Organic Layer Bonding Pad Prevents Copper Diffusion
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Solution Overview
Problem
The direct contact between copper and gold in bonding pads on semiconductor chips leads to copper diffusion and galvanic corrosion, which weakens adhesion and increases manufacturing costs, as seen in existing solutions that use nickel as a diffusion barrier.
Innovation Solution
A multilayer bonding pad structure comprising a copper layer, an organic layer (such as imidazole) exposed in a reticular pattern, and a gold layer, where the organic layer prevents copper diffusion without the need for nickel, thereby reducing production costs and simplifying the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If copper layer is directly plated with gold layer to reduce manufacturing cost, then manufacturing cost is reduced, but copper diffusion into gold occurs causing galvanic corrosion and weakened adhesion
Solution Approach 1:
The patent introduces an organic layer as an intermediary substance between the copper layer and gold layer. This organic layer acts as a diffusion barrier that prevents copper atoms from migrating into the gold layer, thereby eliminating galvanic corrosion while maintaining the copper-gold bonding structure. The organic layer specifically blocks the harmful diffusion path without requiring additional metal barrier layers like nickel, thus resolving the contradiction between cost reduction and adhesion maintenance.
2Reliability
If nickel layer is added as diffusion barrier film to prevent copper diffusion, then copper diffusion is reduced, but manufacturing cost increases
Solution Approach 1:
The patent replaces the expensive nickel diffusion barrier with an organic layer that can be applied more cost-effectively. The organic layer serves the same protective function of preventing copper diffusion but at a lower material and processing cost. This substitution maintains the essential barrier function while reducing manufacturing expenses, directly addressing the contradiction between reliability and ease of manufacture.
3Ease of manufacture
If copper layer is used instead of gold for bonding pad to reduce cost, then manufacturing cost is reduced, but galvanic corrosion occurs when in direct contact with gold
Solution Approach 1:
The organic layer serves as a protective intermediary that allows the copper-gold bonding pad structure to maintain its cost advantage while eliminating the harmful galvanic corrosion effect. By positioning the organic layer between copper and gold, it blocks the electrochemical reactions that cause galvanic corrosion, thus preserving both the economic benefit of using copper and the reliability of the bonding interface.
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
This configuration effectively prevents copper diffusion into gold, maintaining adhesion and reducing manufacturing costs while ensuring reliable electrical connections, as demonstrated by insertion loss graphs showing improved performance compared to nickel-based solutions.
Implementation Method 1
an organic layer disposed on the copper layer in a pattern such that part of the copper layer is exposed; and a gold layer disposed on the organic layer and in contact with the exposed part of the copper layer
Data Source
AI summary
A bonding pad for use in attaching a semiconductor chip to a printed circuit board, includes: a copper layer; an organic layer disposed over the copper layer in a pattern such that part of the copper layer is exposed; and a gold layer disposed over the organic layer and in contact with the exposed part of the copper layer.