Hi, Yehuda,
There have been countles posts on this subject in the past, and a trawl
through the archives searching for either HASL or ENIG should yield you
more reading material than you can comfortably handle this side of
Christmas.
Simply, though, I use both finishes on boards in a single piece of
equipment. I chose HASL for boards that don't contain any BGA's or other
components that require a particularly flat mounting surface, and ENIG for
boards with BGA's on them. At the time ENIG was known to have possible
problems (the dreaded Black Pad), but the causes and cures were also known.
Overall, if the problems could be avoided, ENIG seemed to be the best
finish for my application. An alternative that provided equally good
flatness was Immersion Tin, but I was shy of this because of all the talk
of whiskers, oxidation and other issues that I didn't want to get into.
ENIG, properly done, seemed stable and durable for boards that were
possibly going to be around for a while before being soldered.
Given a new-design project, I would now look at something like Immersion
Tin for everything, to have a common finish and to avoid the hot dip
process involved in HASL coating. The whiskers issue, such as it was, now
seems to have been largely overcome. I am still in the PbSn solder game for
my Class 3 boards, and use pretty large BGA's by current standards - 35mm
square with 1.27mm pitch - but we'll use smaller ones, no doubt, as time
goes on.
Peter
Ervin Weisz <[log in to unmask]> 30/05/2003 05:38 AM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Ervin Weisz
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Enig? HASL?
Dear Technetters,
As many others, I am considered about the "ENIG vs. HASL vs. another few
finishes".
I wonder what do people specify in those industries that require 0
failures: defense industry, automotive, aerospace, etc.
Mainly, I would like to know what do companies in such fields specify for
boards that are populated with small BGAs (0.032" pitch and lower), also
known as CSPs.Boards that have very high reliability requirements and have
advances packages - what surface finish is required/recommended for the
boards ??
I would appreciate links to existing specs., personal information, or
anything you can spare on this subject.
Thanks,
Yehuda Weisz
Process Engineer - PCB production
Do you Yahoo!?
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