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Alternative High Thermal Conductive Solid Type TIM
Keywords: Solid TIM, Gap Pad, Carbon Fiber
As the number of smartphone rapidly increased, the need of data transfer rate on signal process from base station has also increased significantly. As a result, the need for a high performance cooling solution has become the key requirement to deal with highly thermal loaded LSI from base stations. To find the ultimate solution, we utilize gap filler which is used to reduce thermal resistance between the LSI and the heat sink to develop our carbon fiber thermal conductive sheet. The purpose of the gap filler is to filling in the space between LSI and heat sink to reduce thermal resistance and stabilize thermal performance. However mechanical tolerance and stable thermal performance in wide range compressibility has made this task a very difficult and challenging one. In order to meet these requirements and characteristic, we advanced the development by focusing the high thermal conductivity of carbon fiber’s long axis direction and shape anisotropy. Thermal conductivity in carbon fiber’s long axis direction used is 900W/mK, which is extremely high comparing with general ceramics filler such as Al2O3:30W/mK or AlN:240W/mK, etc. But since carbon fiber has anisotropic thermal conductivity, we have developed our unique carbon fiber alignment technology in the thickness direction so to overcome the issue in making this a high thermal conductivity material. It’s been testified that this carbon fiber technology can reach 30W/mK or more in bulk thermal conductivity. Moreover, hardness and thickness can be adjusted according to the requirement and application, making it applicable for any applications. This time, we will introduce two type sheets. One is model C7 which is useful for BGA (Ball Grid Array) type LSI mounting method, and another is model CX which is useful for LGA (Line Grid Array) type LSI mounting method. C7 is a very soft type sheet as an excellent thermal performance in a low load pressure for which the reliability of solder Ball can be secured enough can be achieved. This sheet can achieve the thermal resistance of 0.3Kcm^2/W at 20psi low load pressure. Moreover, this model can be compressed up to 50% compressibility, so it can follow 1mm gap tolerance in from 20psi to 40 psi load pressure range when 2mm thickness sheet is used. For the CX model we can make 0.1mm thickness sheet in order to minimize thermal resistance. And we can confirmed that the CX model thermal resistance is bellow than 0.1Kcm^2/W at high load pressure load (=100psi). 100psi load pressure is suite for LGA type LSI mounting method. And this 0.1Kcm^2/W thermal resistance is lower than Indium thermal resistance which is 0.15Kcm^2/W.
Hiroyuki Ryoson, Deputy General Manager
Dexerials Corporation
Kanuma-shi, Tochigi

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