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Au–Sn Soldering Using a Micro-heater to Restrain Excess Temperature Rise Inside the Package

The high-melting point solder, approximately 300°C, is often used for assembling reflow-capable devices. When thermally sensitive devices such as PZT sensors with a Curie temperature of approximately 250 °C are encased in a package using solder, the temperature inside the package must be below 250 °C and precisely measured to avoid thermal damage. In this study, the authors proposed a novel in-situ temperature measurement method inside the package based on a chip-sized thermometer. A new soldering method using a micro-heater was developed to heat solder locally without overheating inside the package. In the conventional soldering method of heating the whole package, the temperature inside the package reached 260 °C; in the new soldering method, it was kept to 180 °C. Moreover, the temperature distribution inside the package was examined in detail by transient heat transfer analysis. The analysis results were in agreement with the experimental results using the two soldering methods. From the analysis results, it was found that the electrically conductive vias inside the package assisted in the transfer of heat to the solder and a Si lid played a role as the heat transfer path.