95% of the ENIG bds that we build are processed thru ENIG
after LPI. This is the typical approach with ENIG bds.
As far as adhesion, there are several ways to prepare the
bare copper surface for good LPI adhesion, I.e pumice
scrub, chemical clean, microetching, etc. With the ENIG
surface you don't have all these options, but you still can
achieve acceptable adhesion.
The only valid reason to ENIG before LPI would be that if
the LPI design is covering all the vias with no reliefs.
This means there will be LPI in the holes and that can
cause problems in the ENIG process. I always want to have
all holes open to allow proper rinsing thru the ENIG
process. That's important to me.
Thank you,
Eddie Rocha
South Bay Circuits
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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