Frank: One possibility is that the soldermask was not fully removed from
the bottom side of the hole when processed thru the developer at the bare
board fabricator.
The holes hold more mask and are harder to "clean out" than the surface of
the board when going thru the developer. In the developer the nozzles spray
both sides of the board. If the ones that were spaying on the wavesolder or
bottom side of the board were not functioning properly(low pressure,
plugged, etc)they may not of completely stripped the soldermask from the
hole on the bottom side. The rest of the board would be properly developed.
This residual mask could result in poor or insufficient plating in the
bottom side of the holes. However you would still have good plating on both
top and bottom side surface pads and in the top side of the holes, as they
would be clean of any soldermask residues.
The result would be poor solderability on the bottom side of the hole due to
poor plating and/or interference from trace amounts of residual mask and the
rest of the board soldering fine.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: Frank L Norman [mailto:[log in to unmask]]
Sent: Monday, July 28, 2003 11:14 AM
To: [log in to unmask]
Subject: Re: [TN] Wave solder process issue on ENIG pwa
Carrie,
Yes, the bottom side SMT components were put down with chip bonder and
then wave soldered. That's my question also, why did the SMT joint work
out and the through hole fail so miserably, they both were subjected to
the same assemble processes and then when solder joints were attempted
they did not exhibit the same wetting issues. The only thing I know is
that the fabrication of these PWB's were a challenge for the vendor,
because of the book binding not fitting into standard tooling/processes.
Regards,
Frank Norman
Manufacturing Support Engineer
Raytheon, Space and Airborne Systems (SAS)
(805)879-2745
[log in to unmask]
"Morse, Carrie" <[log in to unmask]>
07/28/03 10:52 AM
To: "TechNet E-Mail Forum." <[log in to unmask]>, "Frank L
Norman"
<[log in to unmask]>
cc:
Subject: RE: [TN] Wave solder process issue on ENIG pwa
Frank,
Did you use a "Glue/Paste" process on the SMT that is on the Wave side,
or,
did you get those nice fillets from the wave?
IF you got them from the wave, the questions become:
1. Why nice wetting on the SMT and not on the TH pads?
2. How was the bare board processed at the Fab level?
Before looking at the photos I thought the leads of the comps were
contaminated,
or, the profile was insufficient, or, your contact angle and dwell times
were
not quite sufficient. But, after looking at the photos and seeing the
nice
topside fillet on the TH and nice SMT fillets, I get the feeling that the
plating on the bottomside of the board at the TH comps was compromised at
the
fab level. Maybe the resist was not sufficiently removed prior to
plating.
It's hard to tell from the photo, but, where there is insufficient wetting
on
the wave side pad, what does that section look like? What color is it?
-Carrie
-----Original Message-----
From: Frank L Norman [mailto:[log in to unmask]]
Sent: Monday, July 28, 2003 1:26 PM
To: [log in to unmask]
Subject: [TN] Wave solder process issue on ENIG pwa
Technet,
Looking for comments for the following...
PWA's experienced solder wetting difficulties to plated through holes
including via's during the wave solder process and are unable to be
touched-up by hand. PWA's are two sided multilayer with combination of
rigid board and flex circuits finished with Electroless Nickel Immersion
Gold (ENIG) for a thickness of 100 microinches of Nickel and 5 microinches
of Gold. Top side SMT components were reflowed and bottom side SMT were
wave soldered with excellent results, but as you can see in the pictures
the plated through holes on the wave soldered side had wetting issues.
Interesting thing is the non wave solder side through holes have good
wetting.
SEE PICTURES of pwa's in question at this website.
http://www.ripus.com/images/pwa/index.htm
Regards,
Frank Norman
Manufacturing Support Engineer
Raytheon, Space and Airborne Systems (SAS)
(805)879-2745
[log in to unmask]
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