If one does not want to look like a dip you should not lose your balance in
the restroom for fear of wetting yourself.
I was amazed that Bev and Gerard waited as long as they did. I support what
they are saying and would require anyone to furnish me data using those
techniques, before I would entertain accepting anything. If I had to make
the final " subjective " decision I would do the test myself with my burnt
nose, failing eyesight, tweezers, special solder pot, special flux, special
technique, special conditioning and a 30 year intuitive knowledge filter.
This does not a process make for the industry as a whole ( or SMT pad ).
Dave Hillman, Bev, Gerard and others have been doing good work lately on
solderability testing for a variety of substrates, alloys and surface
finishes and I applaud and accept their efforts. Of course I also thought
that the crowd was praising my humor when they said I should be drawn and
quoted.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Friday, May 27, 2005 6:25 AM
To: [log in to unmask]
Subject: Re: [TN] Wetting balance
Like Gerard, I can no longer keep silent either. I may have only 15 years
of wetting balance use to his 20, but have used several extensively.
1. Active wetting is a good idea for dip and look testing.
2. As bad as a wetting balance may be for mimicking SMT, it is surely better
than dip and look.
3. The standards for dip and look may say dip at such and such speed to such
and such depth for x seconds, which of course would require essentially a
wetting balance to do it. I bet 90% of people that use dip and look are
using tweezers and eyeball the depth! So much for consistency.
Bev Christian
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerard O'Brien
Sent: May 27, 2005 8:56 AM
To: [log in to unmask]
Subject: Re: [TN] Wetting balance
I have tried to refrain from commenting but this string is just too much. As
some one who has used a wetting balance for 20 years (component
manufacturing, lead frame & connector manufacturing, PWB manufacturing and
Assembly) I have the following comments:
1. Modern wetting balances are not the same items written about by
my esteemed colleagues who used them 35 years ago.
2.dip and look tests do not yield wetting speed data, impact of
temperature on wetting speed/force, show de-wetting ( Brian E - I have
unfortunately many thousand curves showing dewetting which upon further
analysis was confirmed as poor basis metal pre-treatment)
3. To Lee's point - yes anyone can influence the results of a
wetting test but it is more likely to be influenced by a dip and look
(whether intentionally or not) test than by a machine whose parameters are
controlled by a PC.
4.May I remind the reader of the insanity of rejecting a part,
tested by dip and look, that has wetting coverage of 94.9% compared to the
accept criteria of 95% in the critical area! As an assembly engineer I am
more interested in consistency of wetting times, wetting forces, presence of
surface oxides (clearly visible in the wetting curve), basis metal
preparation and hence solderability and no dewetting.
Regards
Gerard O'Brien
Dir. Of Material Test, Reliability and Technology.
Photocircuits Corporation
-----Original Message-----
From: Lee parker [mailto:[log in to unmask]]
Sent: Wednesday, May 25, 2005 3:41 PM
To: [log in to unmask]
Subject: Re: [TN] Wetting balance
Luigi
Since all the other Bell Laboratories retreads have responded I thought I
should as well. George and Greg supported the AT&T assembly locations while
I supported the Western Electric PCB shop in Richmond. You might say they
were my customers. To say the least, there were times that we had different
views of the same issue.
One issue that we all eventually agreed upon was the wetting balance. It was
useless. In fact, after obtaining my first (and last wetting balance), I
quickly learned that by proper adjustment, I could get any result I wanted.
Unfortunately though, George and Greg soon uncovered my unique skill set and
we went back to a less sophisticated, but more accurate technique for
judging solderability.
At the end of the day, however, we all agreed that the dip and look test was
as accurate and repeatable as any test yet devised.
Best regards
Lee
J. L. Parker Ph.D.
JLP Consultants LLC
(804) 779 3389
----- Original Message -----
From: Wenger, George M.<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Wednesday, May 25, 2005 3:36 PM
Subject: Re: [TN] Wetting balance
Luigi,
There are those who might say "there goes Munie again preaching hiearchy".
How could anyone recommend to use a wetting balance as a method to control
the depth and immersion speed for a dip-&-look solderability evaluation?
Well I must be one of those hieratics that agree with him. One of my first
jobs in the Western Electric Company in 1971 was to computerize an old
G.E.C. Meniscograph using a DEC PDP-8 computer to automatically collect
wetting data to take out the subjectiveness of the dip-&-look procedure.
Well after 34 years I'm still relying on use WWR and the dip-&-look
procedure for solderability testing. The only thing that I've changed in 34
years is that I now use "Active Wetting" as my criteria for good
solderability. I too remember John's solder coated toothpick. Also, I used
to have samples of axial leaded components that had "black" colored leads.
When I dipped the entire lead in molten solder solder stuck to the leads.
When removed from the sodler pot 100% of the lead was coated with solder.
According to the dip-&-look criteria they pass solderability. Our problem
was that when they were through-hole insereted and wave soldered the solder
joints looked "bad" and we couldn't get electrical connections. We went
back to the dip-&-look test and found that if we dipped only one-half of the
lead length in solder that although solder would sstick to the lead there
was a slight negative meniscus to the lead rather than a positive menisus.
That is when we adopted the "Positive Menisus" or "Active Wetting" as our
criteria for good solderability.
Regards,
George (The Hieratic)
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908)
546-4531
[log in to unmask]<mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Munie, Gregory
Sent: Wednesday, May 25, 2005 9:18 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Wetting balance
Luigi
You didn't say what flux you were using. I assume it's the flux called out
in the spec.
My experience at AT&T (and resulting contributions to the IPC wetting
balance test) are that if you use ANY flux but water white rosin (WWR) the
results you get in production will NOT equal the results of the wetting
test. The test will always look better.
I and my co-workers published this as a reliability study at the SMI
conference in San Jose, CA in 1995.
I have heard the arguments that wetting balance is inherently too noisy to
provide good repeatable data from site to site if one uses WWR. Yup! A
little activation in the flux definitely improves the repeatability:
It
makes everything good. And when that happens, from an assembly standpoint,
you're the loser.
I suggest a simpler alternative: use the "dip and look" test with WWR and
the wetting balance to control immersion depth and speed. But only accept
the parts if the area wetted exceeds the area dipped. Why? Simple! In
production you want the solder to wet "up" the part/wet "over" the lead.
When you put the part in the solder with WWR and the solder climbs up the
lead you know it's good! If all the solder does is wet the immersed area .
.
. well, on my desk I have some carbon fiber bundles that exhibit good
"wetting" per the current test. They're well covered with SnPb over the
area
immersed. But I defy anyone to actually make good connections in
production
with leads like that. (Years ago John Devore, if I remember correctly,
would
show people a solder surface that was well wetted. Then he'd hand it to
them. It was a wood toothpick with solder adhered to part of the wood.
Sure
looked it'd solder per the spec!)
So, per my opinion, WWR and demonstrated active wetting of the parts are
the
only way to go in solderability testing.
Greg Munie
-----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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