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February 1998

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Mon, 23 Feb 1998 16:42:15 -0600
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     Kathy,

     You should have no problems with using the OSP (any OSP), I'm speaking
     of Enthone Entek 106A for the purpose of this discussion.  From past
     experience we have used OSP over all copper surfaces with no problems.
     We have done experimenting with placing clear soldermask over the
     fiducial area due to copper oxide hindering with P&P.  The reflection
     from the soldermask was the problem.  I would avoid using it.  Later.

     John Gulley


______________________________ Reply Separator _________________________________
Subject: Re: [TN] gold over entire board
Author:  Kathy Palumbo <[log in to unmask]> at Internet
Date:    2/23/98 9:15 AM


Steve,

When you OSP coat your board fiducials is there anything special you
have to do for your Pick & Place (Zevatech) machine to see it?

Thanks in advance,
Kathy Palumbo
Viking Components

> ----------
> From:         Stephen R. Gregory[SMTP:[log in to unmask]]
> Sent:         Friday, February 20, 1998 1:24 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] gold over entire board
>
> I'd like to add to David's comments too...I tend to agree with him on
> his
> point about OSP's. In order of preference, the board finishes I'd
> `druther see
> on SMT boards that I'd have to build are 1. OSP, 2. Flash Gold, and 3.
> HASL.
>
> A few more good things that I've observed with OSP's in addition to
> what David
> said are; 1. Less solder bridges on fine pitch - The solder seems to
> stay
> right where it's printed during reflow on a OSP coated board...it's
> like the
> flux has to use some of it's activity to go through the OSP before it
> reaches
> the pad surface and does it's thing, and all that is confined to the
> area
> where the paste actually is. It's almost like the OSP coating that's
> in
> between the pads acts like a little "dam" if you will, preventing the
> molten
> solder from easily crossing over to an adjacent pad. 2. No heat used
> applying
> OSP's - Less board warping...
>
>      There's a couple of caveats with the board houses that say they
> can do
> OSP's. I've run across a few that say they do OSP's, because it's easy
> to say
> that. Only because one can go out and buy gallons of the chemical,
> pour it in
> some sort of tank to dip the boards in, and  voila'...you're doing OSP
> board
> finishes. But that's really not the best way to apply the coating. The
> thickness of the coating needs to be controlled. It may not be a big
> deal if
> you're in a water soluble process and use flux so active that you can
> solder
> to dirt, but when you're using a no-clean / low activity flux, you'll
> have a
> hard time soldering if the coating is too thick.
>
> One more board house problem I've run across is that they've done the
> bed-of-
> nails testing (or bare board test) after they've applied the
> coating...that's
> a no-no. The probes will break thru the coating and compromise it's
> integrity.
> OSP's are meant to be applied and stay in an unbroken layer until it's
> ready
> to be soldered, that's how it protects the copper from the oxidizing.
>
>                                                         -Steve
> Gregory-
>
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