Patterning Ag nanoparticles by selective wetting for fine size Cu-Ag-Cu bonding

Area of Science:

• Materials Science
• Nanotechnology
• Surface Engineering

Background:

• Metal nanoparticles (NPs) show promise for replacing tin (Sn) alloys in fine-size copper-copper (Cu-Cu) bonding.
• Rapidly patterning NPs on solder joints under 30 µm is a significant challenge for practical application and mass production.

Purpose of the Study:

• To introduce a novel method for patterning silver NPs (Ag NPs) on Cu pads using selective wetting.
• To demonstrate the feasibility of this method for micro-scale Cu-Cu bonding applications.

Main Methods:

• Selective wetting technique applied for Ag NP deposition on Cu pads.
• Characterization of Ag NP coating on Cu pads with diameters down to 5 µm.
• Evaluation of bonding performance through shear strength testing under varying conditions.

Main Results:

• Successful coating of Ag NPs on Cu pads as small as 5 µm in diameter.
• High-density NP patterns achieved on Cu pads >10 µm, with a diameter-to-pitch ratio of 2/3.
• Shear strength reached 22.92 MPa after sintering at 250 °C for 5 min, under 20 MPa pressure in N₂.

Conclusions:

• Selective wetting is a viable method for patterning NPs on Cu pads for Cu-NPs-Cu bonding.
• The technique facilitates the application of NPs in micro-scale bonding, addressing mass production challenges.
• Optimized bonding conditions significantly enhance the shear strength of the resulting joints.