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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