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Substrate vacuum sintering characteristics

There are many ways to sinter substrates in microwave components, but there is a common problem that the sintered void rate is difficult to control, so that the product quality and performance cannot meet the predetermined requirements. The vacuum sintering method is adopted to solve the problem of high void ratio in substrate sintering. At the same time, the substrate sintering process is systematically studied, the process of substrate vacuum sintering is elaborated, the process flow is summarized, and the process details are explained in detail.

Substrate vacuum sintering

Substrate vacuum sintering refers to the use of the vacuum technology of the vacuum sintering furnace to effectively control the atmosphere in the furnace, and through the processes of vacuum, air intake, exhaust, preheating, heating and cooling, the corresponding temperature and gas control curves are set to achieve sintering the whole process. The process parameters of substrate vacuum sintering mainly include sintering temperature, time, type and pressure of process gas.

As the focus of sintering, temperature needs to be precisely controlled. It is generally set according to the size of the box, heat transfer conditions and heat capacity. The preheating temperature is about 70% of the melting point of the solder, and the heating temperature is 30~50C higher than the melting point.

The time is relative to the temperature, mainly to control the solder to reach the melting point and keep it for 1~3min. If the temperature is too low or the time is too short, the solder will not penetrate or melt. If the temperature is too high or the time is too long, the solder will be over-melted, which will affect the reliability of sintering. After setting the temperature, it is necessary to set the gas pressure in the preheating, heating and cooling stages, not only to optimize the process atmosphere in the chamber, but also to effectively control the void rate.

First of all, vacuuming is carried out at the initial stage to discharge the air between the substrate, solder, and the box body. After the air is discharged, the nitrogen gas is repeatedly filled and discharged several times. It is a state of negative pressure, the purpose is to optimize the process atmosphere, and then vacuum again after the solder reaches the melting point, the purpose is to discharge all the gas between the substrate and the box after the solder is melted, and the final cooling stage is through ultra-high pressure. Squeeze out the gas between the substrate and the box body, thereby reducing the void rate. An example of the vacuum sintering process curve is shown in the figure.

Substrate vacuum sintering characteristics

For the “void” problem of substrate sintering, a large number of experiments have been done, trying various sintering solders, changing fixtures and vacuum sintering methods, and constantly adjusting vacuum sintering process parameters. Practice has proved that through these technological measures, it is possible to reduce voids It is possible to reduce the void rate to zero, indicating that the substrate adopts the vacuum sintering process with high quality and reliability.