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Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bev Christian <[log in to unmask]>
Date:
Fri, 27 May 2005 10:29:50 -0400
Content-Type:
text/plain
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text/plain (514 lines)
George,
I think dip and look testing is holding on for a number of reasons:
1) dead easy to do (I am not saying done well)
2) cheap
3) intuitive
4) A wetting balance is going to set a company back  ~$50K and, as you
say, does NOT give you root cause.
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: May 27, 2005 10:21 AM
To: [log in to unmask]
Subject: Re: [TN] Wetting balance

Bev,
If everyone were silent technology would not more forward.

I agree with all of the points you made.

1.  Active wetting is a good idea for dip-7-look testing.  The problem
is the active wetting wording is incorporated in the J-STD-002 suggested
criteria for Test "E", which is a test without established Accept/Reject
Criterion but it isn't incorporated for dip-&-look Test "A".

2.  The wetting balance is most certainly better than dip-&-look
testing.

3. Dip-&-Look testing has lots of variability and doesn't provide
consistency.

The number of years one has in doing wetting balance testing shouldn't
be an issue.  After having worked with old wetting balance, new wetting
balances, and having helped Dr. Kon Lin built wetting balances using
Kahn balances, I realize that what a wetting balance provides is an
assessment of a parts solderability.  When a manufacturing engineer
indicates he has a soldering problem what he is looking for in most
cases is a root cause and corrective action rather than a wetting
balance or Dip-&-Look confirmation that he has a solderability problem.
I also agree with most everything Gerard said in his posting.  The only
difference I have is that if the new wetting balances are considerably
different and better than the old units I would have assumed they would
be widely used and Accept/reject criteria would be established. 

Regards,
George
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]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bev Christian
Sent: Friday, May 27, 2005 9:25 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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