Research On The Fabrication Of Diamond/Al Composites And Their Electroless Nickel Plating

Diamond/Aluminum composites have been widely researched for advantages of high thermal conductivity,low thermal expansion coefficient and light weight,which are ideal for a new generation of electronic packaging materials.In this paper,Diamond/AlSi7 composites were fabricated by gas pressure infiltration.The effects of infiltration temperature and reaction time and diamond particle size on the relative density,thermal conductivity and thermal expansion coefficient of the composites were studied systematically.Electroless nickel plating methods of Diamond/AlSi composites were also been studied,the effects of pH,temperature and planting time on the thickness of Ni,content of P and roughness were investigated.Annealing was used to eliminate internal stress and coating bonding strength was qualitative compared.Some problems in the testing of the composites and recession of thermal conductivity of Diamond/Al composite were also discussed,the main results are as follows:The composites were prepared by selecting the AlSi7 as the matrix and MBD6 diamond with a diameter of 165?m as reinforcement.The results found that the infiltration temperature is too high,the reaction time is prolonged,the interfacial reaction product would be too much.As a result,the interface thermal resistance is large and thermal conductivity reduced.when the infiltration temperature is 650?,the infiltration pressure is 1.5MPa,the reaction time is 320s,the interface is well combined,the prepared composites have a thermal conductivity of 590W/?m·K?,the average thermal expansion coefficient is 7.32ppm/K,which fit in the needs of electronic packaging materials.The electroless nickel planting methods of Diamond/AlSi composites were studied.The nickel cell deposited on the high-active AlSi first and then spread to the diamond surface gradually.By this formula,pH=4.8,temperature is 80?and coating time is 40⁵0min,the nickel can cover the whole surface of Diamond/AlSi composites and the thickness is 9¹2?m,the content of P is about 9%,surface roughness changes a little.Annealing can increase the bounding strength between the coating and composites,the temperature between 160?²30?makes higher bounding strength through thermal shock and tensile test.The study also found that?1?when the thickness of graphite covered on the testing sample is too high,the testing result was lower than its actual thermal conductivity.After error analyzation,it is suggested that the thickness of graphite layer should be included in the total thickness of the sample,which can effectively reduce the testing error and make the testing value closer to the real one.?2?the Al₄C₃ produced by the interfacial reaction undergoes a deliquescence reaction to produce Al?OH?₃,which is finally decomposed into Al₂O₃ to seriously degrade the thermal conductivity.Adding element Si into Aluminum is found to inhibit the decline rate effectively by decreasing the solubility of C in molten Al to decrease the amount of Al₄C₃ and increasing the density of the composites.