Hi Charlie! I hadn't seen an assembler's response so I'll deposit mine for
TechNet dissection. We have qualified immersion gold, immersion tin, and
immersion silver as alternative pwb surface finishes for our manufacturing
processes as HASL replacements. I don't foresee any one of the three
alternatives as becoming "dominate" because each has both pro's and con's:
Immersion gold: wonderfully flat, good long term solderability, good
industry availability, BUT black pad issues, its a nasty chemistry on
soldermask, and soldering to nickel is not soldering to copper
Immersion tin: wonderfully flat, metallurgical compatibility, reworkable,
BUT long term solderability issues, compatibility with soldermasks, and
supply sources
Immersion silver: wonderfully flat, reworkable, great RF design
characteristics, BUT supply source issues, metallurgical questions, and
long term solderability questions
I think that the selection of an alternative surface finishes will become a
question of materials organization within a particular manufacturing
environment - HASL made our choices simpler but was definitely robustness
limiting for certain manufacturing flows (like SMT fine pitch).
Dave Hillman
Rockwell Collins
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Charles McMahon <[log in to unmask]>@ipc.org> on 12/05/2001 11:33:26 AM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: Re: [TN] SURFACE FINISHES
EARL:
Does your view hold the same from an assemblers point of view.
More specifically, in your history, would the assembler prefer ENIG over
SILVER and/or TIN?
THe assemblers I speak with just do not have the background/experience to
decide. However, they
are quick to reject the bare board vendor for what they THINK is a
solderability problem.
(That's when I move with failure review etc. I hope to reduce this
incidence
dramatically by proposing user friendly finishes based on board design.)
Charlie
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
Sent: Wednesday, December 05, 2001 12:14 PM
To: [log in to unmask]
Subject: Re: [TN] SURFACE FINISHES
As a cost factor to you it's nickle and dime stuff. To most board shops I
work with, it is as well. It's a matter of choice so much that it's almost
subjective (whatever looks best though black pad isn't too pretty) -
excluding HASL, or course. I hope you are right about its final demise.
MoonMann
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