Principle and Process Control of Hot-bar Soldering

Principle of hot-bar Hot-bar is also called "pulse hot pressure welding", but most people in the industry call it "hot-bar". The principle of hot-bar is to first print the solder paste on the solder pad of the circuit board (PCB), melt the solder paste after returning to the soldering furnace and solder it on the circuit board in advance, and then place the object to be soldered (generally FPC) on the circuit board with the solder paste printed on it, Then use the heat of the thermal head to melt the solder and connect the two electronic components that need to be connected. It is called hot-bar because the flat object to be soldered (generally FPC) is soldered on the circuit board using a long strip-shaped thermal indenter. Personally, I think its name is to distinguish the heatseal process that also uses a thermal head to adhere ACF to LCD or circuit board. Hot-bar usually solders the flexible board (FPC) to the PCB (as shown in the figure above), so as to achieve the purpose of light, thin, short and small. In addition, the cost can be effectively reduced because 1-2 flexible board connectors (FPC connectors) can be used less. The principle of the general hot-bar hot press is to use the huge [Joule heat] generated when the [pulse current] flows through molybdenum, titanium and other materials with high resistance characteristics to heat the [thermal modes / heater tips], and then use the thermal head to heat the solder paste on the molten PCB to achieve the purpose of mutual welding. Since the pulse is used for heating, the energy and time control of the pulse is very important. The control method is to use the [thermocouple] circuit at the front end of the thermal head to feedback the temperature of the thermal head back to the power control center in real time, so as to control the pulse signal to ensure the correctness of the temperature on the thermal head.