High performance Sn-Cu low temperature bonding based on graphene interlayer

Abstract

The Sn based solder is being widely applied in the electronic device manufacturing process as interconnection material. As for Sn-based lead-free solder and Cu, Cu-Sn intermetallic compounds (IMCs) layer usually forms on the bonding interface. To obtain high performance bonding, Cu/Sn intermetallic compounds (IMCs) layer must be formed at Cu-Sn interface evenly. The irregular growth of the IMCs layer and the transformation of benign and high-strength Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> into malignant and brittle Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn at high process temperatures on interface will lead to the decrease of bonding reliability. In order to improve the reliability of Cu-Sn bonding, a thermal compression bonding method with the use of transferred graphene film as the bonding interlayer were proposed to control the excessive irregular growth of IMCs. 96.5Sn-3.0Ag-0.5Cu (SAC305) solder was covered on the graphene with different transfer times to realize Cu/G/SAC/G/Cu bonding structure at the bonding temperature of 150 °C and the external pressure of 8 MPa by low temperature thermo-compression bonding process. The effects of different graphene transfer times on the growth of IMC and bonding properties were studied. The microstructure, shear strength and contact resistance of the bonding interface were analyzed after aging. It was concluded that the graphene transferred twice as an interlayer could effectively inhibit the immoderate irregular growth of intermetallic compounds (IMCs). After aging for 72 h, the IMCs layer thickness at bonding interface of Cu-2G-SAC is only 1.01 μm, and the shear strength remains 16.7 MPa, which is better compared with Cu-SAC bonding. Thus, the existence of successive transferred graphene layer with appropriate thickness between solder and Cu can suppress the interfacial reaction and the excessive irregular growth IMCs at the bonding interface.