Barry,
You, me, and everyone else knows I've no business contributing to this
discussion and your question. Well, just so happens, I have little else to
do at this moment. Also, I love wave soldering because it is so, how shall I
say it, mechanical and straightforward. My problems is a lack of any type
understanding about IMC stuff. No matter1
You know the mechanisms as flux type and quality/composition, activation
temperature, preheater temperature required to ensure the top side board
temperature is properly reached as an indication of flux activation as
specified, conveyor speed relateive to the foregoing and its relationship to
dwell time on the solder pot, board parallelism on the wave, angle on the
wave, and all the rest.
I like wave soldering because all the above must be interoperable and
correlate with each function, mechanism, time, and chemistry in the whole
process. I call each function, again as above, sub-processes because that's
what they are. Each sub-process must be managed independently and
associatively for the "whole" process to work. If it works, solder joints
meet specified requirements. If it, or any one of the "independent"
sub-processes, don't work, solder joints suck.
To your original question, I make a matrix including all the above
parameters and include the board thermal mass (single, double, MLB, etc.)
and go out and measure each function in each sub-process in the process and
see what happens.
Most new/automatic machines as Electras and the like have computerized
matrices included. However, I always "calibrate" the automated sub-processes
and ensure they meet specified requirements.
Anyway, the process is cool though being pushed to the limits with very high
layer count MLB's with incredibly high thermal masses. Simpler 12 layer
boards used to run at predetermined speed between 3-6 feet/minute and you
could set your watch by it. Now, with some of the 40 and 50 plus layer
boards I, and some of you, have been working, speeds are much slower and
flux often is very active. You can imaging the preheat temps with some of
these things and no IPC through hole acceptance criteria comes close to reality.
And on it goes. Life and the wave soldering process is a continuing
experiment with CPI as its goal - though not often enough realized.
MoonMan
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