Pressure-less Copper Sintering Paste for Die Attach Application

A new version of pressure-less copper (Cu) sintering paste was developed for die-attach and IGBT bonding. The resulting paste achieves a shelf life of greater than 6 months at a storage temperature less or below 5℃ by using a special chemical treatment to resist oxidation. Shear strength was measured at greater than 30 MPa for 3 mm × 3 mm joints with pressure-less sintering and greater than 50 MPa if applied with low sintering pressures (e.g., 5 MPa). The recommended sintering profile was heating from room temperature to peak temperature between 240 and 250℃ for 15 to 30 min and holding at peak temperature for 30 to 35 min. The sintering atmosphere can be selected from nitrogen gas (N
2
), argon (Ar), vacuum and formic acid. With TCT (-40℃ to 175℃) increasing from 0 to 4000 cycles, the shear strength increased from 24 to 42 MPa, then stabilized at approximately 40 MPa. For TST (-65℃ to 150℃) testing, the shear strength remained stable around 40 MPa after 3000 cycles. The shear strength also remained stable after more than 1100 hours under a 250℃ aging test. The pressure-less Cu sintering paste could be applied to many surface finishes, including Cu, gold (Au), silver (Ag) and nickel (Ni). Both printing and dispensing paste deposition methods are available for the pressure-less Cu sintering paste.