Proper PCB Preheating
One of the keys to insuring a proper reflow cycle is getting to and maintaining the proper preheat temperature. This is accomplished with a PCB preheater which heats the board to between 75 and 125� C prior to the application of heat to the part area requiring rework. This part of the rework process is a critical component as done properly it minimizes PCB warpage during component removal while at the same time limiting the thermal shock to the PCB. The maximum temperature is determined by the thermal expansion of the PCB. In order to maintain the integrity of the PCB laminate the maximum preheat temperature is set approximately 10�C or below the Tg (glass transition temperature) of the PCB material. Higher thermal preheat temperatures minimize the potential thermal distortion and shock to the PCB during the reflow process.
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