Reflow soldering is a very widely used method of attaching surface mount components to printed circuit boards (PCBs). One common issue is that after reflow soldering process, SMD LEDs, like on the PCB images below, will unexpectedly slide off of its pads.
In the reflow process, the way the PCB travels through the reflow oven causes two sides of SMD LEDs heat up unevenly. This will cause the LED to shift undesirably on your board. How can you resolve this unexpected issue?
During the reflow process, SMD LEDs should be mounted (with enough solder paste) such that the leads are placed perpendicular to the direction of PCB travel to insure the solder on each lead melts simultaneously during reflow. For instance, the PCB travel direction should be same as the direction of the reflow process.