Denny, thanks. So far, the responses have backed the problem as being
elsewhere. At one suggestion, I'm going to get one cross sectioned.
Bob
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
Sent: Tuesday, May 27, 2008 1:46 PM
To: [log in to unmask]
Subject: Re: [TN] PTH's With Immersion Silver
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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