Charles,

In my experience, copper-tin IMCs are normally 1-2 um (40-80 uin) thick after HASL.  The rule of thumb
minimum solder coating thickness is 300 uin (0.3 mils) for a 1 year shelf life.  This minimum was based on
extensive aging studies of solder coatings by Tin Research Institute (many years ago).
Hope this helps.

Ed Hare
--
               SEM Lab, Inc.
Scanning Electron Microscopy and Failure Analysis
               Snohomish, WA
               (425)335-4400
           http://www.sem-lab.com

Charles Barker wrote:

> I am getting differing information from different suppliers of PWB's with
> regard to solder thickness requirements after HASL. Some say 100 to 500
> u-inches, others say 500-800 u-inches and yet others say 1200-3000 u-inches
> (.0012" to .003"). We are looking for 6 months to one year of solderability
> with storage being in an air-conditioned environment with well less than
> saturation humidity in the stockroom. (Generally temp is in the 70 to 75
> deg F range, relative humidity 50 percentish +/- 10 percentage points.)
>
> Can some one tell me what the height of the "normal" intermetallics is on a
> HASLed SMT pad and how much additional solder coating is needed to prevent
> deterioration of the solderability of the pads?
>
> Thanks all,
>
> Charlie B.
>
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