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 Cu-Al IMC growth rate was found to be slower in the Pd-Cu 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 Pd-Cu ball toward the bond interface. FIB (Focus Ion Beam) studies show crack formation at the Cu-Al 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 Pd-Cu ball bond showed better bonding reliability than the Cu ball bond in all tests. (C) 2012 Elsevier B.V. All rights reserved.