PCBA rework is a relatively common repair, but the key point of PCBA patch soldering is the preheating of PCB components before or during rework. This is a key step in the repair process. So what are the main methods? Let's take a look:
At present, the methods of preheating PCB components by soldering PCBA are divided into three categories: oven, hot plate and hot air slot. It is effective to use an oven to preheat the substrate before parts rework and reflow soldering. In addition, preheating the oven is an advantageous way to bake the moisture inside some integrated circuits and prevent popcorn. The so-called popcorn phenomenon refers to the slight cracking of SMD devices when they are heated suddenly and rapidly when the humidity is higher than that of normal devices. The pcb is baked in a preheated oven for a long time, usually up to 8 hours.
One disadvantage of preheating ovens is that, unlike hot plates and hot vents, it is impossible for technicians to preheat and repair at the same time. In addition, it is impossible for the oven to cool the solder joints quickly.
The hot plate is the least effective method to preheat the pcb board. Because the pcb components to be repaired are not all single-sided, today's world is a world of mixed technology, and pcb components that are all flat or flat on one side are indeed rare. PCBs usually have components mounted on both sides of the substrate. It is impossible to heat these uneven surfaces with a hot plate.
The second disadvantage of the hot plate is that once the solder reflows, the hot plate will continue to release heat to the PCB assembly. This is because even after the power is disconnected, the residual heat stored in the hot plate will continue to be transferred to the PCB to prevent the cooling rate of the soldering. This obstruction to the cooling of the welded joint will cause unnecessary lead-inducing, forming a lead groove, and reducing and changing the strength of the welded joint.
The advantage of hot air hole preheating for PCBA patch welding is that the hot air hole does not consider the shape (and bottom structure) of the PCB component at all. The hot air can directly and quickly enter the corners and cracks of the PCB component and the entire PCB component is heated evenly, shortening the heating time.