You got that right Joyce,
And, at the same time, the they point blame to process or material that
are up or down stream from themselves!
I don't tend to like to be constrained by political correctness, but, in
the sprit season, and in deference to those of all faiths...
Have a Happy Holidays Everyone!
Paul Reid
-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Tuesday, December 23, 2008 10:38 AM
To: [log in to unmask]; Paul Reid
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?
Paul, my old age tells me usually the pwb house point finger to
interconnect, the mfg point to material, and so on. That is why the
expert make their money. The mgr want to hear the independent view they
paid too dollar for.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Dec 23 08:18:22 2008
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?
Hi Rudolph,
All experts find a problem that relates to their area of expertise. If
you are sick and you go to a cardiologist you find you have a heart
condition. Next go to the endocrinologist and there is a hormonal
imbalance causing a heart condition. The dietitian finds a nutritional
deficiency due to imbalanced diet that is expressed as hormonal
imbalance that causes the heart condition. The heck of it is, they can
all be correct.
I am a PWB guy, so I will find a PWB problem. Werner mentioned
interconnect failure and I agree that is a strong possibility. The signs
you describe support interconnect failure.
Well here's my input. We found discrepant microvias and capped buried
vias that where temperature and pressure sensitive. At ambient they are
closed, at operational temperatures they are open. Manually twisted they
open, release they close.
If either is present in your PCB design, I would investigate the
reliability of microvias and capped buried vias. Both interconnects can
produce a failure mode that is self healing at ambient . Barrel cracks
and interconnect separation is less prone to be self healing at ambient
and are further down the list of suspect interconnect structures.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
-----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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