Wire Bonding Structure With Co-Pd Barrier on Al Pads
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Solution Overview
Problem
Current wire bonding techniques face issues with high resistance and galvanic corrosion due to the formation of Cu—Al intermetallic compounds at the copper wire and aluminum pad interface, leading to bonding failures.
Innovation Solution
A method involving the formation of a cobalt layer on an aluminum pad, bonding a copper wire with a palladium coating onto the cobalt layer, and subsequent thermal treatment to form a Co—Pd alloy, which acts as a protective barrier preventing Cu—Al intermetallic compound formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper wire coated with palladium is used for wire bonding, then oxidation of copper is prevented, but high resistance Cu-Al intermetallic compounds are formed at the copper wire and aluminum pad interface causing galvanic corrosion and bonding failure
Solution Approach 1:
A cobalt layer is introduced as an intermediary between the copper wire and aluminum pad. This cobalt layer forms a Co-Al alloy during bonding that prevents the formation of harmful Cu-Al intermetallic compounds and subsequent galvanic corrosion, while maintaining electrical connectivity
Solution Approach 2:
The wire bonding structure uses a composite material approach with multiple layers: copper core, palladium coating, and cobalt interlayer. This composite structure combines the benefits of each material - copper for conductivity, palladium for oxidation resistance, and cobalt for preventing intermetallic formation
2Reliability
If a cobalt layer is formed on the aluminum pad before wire bonding, then Cu-Al intermetallic compound formation is prevented, but the manufacturing process becomes more complex
Solution Approach 1:
The cobalt layer is formed in advance on the aluminum pad before the wire bonding process. This preliminary action ensures that the protective Co-Al alloy forms during bonding, preventing harmful Cu-Al intermetallic compounds while maintaining a streamlined manufacturing process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The Co—Pd alloy effectively prevents the formation of high resistance Cu—Al intermetallic compounds, reducing galvanic corrosion and enhancing the reliability of the wire bonding process.
Implementation Method 1
performing a thermal treatment process to form a Co—Pd alloy on the Al pad
Implementation Method 2
form a Co—Pd alloy through diffusion and intermetallic reaction
Implementation Method 3
forming a cobalt (Co) layer in the opening and on the Al pad, bonding a wire onto the Co layer
Data Source
AI summary
A semiconductor device includes an aluminum (Al) pad on a substrate, a wire bonded onto the Al pad, a cobalt (Co) layer between and directly contacting the Al pad and the wire, and a Co—Pd alloy on the Al pad and divide the Co layer into a first portion, a second portion, and a third portion. Preferably, the wire includes a copper (Cu) wire and a palladium (Pd) layer coated on the Cu wire.