Nanofluids, nanogels and nanopastes for electronic packaging

This paper discusses polymer based nanogels, nanofluids and nanopastes for thermal interface material (TIM) applications. Nanopaste and nanogel formulated using controlled-sized particles to fill small bond lines is highlighted. A variety of nanopaste with particle sizes ranging from 5 nm to 15 μm was bonded between metal plates. SEM and optical microscopy were used to investigate the micro-structures, conducting mechanism and path. Thermal impedance decreased with increasing curing temperature. It was found that with increasing curing temperature of the paste, the thermal impedance decreased due to sintering of metal particles. Paste modified with nanoparticles showed 30-90% thermal impedance drop when cured at 275°C instead of 200°C. Paste formulated with a low melting point (LMP) filler exhibited a thermal impedance as low as 48 mm
²
C/W. The paper also describes a nanoparticle dispersion approach to prepare nanogels and nanofluids. Several nanogels were tested in a thin bond line construction as thermal interface materials. Here we highlight recent developments on nanogels. The content of nanoparticles in the gels ranged from 4% to 20% by weight. Materials exhibited viscosities as high as 1000 Pa s for gels, and as low as 200 Pa s for low flow liquid like materials. Similarly, viscosities for oils and solvent based fluids were 500 cp and 10 cp respectively. Stability of nanoparticles with in the gel was ascertained by thermal treatments. The thermal performance of gels was characterized using thermal impedance measurements. The thermal impedance of gel, liquid like materials and oil based fluids were in the range of 70-75, 46-52 and 53-65 mm
²
C/W respectively. The present processes and materials allow fabrication of robust thinner bondline TIM structures.