Study On The Reliability Of New Nano-structured Polymer-metal Composite For Thermal Interface Material (Nano-TIM)

With the increasing power and miniaturization of microelectronics, heat dissipationhas become more critical to the reliability, performance, and further miniaturization ofmicroelectronics. Thus, it is an urgent challenge for us to come up with assemblytechnology solution to effectively and efficiently transport the increased heatgenerated by the microprocessors away from the silicon.A new Nano-structured Polymer-Metal Composite Thermal Interface Material(Nano-TIM) with potential high thermal conductivity and excellent mechanicalproperties was introduced in this study. According to ASTM D5470standard, anaccurate thermal measure system is built to test the thermal conductivity and thermalresistance. Pull tests are used to investigate the shear strength of samples withNano-TIM coalesced between two PCBs by an Intron Mech-Elec Machine. ScanningElectron Microscopy (SEM) analysis techniques and XRD analysis techniques areused to determine the morphology of the shear fracture section after pull tests and toobserve the structure of the cross section of Nano-TIM. Also, thermal and humidityaging test and thermal cycling test are taken for the reliability of the samples withNano-TIM reflowed and bonded between two PCBs.The results show that thermal resistances as low as0.047K/W of Nano-TIM,corresponding to an effective thermal conductivity of6.745Wm-1K-1. According tothe results of the shear strength and SEM pictures, the alloys flow out when thesample reflowed under high pressure, greatly affecting the reliability of the samples.In this research, the samples made with the pressure of3and4Psi show greatestshear strength. If pressure is too low during the reflow process, the shear strengthcould be very poor because the Nano-TIM could not bond the PCBs very closely andstrongly. When reflow takes place under a pressure higher than a certain point, theshear strength drops dramatically with increasing reflow pressure because ofincreasing of overflow. This indicates that the alloy contributes much more to theadhesive strength of the samples, and when manufacturing samples, pressure is very important for shear strength. The results do not show much difference for the shearstrength and the micro-structure of the samples after thermal and humidity test at40℃,93%RH with different days. It is indicated that the thermal and humidity testhas little influence on the shear strength of the samples, and the reliability of theNano-TIM is very good after thermal and humidity test. However, after thermalcycling tests for500cycles, the shear strength drops a lot. The alloy and the fibercontact not very well during thermal cycling tests. After thermal cycling tests, theshear strength of the samples drops to about50%of the samples without thermalcycling tests.From the above work, we find that the new Nano-TIM is a promising thermalinterface material for semiconductor industry in the future for it has an excellentreliability during the environmental tests.