George,
Do you have some pictures of what to look for?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of George H Franck
Sent: Monday, December 15, 2003 10:41 AM
To: [log in to unmask]
Subject: Re: [TN] Problem With PCB Opens
I concur with everyone's comments made so far. This (my opinion) is the
last Printed Wiring Board defect which can slip through all the quality and
inspection processes and create a field failure. The causes of the opens
will point back to poor process controls on some rather mundane chemical
tanks in your supplier's process. Having run a board shop in the 1980's, I
learned this the hard way. (Continued thanks to Ken Nevar, a now retired
Shipley rep. He had Shipley Employee number 6.)
If the defect is caused by process controls in the chemical process, the
defect can be expected to develop in every board in that lot, (and probably
a few other lots too.) You might want to consider a recall of the boards,
if yours is that kind of product.
The beginnings of these defects can be seen during cross section analysis.
I have been able to verify that some evidence is present in the lot
acceptance cross sections of boards I had returns on. However, I usually
could only identify the innerconnect defects prior to particular cross
section treatment. This treatment is done to the cross section to bring
out the grain structure and interfaces in the metal. This is done with a
light etchant applied to the polished cross section for a few seconds.
This etching tends to mask the defect.
Also, if the cross sections are not well polished, the innerconnect defect
can also be masked.
It is a very easy defect to miss in typical cross section inspections
processes. I have brought section mounts on my visits to suppliers (only
one with known innerconnect defect in it ) to have their operators prepare
and inspect them to see what defects they find. If they don't find the
defect, I point them out, and then do some training to help them to find
them in the future.
One of the responses suggested the use of electrical test to find this
defect, looking for higher resistance connections. While this will find
some of the defects, it will not find them all. Neither will it fix the
problem in the chemical tanks. You will also find that suppliers will
begin to charge you more for this testing, as they will test boards
multiple times to get them to pass. Usually the high resistances are
caused by higher test pin to board resistances, not innerconnect defects,
which is why they will run the board multiple times to get a better
contact. This takes more time on the test equipment, which is usually a
limiting step in the suppliers mfg process, hence the higher charges.
Be sure you consider this experience when you next select a supplier for
your PWB needs.
Good Luck,
George Franck, CID+
Quality Assurance
703 295 2635
Eric Stellrecht
<estellrecht@DRS To: [log in to unmask]
-EWNS.COM> cc:
Sent by: TechNet Subject: [TN] Problem With
PCB Opens
<[log in to unmask]
>
12/15/2003 09:10
AM
Please respond
to "TechNet
E-Mail Forum.";
Please respond
to Eric
Stellrecht
Technet Members,
We have identified a field return trend in a line of circuit boards.
The problem is occurs which a trace separates from the plated through hole
causing an open circuit. Unfortunatly, we had to destructively analyze two
boards to reach this solution. The failure analysis points to a
manufacturing defect that will potentially affect an entire lot of boards.
We are looking for a non-destructive way to analyze this lot of boards to
determine whether or not a particular board suffers from a partially or
intermittant open condition, on its way to becoming a hard open. Any
recommendations would be greatly appreciated. Thanks in advance...
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