Hi Kevin,
I like OSP. When done properly, it solders great. 

The material is not a conductor, but it is easily pierced by a probe. It
might not be good for a test point. Printing solder on the test points
probably makes sense.

As I understand it, Immersion Ag is protected with an OSP as part of the
plating chemistry. So, there is some truth to what you read. However, the
finishes are different. Silver oxide is easily reduced. In my experience the
finish is more forgiving than OSP over copper. And, because it is a plating
process, unlike OSP over copper, you get the assurance that the copper on
the board will accept plating. 

Your process, optimized for ImAg should be fine with OSP.


Guy  


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Tuesday, May 21, 2013 12:39 PM
To: [log in to unmask]
Subject: [TN] OSP processing inputs?

Hi all,

It looks like I will be getting some PCBs with OSP finish on them to process
thru SMT.  I've not yet used this surface finish, so for me there are a lot
of unknowns.
Some background info:
1 The PCBs will be single sided SMT, so I will not have to worry about
solderability of second side reflow.
2 We are using Sn63Pb37, not lead-free.
3 We are using water soluble ORM0 paste and DI water wash only (no chemical)
4 We typically process with ImAg.
5 MIL/AERO target service environment

I have read some that shelf life is reduced to around 6 months and that OSP
covered pads cannot be used as test points and therefore test pads need to
be solder coated.  I've also read some of the conference papers which seem
to indicate corrosion/environmental performance is at least as good as what
we would get with ImAg.

Any other suggestions / caveats ?

Is there an IPC spec for this finish?

Thanks in advance!

Kevin


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