While building up another taillight for Mary’s Tour Easy (about which, more later) and based on previous experience, I wondered if the 1 W red LED’s thermal pad was soldered to the circuit board as it should be.
Lo and behold, the solder paste was reflowed, likely while tinning the six solder pads:
But not with the LED in place:
What looks like melted solder is really an adhesive layer, much like the craft adhesive sheet I use to stick things together. Presumably, they just glue the LEDs to the PCB / heatsink, solder its two leads by hand, and call it done.
Checking an LED marked “Dead” on the backside of its heatsink shows the amount of solder paste varies, but the LED wasn’t there when it melted:
This not being the first time, I cleaned the adhesive off the center pad and the LED, removed the solder, applied a dab of heatsink grease, and soldered the LED in place.
Which looked like this on the previous taillight:
Might be a bit too much grease, but it’s certainly a better heat conductor than adhesive.
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