Hi Werner,

I once read about a study in which the shelf life of 1 year was
simulated by a baking process. Then the grow of the intermetalic layer
Cu/PbSn was measured. The outcome of this investigation was that the
intermetalic layer increased by 0.8 microns. So to have a good
solderability after storage 1 year
(normal conditions) you only need a minimum of 1 micron of PBSn.
So I don't think that having less than 5 microns will give problems as
long as it is not below 1 micron.

Kind regards
Frank Petit

>----------
>From: 	[log in to unmask][SMTP:[log in to unmask]]
>Sent: 	Saturday, May 24, 1997 4:03 AM
>To: 	[log in to unmask]
>Subject: 	Re: IPC A 600 E:vert hasl
>
>Be careful about thin HASL solder layers; below 5 micro-meters (200
>micro-inches) solderability can decrease rapidly with shelf life. 
>
>Werner Engelmaier
>Engelmaier Associates, Inc.
>Electronic Packaging, Interconnection and Reliability Consulting
>23 Gunther Street
>Mendham, NJ  07945  USA
>Phone & Fax: 201-543-2747
>E-mail: [log in to unmask]
>
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