Metal Bump Structure with Protective Layer for Driver IC
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Solution Overview
Problem
Metal bumps, particularly copper and gold, are susceptible to the galvanic effect and corrosion under extreme conditions, compromising the reliability of electronic circuits, and are difficult to rework without damaging the circuits.
Innovation Solution
A metal bump structure with a protective layer, such as a thin gold layer, is formed using a method that includes a substrate, metal pad, passivation layer, adhesion layer, and a cover layer with a lateral fringe, which protects the bump from ambient atmosphere and prevents galvanic effects, allowing for easy reworking without compromising circuit reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If copper is used as metal bump material to achieve low electric resistance, then electrical conductivity is improved, but the metal bump becomes susceptible to galvanic effect and corrosion under extreme conditions
Solution Approach 1:
A protective layer is introduced as an intermediary between the copper metal bump and the ambient environment. This protective layer acts as a mediator that prevents direct contact between the copper and corrosive elements (halogens, moisture), thereby eliminating the galvanic effect while maintaining the electrical conductivity of the copper bump.
Solution Approach 2:
The invention creates a composite structure consisting of multiple layers: the copper metal bump core, adhesion layer, and protective outer layer. This composite material structure combines the low electrical resistance of copper with the corrosion resistance of the protective layer, achieving both electrical performance and environmental stability.
2Reliability
If gold is used as metal bump material to resist corrosion, then reliability is improved, but rework becomes extremely difficult due to corrosive aqua regia requirements
Solution Approach 1:
The protective layer is designed as a sacrificial, easily removable component that protects the valuable metal bump during service but can be quickly removed during rework. This disposable protective layer eliminates the need for aggressive aqua regia by providing a simple mechanical or chemical removal method for rework scenarios.
Solution Approach 2:
The protective layer serves as a removable intermediary that provides corrosion resistance during operation but can be easily removed during rework without damaging the underlying metal bump or circuit board, thus enabling simple repair processes.
3Reliability
If a thick protective layer is applied to prevent galvanic effect, then reliability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The protective layer thickness is optimized to the minimum necessary value that provides sufficient protection against galvanic effect. By carefully controlling the thickness parameter, the invention achieves adequate corrosion resistance while minimizing material usage, manufacturing complexity, and cost.
Solution Approach 2:
The protective layer is applied selectively only where needed - specifically on the exposed surfaces of the metal bump that are susceptible to environmental corrosion. This localized application approach provides maximum protection with minimum material and manufacturing complexity.
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 metal bump structure is resistant to galvanic effects and easy to rework, maintaining circuit reliability even under high electric fields or in the presence of halogens, and can be used in driver ICs and various packages like COG and COF.
Implementation Method 1
The adhesion layer is completely disposed in the recess, disposed on the metal pad and partially disposed on the passivation layer so that the adhesion layer is in direct contact with the metal pad and with the passivation layer
Implementation Method 2
The cover layer completely covers the metal bump so that the metal bump is not exposed to an ambient atmosphere
Implementation Method 3
In particular, a lateral fringe is formed during a plating process
Data Source
AI summary
A metal bump structure for use in a driver IC includes a metal bump disposed on a matrix, an optional capping layer disposed on the metal bump to completely cover the metal bump and a protective layer disposed on the metal bump to completely cover and protect the metal bump or the optional capping layer and so that the metal bump is not exposed to an ambient atmosphere. The protective layer or the optional capping layer may have a fringe disposed on the matrix.