The plate industry will enter a high-speed growth period under the situation of domestic sales growth and global production capacity. By 2014, the proportion of China's printed circuit board industry will increase to 41.92%.
First, degreasing (temperature 60-65 ° C)
1. There are many foams: The quality of the foam is abnormal: it will cause poor degreasing effect. Cause: Mismatched tank solution.
2, there are particulate matter composition: there are particulate matter composition reasons: the filter is bad or the high pressure water washing of the grinding machine is insufficient, the outside brings dust.
3, finger prints can not remove oil: finger prints can not remove oil reasons: in addition to oil temperature, syrup mismatch.
Second, micro-etching (NPS 80-120G / L H2SO4 5% temperature 25-35 ° C)
1. The copper surface of the board is slightly white: the reason is that the grinding plate, degreasing or pollution, the concentration of the syrup is low.
2, the surface of the copper plate is black: after degreasing, the water is not cleaned by oil removal. The pink surface of the copper is a normal effect of micro-etching.
Third, activation (the color of the bath is black, the temperature can not exceed 38 ° C, can not breathe)
1. Precipitation and clarification of the bath:
The reason for the precipitation of the bath:
(1) The concentration of water palladium is added immediately, and the content is changed at the bottom (normally added liquid level is applied with prepreg)
(2) The Sn2+ concentration is low, the Cl- content is low, and the temperature is too high.
(3) Too much introduction of air leads to oxidation of palladium.
(4) It is contaminated by Fe+.
2. A layer of silvery white film appears on the surface of the potion:
A silvery white film appears on the surface of the syrup. Cause: The oxide produced by the oxidation of Pd.
Fourth, speed (processing time 1-2 minutes temperature 60-65 ° C)
1. No copper in the hole: Cause: The accelerated processing time is too long, and Pd is also removed while removing Sn.
2, high temperature Pd is easy to fall off.
5. Chemical copper cylinder liquid is contaminated
Causes of contamination of the drug solution: 1. Insufficient water washing before PTH 2, Pd water is brought into the copper cylinder 3. There is a plate falling out of the tank 4, no long-term frying tank 5, insufficient filtration
Washing: Soak for 10 hours with 10% H2SO4, neutralize with 10% NAOH, and finally rinse with water.
Sixth, the hole wall can not sink copper
Reasons: 1. Poor oil removal effect 2. Insufficient slag removal 3. Excessive slag removal
7. After the thermal shock, the hole copper is separated from the hole wall.
Reasons: 1. In addition to poor slag, poor water absorption of the substrate
Eight, the board has a strip of water
Reasons: 1. The design of the hanger is not reasonable. 2. The mixing of the sinking copper cylinder is excessive. 3. The washing is not sufficient after the acceleration.
Nine, the temperature of the chemical copper solution
If the temperature is too high, the chemical copper liquid will be rapidly decomposed, and the composition of the solution will change to affect the quality of the electroless copper plating. High temperatures also produce large amounts of copper powder, causing copper on the board and holes. Generally controlled at around 25-35 °C.
1 Process Control Block: The function of the process control block is to make a program (including data) that cannot run independently in a multi-program environment, become a basic unit that can run independently, and a process that can be executed concurrently with other processes.
2 Block: It is the program code segment in the process that can be executed by the process scheduler on the CPU.
3 Data segment: The data segment of a process, which can be the raw data processed by the program corresponding to the process, or the intermediate or final data generated after the program is executed.
Information used in the PCB to describe and control the operation of the process
1, process identifier information
The process identifier is used to uniquely identify a process. A process usually has the following two identifiers.
External identifier. Provided by the creator, usually composed of letters and numbers, often used by users (processes) to access the process. External identifiers are easy to remember, such as: calculation process, print process, send process, receive process, and so on.
Internal identifier: set to facilitate system use. In all OSs, each process is given a unique integer as an internal identifier. It is usually a symbol of a process. To describe the family relationship of a process, you should also set the parent process identifier and the child process identifier. You can also set a user identifier to indicate which user owns the process.
2, processor status information
The processor status information is mainly composed of the contents of the various registers of the processor.
General purpose register. Also known as user visual registers, they can be accessed by user programs for temporary storage of information.
Instruction register. Store the address of the next instruction to be accessed.
Program status word PSW. It contains status information. (condition code, execution mode, interrupt mask flag, etc.)
User stack pointer. Each user process has one or several associated system stacks that store process and system call parameters and call addresses. The stack pointer points to the top of the stack.
3. Process scheduling information
Some information related to process scheduling and process swapping is also stored in the PCB.
(1) Process status. Indicates the current state of the process as the basis for process scheduling and swapping.
(2) Process priority. An integer used to describe the priority level of the process using the processor, and the process with the highest priority takes precedence over the processor.
