Fabrication And Properties Of Cu/Mo/Cu Laminated Composite Substrates

In this article, the fabrication, thermal expansion and conduction properties ofCu/Mo/Cu laminated composite substrates were investigated. The results showedthat the combinations of the substrates were well-defined by hot rolling. Thecoefficient of thermal expansion and thermal conductivity were tested and hadcompared with the theoretical ones. To improve the heat-conducting property,thermal holes of Mo layer was designed within the substrates to meet different fieldsfor electronics packaging development.The approach of surface preparation, hot rolling process and parameters,post-heat treatment and cool rolling were investigated. The selected temperature forhot rolling were850℃,900℃and950℃. In the meantime, the first reduction wereassined for30%,40%,50%,60%and70%. The morphology of the interfacecombinations were obtained by optical microscope (OM), scanning electronmicroscope (SEM). In addition, the elements diffusion state was analyzed byenergy dispersive spectrometer (EDS) method. It was exhibited that the mechanicalproperties of copper and molybdenum and their interface bonding were to achievethe best with the heating temperature of950℃and the reduction of60%. Primarybonding mechanisms in the process were mechanic joggle and hardened surface.Moreover, the reason was analyzed for the Mo layer cracked with the deformationratio to70%.The bending experiment was illustrated that Mo in the substrate had goodplasticity to achieve large-angle bending. Based on the thickness of the wholesubstrate, the distortion rules of the thickness were established. Simutaneously, theempirical formulas and deviation formulas for the distortion processing werederived, which was considered to reduce the production cost.The theoretical models of coefficient of thermal expansion (CTE) of thecomposite substrates were displayed and compared with the experimental results. Itindicated that at relatively low temperature, the experimental CTE were low inaccordance with the theoretical values. However, both results varied a lot at hightemperature. With increasing of the temperature, the CTE of the substrates showedthe trends of first increased and then decreased slowly.The flash method was applied to test the thermal diffusion coefficient for thesubstrates to obtain the thermal conductivity (TC). The theoretical values werediscussed by TC formulas for laminated composites. It was clearly seen that theexperimental values were smaller than the calculated ones.Substrates with different thickness ratios were fabricated and the ratios were 1:1:1,1:3:1,1:5:1and1:7:1respectively. The CTE and TC of the compositesubstrates decreased with the increasing ratio of Mo layer in the substrates.The composite substrates were studied with modified thermal holes of Mo layer.The performance of thermal conduction and expansion were regulated by changingthe diameters of the thermal holes at1mm,2mm,3mm and intervals of the thermalholes at1.5mm,2.5mm,3.5mm. The TC of the substrates were improved from22.47%to43.71%,63.93%for the former and from23.21%to43.71%,58.60%forthe latter respectively.A novel thermal stresses model of the Mo layer as thermal holes wasestablished to calculate the theoretical values of CTE. The concept of micrometerregion of CTE was proposed to be a feasible scheme of calculation method.