Design, Fabrication and Characterization of Heat Spreaders in Low-Temperature Co-Fired Ceramic (LTCC) utilizing Thick Silver Tape in the Co-Fire Process

摘要

Heat spreading in LTCC is commonly realized by means of screen-printed thick film metallization. However, the cross-sectional area of the spreading structure is technologically limited. In the presented investigation, a thick silver tape is used to form a thick silver heat spreader through the LTCC substrate. An opening is structured by laser cutting in the LTCC tape and filled with a laser-cut silver tape. After lamination, the substrate is fired in a constraint sintering process. The bond strength of the silver to LTCC interface is approx. 5.6 MPa. The thermal resistance of the silver structure is measured by means of a thermal test chip glued with a high-thermal-conducting epoxy to the silver structure. The chip contains a resistor and diodes to generate heat and to determine the junction temperature respectively. The rear side of the test structure is temperature-stabilized by means of a temperature-controlled heat sink. The resulting thermal resistance is in the range of 1.1 K/W to 1.5 K/W depending on the length of silver structure (5 mm to 7 mm). Advantages of the presented heat spreader are the low thermal resistance and the good embedding capability in the co-fire LTCC process.