Resin starvation (not measling) often occurs on dry builds in low pressure
areas.
Do you have areas of the panel with stacked internal ground planes (e.g., 1
or 2 oz. Cu)?
These are the high pressure areas; indeed, prior to the resin's melt temp.,
they may be
the ONLY areas with significant pressure. Add copper fill to equalize the
lam pressure
across the panel. What % fill is your border copper? You might try a
solid copper border
(with vacuum channels carved out) for internal ground plane layers. Often
low-tech 4-layer
boards are built using only 7628/7629 for dielectrics - this is economical
but also quite dry
(i.e., low resin content). If the extra border copper doesn't do the
trick, crank up your
lamination pressure to 250-300 psi (assuming it's not a CI job with
critical dielectrics).
Make sure your transition from kiss pressure to full pressure precedes the
melt temp
(210F-220F for FR4) on the outer panels; if anything, hit it early - never
late. You might
also verify that your vacuum cycle is adequate.
Joe Felts
-----Original Message-----
From: Franklin [SMTP:[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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