With the continuous trend of miniaturization in electronic devices, the processing speed of processing chips is becoming higher and higher. Whether it is laptops, smartphones, medical machinery, automotive electronic products, military and aerospace products, the use of BGA, CSP and other components in matrix packaging forms in products is increasing, and there are also more and more requirements for product quality. This requires everyone to continuously improve the SMT process capability, enhance high-end CNC machine tools, and ensure high reliability of products based on high-quality welding.

After SMT chip welding, there will be some residual cracks in the welding of components, which poses a certain potential risk to the stability of product quality. Although there are many factors that can cause this type of crack, such as solder paste, surface treatment method for PCB solder layer, setting of countercurrent curve, natural countercurrent environment, solder layer design scheme, microporous plate, and internal cavity, the main reason is usually caused by the melting of residual vapor in the welding material during electric welding.

When the melted welding material condenses, this type of bubble freezes out and causes cracks. Cracks are a common condition in electric welding, and it is impossible for electronic products to be assembled without cracks in every weld. Due to the limitations of crack conditions, the reliability of most welded products is entirely uncertain, leading to a decrease in welding impact toughness and affecting the heat transfer and conductivity of welding, thereby seriously endangering the electrical characteristics of devices. Based on this, for welding in power electronics technology based PCBs, the crack composition seen in X-ray images cannot exceed 5% of the total welding area. The minimum area of this type of scale cannot be achieved by adjusting the current processing technology, which means that new welding methods, such as vacuum pump reflux furnace welding process, must be used.

The vacuum pump reflow welding process is a technical process that requires welding under vacuum. This can effectively solve the problem of air oxidation of welding materials under general vacuum pump conditions in SMT chip sampling or production processing, and due to the effect of pressure difference between inside and outside the welding, the bubbles in the welding are very easy to overflow from the welding, achieving a low probability or even no bubbles in the welding, achieving the expected goal. The technical nature of vacuum pump reflow welding has brought about the probability of avoiding the formation of cracks in deep steam welding, which is particularly important in large-scale welding processes. Therefore, these large-scale welding processes need to transmit high-power power and heat, so reducing cracks in the welding can improve the heat transfer conductivity of the device from the source. Vacuum pump welding is sometimes used in combination with reducing gases and H2 to reduce air oxidation and remove metal oxides.

The key principle of reducing cracks in welding operations by vacuum pump reflux furnace can be analyzed from four aspects:

1. The vacuum pump reflux furnace can provide extremely low oxygen content and moderate reducing atmosphere, which greatly reduces the oxidation level of welding materials;

2. Due to the decrease in air oxidation level of welding materials, the metal oxide and flux reflect gas, which greatly reduces the probability of cracking;

3. Vacuum pumps can enhance the flowability of molten welding materials and reduce pressure loss. In this way, the buoyancy of the water in the molten welding material is much greater than the pressure loss of the welding material, and the bubbles are easily discharged from the molten welding material;

4. Because there is a pressure difference between the bubble and the vacuum outside, the buoyancy of the water in the bubble will be very large, making it easy for the bubble to solve the limitations of melting welding materials. The reduction rate of steam bubbles after vacuum pump reflow welding can reach 99%, the porosity rate of individual welding can be less than 1%, and the porosity rate of the entire plate can be less than 5%.

On the one hand, it can promote the improvement of welding stability and bonding strength, as well as the lubrication performance of the solder wire. On the other hand, it can also minimize the application of solder paste during use and improve the integration of welding into different environmental conditions, especially in high humidity, ultra-low temperature, and high temperature natural environments.