Those PCB's look kind of neat, I may have to order a few to try em out.
1. In terms of the PCB, you should be able to trace the copper conductive pathway to double check the orientation. Could be the silkscreen is screwed up. I think with SMD 5xxx series LED's the thermal pad is connected either the anode, so check the datasheet of the LED's you are looking to use to confirm and check the PCB with voltmeter (conductivity setting) to check this connection. Likely you are right, the issue is probably cosmetic, but hard to tell without a voltmeter.
2. YES, your intuition is correct. Thermal pads need to be soldered down. Use thermal paste or solder flux to help you get the job done. Typically thermal pads need at least 50% solder connection in order to be considered viable. Unlike a computer CPU, most microelectronic components rely on their metal solder connections for everything.
~600 to 700 F (?) is typically the temp I solder at
A. Apply flux (small amount)
B. Dot some solder on each pad, coating the pad in a thin layer of solder (smooth and even)
C. Apply more flux (small amount)
D. Apply some solder to the tip of the soldering iron ("tin the tip")
E. Place the LED down and head the pad up from the side. The Thermal pad should heat up with the anode, as they should be connected. They should both solder down together. Get practice with the first few until you feel comfortable with what you are doing, have a magnifier glass near by to check your work. The best solder is the one that was just long enough to heat up the pad to melt the solder and 'glue' the metal contacts together, but not too much as to damage the LED or other electronic component.
-Solder and solder flux when heated can release unsafe chemicals into the air. Do not solder in a confined room without air filtration or without ventilation. If you are female, take extra precautions, as many of these chemicals can harm reproductive health.
-I recommend lead free solder ("silver solder"), but the PCB's could come with lead on them and you wouldn't know (this is made in china after all, save 2 cents)
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Last edited by Cmeister; 01-12-2016 at 08:57 PM.
Reason: Additional notes