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Date: | Fri, 29 Sep 95 13:20:42 EST |
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Tin/Nickel has been around for along time. You're absolutely right.
The conductor overhang can be such as to produce bad slivers that can
easily create shorts. A good way to overcome that issue is to tightly
control the plated thickness to an extreme minimal. (Generally this
must be negotiated with the customer up front due to customary Nickel
requirements.) If the deposit thickness is <250 u inches, (50-100
preferred, 100-200 with fairly good results) you can generally cleanly
etch the circuitry with the overhang at a minimal or even removed
during the etching process. If a mild scrub is required, at that
thickness you can eliminate the overhang issue(s). Tin/Nickel,
however, has really only focused on niche markets such as high temp
boards (BIB)and a few others. It really never was widely accepted
due to similar issues that you listed. The tin surface is more
user friendly.
Surface Tin plating is something that many large volume shops
are doing that has been successful. (No solderstrip required. HASL
readily takes to the solderable surfaces with tin over copper.)
I'm waiting to see what their comments are.
______________________________ Reply Separator _________________________________
Subject: Re: Solderability of Electrolytic Tin Plating
Author: [log in to unmask] at SMTPLINK-HADCO
Date: 9/27/95 9:34 PM
In a previous life I worked for a place that made thousands of tin boards.
The customer (Texas Instruments) specified nickel as a migration barrier
between the copper and tin. There is no reason you can't use bright acid
tin as a surface finish. The one caveat we encountered was that using
tin nickel as an etch resist tended to give very sharp edges to the lines
where the etchant undercuts the nickel. Operators can cut their hands
and if you overetch and get slivers they are like little razors.
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On Wed, 27 Sep 1995 [log in to unmask] wrote:
> Does anyone have any experience soldering surface mount devices to
> Electrolytic Tin plating as opposed to Tin/Lead reflow or HAL? We have a
> customer that is interested in this but wants us to ensure that they'll be
> able to solder the boards. They are using a BTU convection oven for
> reflowing the boards after assembly. Thanks in advance for any
> correspondence.
>
>
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