Thermal improvement of die attach by using PDMS-grafted particles as filler and Its application in solid state lighting

Die attach material (DA) is important to heat dissipation and light output of solid state lighting (SSL) packages. Even though high thermal conductivity benefits to reduce the bulk thermal resistance of die attach, high viscosity will increase the contact thermal resistance in the packages. To face such a dilemma, it is of desirable to develop new technique to increase the filler loading without sacrificing the rheological properties. In this paper, we propose surface treatment of fillers with PDMS to keep the viscosity at a relatively low level while achieve high thermal performance. It has been demonstrated that surface-grafting can significantly reduce the viscosity of the die attach and increase the filler loading. The thermal concutvity of the die attach increased with the increase of the filler loading. However, there wasn't any percolation-like transition of thermal conductivity observed at high loading up to 50%, which might limit achieving better thermal performance in LED packages through surface-grafting technique. It is expected that the decease of percolation threshold of die attach materials and increase of percolative thermal conductivity are the complementing approach to fully exploit the benefit from surface grafting techniques to enhance the thermal performance.