A UNIQUE HEATING/REFLOW TECHNIQUE TO MINIMIZE SOLDER PASTE-INDUCED VOIDING UNDER LEDS

摘要

When soldering LEDs to a circuit board, voiding can be a critical issue. Just as with other bottom terminated components, the thermal pad is used to transfer heat away from the part, allowing it to function at a cooler temperature. Voiding within the solder joint will interfere in heat transfer, causing the component to run hotter, and shortening the working life of the LED. As is known in the industry, solder paste-induced voiding on these thermal pads is a common problem. A novel process has been developed where solder paste is printed, the paste is then dried, fresh paste is printed over the original deposits, and the assembly is then reflowed using standard reflow practices. Aspects of the printing and reflow process considered in this paper include drying temperature, stencil thickness, aperture size, pitch, slump of the paste, and amount of void reduction.