Kathy,
If the PWA pass the electrical test (in-line test), it does not mean it is
realiable. Depend on the test you have set up, normally, the in-line
testing is open/short test at PWA level (sub-assembly), not the full
functional test (including testing related to timing = delay, clock
frequency for example). Poor solderability will cause potential failure in
following area:
(1) high resistance joint may result excessive heat, which may cause various
failures related to over heating (high junction temperature, timing,
frequency, delay etc.). The in-line test of <15 min. would not even start
to reveal any of over heating related fault. In addition, testing
sub-assembly in an open area (assembly line house), the over heating issue
is normally not observed due to the convection in the area. When the
sub-assembly being put into the box, you may see the difference.
(2) poor quality solder joints may also cause intermittent (normally at
cold). It is cause by that inability of form metallurgical joints due to
presence of oxide or contaminent (poor solderability). The failure could be
appear to be random over the assembly (drive the poor soul of FA engineer
crazy). If it is in the TH, unless you have x-ray, cross section work alone
possibly exceed the PWA cost. You may catch intermittent if you have test
requirement like ESS (test hot and cold functional).
(3) I just start the list and Bev and others can add more...
When PWB supplier sign up a contract, the qualification is required for
solderability. If the subsequent shipment deviated from the qualification
lot, I believe it is more serious problem than just the poor solderability.
Normally, it should be no problem for vendor to take it back and
re-activated the HASL using something like "Solder Nu" from Kester if it is
an oxide problem. If the vendor refuse to accept problematic lot within the
AGREED shelf life, I'll think your company may see "$" going out of door (at
product level! the cost is 1x at PWB, 10x at sub-assembly, 100x at box
level, priceless for reputation on my equation).
Shelf life and proper storage of the PWB are keys for good solderability.
Hopefully, the PWB in question is not a "vintage" lot (like someone in
purchesing try to save few $ and bought large quantity for "cost cutting
measure")...It is an old story...you are not alone...(you may have a
difficult task to get them return...in this case, my sympathy)...
jk
At 12:44 PM 7/28/99 -0700, you wrote:
>FYI
>
>They (purchasing) did not believe the solderability testing so they had us
>build up boards anyway. When the boards passed test they said there was no
>problem with the boards.
>
>We all know this is not accurrate, because if you put enough solder down you
>can mask off just about any dewetting problem out there.
>
>Believe me I have already pondered the worse case senerio!
>
>Regards,
>Kathy Palumbo
>
>-----Original Message-----
>From: Franklin [mailto:[log in to unmask]]
>Sent: Wednesday, July 28, 1999 12:20 PM
>To: [log in to unmask]
>Subject: Re: [TN] Dewetting Issues
>
>
>Kathy,
>
>Why would you be concerned with 'long term solderability' issues when you
>have this initial solderability condition to deal with? Seems to me the
>argument should be the 'here and now', and not the 'what if'.
>
>All I know about reliability studies are those I have first hand experience
>with, and that being as I wrote above, if they fail from the beginning, they
>will not get any better sitting on a shelf.
>
><smile> Something to ponder.
>
>Franklin D Asbell, CQA
>Network Circuits, Inc.
>Irving, Texas
>
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