PCBA Tech - SMT surface wettability and processing characteristics

Surface wettability in SMT patch processing

Surface wetting in SMT chip processing refers to a phenomenon in which the solder spreads and covers the surface of the metal to be soldered during soldering. The surface wetting of SMT chip processing generally occurs when the liquid solder is in close contact with the surface of the metal to be welded, and only when there is close contact can there be sufficient attraction. Correspondingly, when there are contaminants on the surface of the welded metal, it must not be in close contact. In the absence of contaminants, when solid substances and liquid substances are in contact during SMT patch processing, once an interface is formed, degradation will occur. The phenomenon of adsorption of surface energy, the liquid substance will spread out on the surface of the solid substance, and this is the wetting phenomenon.

In the dipping test, the following phenomena will exist on the surface of the pattern taken out of the molten solder tank:

1. No wetting

The surface is restored to the state before it was not covered, and the original color of the welded surface remains unchanged.

2. Wetting

After the molten solder is removed, a layer of uniform, smooth, crack-free, and adhered solder will remain on the soldered surface.

3. Partial wetting

Part of the area of the welded surface appears to be wetted, and part of it is not wetted.

4 Weak wetting:

The surface of the metal to be soldered is initially wetted, but after a period of time, the solder will shrink from part of the soldered surface to droplets and finally leave only a thin layer of solder in the weakly wetted area.

SMT chip processing is also surface mount technology. The specific content refers to the placement of chip-shaped components or miniaturized components suitable for surface assembly on the surface of the PCB board as required, and then use reflow soldering and other soldering processes to solder them., Complete the technology of electronic components assembly. On the SMT circuit board, the solder joints and components are on the same side of the board, so on the PCB board processed by the SMT patch, the through holes are only used to connect the wires on both sides of the circuit board, and the number of holes is much less., The diameter of the hole is also much smaller. And such a design can greatly improve the mounting density of PCB components.

1. Miniaturization

The size and volume of chip components used in SMT chip processing are much smaller than those of traditional plug-in components, which can generally be reduced by 60% to 70%, or even by 90%. The weight is reduced by 60% to 90%. This can meet the development needs of miniaturization of electronic products.

2. High signal transmission speed

The PCB board processed by SMT patch has a compact structure and high placement density, which can achieve the effect of short connection and low delay, and thus achieve high-speed signal transmission. At the same time, electronic products can be more resistant to vibration and shock.

3. High frequency characteristics

The components processed by SMT patches are generally leadless or short leads, which reduces the distribution parameters of the circuit and thus reduces radio frequency interference.

4. Conducive to automated production

SMT chip processing chip components have multiple characteristics such as size standardization, serialization and uniform welding conditions, which can make SMT chip processing a high degree of automation.

5. Low material cost

The packaging cost of most PCBA patch processing components is already lower than that of plug-in processing components of the same type and function.

6. High production efficiency

SMT placement technology simplifies the production process of electronic products and reduces production costs. The entire production process is shortened and production efficiency is improved.