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Introduction about the technology of BGA assembly


BGA IC is a type of large-scale integrated circuit, mainly developed for small electronic products. Because its pins are located at the bottom of the IC, although it can save most of the space, it is very easy because its pins are very dense Causes virtual welding. Desoldering. The failure rate is fairly high. Now some maintenance personnel, especially those who are new to this industry, have a headache for it. Below I will introduce the BGA welding method in detail in PCB assembly process.


1. Due to the denser pins, it is generally not possible to directly lead from the top layer, and it is necessary to drill holes through the misalignment and lead to the bottom layer, except for the outermost pin. But if you want to use a hot air gun, you should punch all the holes to the bottom, and pay attention to the neat arrangement.


2. Apply the BGA solder solution to the top pad and the lead-out via, and then apply the coating to the bottom pad via. The rosin in the solution must be clean, and the washing water must be clean.


3. It is the most difficult to align the BGA chip with the pins, but it is enough to align the pins, as long as the pins do not touch the vias of the adjacent pin pads.


4. Use a hot air gun to blow, but not the top layer (the top layer of the chip is covered cannot be blown), but the bottom layer of the pad to lead out the via hole. Of course, you may need two things to raise the circuit board overhead. Your hot air gun (I use two very high and thick bookshelves to hold the two ends of the circuit board). I want to blow the lead-out holes of these pads from below. Be careful not to add a blower to the hot air gun to avoid uneven heating. It is best to use a thick mouth directly. Generally It can be heated evenly because the chip area of the BGA package is not large. Because each pad has a lead-through hole, it can quickly transfer heat to the top pad, and the top pad is coated with solder solvent, and the pins on the BGA chip are easily melted. About 10 seconds, just wait for the rosin smoke to disappear.


5. Use clean wash water to wash away the black traces of rosin


There is a trick to judge if welding is good:


Because there is a reverse diode to the ground inside the CPU pins, use a digital multimeter red test lead to ground, and a black test lead to scan each pin in turn to find that there is no soldered CPU. Before BGA soldering, you can verify whether your chip has this reverse-connected diode on each pin.




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