Important data of SMT processing and solder joint quality
1 SMT patch processing solder paste
Solder paste is a paste made of alloy solder powder and solder paste flux. It is an indispensable welding material in SMT wafer processing. It is widely used for reflow soldering. The solder paste has a certain stability at room temperature. StICkiness, which can initially stick the electronIC components in a predetermined position. At the welding temperature, as the solvent and some additives volatilize, the welding parts and PCB will be connected to each other to form a permanent connection.
At present, the SMT patch processing factory adopts the solder paste method and screen printing method, which has the advantages of SIMple operation and quick use after printing However, there are still some defects, for example, it is difficult to ensure the reliability of solder joints, which is easy to lead to false soldering, waste of solder paste, and high cost

2. SMT chip processing technology
Patch glue, also known as SMT adhesive, SMT red glue, usually red (also yellow or white) paste is uniformly distributed with adhesives, pigments, solvents and other adhesives, mainly used to fix equipment on PCB, and is generally distributed by monitoring or stencil printing After pasting the components, place them in an oven or a reflux oven for heating and hardening
The difference between patch adhesive and solder paste is that it will solidify after heating, and its freezing point temperature is 150 ℃, which will not melt after heating. In other words, the heat hardening process of the patch adhesive is irreversible. The use effect of SMT patch adhesive varies with the heat curing conditions, connecting objects, using equipment and operating environment. When using, the adhesive for mounting should be selected according to the process of PCB assembly (PCBA, PCA).
3. SMT wafer processing technology flux
Flux is the carrier of tin powder, and its composition is basically the same as that of ordinary flux. In order to improve the printing effect, it is sometimes necessary to add an appropriate amount of solvent. The solder surface and tin powder itself can be removed by the action of the active agent in the flux. Oxide, which makes the solder rapidly diffuse and adhere to the surface of the metal to be welded. The composition of the flux plays a decisive role in the expansion, wettability, collapse, viscosity change, cleanliness and shelf life of the solder paste.
SMT wafer processing solder joint quality
1. Welding judgment
1. Use professional equipment of online tester for testing.
2. Visual inspection or AOI inspection. When you find that there is too little solder in the solder joint, the solder permeability is poor, or there is a crack in the middle of the solder joint, or the solder surface is convex and spherical, or the solder does not melt with the SMD, you need to pay attention to that even minor conditions will cause hidden dangers, and you should immediately judge whether there is a large number of false soldering problems. The judgment method is: check whether there are multiple solder joints at the same position on the PCB, such as problems on some PCBs, which may be caused by solder paste scratches, pin deformation, etc., such as problems on many PCBs. There is a problem with the same location. At this time, it is likely to be caused by poor components or gasket problems.
Second, the reason and solution of virtual welding
1. The design of the base plate is defective. The existence of through holes in pads is a major disadvantage of PCB design. If it is not necessary, there is no need to use them. Through holes will cause loss of solder and lead to insufficient welding material. The spacing and area of pads also need to be standardized, otherwise the design should be corrected as soon as possible.
2. PCB board is oxidized, that is, the mat is black and does not EMIt light You can use an eraser to remove the oxide layer to make it bright again If PCB board is wet, it can be dried in the drying box if suspected PCB board has oil stain, sweat stain and other pollution, so use absolute ethanol to clean it
3. For printed circuit boards printed with solder paste, the solder paste is scraped, thus reducing the amount of solder paste on the related pads and making solder insufficient. It should be added immediately. You can use a vending machine or a bamboo stick to choose some supplements.