Reflow soldering using selective infrared radiation

We developed a new reflow soldering technique, which uses selective infrared radiation. We use an aluminum-oxide heater and a halogen-heater for the IR sources. The aluminum-oxide heater radiates intensive infrared rays between about 5 to 8 μm. This wavelength is readily absorbed by a glass-epoxy substrate. The halogen-heater radiates intensive infrared rays between about 1 to 2 μm. This wavelength is readily absorbed by the resin used in quad flat packages (QFPs). By using these heaters, we can selectively heat the devices on a printed circuit board (PCB). The temperature difference between the PCB substrate and the large QFPs was reduced to about half that for conventional heating. This reduced temperature difference allows us to reflow solder the PCB at about 215°C. This temperature is the same temperature as vapor phase soldering and is about 20°C to 30°C lower than conventional infrared reflow soldering