In a message dated 2/9/2004 4:55:42 PM Central Standard Time,
[log in to unmask] writes:
Okay, and those times not 'most often' what are the causes in your
experience, of flaking mask?

Hi Franklin!

Not sure who you're directing your question to, but I'll tell you my
experience.

I've just experienced three scenarios for mask failure.

1. The mask was applied over tin (very old design, and SMOBC wasn't called
out on the drawing), and it wasn't caught until the assembly was waved...this
was was quite a while ago.

2. Incompatibility with a certain dry film mask and cleaning chemistry. To be
specific; Dynachem Dynamask (now Shipley's line since they bought it from
Dynachem) and Kyzen Aquanox XJN don't like each other.

3. The last incident was bad surface prep that was acknowledged by the fab
vendor, and what I have pictures of on my page.

Number one of my three occasions was like I said, a long time ago...nobody
should see that anymore. I'd like to think that everybody nowdays know that
solder mask needs to go on over bare copper.

Number two could happen if you happen to use XJN and have a board with the
Dynachem dry film on the board.

Number three could happen to anybody if your fab vendor doesn't have good
checks and balances on the production floor to make sure a step isn't skipped.

The pictures that Sue sent me, looks like an LPI was used. I have never, ever
had any trouble with LPI mask coming off a fab unless it was applied over
something other than bare copper. This tells me that something wasn't quite right
when it was applied. I have a hard time trying to think of what could cause
the mask to come off the board the way that it did on Sue's boards during the
assembly process. I know you haven't seen the pictures yet, but there's great
big areas where the mask came off. The difference between what I saw between
her case and mine, was that the copper is not as shiny on her boards as was
mine, and to me it looks like a LPI was used...which kind of suprises me. LPI
usually is pretty bullet-proof, unless something wasn't right during application.

My 2-cents...

-Steve Gregory-

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