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BGA, stress on the PCB


BGA, stress on the PCB | 16 April, 2004


I've a problem with a BGA. I've the impression that the balls broke then there is a too big mecanical stress on the PCB. I lost some dBm and when I press on the BGA I measure the good value! It's like the balls are take off the BGA or PCB and when you press on it the balls paste to the BGA or PCB.

As anybody already saw this problem? Thanks, Denis

PS: sorry for my English

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Bob L.


BGA, stress on the PCB | 16 April, 2004

We've seen problems with BGA balls breaking at in-circuit test. I did some bend testing and found that our large BGA's can handle amazing stresses at low strain rates but we get brittle fractures at high strain rates, especially with Ni/Au surface finishes on the board. We've measured strain rates as high as 20,000 microstrain/second at in-circuit test. On Ni/Au we saw brittle fractures at the Sn-Ni interface. OSP and HASL aren't nearly as susceptible to brittle fracture. We've got it under control by putting a 650 microstrain limit near BGA's at in-circuit test which means the test engineers have had to be more thoughtful in their fixturing and board supports. I wish we could get them to slow down the strain rate but they claim they can't get good probe contact unless they really slam the board down. At low strain rates (10 microstrain/sec) I was able to bend BGA coupons to well over 5000 microstrain without failure.

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BGA, stress on the PCB | 16 April, 2004

Possibilities are: * Handling problems, like Bob L [the previous poster in this thread] mentioned. * Poor reflow recipe selection. Search the SMTnet Archives for previous discussion.

[Your English is fine. Most of us "English" writers don't do any better.]

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