Study On Low Temperature Cu-cu Bonding Based On Graphene/lead-free Solder

Environmentally friendly electronic packaging using lead-free solder has become a global trend,but even metal bonding based on lead-free solder still has a key factor limiting its reliability: the immoderate growth of intermetallic compounds(IMC).Due to the brittleness of IMC,its generation will accelerate the aging of the device.And the life and performance of the device will be affected.In order to suppress the immoderate growth of intermetallic compounds at the Sn-Cu bonding interface,we used a graphene layer as the intermediate layer between the leadfree solder and the Cu film sample,or mixed multilayer graphene powder in the lead-free solder to achieve Cu/lead-free solder bonding.The bonding was successfully achieved under the conditions of 150? and 350 N.After bonding,an aging test was performed to study the effects of different aging times on the thickness of the IMC layer at the bonding interface,bonding strength and electrical properties.With the increase of aging time,the growth rate of the IMC layer is much lower than that of the IMC layer without graphene when the graphene intermediate layer is used or the graphene powder is mixed in the solder.The reduction rate of the bonding strength of the samples using graphene was also much lower than that of the samples without graphene.For 72 h aging,the bonding strength of the samples using graphene was higher than that of Sn-Cu bonding without graphene.Before and after aging,the contact resistances of Sn-graphene-Cu bonding have no obvious difference with that of Sn-Cu bonding,and the solder resistance after mixing graphene powder also did not change significantly.Therefore,the use of graphene and low temperature thermocompression bonding can effectively suppress the growth of IMC layer at the bonding interface to retard the aging of the interface,and have no negative impact on the electrical properties after bonding.