Bill innocently asks a question on J1C. Doug, coming off a night of
minimal sleep comes out of left field with a response:
I have a general question for those folks out there who do J-Std-001C,
class
3 work. We use fluxes that are stronger than the "allowed" L0 or L1
activity
levels. Because of this I had to "qualify" our process per Appendix B of
the
J-Std-001C. This according to J-Std-001C, paragraph 4.2b. The cost of doing
this test, including materials, labor and whatever is approximately $7000.
**First off, you can use whatever flux you want, but if it is more active
than the L1 or L0 level, you have to do additional testing to demonstrate
you have removed the flux. L0 or L1 fluxes are not "allowed fluxes", it
just means that there was a concensus at the time of drafting that the L0
and L1 fluxes were benign enough and were designed to be left on the board,
such that you did not have to do the testing to show materials
compatibility. The whole intent of the paragraph on materials
compatibility is that you either use a benign flux or you do testing to
show you have removed the active flux residues to benign levels.
Now I have a couple of questions...
1) If one of the solder pastes that you qualified is no longer available,
do
you have to do a re-qualification if the manufacturer of the paste suggests
a new material? (This implies a material change)
**In my opinion, yes. You have changed materials. But my opinions mean
squat. What do your customers feel? The biggest background philosophy of
J1C is that quality is whatever you and your customer agree to. If the new
paste you are using has nearly identical properties to the old paste, are
they comfortable with the swap without a requalification? Simple question,
tough answer though. Would they accept a smaller, more focussed
engineering study on the chemical residues present with the new flux, in
lieu of a full requalification?
2) If you swap out a spray fluxer for a foam fluxer or apply flux with a
different method at the wavesolder machine, do you have to do a
re-qualification? (This implies a process change)
**Again, in my opinion, yes. But, my opinion and 50 cents will get you a
cup of coffee (well outside of Starbucks). Same reasons as above. I would
be more concerned about this change than with the paste change. 90% of
solder paste is metal, only about 2% actual flux, and after reflow it does
not leave a great deal of residue, compared to wave solder. A foam fluxer
(and why are you taking a step back into the evil dark ages?) will put on
3-4 times the amount of flux. If you do not adequately modify your reflow
process to dry and activate that much extra flux, there is a high
probability that you would have unreacted flux, which is a reliability
hazard. If I were your customer, danger klaxons would be going off (Danger
Will Robinson Danger) regarding this change.
I suspect the answer to both questions is yes.
**No, the answer to both questions is "It depends". On your customer
primarily.
With the number of possible
changes within a soldering process, it seems inevitable that process
qualification and re-qualification could happen on a regular basis due to
circumstances beyond your control.
**Not really. Again, it comes down to the relationship with your customer.
The whole point of paragraph 4.2 or the paragraphs on materials
compatibility was that the manufacturer had better understand the
compatibility of the chemicals in their assembly process and their long
term effects on reliability. The re-qualification thing is really a hold
over from the good old days of mil-specs. It is sort of the same arguments
that come up with lot sampling vs. SPC. The bottom line is that when
changes occur in your process, how do you assess the impact of those
changes. The Appendix B testing won't guarantee that you are making good
product. It is only ***one*** default way of demonstrating that you have
done some investigations into the long term effects of the change. Other
methods are perfectly valid and a "requalification" may not be needed each
time, but a re-evaluation is.
So are the class 3 guys out there either doing regular qualification
testing
or are you all using L0 or L1 (no clean/Rosin) fluxes.
**We have been transitioning to L0 or L1 fluxes and pastes and much of our
stuff is class 3. Hell, even our class 2 stuff is class 3. Me and Hillman
make some damn good stuff here......
Is there anyone out there who participated in the writing of this section
who can shed some light on the thought process behind this section of the
spec.
**I have been involved with that spec. A little less on the C revision,
but Jim Maguire and I pretty much wrote the Appendix B protocol. There is
an IPC technical paper, IPC-TR-467, that Jim and I wrote to explain the
reasoning behind the protocol. You might want to read that. If you have
other questions, send them my way. Just be aware that as the day
progresses, the Diet Mt. Dew count increases and the answers get
progressively wackier.
Doug Pauls
Rockwell Collins
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