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Some common sense about SMT technology, explained by a PCBA OEM and component supplier
PCBA manufacturers believe that the characteristics of SMT technology can be highlighted by comparing it with traditional through-hole insertion technology (THT). From the perspective of assembly technology, the fundamental difference between SMT and THT is "paste" and "insert". The differences also lie in the substrate, components, component shapes, solder joint shapes, and assembly processes.
PCBA contract manufacturers believe that the characteristics of SMT technology can be highlighted by comparing it with traditional through-hole insertion technology (THT). From the perspective of assembly technology, the fundamental difference between SMT and THT is "pasting" and "insertion." The differences also lie in the substrate, components, component shapes, solder joint shapes, and assembly processes.
PCBA contract manufacturers believe that THT uses leaded components. Circuit connection lines and mounting holes are designed on the printed circuit board, and the component leads are inserted into the pre-drilled through-holes on the PCB, temporarily fixed, and then soldered using wave soldering or other welding technologies on the other side of the substrate to form reliable solder joints, establishing long-term mechanical and electrical connections. The main body of the component and the solder joints are distributed on both sides of the substrate. With this method, due to the leads of the components, when the circuit density reaches a certain level, the problem of size reduction cannot be solved. At the same time, faults caused by the proximity of the leads and interference caused by the length of the leads are almost impossible to eliminate.
PCBA contract manufacturers believe that DIP packaging is a type of component packaging in THT plug-in technology, also known as dual in-line packaging technology, and is the simplest packaging method. It refers to dual in-line packaged integrated circuit chips. Most small and medium-sized integrated circuits use this packaging form, and the number of pins generally does not exceed 100. DIP-packaged CPU chips have two rows of pins and need to be inserted into DIP-structured chip sockets.
In the traditional THT printed circuit board, the components and solder joints are located on both sides of the circuit board. On the SMT circuit board, the solder joints and components are on the same side of the circuit board. Therefore, on the SMT printed circuit board, through-holes are only used to connect the conductors PTH on both sides of the board, so the number of holes is much smaller, and the diameter of the holes is also much smaller. In this way, the assembly density of the circuit board can be greatly improved.
PCBA contract manufacturers believe that common defects and solutions in the SMT dispensing process:
1. Component displacement phenomenon: After the paste is cured, the component is displaced. In severe cases, the component pins are not on the pads. The reason is that the amount of paste is uneven, such as one more drop of glue on two points of the surface mount component than one less; component displacement during pasting or low initial adhesion of the adhesive; the PCB is left for too long after dispensing, and the glue is semi-cured.
Solution: Check if the nozzle is blocked and eliminate the phenomenon of uneven glue dispensing; adjust the working status of the placement machine; change the glue; after dispensing The PCB should not be left for too long (less than 4h).
2. PCBA contract manufacturers believe that the phenomenon of component dropping after wave soldering is that the bonding strength of the components after curing is insufficient and lower than the specified value. Sometimes, components will fall off when touched by hand. The reasons are that the curing process parameters are not in place, especially the temperature is insufficient, the component size is too large, and the heat absorption is large; aging of the photocuring lamp; insufficient amount of glue; contamination of components/PCB.
Solution: Adjust the curing curve, especially increase the curing temperature. Usually, the peak curing temperature of thermosetting glue is around 150, and failure to reach the peak temperature easily causes flaky peeling. For photocuring glue, observe whether the photocuring lamp is aging and whether the tube is blackened. The amount of glue and the contamination of components/PCB should be considered.
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