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I’ve noticed that 1 in 10 units, I’ve had an issue with the rotary working properly (either rotary doesn’t work at all or it is jumpy, some clicks aren’t registered). The solder joints look good, properly wetted, full coverage on the pad, pins are all the way through, etc. There is no problem with the button press.
In fixing the units, I just touch each of the pins until the solder melts and readjust the pin just a bit. I don’t add any solder, and I don’t change the pin penetration at all.
This fixes it 100% of the time for some reason. I’m trying to better understand, what is this failure mode? Is it the type of solder I’m using (resin-core, 63-37)? Is it the flux type? Is the rotary pins super sensitive to position?
According to the datasheet, Bourns do not recommend hand soldering. Probably the plastic body that supports the pins gets soft if the soldering temperature is too high.
The datasheet for part number PEC11R-4220K-S0024 recommends wave soldering using Sn95.5/Ag2.8/Cu0.7 solder with no-clean flux: 260 °C max. for 3 ±1 sec. So, it’s possible that the conditions during hand soldering with 63/37 might be different enough to cause an issue.
Although 63/37 is eutectic in nature (as compared to 60/40, for example), it doesn’t guarantee that the alloy will solidify quick enough to prevent a “cold solder joint” that occurs more often with a non-eutectic solder and any movement during the process. Conditions during soldering could still be volatile enough to cause something similar to a cold solder joint–especially if reheating solves the problem.
Try removing variables. Eliminate any chance of movement during soldering. Try a different flux and compare the error rate. Try a different batch of solder to eliminate any small amount of variability in the product. Also, check your solder routine. Is it a certain pin that always has the bad connection (reheat one terminal and check the part before reheating the next terminal)? Hand soldering is always more variable, so there may be a point in your procedure where an error is more likely to occur due to temperatures, amounts of solder, timing, etc.
