Optimum pressure in low temperature direct metal bonding

The influence of bonding pressure during low temperature direct metal bond formation between gold studs and electroplated copper joints respectively was evaluated. The findings obtained showed an optimum pressure where bond strength peaks before degrading at further increase in bond pressure. Furthermore, it was found that the increase in bond strength does not correspond to a relative dilation of the bonded area. Both observations deviate from the common understanding that higher bond strength can be achieved with higher bonding pressure and corresponding increase in bonded area. Such contradiction is possibly related to the interfacial deformation phenomenon between locally bonded sites at the interface rather than the bulk deformation behaviour of the bump when bonding pressure exceeds a critical value.