INDIRECT BONDING OF NI-ELECTROLESS PLATED ALN AND CU BY HOT-PRESSING METHOD

The eiectroless Ni (EN) plating method was employed to metallize the A lN ceramic substrates. The EN-plated AlN substrate was bonded with the Cu foil to form a sandwich-like AlN-EN/Cu/EN-AlN assembly by hot pres sing in vacuum with a pressure of 6.5 MPa for 30 min. For the bonding temperature below the Ni-P eutectic temperature of EN at 880 degrees C , the samples were bonded through solid state diffusion. On the other hand, the samples were bonded via a liquid phase media through both we tting and diffusion if the bonding temperature was above 880 degrees C . An optimum adhesion strength around 10 MPa occurred within bonding t emperature range 600-700 degrees C. The fracture took place in the EN/ Cu interface for samples bonded below 600 degrees C, while fracture to ok place in the AlN/EN interface above 700 Angstrom C. The increasing temperature enhanced interdiffusion of Cu and EN to form a strong bond , yet resulted in a large residual thermal stress in the AlN/EN interf ace. The bonded samples with as-received AlN exhibited higher adhesion strength than those with polished AlN because there existed a residua l compression perpendicular to the AlN/EN interface at surface irregul arities in the as-received AlN, which resulted in an additional shear strength offset in the adhesion test. The adhesion strength of samples with etched AIN was the highest as compared to those of as-received a nd polished AlN, although the surface roughness of the etched AlN was the same as that of the as-received one. It is argued that the etched surface of AlN with micro-etched holes provides the anchor sites for i nterlocking with the EN him, which results in a good mechanical bondin g in the joint. However, a mechanical trimming on the edges of bonded samples would damage the joint, and a low adhesion strength is instead observed.