Importance of BGA soldering temperature control in PCB surface mount
BGA soldering station welding precautions First point: reasonable adjustment of preheating temperature
Before performing PCB BGA soldering, the motherboard should first be fully preheated, which can effectively ensure that the motherboard does not deform during heating and can provide temperature compensation for later heating.
Regarding the preheating temperature, this should be flexibly adjusted according to the room temperature and the thickness of the PCB. For example, when the room temperature is low in winter, the preheating temperature can be appropriately increased, and in the summer, it should be lowered accordingly. If the PCB is relatively thin, you need to increase the preheating temperature appropriately! The specific temperature varies with the BGA soldering station. Some fixed heights of the soldering station PCB are closer to the preheating brick of the soldering station. It can be set at 100-110 degrees Celsius in summer and 130-150 degrees Celsius in low temperature in winter. If the distance is far away, this temperature setting should be increased. Please refer to the respective soldering station manual.
BGA soldering station welding precautions second point: BGA soldering station with humanized parameter setting
When the BGA is performing chip soldering, it is necessary to adjust the position reasonably to ensure that the chip is between the upper and lower air outlets, and it is necessary to tighten the PCB with the clamp to both ends and fix it! It is standard to touch the motherboard with the hand without shaking.
1: It is very important to fasten the PCB to ensure that the PCB does not deform during heating!
2: Set a reasonable welding curve
BGA soldering station welding precautions third point: reasonable adjustment of welding curve
The curve used in the rework station we are currently using is divided into 5 segments.
Each curve has three parameters to control:
Parameter 1, the temperature rise slope of the curve, that is, the temperature rise rate. Generally set to 3 degrees Celsius per second
Parameter 2, the highest temperature to be reached for this segment of the curve. This should be flexibly adjusted according to the type of solder ball used and the size of the PCB.
Parameter 3, the holding time at this temperature after the heating reaches the maximum temperature of the section. Usually set to 40 seconds.
Adjust the general method: find a PCB with a flat and unformed motherboard, and use the soldering station to carry out the welding with the curve. When the fourth curve is completed, insert the temperature measurement line of the soldering station between the chip and the PCB to obtain the current time. temperature.
The ideal value of lead-free can reach 217 degrees, and lead can reach 183 degrees. These two temperatures are the theoretical melting points of the above two solder balls! However, at this time, the solder balls in the lower part of the chip are not completely melted. From the corner of the maintenance, the ideal temperature is about 235 degrees lead-free and about 200 degrees lead.
At this point, the chip solder ball is melted and then cooled to achieve the best strength. Taking lead-free as an example: after the end of the four-segment curve, the temperature does not reach 217 degrees, and the temperature of the third and fourth sections is moderately increased according to the difference.
For example, if the measured temperature is 205 degrees, the upper and lower air outlet temperatures are increased by 10 degrees. If the difference is large, for example, if the measured temperature is 195 degrees, the lower air temperature can be increased by 30 degrees, and the upper air temperature is increased by 20 degrees. Do not increase the temperature too much to avoid damage to the chip! After the completion of heating, the measured value is 217 degrees. If it exceeds 220 degrees, the maximum temperature reached by the chip before the end of the fifth curve should be observed. Generally, it should avoid exceeding 245 degrees. If it exceeds too much, the curve can be moderately reduced. The set temperature.
Note 4: The alignment of the chip must be accurate when soldering.
Note 5: Use the right amount of solder paste!
PCB board BGA solder paste works great in the soldering process! Whether it is re-welding or direct repair welding, it is necessary to apply a solder paste first. When soldering the chip, use a small brush to apply a thin layer on the cleaned pad. Spread as much as possible. Do not brush too much, otherwise it will affect the soldering. In the repair welding, you can use a brush to draw a small amount of solder paste on the chip. Please use BGA soldering special solder paste for solder paste!
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