Hi Patricia
Do you mean the boards were stored one year before assembly and failed or were assembled and in field use or storage before failure? Thids could help diagnose potential root cuase.
Are the defective microsections voids or cracks? If you can post photos, Bob Neves or I can give you a second opinion.
I generally agree with Bob's remarks, likely to be a fatigue fracture from (initial) thermal expansion during soldering (which can nucleate fractures) combined with cyclic stress from operation, a common wearout mechanism.
However, if plating voids are present you make have multiple problems or simply haven't found voids in other holes (can be hit or miss).
But the symptom of intermitent opens at elevated temperature is usually what Bob described.
Regards
C.B. Katzko
Research + Development
Meadville Group
by Blackberry
From: Patricia Lui [[log in to unmask]]
Sent: 10/26/2009 10:59 PM ZE8
To: [log in to unmask]
Subject: [TGAsia] help in determining an appropriate test
Dear Friends,
I have the following issue which is not able to determine the exact cause of the failure, the details are as follows:
PCBA boards which is already 1 year old
put to thermal aging cycle
go through functional test (boards are run at low current)
via hole at a certain location failed with open circuit when boards are hot
when boards are cold via holes become connected and ok
Checks done:
Micro section on failed via holes
2pcs PCBA boards failed via holes found voids
3pcs PCBA boards failed via holes found no abnormility, hole walls are all within specs, all are ok
so root cause is still unknown
Suspected failure due to the folowing:
moisture absorption in the PCBA
material cannot withstand thermal cycle
a wrong material is sellected, maybe a higher Tg / Td material should be selected
customer design issue
Currently we have the following boards on hand and is deciding sending to a lab for analysis but do not know what test is the most appropriate. We have:
10pcs of the same batch bareboards on hand
2pcs PCBA with identified via hole failure boards
I am hoping that someone can give me a piece of advise on what test I should engage a PCB test lab to do inorder to be able to determine the cause of this issue.
Hope to have your favourable advise.
Thanks & Best Regards
Patricia Lui
Xuan Technologies
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