Quantitative Metallography Analysis Of Cu-Cr-RE Leadframe Material

Leadframe materials are very important in IC packaging, which is required to have high strength and electrical conductivity. CuCr alloys have wide value of use as leadframe materials because of their high strength and electrical conductivity. To further enhance the properties of the CuCr alloys and meet more high-performance demand for electronic industrial development, it is necessary to further research on this alloy. In order to offer more useful information about choosing the best process conditions, this thesis will research on CuCr and CuCrRE alloy by quantitative metallographic method, which is prepared by diverse heat-treated systems.In this thesis, Optical microscope, quantitative metallographic analysis, X-ray diffractometer, SEM, EDS are used to observe and research the microstructures and phases of the alloys of CuCr and CuCrRE on conventional aging(solution anneal at 950℃ + aging treatment at 480℃) and the thermomechanical processing(solution anneal at 980℃ + cold deformation + aging treatment at 480℃), in which different sorts and contents of RE(they are the pure RE of La, Nd, Y) are added. Properties of them are measured by electrical conductivity meter and hardness meter and the relationship between microstructures and properties are debated too. The result shows:1. Electro-etching method may not only effectively avoid the scratch appearance during the sample grind, but also more clearly reveal microstructure and improve the efficiency and accuracy of quantitative metallographic analysis. Consequently, it is feasible to determine electro-etching method as the sample preparation method about quantitative metallographic analysis in CuCrRE alloy.2. After solution for 2 hours at 950℃ and aging for 2 hours at 480℃, Cu_0.8Cr_0.4La alloy can reach the peak microhardness, in which Roundness of Cr particles is better and Cr particles is more dispersed. The longer the aging time is, the higher the electrical conductivity is, but the microhardness will decrease if the aging time is more than 2 hours and the overaging happens. Consequently, the optimum heat treatment pattern is solution at 950℃ for 2 hours and aging at 480℃ for 2 hours. Andit is feasible to study the dynamical changes of Cr phase in precipitation process by using quantitative metallographic method.3. The more heavily the alloy is deformed prior to aging, the higher the hardness is obtained and the more evidently the grains are elongated in the direction perpendicular to the compression axis. At small prior strains, there are certain relations between the hardness and grain size of the alloy, that is to say, the higher the hardness is obtained, the smaller its corresponding grain size is. At large prior strains, grain size have little influence upon the hardness.4. When aging at 480°C, even a long time aging(e.g.60min) has not initialized recrystallization in Cu0.8Cr0.05Y alloy after solution at 980°C and cold deformation. The reason of this situation can be outlined as follows: First, recovery and recrystallization process is retarded by small additament of RE. Second, the pinning effect of precipitates can reduce the mobility of dislocations and obstruct their rearrangement, thereby delaying the onset of recrystallization.5. When aging at 480 °C, at short aging time precipitation of Cr particles takes the main advantage in Cu0.8Cr0.05Y alloy after solution at 980 °C and cold deformation. Hence, the heavily predeformed specimens show almost the same hardening effect as those lightly predeformed. At long aging time, coarsening of Cr particles takes the main advantage in the alloy. Consequently, the heavily predeformed specimens show less efficient hardening by aging for 60min at 480 °C.6. The condition tR ? tp is considered to be an optimal situation for producing a good combination of strength and electrical conductivity. (Where tR and tp are the starting time of recrystallization and precipitation)...