Ed,
Thank you for the explanations! We did have some increased solder bridging
recently and I went for changing the flux (I was not aware of the dev in the
pot composition). We had been using for years a no-clean low solid 2.5% flux
(I am not sure whether it is appropriate to point at the manufacturer) and
in general we were satisfied with it. Since it is known that low solids tend
to solder bridging I decided to use some newer, of course no-clean and
relatively low solid flux which was claimed to be better as far as bridging
is concerned. And, yes we have achieved better results! This was just before
the analysis! Taking in mind yours and all other inputs, which I am very
thankful for, I have decided to order another analysis. I have been
wondering as well why the tin went down - we do not process pure tin plated
components nor finished PCBs. I would say we have assembled 50/50 SnPb and
AuNi finished PCBs.
Best regards to all,
Yordan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ed Popielarski
Sent: Thursday, December 04, 2003 7:41 PM
To: [log in to unmask]
Subject: Re: [TN] SnPb Solder pot composition
Yordan,
Deviation from 63/37 can cause increased solder shorts in a wave soldering
machine. At 63/37 (eutectic) the melt point is minimum, and there is no
plasticus range. As you drift from there the melt point increases and the
plastic range increases. This is why hand solder is preferred at 60/40...
there IS plastic range and makes it easier to judge the joint as you solder.
This is also the main cause of "frosty" joints (I hate to say "cold" since
it is a very inaccurate term).
Another thought to add to the mix is the accuracy of the lab. I recommend
using either Alpha Metals or Kester to do the analysis (Type C which is the
"whole enchilada" variety) and perhaps to rule out other variables discussed
in other's postings, take a few samples, from the static part of the pot,
from the wave after running at temperature, etc. If all the samples come
back relatively the same, then you are good to go, but if one or two stand
out, there could be something worth looking into.
Additionally, (yes, another variable) the tin is usually the element that
drops, not the lead. This has me wondering as well. Why?
Have a safe and happy holiday!
Regards,
Ed Popielarski
QTA Machine
27291 Jardines
Mission Viejo, Ca. 92692
Phone:949-581-6601
Fax: 949-581-2448
Cel: 949-337-2578
WWW.QTA.NET
"Thank God for America...
before it's too late!"
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