(3) Other information required for process scheduling. (The sum of the time the process has waited for the CPU, the sum of the time the process has been executed)
(4) Events. This is the event that the process waits for the transition from the execution state to the blocking state. (cause of blocking)
Is a static description of the entire process of the process execution activities. It includes the values of various registers in the computer system related to the execution of the process, the set of machine instruction codes formed by the program segments after compilation, the data set, and various stack values and PCB structures. Can be combined according to a certain level of execution, such as user-level context, system-level context, and so on.
Unique sign of the existence of the process
Throughout the life cycle of the process, the system always controls the process through the PCB, that is, the system senses the existence of the process according to the PCB of the process rather than anything else, so the PCB is the process. The only sign.
1 foot = 12 inches
1mil=1000uin mil mil sometimes becomes silk
1um = 40uin (some companies say micro inches are wheat, actually micro inches)
1OZ = 28.35 g / square foot = 35 microns
H = 18 microns
T = 12 microns
4mil/4mil=0.1mm/0.1mm line width/line spacing
1ASD = 1 amp / square demeter = 10.6 amps / square foot (ASF)
1AM=1 amp minutes=60 coulomb Mainly used for precious metal plating such as gold plating
1 square demeter = 10.76 square feet
1 ounce = 28.35 grams, this is an English unit
1 gallon (imperial) = 4.5 liters
1 gallon US system = 3.785 liters
1 amp hour = 3600 coulombs
Baume degree = 145-145 / specific gravity SG.
SG. Specific gravity (g/cm3) = 145/(145-pome)
PCB related terminology:
1. PCBedge printed circuit board edge
2. PCBcleaning printed circuit board cleaning
3. board, printed circuit (PCB) printed circuit board
Printed circuit board (PCB) printed circuit board
5. depanelPCB segmentation
Allegro provides a good and interactive working interface and powerful features to provide the perfect solution for today's high-speed, high-density, multi-layer complex PCB design and routing.
PADS is mainly suitable for high speed circuit design. The software is mainly divided into design multiplexing module, manufacturability inspection module, analog PCB design toolkit, fast interactive manual router, fast interactive manual high-speed wiring module, advanced PCB testability inspection module, advanced design rule definition module. Designed for high speed circuit boards.
Protel is mainly composed of two parts: schematic design system and printed circuit board design system. It is an easy-to-use schematic editor with a large library of components, primarily for schematic design. Has a powerful printed circuit board design editor with very professional interactive wiring and component layout features for printed circuit board design and ultimately PCB files. Is a very suitable circuit board design software. Highly recommended.
Radiated EMI interference can come from an undirected source and an unintentional antenna. Conductive EMI interference can also come from a source of radiated EMI interference or caused by some board components. Once your board receives conductive interference, it resides in the PCB trace of the application circuit. Some common sources of radiated EMI interference include the components discussed in previous articles, as well as switched-mode power supplies, cables and switches or clock networks on the PCB.
Conductive EMI interference is the result of the normal operation of the switching circuit and the parasitic capacitance and inductance. Figure 1 shows some of the EMI sources that will enter your PCB traces. Vemi1 is derived from a switching network such as a clock signal or a digital signal trace. The coupling of these sources of interference is through the parasitic capacitance between the traces. These signals bring current spikes into adjacent PCB traces. Similarly, Vemi2 is derived from a switching network or from an antenna on a PCB. The coupling of these sources of interference is through the parasitic inductance between the traces. This signal brings voltage disturbances into adjacent PCB traces. Every three EMI sources come from adjacent wires within the cable. Signals propagating along these wires can create crosstalk effects.
The switched mode power supply produces Vemi4. Interference from the switched-mode power supply resides on the power trace and appears as a Vemi4 signal.
Switched-mode power supply (SMPS) circuits present opportunities for the formation of conductive EMI during normal operation. The "on" and "off" switching operations within these supplies produce a strong discontinuous current. These discontinuous currents are present at the input of the buck converter, at the output of the boost converter, and at the input and output of the flyback and boost topology. The discontinuous current caused by the switching action produces a voltage ripple that propagates through the PCB traces to other parts of the system. The input and/or output voltage ripple caused by the SMPS can jeopardize the operation of the load circuit. Figure 2 shows an example of the frequency composition of a DC/DC buck SMPS input operating at 2 MHz. The basic frequency composition of SMPS conducted interference ranges from 90 – 100 MHz.
Conductive EMI measurements with 10 μF filters for input and output pins.
There are two types of conducted interference: differential mode interference and common mode interference. Differential mode interference signals appear between the input terminals of the circuit, such as signal and ground. Current flows through the two inputs of the same phase. However, the current input size 1 is equal to the 2nd, but the direction is opposite (differential reference). The loads at these two inputs form a voltage that varies with current strength. This voltage change between stitch 1 and the differential reference creates interference or communication errors in the system.
Common mode interference occurs when you add a ground loop or a bad current path to the circuit. If there is a source of interference, common mode current and common mode voltage are formed on trace 1 and trace 2, and the ground loop acts as a common mode interference source. Both differential and common mode interference require special filters to handle the adverse effects of EMI interference.