Welding must first have a good tool: a good tweezers, wind gun, flux (best to use a yellow paste tube), the board (available hardwood or tile, mainly to prevent scalding the desktop, it is best not to use steel plate, its heat conduction fast, has an impact on welding), anti-static soldering iron. The operation method is as follows: the chip is roughly divided into two kinds, one is BGA package; A QFN package. The I\/O terminals of BGA package are distributed under the package in the form of circular or cylindrical solder joints in the form of array. The advantage of BGA technology is that although the number of I\/O pins increases, the spacing of pins increases rather than decreases, thus improving the assembly yield. Although its power consumption increases, BGA can be welded by controlled collapse chip method, which can improve its electric heating performance. The thickness and weight are reduced compared with previous packaging technologies; The parasitic parameter is reduced, the signal transmission delay is small, and the use frequency is greatly increased. Assembly can be coplanar welding, high reliability. QFN: four-sided pin-less flat package. One of the surface mount type packages. It is now more commonly referred to as LCC. QFN is the name prescribed by the Japanese Electronic Machinery Industry Association. The four sides of the package are equipped with electrode contacts, because there is no pin, the mounting area is smaller than QFP, and the height is lower than QFP. However, when stress occurs between the printed substrate and the package, it cannot be relieved at the electrode contact. Therefore, it is difficult to make electrode contacts as many as the pins of QFP, generally from 14 to about 100. The materials are ceramic and plastic. When there is an LCC mark, it is basically ceramic QFN. Electrode contact center distance 1.27mm. Plastic QFN is a low-cost package of glass epoxy printed substrates. Electrode contact center distance in addition to 1.27mm, there are two kinds of 0.65mm and 0.5mm. This type of package is also known as plastic LCC, PCLC, P-LCC, etc. Welding precautions: When welding the BGA encapsulated chip, the motherboard PAD must be smooched with a soldering iron, put a little flux, place the chip in the direction of screen printing, heat the chip vertically from the top with a wind gun, and adjust the temperature of the wind gun to 320 degrees (the temperature of lead solder is 280 degrees). After the solder melts, gently pluck the chip with tweezers and use the surface tension of the solder to return it to its position. Note that the fluctuation range must be small, otherwise it is easy to short circuit. When welding the QFA package chip, the motherboard PAD needs to be tinned with a soldering iron, and pay attention to the large \"ground PAD\" tin plating in the middle. The pin on the chip of QFA package also needs to be tinned, and the large \"ground PAD\" on the chip is best not tinned, otherwise it will easily cause other pin virtual welding. Put a little flux on the PAD of the motherboard, place the chip in the direction of screen printing, and heat it vertically with the wind gun at the same temperature as above (BGA). When the solder paste is melted, press the chip gently with tweezers, be careful not to press too hard, otherwise it is easy to short circuit or deformation of the main board. Finally, be sure to pay attention to: when welding, use a large mouth gun, do not use a small mouth gun, small mouth gun wind and heat concentration, easy to damage the chip. Welding more, they will naturally find a set of good experience. I wish you success!