Bev,
I'll give the instrument another opportunity, we have a promising chinese guy in the group, and being a
researcher, he'll hopefully snap to the task easily... You are right, one could of course use the machine for snapshots.
Hard-to-kill: people around are still expecting that the machine is a gonogogonggong. When I tell them the truth, they become very confused and disappointed.
HP's conclusion is good: " the wetting balance as a method to DISCRIMINATE the wetting behaviours of different solders and fluxes has been successful..." see last pages
http://www.hpl.hp.com/hpjournal/96aug/aug96a11.pdf
But still: interpretation of a bunch of curves is not for everyone to do.
Regards
Ingemar
PS. How do your nails look like?...he-he
-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: den 31 maj 2005 15:15
To: TechNet E-Mail Forum; Ingemar Hernefjord (KC/EMW)
Subject: RE: [TN] Wetting balance
Ingemar,
I am somewhat surprised by your abandonment of your wetting balance.
Although I am "married" to it, here it is usually run by a continuing
rotation of co-op students, changing every four months. Are you sure
the variation is not in the components rather than the operators?
If there is one downfall of a wetting balance, or for that matter ANY
solderability test, short of building actual product, it is THEY WILL
NEVER BE STATISTICALLY SIGNIFICANT FOR SMALL DPMO. Do the math, the
number of parts you would have to test is horrendous. So I am not
surprised by Luigi talking about pass wetting balance/fail on line. It
is NOT a function of the relatively conservative wetting balance test,
but the statistics of where you took the parts out of the reel. We use
the wetting balance to get a snapshot. Sometimes we are lucky. And if
the whole reel is indeed crummy then we have the evidence to bludgeon
the supplier.
And you are 100% right about needing a person who knows about soldering
and the book you mention is THE BEST.
Regards,
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
(KC/EMW)
Sent: May 31, 2005 3:38 AM
To: [log in to unmask]
Subject: Re: [TN] Wetting balance
Bon giorno,
My response is late, been in Rome for some days, 35 Centigrades and
polluted city air, could study the wetting of sweat very well. If it
were not for the watching police, I had jumped into Fontana di Trevi.
Very interesting to see the answers on solder wetting. We have a
Multicore WB, but it's abandoned, been placed in a corner and never
asked for. The reason is that we could not find a person that got enough
in love and married the machine and who promised to be a good husband
for decades. With different operators we got too much variations of
parameters.
If inspecting just a few items per day, I think Bev's recipe is working,
but if you have hundreds and hundreds of samples to test, I ask myself
if not WB is necessary to use. At least if you have a WB enthusiast and
someone who can use statistics.
We have found that better than a machine or any dip pots or whatever, is
a person who KNOWS about soldering. Even if samples are WB tested from a
lot of 100,000 chip caps, and that sample looks nice, we know that there
can still be soldering trouble. When you get soldering problems in the
line, the root cause must be found in hours. A person who KNOWS about
soldering use to have that ability. Usually, those guys are greyhaired
gentlemen with shit under the nails despite a PhD grade, and with no
take-overs. Two of the guys at our company left big holes when they
withdraw. There are a few left, don't see how we will manage the time
they too leave. Knowing a lot about soldering is not on the hit
list.....
For those who are interested in KNOWING about soldering and wetting, I
recommend this book:
"The Mechanisms of Solder Alloy Wetting and Spreading" written by
Frederick G. Yost, F.Michael Hosking and Darrel R. Frear. Sandia Lab
guys. ISBN-0-442-01752-9 Van Nostrand Reinhold, 115 Fifth Avenue, New
York,
NY 10003.
300 pages about wetting and only wetting!
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: Luigi Cantagallo [mailto:[log in to unmask]]
Sent: Wednesday, May 25, 2005 2:00 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [TN] Wetting balance
Hello Technetters,
I have questions about wetting balance.
We intend to use a wetting balance not to accept/reject supplied SMD's
(Our
SMD's are 1 to 5 years old) but to minimize the risk of solderability
defects in production (Low volume, SnPb technology).
So we don't apply J-STD-002D criterium but we try to find them to
corroborate wetting balance and production results.
On some tests (Wetting balance calibrated and in order, same type of
flux,
same alloy) on same component lots, we have not a perfect
correspondence
between wetting balance and visual inspections results in production
(Vapor
phase soldering). One of the case is "Good at the solderability
test/Defect
in production" and this one is the most risky.
Somebody have experience with that kind of problem?
What actions have you made ?
Thanks for answers.
Best regards,
CANTAGALLO Luigi
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