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Date: | Fri, 12 Jan 1996 15:43:22 PST |
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On Fri, 12 Jan 96 11:05:23 CST Nancy Nelson wrote:
> From: Nancy Nelson <[log in to unmask]>
> Date: Fri, 12 Jan 96 11:05:23 CST
> Subject: OSP Questions
> To: [log in to unmask]
>
> Can anyone tell me where to get Data on a "Silver Nitrate Test" to
> check thickness on OSP's.
>
> Has anyone arrived on an acceptable thickness range on OSP's at this
> time?
>
> Thanks in Advance for any response
>
> Nancy Nelson PCA Eng. Services
> Dell Computer
> 512.728.0016
> Fax 512.728.3653
>
Nancy: A silver nitrate test doesn't actually "check thickness".
It is a tool that can be used to verify the presence and
integrity of the coating.Silver nitrate of a known normality
(0.01-0.10N) is placed by dropper on the board and held for
a given time (10-60sec.).This is rinsed dried and inspected.
A discolored or darkened appearance of the copper MAY indi-
cate an insufficient coating.
There isn't any one acceptable thickness,it really depends
on the type of OSP being used and your assembly process
and chemistries.If possible work with the PCB supplier and
their OSP vendor.They should be able to give you a starting
point to test from.Then determine what thicness works best
for your application.
Assuming your PCB supplier has the capability to do quan-
atative thickness testing(typically I.R.or U.V.)you can
establish an acceptable thickness range with them.
Since the formation of the OSP coating thickness is pretty
much self limiting,thin coating will probably be more of a
concern.By empirically testing boards below and within the
specification with silver nitrate at a given normality and
time you could arrive at a spot test for coating integrity.
If possible the best test is to run an unpopulated PCB thru
your processes.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
(206)356-6076
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