If there are problems soldering to OSP check the quality of the OSP coating,
too thick and there'll be soldering problems, too thin and there'll be too
much copper oxidation, hence the variability in results. I spent years
following the route that OSP coatings had some magical property that
interfered with soldering. WRONG! OSP coatings are very simple chemistry
that are relatively easily soldered to, however although relatively simple
chemistry they are not necessarily easy to lay down, careful process control
is required to get the correct thickness of coating. Get it wrong and the
above circumstances can occur.
If anyone has OSP issues contact me offline and I can perhaps give you a bit
more info. I have a background in these and soldering materials, note though
that I don't currently work for any suppliers, I am completely independent
these days.
Andrew Hoggan
BBA Associates
www.bba-associates.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of
[log in to unmask]
Sent: Thursday, June 28, 2001 09:12
To: [log in to unmask]
Subject: Re: [TN] **** PCB's - HASL -v- OSP
I am an NPI Engineer at Artesyn technologies and I am new to the Surface
Mount
Technology. Can anyone shed some light on the differences between HASL and
OSP.
We are currently using HASL but are looking at migrating to OSP. What are
the
pros and cons of one over the other? What sort of processing issues do we
see
with OSP on SMT lines?
**Cormac, one responder said co-planarity is one factor to consider in a
comparison, which is true, but not the ONLY reason. If you believe the
marketing literature for OSPs (and if you do, you deserve all the agony you
are about to experience), then the OSP is sacrificial and only survives 1
pass in reflow. Sometimes this is true, other times not true. I have seen
OSP survive 5-6 exposures to reflow conditions without burning off. Lots
of solderability issues if you have multiple passes through reflow. A
significant factor is also the aggressiveness of the flux you will be
using. I have seen a number of manufacturers go to no clean, for the
benefits afforded by a low solids flux, only to find that it was not
aggressive enough to overcome the OSP. If you are using a water soluble
flux, you should not have this problem. If you are going no-clean, then
you have some homework to do.
In addition, we all know that HASL is a nasty, dirty, filthy, rotton (fill
in the descriptor of your choice) process and often leaves nasty, dirty
filthy rotton residues behind. It does nasty things to insulation
resistance. If you are going the no-clean route, HASL residues can kill
your product and sometimes, users of your product. By comparison, OSP is a
much cleaner process and does not impact insulation resistance.
Doug Pauls
Rockwell Collins
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