A year ago I saw this Youtube video where Steve Dahl at DigiKey demonstrates a method of soldering high-brightness LEDs to a Metal Core Printed Circuit Board (MCPCB) using a heat gun.
Though I’ve seen an electric skillet used for reflow soldering, I decided to try using the above technique when I wanted to replace an LED on a drop-in. I ordered some neutral Cree XP-G LEDs from DigiKey, some 16mm circuit boards and some LodeStar solder paste.
I don’t have an expensive heat gun – just one for removing paint. I thought if I used my infrared thermometer, I could measure the temperature at the tip of the gun and when it was maintaining the correct temperature, I would hold the board/LED in the heat.
I put dabs of solder paste on the contact pads where the LED would be soldered and placed the LED on the pad. It doesn’t need to be precise because the solder will only flow onto the contact pads.
The Cree XP-G specs (PDF) have 215 degrees C (~419 degrees F) for Peak/Classification temperature. When my thermometer read that, I put the board in the heat. (In the video, they use 600 degrees, which seems way out of spec and may be the reason the board turned brown). In a few seconds the paste melted and the LED centered itself, just like in the video. I immediately turned the heat off and kept the fan running to cool the board.
In the photo, the bottom board has been soldered. The upper left board shows the amount of paste I used. The upper right board has the LED on it before soldering.