In SMT (Surface Mount Technology) assembly, it’s common to need rework on BGA (Ball Grid Array) chips. Repairing BGA chips is not a simple task, so it’s essential to master certain techniques for BGA soldering. BGA soldering can be categorized into several methods: manual soldering using a hot air gun or a BGA rework station, and reflow soldering on the production line.
The principle of soldering is straightforward: BGA pins are tiny balls (approximately 0.6mm in diameter) made of solder material. When the BGA component and the PCB reach temperatures of 180 degrees Celsius (for leaded solder) or 210 degrees Celsius (for lead-free solder), these solder balls will melt automatically and form connections with the corresponding pads on the PCB through liquid adhesion.
Steps:
- Ensure the solder pads of the BGA are clean and tidy, and flat.
- Apply a thin and even layer of solid flux to the solder pads on the BGA (a thin layer is sufficient).
- Place the solder balls onto the corresponding positions of the solder pads (it’s preferable to use a fixture for convenience).
- After placing the solder balls, use a hot air gun to preheat them until they make initial contact with the solder pads and are fixed in place.
Remove any misaligned solder balls and replace them, then re-fix.
- Soldering. There are two methods: the first is manual heating using a hot air gun (note that heating should be uniform); the second is using a dedicated BGA rework station, which is more convenient to control and has a higher success rate for soldering. (The differences and advantages between high-precision optical BGA rework stations and regular BGA rework stations)
After completion, it’s advisable to use X-RAY inspection equipment to observe the soldering status.
In summary, good tools are indispensable, and the soldering temperature for BGA is crucial. If the temperature is too high, it can damage the chips; if it’s too low, the solder won’t melt. Flux is essential and can be in the form of solder paste or flux paste. However, they both need to be of good quality. Otherwise, soldering failures are highly likely to occur!
