Electroplated indium bump stacks for cryogenic electronics

• Main Authors: Cantaloube, Christopher, Rouse, Richard P
• Format: Patent
• Language: English
• Published: 02.01.2024
• Subjects: BASIC ELECTRIC ELEMENTS; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR; ELECTRICITY; SEMICONDUCTOR DEVICES

A cryogenic under bump metallization (UBM) stack includes an adhesion and barrier layer and a conductive pillar on the adhesion and barrier layer. The conductive pillar functions as a solder wetting layer of the UBM stack and has a thickness. An indium superconducting solder bump is on the conductive pillar. The thickness of the conductive pillar is sufficient to prevent intermetallic regions, which form in the conductive pillar at room temperature due to interdiffusion, from extending through the entire thickness of the conductive pillar to maintain the structural integrity of the UBM stack. The indium (In) solder bump may be formed through electroplating, with the conductive pillar being copper (Cu) and the adhesion and barrier layer being titanium tungsten (TiW) and a thin seed layer of copper (Cu), or a layer of titanium (Ti).