BGA IC is a kind of large-scale integrated circuit, which is mainly developed for small pcb products. Because its pins are located at the bottom of the IC, it can save most space, but because its pins are very dense, it is very easy to cause false soldering. Desoldering. The failure rate is still very high. Now some maintenance personnel, especially those who are new to this industry, have a headache about it (including the time when I started). Now I will introduce the BGA welding method in detail and pay attention to several points
1、 Because the pins are called "dense", they cannot be directly led out from the top layer, and they need to be led out from the bottom layer through staggered holes, except for the outermost pins. However, if the hot air gun is to be used, all holes should be drilled to the bottom layer, and attention should be paid to the neat arrangement.
2、 Apply BGA solder solution (the configuration method of solder is described in the "Supplement to the Method of Welding Surface Mount Chips with More than 100 Feet by Manual BGA" post) to the top pad and the lead out via of the pad, and then load it on the lead out via of the pad at the bottom. The rosin used to prepare the solution must be clean, and the washing water must also be clean.
3、 It is the most difficult to align the BGA chip to the pin, but it is OK to align the pin generally. As for the pin, it is OK not to touch the lead out via of the PCB pad of the adjacent pin.
4、 Use a hot air gun to blow, but not the top layer (the chip on the top layer is covered and cannot be blown), but the bonding pad outlet vias on the bottom layer. Of course, you may need two things to empty the circuit board shelf. Your hot air gun (I use two very tall and thick bookcases to cover both ends of the circuit board) should blow the bonding pad outlet vias from below. Note that the hot air gun should not add a blowing head to avoid uneven heating. It is better to blow directly with a rough mouth, Generally, it can be heated evenly because the chip area of BGA package is small. Since each pad has an outlet via, the heat can be quickly transferred to the top pad, and the top pad is coated with solder solvent, the pins on the BGA chip are easy to melt. In about 10 seconds, wait until the rosin smoke is gone.
5、 Use clean washing water to wash away the black traces of rosin. But it may take courage to try. If you don't have confidence in yourself, don't do it. Ask someone else to weld it, or you'll regret it.
There is a unique way to judge whether the welding is completed
Because there is a reverse diode to the ground inside the CPU pins, the red probe of the digital multimeter is used for grounding, and the black probe scans each pin in turn to find that the CPU is not welded well. Before BGA welding, you can verify whether each pin of your chip has this reverse diode.