One issue that OSP's can not resolve that HASL can, is confirming the
inherent solderability of the copper. We have experienced busts where very
thin layers of soldermask residue or else incomplete tin stripping has
caused what looks like a nice clean copper surface to be unsolderable. With
OSP's you don't realize the problem until after many expensive components
have been placed. It is possible to scrape the pads that don't wet and
repair, but there is the question of all the other areas on the board being
suspect. We end up scrapping this product rather than repairing. An even
more prevalent issue is if the product has via in pads, then if the via hole
is not sufficiently rinsed and thoroughly dried, the OSP protection on the
surface of the pad is degraded over time and can cause soldering issues.
Again, this is not seen until after surface mount and is not something we
would repair. It doesn't take too many issues such as this to make OSP's
less desirable. HASL has its own issues (coplanarity and cleanliness) being
the two that most effect the assembler. With all this being said, many
Lucent locations have decided upon Immersion Silver as the coating of
choice.
Thanks,
Robert Furrow
Printed Wiring Board Engineer
Strategic Supply Global Account Manager
Supply Chain Networks
Lucent Technologies
978-960-3224 [log in to unmask]
-----Original Message-----
From: Andrew Hoggan [mailto:[log in to unmask]]
Sent: Friday, June 29, 2001 3:44 AM
To: [log in to unmask]
Subject: Re: [TN] **** PCB's - HASL -v- OSP
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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