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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