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April 2002

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 19 Apr 2002 14:47:35 -0700
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Brian:
There are several vinyl based temporary peelable masks that should work.
These products can be applied by printing using an imaged screen, similar
to(non-photoimageable)permanent soldermask application. They normally
require a post application bake to achieve the proper chemical resistant
properties and release characteristics.
It should stand up to your electroplated Ni and Au processes. In some cases
it is somewhat of a pain to remove depending on the size and configuration,
but worth a try.
Lackwerke Peters GmbH, MacDermid, Electra and Alpha Metals all used to carry
these types of products.


Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076

-----Original Message-----
From: Brian L. Guidi [mailto:[log in to unmask]]
Sent: Friday, April 19, 2002 12:45 PM
To: [log in to unmask]
Subject: [TN] Peelable Soldermask


Good afternoon fellow techies...
     I am searching for information on peelable soldermask, or an
acceptable alternative. I have an application which requires temporary
coverage of immersion gold plated fingers, through subsequent wet process
operations (additional 'electrolytic' gold plating). I need to cover the
fingers so they do not plate up when the electro-deposited gold is added
(the nets are connected) to the other end of the board. The situation is
complicated by the fact that the area requiring coverage is approximately
.012" below the external surface of the board, therefore standard
etch/plate dryfilm is not practical due to voiding. I'll try to provide a
mental picture: Imaging a rectangular board 2" long by .500" wide. It's a 6
layer board. On one end, a portion of L4/5 about .750" long, extends beyond
the rest of the part (along the length) about .400". These "wings" are the
portion requiring coverage during the plating process that is happening at
the other end of the board.
     Platers tape has been ruled out as an option due to volume. The plan
is to apply a dryfilm soldermask to the external board surfaces to
permanently protect/insulate the via's, and then apply a peelable mask over
the same area which would conform to the 'drop-down' (.012") and cover the
exposed fingers on L4/5. The peelable soldermask would then be removed to
expose the fingers to the cleaning solutions.
     I am looking for material recommendations, vendors providing peelable
mask application services, and any practical experience anyone has had with
a similar situation. I hope the explanation is not too foggy. It is Friday
after all, and I have a meeting with Sam Adams in about an hour and a half!
     Thanks in advance for your help and insight...

Brian Guidi
Product Engineer
Teledyne Electronic Technologies
Tel: (603) 889-6191  X:310
Fax: (603) 886-2977
E-mail: [log in to unmask]

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