LED Solder Tabs
I use your 21.6x 0.5 circuit boards and am very pleased with them. I solder the diode base flush with the board ignoring the leg node soldering point indicator in the belief that the metal coated through holes provide sufficient heat sink to protect the diode. I would like to be sure that I am not damaging the diodes by applying heat closer to the diode than the leg nodes prescribe. What is the official wisdom in this regard?
Soldering LEDs Beyond Solder Tabs
The plated holes in the circuit board will help transfer the heat. However, to achieve a good solder joint, the surface temperature of your LED lead must reach a certain point. This means that you may need to hold your iron tip onto the soldering surface a bit longer, to allow both metal surfaces to heat up and accept the solder. Here is an extreme example. Imagine trying to solder an LED lead to a 1 inch metal pipe. It would take a very long time to heat the pipe before the solder reflows, thus damaging the LED in the process. However, if your board pads have thermal spokes, this should not be a problem at all. This is only one aspect of the soldering process. When you solder before the solder tabs, you are respecting the protective margin designed into the package. When soldering beyond the tabs, there is no guarantee. One option is to use a slightly lower temperature setting on your iron, which may help prevent thermal shock. Also consider a thinner solder wire, such as 0.20" or 0.15", which will reflow much faster and is much easier to work with. A no-clean flux can also help. I have seen numerous LED products that have been soldered beyond the solder tabs, and they have apparently had no known issues. In fact, our LED tubes feature LEDs that have been soldered beyond the tabs. The quality of the LED also has allot to do with reliability. I highly recommend purchasing form a well known respectable company such as Nichia, Cree, or Lumileds.