Deposition of a Porous Cu Layer by Electroplating and Feasibility Evaluation of Cu-Cu Die Attachment by Sinter Bonding Using Thermo-Compression

A porous Cu layer was deposited on a dummy Cu die and a dummy substrate, respectively, by electroplating to form a bondline that can endure high temperatures, such as 300 °C. The plating at a current density of 40 mA/cm2 in a plating solution containing a crystal controlling agent resulted in different porous layers from fine dendritic grains to coarse a typical grains and an increased layer thickness with increasing plating time. Die-attachment sinter bonding at 5 MPa and 300 °C in the air by thermo-compression using a 2-min-plated die and substrate after drying a reducing agent absorbed in the layer on a substrate. The boding for 1 min resulted in sufficient bondline shear strength of 26.6 MPa with an excellent microstructure of near full density. Identical bonding with exchanging nitrogen blowing increased the shear strength to 30.3 MPa with significantly reduced oxidation area in the inner edge of the die. The 1- and 3-min samples exhibited lower strength values owing to the local formation of large voids between non-uniform thickness of the deposited layers and the relatively less dense bondline structure, respectively.