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June 2003

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Subject:
From:
Ofer Cohen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 11 Jun 2003 08:25:27 +0200
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Peter,
Although the question is to Dave, I will contribute my own 2 cents. Because
I made the decision some time ago, I would be glad to hear (=read, in this
case) comments.

As long as the components were in the sizes down to minimum of 0402 for
discrete components, and pitch of 1 mm for BGAs and 0.5 mm for other
components I lived (and still do) happily with HASL. This is my preferable
coating, because a) every PCB manufacturer does it best; b) the handling
during the assembly and the assembly processes are simple and commonly
known.

The problems started when the army of the R&D people conquered the 0.8 mm
pitch BGAs. I know that HASL is still acceptable in this pitch. However, the
circuit is sensitive and I wanted to make it more robust. I considered 4
choices:
a) immersion tin and OSP - problematic in handling. I have to trust my CM
that even in the third shift the SMT line operators will wear clean gloves.
I am a little paranoid about compliance of employees to procedures that are
less comfortable to implement. Apart of it, I had bad experience with some
PCB manufacturers performing this finish.
b) ENIG - not to speak of black pads, I have many press-fit connectors, and
the nickel layer is known to have long-term reliability problems in this
case, because it cracks and causes disconnections.
c) Immersion silver - was left alone and selected as default. Indeed, it
needs some time to get used to it: the wetting is not perfect, handling and
storage period are still have to be monitored. Yet, it seems to be the
optimal solution.

Yet, I want to emphasize that my default finish is HASL.

Regards
Ofer Cohen
Quality Assurance Manager
Seabridge Ltd.

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, June 11, 2003 1:52 AM
To: [log in to unmask]
Subject: Re: [TN] LCC HASL and Immersion Silver


Hi, Dave,

Can you shed a little more light in this dark world and give us the story
of why you choose Immersion Silver over, say, Immsersion Tin for BGAs and
Fine-Pitch stuff. I'm interested from the Class 3 High Reliability
perspective and currently use ENIG for this type of assembly. For future
designs, though, I intend to move to either ImAg or ImSn, but haven't
determined which one yet.

TIA

Peter

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