Fabrication And Characterization Of Combined Heat-sink By Embedding Cu-Diamond Composite Layer Into Copper Substrate

Heat dissipation in electronic package design has become increasingly important because the continuing miniaturization and integration of microelectronics requires ever more efficient heat removal. The ideal material acting as heat sink should have high thermal conductivity and low mismatch of the coefficient of thermal expansion?CTE? with semi-conductor such as Si, GaAs. A common methodology is to mix and sinter the copper and diamond powder, forming Cu-Diamond composite material which owns the matched coefficient of thermal expansion?CTE? with semi-conductor and high thermal conductivity. However, the high volume content of diamond in Cu-Diamond composite leads to low strength and high brittleness problems which limited to miniaturization of heat sink. This thesis reports our initial research work on fabricating a mono layer of Cu-Diamond on Cu-Cr substrate by composite plating and pressing the protruding diamond particles into Cu-Cr substrate by mechanical pressure. This new kind of combined heat sink reduces the surface CTE by mono layer of Cu-Diamond and remains the most of excellent mechanical properties of Cu-Cr. The results show as follows.The mono layer of Cu-Diamond composite was prepared by using composite plating and subsequent pressing treatment. The effect of sedimentation time on the density of sand diamond and the influence of pressure value on the indentation depth were intensively investigated. The results showed that proper sedimentation time is required to obtain a good sand coating with well distributed and moderate density diamond layer. And the sedimentation time decreased with increasing diamond size. To ensure the diamond particles completely pushed into the substrate, the pressure of 8.4×10⁴ N is needed.To remedy the surface cracks after pressing treatment, the annealing treatment and electrical stripping method were employed. The results illustrated that the surface crack can be effectively removed by using electrical stripping method. Additionally, non-microporous and flat surface can be achieved when applied current density is 3 A/dm².Finally, in order to eliminate the V groove in the composites, chemical vapor deposition and high-temperature sintering treatment, filled with copper in advance, were applied. The results indicated that the diamond with good crystal structure of diamond was obtained under 10 h CVD, meanwhile, the size of V groove had been reduced to some extent. Flat Cu-Diamond layer can be obtained by using copper filling and high-temperature sintering. Under this condition, Cr element was continuously accumulated on the surface of diamond particles through vertical diffusion. After the sintering treatment of 1000 °C, the interlayer whose thickness is about 0.6?1.2 ? can be detected. Moreover, the ratio of Cr element to C element in this interlayer is 1.23:1, which is close to the ratio in Cr₃C₂. Hence, we can conclude that the interlayer should be Cr₃C₂.Thermal conductivity measurement verified that the thermal conductivity of combined heat-sink prepared by this research has been improved, compared to Cu-Cr substrate. Besides, the thermal conductivity was influenced by the size of diamond. With a low roughness of 0.54 ?m, the CTE of w40 combined heat-sink under 1000 °C sintering treatment dropped to a low value, whose theoretical value is about 9×10^-6 /K. Thereby, it would be matched with semiconductor materials.