At the moment, we are looking at xray of the solder joints as a process control if we can correlate the peel test results from good and bad connections to the xray image.
The manufacturer recommended method of removing residue from the head was to use an abrasive metal polish. This naturally gives me nightmares so I will need to find a better method of cleaning the residues off.
The connection in this situation is basically a plated through hole bonding two metal layers with polyimide layers in the middle. This seems very unreliable as the only two stable locations are the PTH and the castellation at the end of the flex circuit (near the end of the pad).
Does anyone know of any published guidelines for flex circuitry design that I might be able to find out more about this type of soldering connection?
Thanks in advance,
Phil
Werner Engelmaier <[log in to unmask]> wrote:
Hi Phil,
Depending on design, the commercially available soldering bars remain
sufficiently flat up to about 2 inches in length [for more details, see my papers
Engelmaier, W., “Transverse Joulean Heated Soldering Tool for Mass Terminations,”
Proc. NEPCON/West, Anaheim, CA, February 1979, pp. 228-235.; and Engelmaier,
W., “Transverse Joulean Heated Double-Sided Reflow Soldering Machine for Mass
Terminations,” Proc. NEPCON/West, Anaheim, CA, February 1981, pp. 333-339].
Actually more of a concern may be temperature uniformity, which becomes even
more of a concern with lead-free solders.
One other concern is the amout of solder present—too much and you get shorts,
too litlle, well...One solution is a soldering bar with a bottom surface that
is not flat, but rounded, thus giving you solder joints that get thicker away
from the bar center and thus being able to successfully accommodate a larger
variation in solder volume.
Werner
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