Nowadays, the methods of preheating PCB components are divided into three categories: oven, hot plate and hot air groove. It is effective to use the oven to preheat the substrate prior to repair and reflow welding of components. Also, preheating the oven is a good way to remove moisture from some integrated circuits and prevent popcorn. The popcorn phenomenon refers to the micro-cracking of the repaired SMD device when the humidity is higher than that of the normal device. The baking time of PCB in preheating oven is long, generally about 8 hours.
One of the drawbacks of the preheating oven is that unlike the hot plate and the hot air trough, it is not feasible to have a technician preheat the oven and repair it at the same time. Also, it is not possible for the oven to cool the solder joints quickly.
Hot plate is the most ineffective way to preheat PCB. Because PCB components to be repaired are not all single sided, in today's world of hybrid technology, it is rare for PCB components to be completely flat or flat. PCB should be installed on both sides of the substrate. It is impossible to preheat these uneven surfaces with hot plates.
The second defect of the hot plate is that once the solder reflows, the hot plate continues to release heat to the PCB assembly. This is because, even after the power is removed, residual heat stored in the hot plate continues to transfer to the PCB, impeding the cooling rate of the solder joint. This blocking of solder joint cooling can cause unnecessary lead precipitation to form a lead pool, reducing the strength of the solder joint and become poor.
The advantage of using hot air groove preheating is that the hot air groove has no regard for the shape (and bottom structure) of the PCB assembly, and the hot air can enter all corners and cracks of the PCB assembly directly and quickly. The whole PCB assembly is heated evenly and the heating time is shortened.