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Date: | Thu, 1 May 1997 17:14:07 -0400 |
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I have a multilayer RF PWB application, using Rogers' Duroid 6002,
procured to IPC-HF-318. FEP film is being used as the bond film, 1/2
ounce copper is used on the innerlayers. The part is used in a
high-reliability application.
The problem is that a large percentage of product is being failed at
microsection due to excessive smear. IPC-HF-318 allows up to 25%
smear along the vertical interconnect at the T-Joint. We regularly
see T-Joints with up to 50% and 75% smear. Not all holes in all
sections have this much smear, but if it happens in one hole, the
entire panel is rejected.
RF tests show that, regardless of the amount of smear seen in the
cross-section, the boards are electrically (RF) acceptable. Also,
we've performed thermal cycle testing which indicated no degradation
in RF performance.
SEM micrographs of "as drilled" holes confirm that the smear is due to
the drill operation. Two sets of drill studies have been performed,
with only marginal improvement. The smear is not removed when
subjected to plasma cleaning.
My questions include:
- Is this amount of smear unusual? If it's not, should IPC-HF-318 (or
its successor) be changed?
- Have others seen it before?
- Is this another quirk of 6002?
- Was IPC-HF-318 written for 1 ounce copper, therefore implying that
.00035 inches of smear (25% of 1 ounce copper) is really acceptable?
- Is there any embraced reliability data that may indicate it is not a
reliability problem?
I would appreciate any help in either reducing the problem (smear) or
in determining that IPC-HF-318 is not the appropriate criteria to be
used in accepting/rejecting this condition.
Andy Pedersen
Harris Corp.
[log in to unmask]
407-729-2143
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