Copper-Gold Bump Stack with UBM Sidewall Coverage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional under bump metallurgic (UBM) layers in semiconductor fabrication are prone to under cut effects due to cracks between the UBM layer and bumps or passivation layers, leading to reduced bonding reliability and increased manufacturing costs, especially with gold bumps, which are costly and susceptible to oxidation.
Innovation Solution
A manufacturing method involving a substrate with pads and passivation layers, where an insulating layer with openings is formed, followed by a copper bump and a gold bump stacked on top, with a UBM layer covering the inner walls and the copper bump, and the gold bump extending to cover the UBM layer, preventing under cut effects and enhancing bonding reliability while reducing costs by using copper and gold bumps in a stacked configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper bumps are used to reduce manufacturing costs, then manufacturing cost is reduced, but oxidation resistance deteriorates
Solution Approach 1:
The patent employs a composite bump structure consisting of a copper bump at the bottom and a gold bump at the top. The copper bump provides excellent electrical conductivity and bonding reliability, while the gold bump serves as an oxidation-resistant protective layer. This composite structure combines the advantages of both materials to achieve both cost-effectiveness and oxidation resistance.
2Object-affected harmful factors
If gold bumps are used to ensure oxidation resistance, then oxidation resistance is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies the local quality principle by using gold only where it is most needed - at the top surface of the bump structure where oxidation resistance is critical. The copper material is used for the bulk of the bump structure where cost-effectiveness and electrical conductivity are priorities. This localized material distribution optimizes both cost and performance.
3Ease of manufacture
If UBM layer is placed only below the bumps, then manufacturing process is simplified, but under cut effect occurs due to cracks
Solution Approach 1:
The patent extends the UBM layer from a one-dimensional configuration (only below the bumps) to a two-dimensional configuration that also covers the sidewalls of the bumps. This dimensional extension ensures that the UBM layer provides continuous protection and bonding support, preventing the under cut effect that occurs when cracks develop in the traditionally configured UBM layer.
Data Source
AI summary
A manufacturing method of a bump structure is provided. A substrate having at least one pad and a passivation layer is provided. The passivation layer has at least one first opening exposing the pad. An insulating layer is formed on the passivation layer. The insulating layer has at least one second opening located above the first opening. A metal layer is formed on the insulating layer. The metal layer electrically connects the pad through the first and second openings. A first bump is formed in the first and second openings. A second bump is formed on the first bump and a portion of the metal layer. The metal layer not covered by the second bump is partially removed by using the second bump as a mask, so as to form at least one UBM layer. The first bump is completely covered by the UBM layer and the second bump.