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| Date: | Tue, 15 Aug 95 10:37:28 EDT |
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From: Kelly Kovalovsky, Raw Card Quality Engineering
Phone:704-595-7336 Tie Line:795-7336 FAX Ext. 4727
Subject: 0.020" pitch SMT pad widths
We design our 0.020" pitch SMT pads at an 0.011" pad width. Our
specification calls for these pads to finish at 0.011" +/- 0.002" as
measured at the laminate.
The problem is that the pads tend to come in at 0.0085" to 0.0095" at
the top of the pad due to etch factor. Our SMT paste screens are
manufactured at 0.011" nominal. It is the dimension at the top of the
pad that is important to the card assembler. We have requested that
the raw boards be built to meet 0.011" +/- 0.002" as measured at the
top of the pad. This involves compensating the artwork to meet our
requirement.
My questions to the raw board manufacturers are:
1) Is 0.011" +/- 0.002" as measured at the top of a 0.020" pitch pad a
manufacturable feature at an acceptable yield?
2) If so, what comp factor would you use to achieve this finished
dimension?
3) Does board finish (HASL, entek, etc.) put any limitations on your
ability to manufacture this?
IBM Microelectronics Division
6800 IBM Drive MG12/251
Charlotte, NC 28262-8563
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