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Date: | Tue, 27 May 2008 13:46:12 EDT |
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The IPC 4553 spec for immersion silver gives a "typical" immersion silver
thickness for the vendors of "thick" plating as 8-12 MICROinches. That means
that with both sides of the hole plated, you could get 16-24 MICROinches of
hole diameter reduction. That is .016 to .025 MILLIinches of hole reduction,
or .016 to .024 mils of reduction from the silver - that is 1/60th to 1/40th
of a mil. I cannot imagine that since you are specifying holes in mils, that
you can even see the reduction in hole diameter due to silver. HASL
tolerance may cause a hole diameter to be reduced a mil or slightly more due to the
curvature due to solder surface tension, as HASL therefor might be say 40
times as thick in the center of the hole barrel as immersion silver, but you/your
board fabricator has problem somewhere else - drilling, copper
electroplating, etc.
Denny Fritz
MacDermid, Inc.
In a message dated 5/27/2008 10:58:07 A.M. Eastern Daylight Time,
[log in to unmask] writes:
We've been using immersion silver on our boards for quite a while with
great success, but in a recent run of a new product, we had the boards
come in with the PTH's used to mount RCA and audio connectors smaller
that usual. The parts came in on the large end so it became very
difficult for the operator to insert them into the board. Both holes
and parts were in tolerance and the holes were specified at the
recommended diameters. Our CM has a woman who spent 20 years working in
pcb fab houses and she tells me that it's not at all unusual to have IS
boards with reduced ID's on the holes as opposed to HASL. Has anyone
else experienced this? If this is the case, we'll have to adjust for
this in the future, but it would be useful to know if this was an
anomaly or a normal condition?
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