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CBGA CTE Mismatch

C.J. Long

#3263

CBGA CTE Mismatch | 17 August, 2000

Hi erverybody:

I am from a PCB shop. One of our product is with 19 X 19 ceramic BGA and my customer is experiencing 0.1 - 04 % failure of open trace on cornoer BGA pad. Substrate is FR4 with TG 135 degree C and delta Tg is well below 3 degree C. Trace width is 4 mil. Defect is fixed to cornor BGA land connecting 4 mil trace. Solder joint is good and and defect is fracture between BGA land and 4-mil wide signal trace.

To me, it is clear that root cause is from CTE mismatch and customer is not willing to use lower CTE material due to cost concern. Anyone out there can give me advise how to prove failure is from CTE and any solution to this failure.

Thanks

C.J. Long

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#3264

Re: CBGA CTE Mismatch | 21 August, 2000

Hi CJ: I guarantee you that the portions of you BGA that will physically move the most as a result of changing temperature are the corners. For this very reason, many BGA have BT substrates that have a tg of 210�C.

I would demonstrate the potential problems of this material selection by testing a batch of BGA, reflowing the BGA [bug down] on a glass plate, and then retesting the BGA. You and I will both be surprised if the failure rate of these test BGA is anything but the same as the rate you are seeing in your customers boards.

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