Advantages of vacuum reflow welding process

With the increasing functions of electronic products, the integration of printed circuit boards is becoming higher and higher, and the unit power of devices is also increasing. Especially in the fields of communication, automobile, rail transit, photovoltaic, military, aerospace and so on, high-power transistors, RF power supply, led, IGBT, MOSFET and other devices are more and more used. The packaging forms of these components are usually BGA, QFN, LGA, CSP, to packaging, etc, Its common feature is that the device has high power consumption and high requirements for heat dissipation performance, and the void rate of heat dissipation pad will directly affect the reliability of products. Due to the influence of cavity, the mechanical strength of the solder joint will decrease, the thermal resistance will increase and the current path will decrease, which will affect the thermal conductivity and conductivity of the solder joint, so as to reduce the electrical reliability of the device.

For bga-610 devices, the manufacturer's standard for BGA and c70c-610 is not specified in detail, while the manufacturer's standard for BGA and c70c-610 devices is not specified in the specification, and the collapse rate of other devices can be determined in detail; For the grounding pads of high-power devices, the requirements of users of some high reliability products for void rate are often higher than the industry standard, further reduced to 10% or even lower.

Therefore, how to reduce the voids in the solder joints of such SMT devices is one of the key problems to improve the product quality and reliability. At present, there are many solutions in the industry, such as using low hole rate solder paste, optimizing PCB pad design, using dot matrix mesh plate opening, welding in nitrogen environment, using preformed pads, and so on. However, the final effect is not very ideal. For large-area grounding pads, it is difficult to stably control the void rate below 10%. After reflow soldering of SMD devices, there are usually some cavities in the solder joint. The larger the solder joint area, the larger the cavity area will be; The reason is that when the molten solder cools and solidifies, the gas generated in the solder does not escape, but is "frozen" to form a cavity. There are many factors affecting the generation of voids, which are related to the selection of solder paste, device packaging form, pad design, PCB pad surface treatment method, mesh plate opening method, reflow curve setting and so on.

Vacuum reflow welding process can stably achieve the void rate below 5%, which is a very effective means to solve the problem of void rate. Vacuum reflow welding process plays a very significant role in removing solder joint voids. Under vacuum conditions, by reasonably setting process parameters, batch production with void rate below 5% can be stably realized.