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by vonmoltke
4482 days ago
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> This happens all too often unfortunately. It's why you didn't see anything BGA packaged in the defence industry for a number of years -- they are not mechanically stable. I did have a reference for this but I can't find it now. There is also a problem with rework. BGAs are hard to get off the board without destroying the board in the process, especially on multi-layer boards. For cheap commercial boards where the automatic decision is to scrap the board when the chip fails, that's fine. For $10k+ circuit card assemblies on a low volume defense production line, scrapping the board is a last resort. This applies to production defects as well as field returns. > Also the multi-layer boards tend to bend when you repetitively heat/cool them resulting in the actual metal traces cracking inside. Another problem is delamination (separation of the board layers). Delamination allows contaminants to get in on the traces and possibly start shorting things out. It seriously degrades the reliability of the board. That was the biggest problem for us when trying to rework CCAs. We had no BGAs, but we did have a card that used a few parts with thermal pads on the bottom. It took heat from both sides of the board to get the chip off, and it was very easy to apply too much heat and delaminate the board in the process. |
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