Larry: First of all their is a ton of information on this topic in the IPC
TechNet archives, take a look at it.

Regarding your questions, the short answer is; it depends.

There are many different OSP coatings available that produce varying
performance based on the coating and it's application by the board
fabricator.
Environmental storage conditions will effect it.
The thermal cycle time, temperature, type of oven etc will effect it.
The type of flux you are using will effect it.
etc etc etc...

I will speak based only on what is seen for the type of OSP coating and
assembly processes we use. You need to qualify the coating type and
processes together.

To answer your questions:
1. We have boards up to a year+ in inventory that do not have soldering
problems. These are stacked together wrapped in plastic. Conditions are
68-78F, 35-55% RH. The OSP coatings are part of the Enthone 106 family.

2.The heat cycles break down the coatings protective properties that prevent
oxidation of the underlying copper. Both time and temperature destroy the
coating, however higher temps(>200F)are more detrimental than just time. The
more thermal cycles the board sees the more oxidized the copper becomes,
making it harder to activate and solder to.
Our worst case process; Kester No-Clean paste with up to two reflow passes
and a glue cure, all using forced air convection ovens. This is followed by
wavesolder with an Alpha WSF. We do not have solderability issues but that's
about as far as we can push the envelope. Any additional thermal exposure
affects solderability.

3. We have gone up to a month between reflow steps and up to a month between
reflow and wavesolder. Obviously you want to complete soldering operations
as quickly as possible. Our goal is usually 2-3 days max, unless something
unforeseen comes up. Also note that we are using a WSF at wavesolder.

Hope this helps.

                                                                Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076

-----Original Message-----
From: Larry Koens [mailto:[log in to unmask]]
Sent: Friday, July 19, 2002 11:57 AM
To: [log in to unmask]
Subject: [TN] OSP


Technet,
I would like to have Technet clarify some questions that I have on OSP
boards. I got into a discussion with some other of my fellow Engineers
today about OSP and we had different opinions and ideas on several
topics related to this.

1.      What is the expected stockroom shelf life of  board? The boards
would sitting on a shelf, unwrapped and stacked one on top of the other.
2.      What happens to the coating after each heat cycle? Does the heat
dissolve the coating or does it make it just stronger and such more
difficult for the flux to penetrate the coating?
3.      Is there any time frame that you would try to complete the
entire assembly in? Would the assembly be more difficult to solder if
there was days between the reflow and wave time frames then if they were
all completed within hours?

thanks in advance
-Larry Koens-


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