Guy, you're dead-on...
We had the same situation happen with a major customer. Processor boards would pass F/T here, then sometimes fail at their F/T. Found out later that each of us was running a slightly different firmware-based test on the assembly. The execution code was close, but not the same, and the test they were running was a little longer test with more time to exercise the circuitry.
But, the clincher was when we put our test fixture and theirs side by side and ran boards through both in tandem. Some failed in their fixture while passing in ours. Some failed in ours and passed in theirs... Some did a pass/fail switch between fixtures when run again on each one. It was bizarre! But, the problem was observed first-hand by both parties.
The customer investigated and ran across a possible design issue where system processor memory was designed onto a separate RAM board, which was connected to the processor board via an interconnect "backplane". Depending on the proximity of the boards, and the race conditions set up by the minute differences in signal strength each time a board was inserted into the backplane, we could have a fail or a pass on either set. The fix was using a processor board with on-board memory, and leaving the old design behind.
Bottom line: There is a lot more to this than what meets the eye sometimes, so pursue this with the customer. It becomes a team effort where both of you may eventually understand the source of the problem and arrive at a reasonable approach to address it at either or both locations. It did take us awhile to convince the customer it wasn't something we were doing (or weren't doing), and for them to take a look at the differences in test configuration. It may not be an easy fix. It took us 4 years (yes, that is the number four) to convince them that something beyond our control was happening...
Dale Ritzen, CQA
Quality Manager/ISO Management Representative
Austin Manufacturing Services
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Tuesday, December 23, 2008 10:34 PM
To: [log in to unmask]
Subject: Re: [TN] What could be the root cause for a failed board that passed functiona test after going through reflow for the 2nd time?
It could be the functional test itself. Perhaps the board is fine but the test is flakey.
Do the board fail your functional test on return? Does reflow result in a pass?
Picture this: boards pass your test. Boards fail their test. Presume they are the same test. Return boards . . . Reflow, pass test. Send back, pass tests on customer's site, pure coincidence.
Possible issues, program problems at functional test, clock problems on functional testers.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rudolph yu
Sent: Monday, December 22, 2008 1:35 PM
To: [log in to unmask]
Subject: [TN] What could be the root cause for a failed board that passed functiona test after going through reflow for the 2nd time?
Hi:
We have a proto assembly that passed the functional test initially. But after we shipped it to the customer, it failed at the their site for the same kind of test. After we received the board back, we reflowed it using the same reflow profile, and the board would funcation once again...
We checked the boards under 5DX after we received it back from the customer and found no defects on it.
What could be causing this? and why the assembly would pass the test in the first place?
Here iare couple areas that I could think of...but not sure if they are valid.
1. Certain parts (microBGA) may be better off to have underfill underneath for thermal mismatch? ( Need to check spec) 2. During handling and shipping, the board may be stressed to a degree that a microfacture is formed.
What other areas could cause this problem.
Thanks
Rudolph
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