Hi Steve,

Myself, I would NOT accept ENIG under the solder mask.  If the board
shop doesn't have an LPI that can survive ENIG...well, that's a big red
flag!  For a second opinion, go ask your rework operators.  If this
board has BGA, then WHEN you rework (and you know you will), you will
pop off the soldermask web far more often with ENIG under the soldermask
than with SMOC.  

-Ryan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Gregory
Sent: Wednesday, May 11, 2005 7:33 AM
To: [log in to unmask]
Subject: [TN] LPI adhesion on ENIG vs. copper...

Mornin' all you 'Netters!

Gotta question. We're getting a board quoted to buy, and the shop has
come back for some relief on some notes on the drawing that state:

Process Notes:

1. Plate all exposed areas with Electroless Immersion Gold
Nickel 100 microinches thk., Gold 2-10 microinches thk. min.

2. Apply LPI soldermask over bare copper (SMOBC)
Color: Green
Conform to IPC-SM-840, Class H Current rev.
Resizing of soldermask pad clearances may be
required due to suppliers choice of material and/or
process. soldermask clearance for vias to be .004 larger than drill
hole.

The fab house is asking to plate the whole board with ENIG, and then
apply
the soldermask because they say that the ENIG process after applying the
LPI
will make the mask look ugly.

I know the ENIG process can be tough on soldermasks, but I thought that
problem
has already been worked out...

I gues my real question is; is the adhesion of LPI over ENIG any worse
or
better than
SMOBC?

My gut feel is to tell the fab house to comply with the notes on the
drawing, I really
don't want to ask our customer if the fab house can deviate from the
notes
on the
drawing. But on the other hand, I don't want to get a raggedy looking
board
from
them if they don't have their ENIG processes in control...

Kind regards,

-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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If you are not the intended recipient, you may not copy, use or deliver
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