Experimental Study on Reactive Joining Processes on LTCC Substrates

Reducing the thermo-mechanical stress during manufacturing respectively during soldering processes is very important to avoid high failure rates. As an example, a reactive multilayer system (RMS) can be used to transfer the heat only locally to the solder joints instead of heating the entire system, what is already a well-established process on silicon and metal substrates. The adaptation of this high-temperature process to the field of low-temperature cofired ceramic (LTCC) substrates would offer new technological possibilities but is very challenging due to their specific properties like higher roughness and lower thermal conductivity compared to silicon. Among other things, one parameter that influences the quality of the joining process using an RMS is the joining pressure. For an analysis of this aspect, LTCC chips with a full-surface metallization consisting of AgPd and their corresponding counter pieces were manufactured and bonded together with a commercially available reactive multilayer foil using different settings. Cross-sections of the samples were then prepared and analyzed by light microscopy, revealing the differences in respect to different joining pressures.