Solder Matrix Fiber Composite Thermal Interface Materials
Licentiatavhandling, 2018

Overheating has been a problem for microelectronics devices for decades, and the problem is exacerbated by the continued trend of miniaturization of features and the corresponding increase in power density. Thermal interface materials (TIMs) target one of the main bottlenecks in heat transfer: the interface between two materials, such as between a heat-generating microchip and a heatsink. By filling out microgaps caused by the roughness of the mating surfaces, TIMs improve the heat transfer over the interface by orders of magnitude. Nonetheless, even with a TIM the interface can be a limiting factor for the overall cooling. Thus, the development of new and improved TIMs is a big challenge for the electronics field.

This thesis thoroughly reviews the overall status of the field of TIM research, and identifies three main tracks for novel research. First, particle laden polymers, which utilizes thermally conductive particles inside a polymer matrix which can conform to surfaces. Second, continuous metal phase TIM, which forms metallurgical bonds to both surfaces, and utilizes the inherently high thermal conductivity of metals. Third, carbon nanotube (CNT) array TIMs, which utilize the incredible thermal conductivity of CNTs. Here, an array of vertically aligned CNTs is used as nanosprings to connect the two surfaces together. In addition to these main tracks, various novel ideas based on polymers, metal and carbonaceous materials are explored.

From the reviewed categories, continuous metal phase TIM in the form of solder is already widely used in industry, but comes with severe drawbacks in terms of mechanical properties and handling issues. Solder matrix fiber composites (SMFCs) have been shown to address these challenges, but have so far required complicated procedures and components. In this thesis, we present the fabrication of a new SMFCs based on commercially available polymer and carbon fiber networks infiltrated with Sn-Ag-Cu alloy (SAC) or Indium using equipment for large volume production. The composite material exhibits similar thermal properties compared to pure solder, and mechanical properties that can be tailored towards specific applications. We also show that the handling properties of the SMFC allows it to be used in process flows where multiple reflow cycles are required, and can achieve a well-defined bond line thickness and good bonding using fluxless reflow under pressure.

thermal management

composite materials


thermal interface material

Opponent: Peter Melin, Ericsson AB, Sweden


Josef Hansson

Chalmers, Mikroteknologi och nanovetenskap (MC2), Elektronikmaterial och system

Novel nanostructured thermal interface materials: a review

International Materials Reviews,; Vol. 63(2018)p. 22-45

Artikel i vetenskaplig tidskrift

Fabrication and characterization of a carbon fiber solder composite thermal interface material

2017 IMAPS Nordic Conference on Microelectronics Packaging (NordPac),; (2017)p. 97-100

Paper i proceeding

Josef Hansson, Torbjörn Nilsson, Lilei Ye, Johan Liu; Effect of fiber concentration on mechanical and thermal properties of a solder matrix finer composite thermal interface material



Metallurgi och metalliska material

Annan elektroteknik och elektronik



Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 397


Chalmers tekniska högskola


Opponent: Peter Melin, Ericsson AB, Sweden