Peter: I will try and address your issues.
1. Yes, the OSP coating should uniformly coat the holes. The board thickness
and hole size should not affect the coating thickness. However if the bare
board fabricator does not have his process under control(chemistry,
application, rinsing, drying, etc.) you could see inconsistencies in the
coating. But I would suspect it to be over the entire board and not
selectively in a given hole size.
2. The barrels of the incoming board should not be oxidized, again this is
assuming the fabricator has his process under control. The coating thickness
is not optically measurable in a cross-section, it is too thin and basically
transparent. However there is a test we have done in the past using a 0.1N
silver nitrate. The solution is applied to the board in dropper form then
rinsed off after a determined amount of time. If the coating is sufficient
the copper should not turn dark up to about 45-60 secs of exposure.
There are other more sophisticated tests that can be done to measure coating
thickness and performance. You might want to contact the local Enthone rep
and discuss this with him.
3. We have used various CU-106 coatings in production for about 8-10 years.
This includes single, double sided reflow, mixed technology, wavesolder,
aqueous wash and semi-aqueous wash. The more process cycles and exposure to
fluxes, chemistry and heat the board sees the more deterioration of the
coating. Reflow temperatures will have the biggest negative impact on the
coating.
We have been successful on a daily basis in producing PCA's that are double
sided no-clean SMT, semi-aqueous washed, wavesoldered OA flux and aqueous
washed.
A couple of key points are:
1. Try and minimize hold times between process steps. We normally will
process thru SM within 8-16 hrs and wavesolder within 24 hrs after that. We
have tested to much longer times but the coating does continues to
deteriorate making it harder to activate.
2. It sounds like you are using organic acid water soluble flux in
wavesolder. If you are that's good, if not look into it. You need the OA
activity level.
3. Regarding inconstant hole fill at wavesolder. If your OSP coating is
properly applied by the fabricator I would suspect your wavesolder flux
application. The OSP coating is destroyed by contact with the flux and
preheat. So if the flux is not fully coating and coming up thru to the
topside of the hole the copper at the top of the hole will not be activated
and will not take solder.
Good Luck
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: Peter Verbiest [mailto:[log in to unmask]]
Sent: Friday, March 26, 2004 4:31 PM
To: 'Barmuta, Mike'; 'TechNet E-Mail Forum.'
Subject: RE: [TN] Measuring OSP in PTH's
Thanks Mike,
We are seeing inconsistencies in hole fill during wave solder on a card that
was previously immersion Ag finished and yielded minimal hole fill problems.
It is true that we may be able to overcome the inconsistencies by process
changes (i.e. selective pallet redesign, different fluxes/preheat settings,
etc.) but first we would like to understand;
1. Is OSP uniformly coating the inside of PTH barrels on virgin PCBs and to
what extent is PCB thickness and/or hole size affecting the coating
thickness.
2. Is CuO present in barrels in virgin cards. (Could perform x-sections and
analyze but this could be hit and miss.)
3. Is CuO present after 1 SMT reflow, 1 aqueous wash, 2 SMT reflows, 2
aqueous washes, etc.
Thanks all,
Peter
-----Original Message-----
From: Barmuta, Mike [mailto:[log in to unmask]]
Sent: Thursday, March 25, 2004 3:25 PM
To: 'TechNet E-Mail Forum.'; 'Peter Verbiest'
Cc: Barmuta, Mike
Subject: RE: [TN] Measuring OSP in PTH's
Peter: You may want to check the TechNet archives there's a lot of
information on OSP coatings.
The coating itself is a reaction mechanism with the exposed surface copper
of the PCB. It forms be a uniform thickness on the holes and surfaces and is
pretty much self limiting. It is not like a paint or even a rosin type
coating that would have various types of build-up thickness at edges, lips,
large flat areas, etc. Where viscosity and topography can affect the deposit
thickness.
It is possible that extremely small vias may not have the same amount of
coating due to solution transfer and rinsing. However I've never found that
to be a problem.
What exactly is it that you are trying to determine? Are you having process
problems? There are many things that can impact this and ways to measure,
test and overcome them depending on the situation.
Regards
Mike Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Peter Verbiest
Sent: Thursday, March 25, 2004 1:18 PM
To: [log in to unmask]
Subject: [TN] Measuring OSP in PTH's
Hi All,
I have a need to better understand the distribution of OSP (i.e. Entek
Cu-106 A) along the wall surfaces of different size PTH's.
I would appreciate any literature, ideas, or recommendations on approaches
to collect such information.
Thank you,
Peter Verbiest
Jabil Circuit
San Jose, CA
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