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20 SMT007 MAGAZINE I DECEMBER 2024 Feature Article by Dr. Paul Wild REHM THERMAL SYSTEMS GMBH When soldering electronic assemblies, the focus of the vacuum application is on the removal of volatile substances from the solder joints and the associated reduction of pore for- mation. Particularly in the thermal manage- ment of power electronics components, pores can cause so-called hotspots with higher tem- peratures due to their poor heat conduction. ese hotspots can lead to overheating of the components on the one hand and to thermally induced destruction of the solder structure on the other. Vacuum soldering is used in the production of assemblies in the field of power electronics (e.g., inverters for electric cars and renewable energy sources). Figure 1 shows various SMD components aer soldering with and without vacuum. A compar- ison shows that with a vacuum of 10 mbar, both the number of pores and the pore area can be drastically minimized. In the case of flat solder joints, such as QFNs or Si chips, a low propor- tion of pores results in better thermal perfor- mance as well as less tilting of the component. In addition to temperature profiling, the neg- ative pressure in the vacuum chamber and the duration of the negative pressure are also set during vacuum soldering. Figure 2 shows the influence of these parameters on the propor- tion of pore area in the thermal pad of a QFN64 component. Overview of Soldering Systems With Vacuum Figure 1: X-ray images of various SMD components after soldering with 10 mbar vacuum (top) and without vacuum (bottom).