Phil,

We are also considering making the switch from tin/lead to tin plating as initially an etch resist only.  We are however interested in your comment on using tin only as a final finish.  Standard production would remain SMOBC...

1. Can tin plating be offered as an alternative to our customers concerned about pad finish for SMT applications?

2.  Are there problems with bonding between LPI mask and the tin plating?

Any information, pro's con's, on this with respect to fabrication and assembly would be appreciated.

Regards
John Parsons
Circuit Graphics Ltd.
[log in to unmask]

----------
From: 	[log in to unmask][SMTP:[log in to unmask]]
Sent: 	Tuesday, June 18, 1996 11:13 AM
To: 	[log in to unmask]
Subject: 	FAB Re Tin plt. instead of Sn/Pb

Paul.

If I understand your process, you are only going to use tin as an etch resist
and strip it and go SMOBC

A supplier down in Conn., MacDermid, sells a tin electroplate formulation
used mainly for your type of process and is one of the cheapest based on a
tin sulphate bath.  You will find the tin stripping easier and faster than
the tin/lead.  Obviously, after etching don't fuse it and don't use
solderbright.  The plating is pretty normal and you can convert your tin/lead
process and pre-tin/lead pickle using the same process line and change the
acid predip accordingly.   
The tin thickness minimum is about 0.0003 inch, but to be safe a 0.0005 is
often used.

Your process removes all of the tin plating and you  are not concerned with
whiskers, slivers and gray tin.  If you are going to use the tin as a final
finish, put another note on technet and I can furnish additional information.

Phil Hinton 
[log in to unmask]