LTCC With Temperature Sensor Array for Monitoring of Reactive Die Bond Processes–Design Optimization Using CFD

This article discusses a design optimization for the integration of a temperature sensor array for monitoring the spatially distributed course of process temperature during a reactive die bond process. Since reactive multilayer systems produce the entire fusion heat in a millisecond time frame, it is very difficult to get information about the dynamics of a joining process that they are employed for. Most of the monitoring methods for reactive multilayers are based on high-speed cameras, which cannot be employed in the case of a die bond process. Therefore, this article studies the influence on temperature measurements in a low-temperature cofired ceramics (LTCC) substrate for different propagation speeds of reactive foils used during bonding processes by computational fluid dynamics (CFD) simulation methods. The assumed reactive multilayer foil thickness is
$40 \mu \text{m}$
. Different speeds of 1, 10, and 100 m/s were studied, and temperature probes in the substrate were analyzed to try and ascertain the potential limitations of temperature measurements made through probes embedded in an LTCC substrate. It was found that the temperature probes would tend to underestimate the reaction speed, particularly at increased depth, but this can be recovered relatively successfully with judicious selection of criteria for experimentally determining the reaction speed. The results of the simulation study give valuable information for the LTCC layout process with regard to the lateral and the
${z}$
-axis position of multiple temperature probes forming a 3-D sensor array in the multilayer LTCC substrate. Moreover, the simulation can provide a calibration factor to estimate the real course of process temperature during a reactive die bond process from the lagged temperature responses of the temperature probes inside the LTCC substrate.