As discussed previously, the temperature of the preheater has little comparison with the actual temperature of the PCB. By implementing a dual preheater system, where there is an infrared heat sensor in between the two preheaters, you can ensure more even heating throughout the assembly. The way this works is to set the first preheater to approximately 70 percent of the desired heat required. After the board has passed through this phase, its heat is measured by the infrared detector. This detector feeds data back to the computer, which adjusts the set point for the second preheater to ensure that the entire assembly is adequately heated before contact with solder wave. A schematic can be seen below. This system eliminates a large amount of variation in the temperature of the assembly, including operator error in the wave soldering process.
*This is the 10th post in an eleven-piece mini-series entitled Preheating. This mini-series which is part of a larger program entitled Wave Soldering (A Segmented Synopsis).