Micro-bump Joint Strength via Extended Metal Finish
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Solution Overview
Problem
Conventional micro-bump joints in integrated circuits are prone to cracking and breaking due to weak interfaces between the metal finish and the copper bump, leading to reliability issues in bonding.
Innovation Solution
A novel bond structure is developed where a metal finish, such as electroless nickel electroless palladium immersion gold (ENEPIG), is formed over and extending below the interface between the dielectric layer and the copper bump, creating a stronger internal bond and increasing the interface area with the copper layer, thereby enhancing the bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional micro-bump joints are used with standard metal finish interfaces, then manufacturing process is simple, but bonding strength is weak and prone to cracking
Solution Approach 1:
The metal finish is extended from a two-dimensional surface layer into the third dimension by forming it below the dielectric layer interface. This vertical extension into the substrate creates additional bonding interface area and anchors the metal finish more securely, transforming the bonding geometry from a simple surface contact to a multi-level embedded structure that resists cracking and breaking.
Solution Approach 2:
The invention uses a composite metal finish structure consisting of multiple layers (e.g., nickel, palladium, gold) with different properties. Each layer provides specific functions: nickel for adhesion to copper, palladium for intermediate bonding, and gold for surface protection. This composite structure enhances overall bonding strength while distributing stress across multiple material interfaces, preventing crack propagation.
2Reliability
If metal finish is extended below the dielectric layer interface, then bonding reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The metal finish is formed below the dielectric layer interface before the dielectric layer is fully deposited or patterned. This preliminary formation allows the metal finish to be established in its extended position first, then subsequent dielectric layer processing completes the structure. This sequence simplifies manufacturing by avoiding complex post-processing steps to create the extended metal finish geometry.
Solution Approach 2:
The metal finish formation process utilizes the existing substrate structure and dielectric layer as self-aligning features. The extension depth and positioning are determined by the interaction between the metal finish deposition process and the pre-existing dielectric layer geometry, reducing the need for additional alignment steps or complex lithography patterns to define the extended metal finish regions.
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 novel bond structure significantly improves the reliability and strength of the bonding by reducing the likelihood of cracking and breaking at conventional weak points, with experimental results showing improved bonding reliability and reduced failure rates.
Implementation Method 1
A metal finish is formed over and contacting the metal bump. The metal finish extends from over the dielectric layer to below the interface.
Implementation Method 2
A metal finish, such as electroless nickel electroless palladium immersion gold (ENEPIG), is formed over and extending below the interface between the dielectric layer and the copper bump
Data Source
AI summary
A device includes a work piece including a metal bump; and a dielectric layer having a portion directly over the metal bump. The metal bump and a surface of the portion of the dielectric layer form an interface. A metal finish is formed over and contacting the metal bump. The metal finish extends from over the dielectric layer to below the interface.