The influence of Pd on the interfacial reactions between the Pd-plated Cu ball bond and Al pad

The interfacial reactions of the Pd-plated Cu (Pd–Cu) ball bond and 4N Cu (Cu) ball bond on Al were investigated through PCT (Pressure Cooker Test) and HTST (High Temperature Storage Test) tests. The thickness of the interfacial Cu–Al IMC increases as the testing time increases. The CuAl IMC growth rate was found to be slower in the PdCu ball bond than in the Cu ball bond. The growth of the IMC is diffusion-controlled during aging. During the test, the Pd diffuses from the interior of the PdCu ball toward the bond interface. FIB (Focus Ion Beam) studies show crack formation at the CuAl IMC/Al interface in the Cu ball bond. During aging, the Pd-rich layer affected the interdiffusion between Cu and Al and may influence the IMC formation. The PdCu ball bond showed better bonding reliability than the Cu ball bond in all tests.