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May 2005

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Subject:
From:
Frank Kimmey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Frank Kimmey <[log in to unmask]>
Date:
Wed, 11 May 2005 06:50:21 -0700
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Steve,
SMOBC came about due to the reflowing of SnPb under LPI mask during reflow (causes some real ugly blistering and such).
If ENIG is used than there is only the "but we have had that note on our drawing for years" argument
It is my understanding that there are numerous LPI chemistries that will survive ENIG processing today, but there are also many that will not.
Personally I think you may be doing your customer a disservice if you don't at least advise them of the options and then when they are adamant about "build to print" they will understand why you needed to go to a higher cost Fab house to get their product completed.
A suggested addition to their notes may be:

Apply LPI soldermask over bare copper (SMOBC) or gold.

It seems to work for us and allows the supplier to best fit their process abilities.
Good Luck,
FNK

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen Gregory
Sent: Wednesday, May 11, 2005 6:33 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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