What is SMT (Surface Mount Technology) or SMD (Surface Mount Device)?
Before understanding what SMT is, we must first distinguish between SMT and SMD. Although these two terms can sometimes be used interchangeably, there are still some basic differences:
SMD: Surface Mount Device, surface mount parts. Refers to those electronic parts that can use SMT process or technology.
SMT: Surface Mount Technology, surface mount technology. A technique for soldering electronic components to the surface of a circuit board.
According to the literal interpretation, SMT is a technology for soldering electronic parts on the surface of a circuit board (PCB, Printed Circuit Board). Different from earlier through-hole parts, SMT can greatly reduce the volume of electronic products to achieve lighter, thinner, shorter, and smaller.
Early electronic parts only have traditional through-hole soldering technology (THT, Through-Hole Technology), (DIP, Dual-In line Package). Electronic parts must be additionally designed to pass through the circuit board to achieve the purpose of soldering the parts on the circuit board.
This through-hole part has a minimum size limit of about 5mmX5mm. If it is smaller than this size, the solder fillet is easily broken due to falling or external force. And now SMD parts, the smallest size can be 01005 (0.4mmx0.2mm), or even smaller, which is why the original Black King Kong phone is as big as a brick, and can only make calls; the current wisdom The volume of the mobile phone is less than 1/5 of that of the Black King Kong, but it has more functions.
So what kind of technology does SMT rely on to solder electronic parts to circuit boards? The answer should be solder paste. As long as the solder paste is printed on the pads (pads) of the parts to be soldered, and then the electronic parts are placed on it, the solder feet should be placed at the position of the solder paste, and the solder paste should be passed through the high temperature reflow oven. The temperature must be higher than the melting point of tin, but not so high that it will burn the electronic parts. The reflow oven will melt the solder paste. When the solder paste melts, it will become liquid, and the liquid solder paste will coat it. The solder legs of electronic parts will be soldered on the circuit board after the temperature cools and the solder paste becomes solid again.