Research On DPC Ceramic Substrate Fabrication Technology Using Electroless Plating

With the continuous improvement of the chip's power, shrinking of its area, and development of its high integration, LED packaging puts forward higher requirement on dissipation substrate. Direct plated copper(DPC) can be completed on ceramic matrix by using thin film technology. Due to its stable chemical property, high thermal conductivity, fine lines and CTE matched with the chip material, DPC substrate has become an important direction of high power LED packaging dissipation substrate. However, as it has high price and no corresponding quality and testing standard currently, DPC substrate has been restrained on the application of high LED packaging. Electroless copper layer could be the seed layer of DPC in this paper, which will decrease the use of expensive equipment such as magnetron sputtering machine and reduce fabrication procedures, therefore it will reduce production cost. Instead of traditional DC electroplating, pulse plating could be adopted to thicken the copper circuit layer, which not only improves the efficiency production and optimizes the quality of the coating at the same time. Gold layer could be replaced by silver plating layer to be the welding layer and protective layer of DPC, which can reduce the material cost. Some testing methods on DPC performance have been proposed by comparing with other types of ceramic substrates, which will make a primary exploration for further standardizing DPC performance standards. The research work in this paper is about lowering the DPC substrate price and improving its performance, the main contents are as follows:Firstly, deposited electroless copper layer on ceramic matrix by using formaldehyde reduction copper plating system to complete DPC seed layer. Used orthogonal experiment, single factor analysis and other methods to optimize solution parameters, the optimum parameters of electroless copper plating bath are as follows: CuSO4 8g/L, C4H4O6KNa·4H2O 40g/L, HCHO 10g/L, temperature 35 ?and time 30 min respectively. Adopted scotch tape, microstructure, composition analysis, temperature cycling test and a variety of other test methods to comprehensively analyze the performance of the electroless copper layer, it turned out that electroless copper has fine electrical and mechanical performance;Secondly,investigated the relationship between electric current density and deposition rate of the pulse plating, the resulted showed that the two factors are proportional relationship within a certain range. Under the same current density, pulse plating could obviously reduce the production of nodular structure and improve the quality of coating compared with DC electroplating. The fine morphology circuit layer could be obtained by using the current density of 3ASD ultimately, which will improve the efficiency of electroplating;Thirdly, as a precious metal, the price of silver is relatively cheap. Silver layer could be placed on copper and nickel matrix respectively by using thiosulfate silver plating system. The result indicted that the silver coating on the nickel has better adhesive strength and higher thermal resistance compared the silver on the copper matrix. Except that, the silver coating with better adhesive strength could be obtained when the current density is 0.2ASD;Lastly, Put forward a new relatively accurate thermal resistance test method which could reduce subjective error and improve test accuracy through model comparison; A simple method for comparing the wettability of different ceramic substrates was proposed in this paper; Finally, it turned out that the DPC ceramic substrate has the better comprehensive performance compared with other types of ceramic substrates by the use of surface roughness and thermal shock combining with other test methods.