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Common nouns when making PCB boards

2019-09-16 18:44:44 444

When you make a PCB, you will definitely encounter a solder mask and a paste mask. The solder mask is a solder mask. The paste mask is a solder paste layer. What do they actually mean?


The solder mask is the reverse layer: the pattern appears to indicate no solder mask, and the unpatterned layer has a solder mask.


The solder mask is the place where the green pad on the PCB board (surface mount pad, plug pad, via) is coated with green oil. It is to prevent the soldering of the soldering iron (wave soldering) on the PCB. Tin is placed on the tin, so it is called a solder mask (green oil layer).


The solder mask can be divided into two layers, Top Layers and Bottom Layers. When drawing a rectangle on the solder mask layer, then the inside of the rectangular frame is equivalent to opening a window, and the copper skin will be displayed.


Solder Mask This solder resist has green, blue, red, black, etc. This is why PCB boards have different colors. At the same time, the main thing is that when designing the pad, the solder mask is 0.15mm (6mil) larger than the pad.


Paste Mask layers are positive, and a pattern indicates that solder paste is needed. It is for surface mount (SMD) components.


The Paste Mask layer is used to make a stencil, and the holes in the steel mesh correspond to the solder joints of the SMD devices on the board. When soldering a surface mount (SMD) device, first cover the steel mesh on the circuit board (corresponding to the actual pad), then apply the solder paste, scrape the excess solder paste with a doctor blade, and remove the steel mesh. So that the solder of the SMD device is soldered, then the SMD device is attached to the solder paste (manual or placement machine), and finally the SMD device is soldered by the reflow soldering machine.


Usually the size of the steel mesh aperture will be smaller than the actual soldering on the board. For different requirements of different pads, you can also set multiple rules in the Paste Mask layer. Paste Mask also has 2 layers, Top Paste and Bottom Paste.


Draw a rectangle on the Paste Mask layers, then the inside of the rectangle is equivalent to opening a window, and the machine sprays the solder on the window (in fact, the steel mesh opens a window, and the wave soldering is applied to the tin).


At the same time, Keepout and Mechanical layer are also easy to confuse. Keepout refers to the boundary used to determine various electrical boundaries. Mechanical layer, the real physical boundary. The positioning holes are made according to the size of the mechanical layer.


The assembly layer assembly and the silk layer Silkscreen are often encountered in PCBs. So what do these two layers mean?


Silkscreen, silk screen layer. Refers to the outline of the component's outline, representing the graphical symbol of the device's outline. This layer of data is often used when drawing out data during PCB design. More aptly, Silkscreen lay will be printed on the PCB board.


Assembly lay: PLACE BOUND TOP /BOTTOM, which is the physical shape graphic. Can be used for DFA rules: DFM/DFA, is the DESIGN FOR manufacturing (M) / DESIGN FOR assembly (A).


The assembly layer is used for layout and assembly drawings. It is available to CHECK personnel to check if there is a problem with the placement of components and whether they meet the requirements for manufacturability.


The words positive and negative are often encountered in the PCB. The positive and negative films only refer to two different display effects of one layer. Whether the layer is a positive or negative film, the PCB is made the same. Only in the process of cadence processing, the amount of data, DRC detection, and software processing are different. It's just two ways of expressing things. The positive film is, what do you see, what is it, you see that the wiring is the wiring, it really exists. Negative film is, what you see, there is nothing, what you see is precisely the copper skin that needs to be eroded.


The advantage of the positive film is that if the moving component or via needs to be re-plated, there is a more comprehensive DRC check. The advantage of the negative film is that the moving component or via does not need to be re-plated, the copper is automatically updated, and there is no comprehensive DRC check.


There are many nouns in the PCB manufacturing process, and it is easier to confuse. Have you figured out through this study?


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