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Abstract: 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. [Copyright &y& Elsevier]

Abstract: The Pd plating on the 20μm Cu wire dissolves in the free air ball (FAB) and the Cu ball bond during the wire bonding process without forming intermetallic compounds. The limiting supply of Pd and the short bonding process, 15ms of thermosonic bonding, result in uneven distribution of Pd in the as produced Cu ball bond. Also, the Pd-rich phase may accompany small voids formed within the FAB and the wire bond, and following the direction of semi-solid Cu flow. The Pd distribution, as evidenced by the focused ion beam (FIB) and wavelength dispersive X-ray spectroscopy (WDS) mapping, reveals the whirlpool flow pattern of Cu within the FAB and the ball bond. Pd distributes within the copper ball through convective transport by the copper flow. Additionally, hardness measurements by nanoindentation testing show that the Cu ball bond is harder in the regions where Pd exists. [Copyright &y& Elsevier]