How to choose the particle size of solder paste for PCBA patch soldering

PCBA patch weldingIt is a very important link in the assembly process of electronic products, and it is also an indispensable process. Due to the rapid development of electronic assembly technology, SMC/SMD components have become more and more miniaturized and sophisticated. SMC components range from 3216 to 1005, 0603, 0402, 0201; the spacing of IC pins ranges from 1.27mm to 0.5mm or even 0.3mm. The more precise the components, the smaller the size, the smaller the size of the template and the pad, the smaller the particle size of the solder paste is required for PCBA patch soldering, so that the solder paste can smoothly pass through the template opening under the printing pressure, and print To the PCB pad.

In the process of PCBA patch soldering, the particle size and surface oxidation of the solder alloy have a great influence on the performance of the solder paste. The currently used solder paste solder has a particle size of 25-40μm. The solder paste with large particle size is easy to block the template and affect the printability of the solder paste. It is not suitable for the printing of PCB with small pitch, but the price is relatively cheaper. Solder paste with a small particle size has better printability, but it is prone to solder paste collapse. Especially when the printing thickness is large, not only the requirements for the PCBA patch soldering process are high, but the price is also expensive. Therefore, in practical applications, the particle size of the solder paste should be selected reasonably with reference to the IC pin spacing and cost on the PCB, as shown in the figure below.

The smaller the particle size of the solder alloy powder, although the fine-pitch printing performance, collapse resistance, adhesion, etc. can be improved, but the smaller the particle size of the solder powder, the larger the total surface area of ​​the PCBA patch soldering, which makes the flux The burden of the clean surface increases, the surface oxidized during the reflow process increases, and the risk of producing solder balls increases, thereby reducing the entire process window.