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August 2005

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From:
"TUGMEN UNSAL (MIKES INTERNET)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, TUGMEN UNSAL (MIKES INTERNET)
Date:
Fri, 12 Aug 2005 09:04:06 +0300
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Hello again .. Good morning,

**Hi Doug Pauls (thank you very much for your answers)

Below you could find one more question that is really important.

"Do you please check if the following process can be sufficient to
eliminate all the risks which is coming from the use of H type flux;
After completing the soldering process; 1. "well done" cleaning with
water, 2. visual inspection for detecting the flux residues and checking
corrosion and dendritic formation, 3. performing the ionic contamination
testing, 4. conformal coating application 5. visual inspection for
checking corrosion, dendritic formation and mealing of conformal
coating, 6. burn-in testing, 7. vibration testing (at least in the two
axises)"

Thanks in advance.

Tugmen.


From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, August 10, 2005 4:09 PM
To: [log in to unmask]; TUGMEN UNSAL (MIKES INTERNET)
Subject: Re: [TN] Requirements for soldering fluxes

Hello all,
**Good morning

Could you please assist me to find answer of the questions listed
below.?
**I'll give it a shot.

1. Why the use of H type flux in the solder paste is not prefered for
Class III equipment production?

**Because its dangerous, very dangerous.  Type H flux is very very
active and can go from oxide stripper to corrode the trace open very
quickly if you don't know what you are doing.  If you have areas where
your cleaning process is marginal, you can have corrosive residues which
can destroy the assembly.  If you are making garage door openers, no big
deal.  Pacemakers are another issue.

2. Any negative impact recorded at IPC since the use of solder paste
with H type flux and so that corrective action taken?

**Depends on what you mean by "recorded at IPC".  One of the more
enjoyable parts of IPC meetings is the "swapping of the war stories" in
which us old farts trade horror stories about manufacturing.  There are
people who have used type H fluxes in Class 3 manufacturing, but the
process is very well controlled, tested to the nth degree, and very well
monitored.

3. What kind of solder paste is acceptable for DoD requirements and
other Class III equipment production?

**One that works.  One that does not leave harmful residues.  Neither
DoD nor IPC mandate what kind of flux or paste you can or cannot use on
electronic hardware.  What they do mandate is that the more aggressive
your flux is, the more data you better be able to provide to convince
your customer that you know how to control the process, that all of your
chosen materials for manufacturing are compatible with each other, that
your cleaning processes are very robust, and that any residue left
behind will not result in electrochemical failures (dendrites, leakage,
corrosion).
Class III hardware is classified as such because the consequences of
failure are usually catastrophic.  If you were making Class III hardware
for me, and you were using a low activity flux, I would expect a certain
amount of data. If you were making hardware for me using a medium
activity flux, I would expect a lot more.  If you wanted to use a type H
flux, you would have to have a mountain of data and me on site being a
pest (shut up
Dewey) before I would allow it.

4. What type of water soluable solder paste prefferable for Class III
applications?

**Same argument as above.

4. Do IPC suggest any specific method to measure the thickness of the
solder paste on the PWB before beginning the process?

**I have to pass on this one. I can't find anything in J-STD-001 or the
handbook on it.  I know we use a laser device here to measure paste
height.


Doug Pauls
Rockwell Collins

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