Silver sheet for bonding electronic components
April 28, 2022
Background / Context / Abstract:
While lead solder was used to mount components on boards in the past, the development of lead-free solder has been promoted since the RoHS Directive was issued in 2006. Although silver paste is a type of lead-free solder and it exhibits good bonding strength when the bonding area is small, there is a technical problem in which the bonding strength decreases as the area expands, resulting in failure to ensure product reliability.
The inventors have been developing a silver material for bonding over a long time, and have now completed this invention of a bonding material which exhibits favorable joining strength over large areas. The main feature of the material is to use silver shaped into a sheet which is rolled or surface-ground, followed by application of a physical force on the surface, or a silver microporous sheet (temporarily sintered silver sheet) which is obtained by sintering silver powder at a high temperature. When bonding by sintering is performed using the silver sheet obtained above, liquid silver oxide is formed in the surface layer of the silver sheet upon reaction with oxygen in the atmosphere which is absorbed by grain boundaries and defects, erupts to the surface of the silver sheet under compressive stress from bonding, and fills and integrates with the gaps on the interface ascribed to unevenness of the objects to be bonded, while also becoming reduced to metal silver at the same time to bond the objects with good strength. That is, when the silver sheet of this invention is placed between the objects to be bonded and baked under pressure, a hillock of silver is formed so as to fill the gap between the objects to be bonded, and can thus firmly bond the objects.
– A bonding material which conforms to the RoHS Directive with silver as the main component
– Capable of delivering favorable bonding strength especially when the bonding area is 12 mm2 or larger
– Achieved a bonding strength of 30 to 60 MPa under a bonding load of 0.4 MPa or lower as pressure and a bonding temperature, which was also the baking temperature, of 250°C or higher (baking was carried out at 250, 300 or 350°C for 30 to 240 minutes)
– This silver sheet achieves a higher bonding strength than the existing silver paste when the bonding area is 12 mm2 or larger
State of Development / Opportunity / Seeking:
・Available for exclusive and non-exclusive licensing
・Exclusive/non-exclusive evaluation for defined period (set up for options)
1. Development partner