The Research Of Current Carrying Capacity In CuCGA Solder Joints

Improving the reliability of Area Array Packaging is very important, no matter to the high density device package and high frequency, high power, high I/O large chip package with increasing mechanical, electrical and thermodynamic loads,but also to the aerospace, automotive, military electronic products and long service life requirements for telecommunication equipment. Surface grid array is mainly divided into the BGA(Ball Grid Array) and CGA(Column Grid Array). With the development of lead-free CuCGA(Cooper Column Grid Array) is replacing the CCGA(Ceramic Column Grid Array). Comparing with BGA, CuCGA has a greater degree of improve the packing density, better mechanical reliability and better heat dissipation. However, with the package size decreasing quickly, the current density of concentration is higher and higher, it led to the electro-migration and heat-migration. So it is necessary to study the current carrying capacity of CuCGA. In order to provide the mechanical reliability of CuCGA, some scholars have carried on the optimization to its structure. To complete the research of reliability of CuCGA, the optimization of the solder joints of CuCGA is studied from the perspective of improving electro-migration resistance and heat-migration resistance. In this paper, we research the influence of size factor on the current density and temperature distribution in the solder joints by comparing the current density and temperature distribution in solder joints of different cooper columns size, different soldering fillet angle and different wire sizes, then we can improve the current carrying capacity of CuCGA solder joints.The temperature and current density distribution of BGA solder joints, the traditional and optimized CuCGA solder joints in the current situation of the CuCGA solder joints were simulated by the finite element simulation software MSC.MARC. The distribution of current density and temperature in BGA solder joint is consistent with the distribution of temperature, and the peak value of current density appears in the same position as the temperature peak point. current density and temperature distribution in CuCGA solder joints is not uniform, the current density peak appeared in solder fillet and wiring connections, peak temperature appears in the middle of cooper columns; With the D2/l of cooper column decreasing, the traditional and optimized CuCGA solder fillet temperature increased significantly, but the peak current density has only a slight increase; With the soldering fillet angle ? decreasing, the peak temperature of the traditional and optimized CuCGA in soldering fillet changes slightly, but the peak value of the current density in the soldering fillets decrease with the decrease of the angle of soldering fillet; The peak of the temperature and current density in the solder fillet are increasing with the decrease of the wiring width B; Under the same soldering joint size parameters, the peak of current density and temperature in the optimized CuCGA solder joint are lower than that in the traditional CuCGA.In addition, the electro-migration and heat-migration resistance of the same solder pad size were determined by electro-migration test of BGA solder and CuCGA solder joints. The test turned out that: under the same conditions, the IMC thickness change of CuCGA solder joints and the IMC of BGA solder joints all present the polarity effect, and generally meet the parabolic law. The formation speed of the IMC in anode of CuCGA is greater than the generation rate of the IMC in anode of BGA, and the dissolution rate of the IMC in cathode of CuCGA is larger than that of BGA, After 200 h, IMC thickness difference of the cathode and the anode in CuCGA solder joints is 5.3 ?m and it is 2.61 ?m in BGA. Therefore, it can be determined that the resistance of electro-migration and heat-migration of CuCGA solder joints is weaker than that of BGA solder joints. The correctness of the simulation results also verified.