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July 2000

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Subject:
From:
"Goldman, Patricia J." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 26 Jul 2000 15:49:48 -0400
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Steve,

From the IPC-PE-740 Troubleshooting Guide, under Section 15.1.3 - Liquid
Photoimageable (LPI) Solder Resist, Problem G:
Problem - "Bubbles or craters in dried resist film (usually in thickest
areas of the resist).  Bubbles or craters following the tack dry are casued
by air entrapment in the dried resist film.  When they appear after
exposure, it is usually the result of solvents left in the dried film which
volatilize and move the film surface when under vacuum."
List of Causes:  "Excessive print/flood speed.  Poor screen release.
Excessive mixing of ink.  Tack dry cycle too short or temperature too low.
Insufficient air flow in oven.  Tack dry temperature too hot (results in
skinning over of mask, causing inefficient solvent release)."
Corresponding Actions are also listed, but I don't think that matters to you
at this point.

I am Chairman of the Process Effects Subcommittee that produced the PE-740.
We are just about to begin another revision (at the fall meeting in Miami,
in mid-Sept.  The photos are great!  I would like to get them  to add to
PE-740, also any replies that don't come through Technet.  How can I
download those photos, or can you send them to me?
Thanks, I really appreciate it!

BTW, PE-740 has 21 Chapters in all, covering all aspects of Troubleshooting
for Printed Board Manufacture and Assembly, including Test/Inspect.

We are looking for volunteers, too, to work on the upcoming revision.
Contact me directly at [log in to unmask] if you are interested in helping us
out!

Patty
Patricia J. Goldman
PPG Industries, Inc.
412-492-5516
[log in to unmask]


-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Wednesday, July 26, 2000 3:11 PM
To: [log in to unmask]
Subject: [TN] "Bubbly Soldermask..."


Hi all!

We just got some boards in at receiving inspection that have thousands of
little "bubbles" in the soldermask all over the boards...they seem to
concentrate all along the edges of the features of the board. You can see
pictures of it at:

http://www.driveway.com/share?sid=e25a88c4.8e904&name=Pictures

One picture is bubblemask.jpg, the other is bubblemask2.jpg...what would
cause that? It's a LPI...don't know the brand name. I'm thinking that either
the boards weren't dry or cleaned well prior to soldermasking them. I'm
rejecting the boards of course...

My freedrive is filling up fast with all the pictures of the "pretty boards"
that we get from our vendors!!!

-Steve Gregory-

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