Before introducing the reasons for the voids in SMT patches, I will give you a brief introduction to the voids. That is, the micro-holes at the welding interface. Such voids are so small that they can only be found by scanning electron microscopy (SEM). The location and distribution of the voids may be the potential cause of electrical connection failure. If the micro-holes are not reserved or the location of the micro-holes is incorrect, voids may occur, especially for power components, which will increase the thermal resistance of the components and cause failure.

At the same time, the existence of voids will also oxidize the product, which will lead to faster product aging. So, how do the hollows in SMT patch processing occur?

Studies have shown that the voids (micropores) in the welding interface are mainly caused by the high solubility of Cu. Due to the high melting point of lead-free solder and high-Sn solder, the dissolution rate of Cu during lead-free soldering is much higher than during Sn-Pb soldering. The high solubility of copper in lead-free solder will produce "voids" at the copper-solder interface. Over time, these voids may weaken the reliability of solder joints.

In addition, there are other reasons for voids in SMT patch processing. For example: 1. The pad design is unreasonable. 2. The cause of solder paste. The alloy composition of the solder paste is different, and the particle size is different, which will cause bubbles during the solder paste printing process, and some air will continue to remain during reflow soldering, and voids will be generated after the bubbles burst at high temperatures. 3. The surface treatment of PCB pads. The surface treatment of the pad also has a crucial influence on the generation of voids. 4. Backflow environment. Whether the equipment is vacuum reflow soldering also affects the generation of voids. 5. Reflow curve setting. If the reflow soldering temperature rises too slowly or cools down too fast, the residual air inside cannot be effectively eliminated, resulting in voids.

Finally, the problem of lead-free solder is high temperature, high surface tension, and high viscosity. The increase in surface tension will make it more difficult for the gas to escape during the cooling stage, and the gas will not be easily discharged, which increases the proportion of voids. Therefore, there are relatively more voids in lead-free solder joints in SMT patches.

The above is the reason for the holes in the SMT patch, I hope it can be helpful to everyone!