Many things can cause measeling. Some of the sources I've seen are:
1) Extreme Thermal Excursions. Like excessive HASL passes.
2) Bending or flexing the PCB while it's still hot from HASL.
3) Excessive heat from assembly.
4) Excessive rework from assembly.
5) Inadequate preheat before a thermal excursion.
6) Excessively fast heat rise during lamination.(Resin starved)
7) Thick PCBs that absorbed moisture.
...to name a few...
The comment "edge of the panel" makes me wonder. Can you explain a
little more indepth on this?
Also...measeling is white crosses where the fiberglass bundles cross.
That becomes the weakest point where fracturing occurs (or slight
disbonding). Make sure we're not confusing measeling with air entrapment
or delamination.
Groovy
-----Original Message-----
From: Franklin [mailto:[log in to unmask]]
Sent: Thursday, August 19, 1999 1:26 PM
To: [log in to unmask]
Subject: [TN] Measling
Here's one for you guys, and gal's.
We are witnessing measling in sporadic fashion.
It usually occurs along the edge of the panel, sometimes encroaching on the
boards, sometimes not.
We have already contacted our supplier, for their huh hum, expertise.
We pulled and reviewed again, all process records. There has been no change
in the process. Verification and calibration records reflect proper
equipment function.
This is happening with 7629 pre-preg in 12 x 18 and 18 x 24 sizes
We had pulled the material with the same lot number, the problem went away
just as quick.
Well, it repeated itself a week or two later, again we switched to a
different batch of material, the problem went away.
With the supplier on-hand, we laid up a book using pre-preg from the batch
we had earlier observed measling from, as well as from another batch, there
were not any measles observed, we repeated this, and again there were
measles.
We went back to the process, re-checked everything, still no significant
changes.
Our supplier has been in-house for three days running experiment's, they
even brought someone in to assist him, they are just as puzzled.
Samples have been sent to Microtek Labs for their analysis/opinion, no
response so far.
Just wondering, does anyone out there want to take a shot at this one.
Thanks,
Franklin D Asbell
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