Interface Thermal Conductance Between Metal Films and Copper
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W thermal interface materials (TIMs) are important to meet thermal performance requirements for future generations of electronic power and laser devices. Solders such as indium with high thermal conductivity are suitable for high-end applications that need improved heat dissipation. Thermal conductance measurements and characterization by scanning electron microscopy, scanning acoustic microscopy, and transmission electron microscopy (TEM) are used to characterize the solder TIM thermal performance, interfacial microstructure, and failure mechanism.[1] Reliable operation of high power light-emitting diodes and lasers is dependent on use of TIMs with higher thermal conductance and heat spreaders that can dissipate the heat.[2,3] The thermal conductance of a TIM depends on the thermal conductivity, thickness, roughness of the interface and the microstructure.[4,5] Copper with high electrical and thermal conductivity is used as a heat spreader in many electronic devices.[6] The active devices are bonded to Cu heat spreader using a TIM. In addition, TIM is also a low melting point material that can deform plastically and accommodate thermal stresses generated during bonding. In or Au-Sn alloys are used as TIMs for special applications as these have higher thermal conductivity[7] than Pb-Sn solders, polymeric materials, and composites. The interface thermal conductance between Cu and the TIM is an important parameter that depends on the transmission
HAI ZHENG, Research Assistant, and K. JAGANNADHAM, Associate Professor, are with Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695. Contact e-mail: [email protected] Manuscript submitted April 22, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
of energetic electrons across the interface as heat in the metals and alloys is carried by electrons.[8,9] Currently in industry, TIM testers are modeled after ASTM D 5470, ‘‘standard test method for steady-state thermal transmission properties of thermally conductive solid electrical insulation material.’’ ASTM D 5470 test uses two metal blocks, one heated and one cooled, between which a TIM is placed. Temperature sensors are placed within the metal blocks. Since the temperature distribution is linear, the temperature of surface of the metal blocks in contact with the specimen can be calculated using the sensor-given temperatures and the distance between the sensors.[10–12] In addition to these measurements on TIMs, self heating of the devices is investigated to characterize the performance.[13] The study of thermal conductivity of composites was responsible for significant understanding of the influence of interface thermal conductance associated with the interfaces. Thermal conductivity of the composites was determined using laser flash technique.[14–16] Modeling of the thermal conductivity of the composites using the thermal conductivity of the individual components and the thermal conductance of the interfaces using effective mean field analysis[15] enabled the determination of the contribu
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