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PCBA double-sided water-cooled IGBT vacuum welding process
2021-09-27
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Author:Frank

PCBA double-sided water-cooled IGBT vacuum welding process
Introduction to Vacuum Welding
For electronic products, the main advantage of vacuum welding is to remove the volatile substances in the solder joints, and correspondingly reduce the voids in the solder joints of the pcb product.

Voids are bubbles created by the release of gas, for example, the chemical reaction between flux residues and products at high temperatures. The experience gained during the process development shows that the ambient pressure of the solder in the molten state is less than 50mbar enough to significantly reduce the number of voids.

For bottom terminal devices (BTC), MOSFET and LED devices, it is very simple to remove air bubbles during vacuum welding. In some customer products, the vacuum pressure value of 20mbar can completely remove the voids.

Double-sided water-cooled GBT

Double-sided water-cooled IGBTs are currently required for the development of new energy vehicles, mainly to solve the problem of power density of on-board inverters. Compared with the existing IGBT module, DCB constitutes a second heat dissipation channel on the top surface of the module, which is used to improve the heat dissipation effect of the module.

As a double-sided water-cooled module, the mechanical consistency of its plastic packaging materials at different temperatures needs to be guaranteed first. Modules at 22°C and 150°C have better surface flatness and excellent moisture resistance. After adding the heat dissipation channel on the top of the module, the heat dissipation effect is increased by 70%. It should be noted that the thermal resistance has a greater influence on the surface, and the best thermal resistance should be achieved.

Double-sided water-cooled GBT vacuum welding

pcb board

As we know, welding will inevitably have void defects due to the gaseous water formed by the flux in the heating process. The welding area of the double-sided water-cooled IGBT module can reach 50mm*50mm, which is a large-area welding process.

Soldering voids will affect the heat dissipation performance of the module, and power loss. In order to reduce the void defects generated in the welding process of the double-sided water-cooled IGBT module, welding under vacuum conditions obviously helps to remove the voids. Please refer to the following test results:

Judging from the previous test results, during the welding process of the IGBT, the vacuum negative pressure value is different and the void result is also different.

From the above test result data, for the welding of double-sided water-cooled IGBT modules, the bubbles in the solder are more helpful to escape under the condition of low vacuum and negative pressure. The final void can be less than 1% under the vacuum condition of 20mbar, and the void rate during the nitrogen reflow soldering process is higher than 30%. Then, vacuum welding is the best choice for double-sided water-cooled IGBTs.

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