ENIG process is hard on SM due to the temperatures that most of the
electroless nickels run at and if the SM coating is not thickness enough it
will break down. Applying the ENIG first over the complete board surface of
course will eliminate this possible problem and should not be a cost driver
unless there is large ground areas. I am not sure actually what the peel
strength of SM is over ENIG compared to Cu but I do remember reading some
time ago that they are lower. What ever lower means. Also if it is a
controlled impedance job the ENIG finish may effect the results if no
calculated correctly.

Scott Westheimer
Colonial Circuits
----- Original Message -----
From: "Stephen Gregory" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, May 11, 2005 9:32 AM
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
> __________________________________________________________________
> This message may contain information that is privileged and confidential
> to
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