The operation method is as follows: there are two kinds of chips, one is BGA package; A QFN package.
I/O terminals of BGA package are distributed under the package in the form of circular or columnar solder joints in the array. The advantage of BGA technology is that although the number of I/O pins has increased, the pin spacing has not decreased, thus improving the assembly yield. Although the power consumption is increased, BGA can be welded by controlled chipping method to improve its electrothermal performance. The thickness and weight are lower than those of the previous packaging technology; The parasitic parameters are reduced, the signal transmission delay is small, and the use frequency is greatly improved; * * * It can be assembled by surface welding with high reliability.
QFN: Four-sided leadless flat package. One of the surface mount packages. It is often called LCC now. QFN is the name stipulated by Japan Electronic Machinery Industry Association. Four sides of the package are equipped with electrode contacts. Because there are no pins, the installation 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 released at the electrode contact. Therefore, it is difficult for the electrode contact to have as many pins as QFP, generally from 14 to 100.
There are two kinds of materials: ceramics and plastics. When there is an LCC logo, it is basically a ceramic QFN. The distance between electrode contact centers is1.27mm.. Plastic QFN is a low-cost glass epoxy printed substrate package. In addition to 1.27mm, there are two kinds of electrode contact center distances of 0.65mm and 0.5mm. This package is also called plastic LCC, PCLC, P-LCC, etc.
Matters needing attention in welding: When soldering BGA package chips, the bonding pad of the motherboard must be leveled with a soldering iron, and a little flux should be put in. The chips should be arranged in the direction of screen printing, heated vertically from above with an air gun, and the temperature of the air gun should be adjusted to 320 degrees (the temperature of lead solder is 280 degrees). After the solder melts, the chip should be gently stirred with tweezers, and the surface tension of the solder should be used to reset. Note that the fluctuation range must be small, otherwise it is easy to short circuit.
When soldering QFA package chip, the main board pad needs to be tinned with soldering iron. Pay attention to the small "grounding pad" in the middle. The pins on the QFA package chip also need to be tinned, and it is best not to tin the large "ground pad" on the chip, otherwise it will easily lead to virtual soldering of other pins. Put a little flux on the motherboard pad, put the chip in the direction of screen printing, and heat it vertically with an air gun at the same temperature as BGA. After the solder paste melts, gently press the chip with tweezers, and be careful not to use too much force, otherwise the pin will be short-circuited or the motherboard will be deformed.
Finally, we must pay attention to: use a large-mouth air gun when welding, not a small-mouth air gun, which is prone to damage the chip because of concentrated wind and heat.