Wire Bond Coating Removal for Corrosion Control
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Solution Overview
Problem
In semiconductor wire bonding, unintentionally exposed areas of the wire during the bonding process lead to corrosion, especially during high temperature baking, due to the formation of electrochemical corrosion cells when the coating is more noble than the underlying metal, causing rapid corrosion and potential conductivity issues.
Innovation Solution
Selectively removing additional portions of the coating material to increase the anode area relative to the cathode area, thereby slowing down the corrosion rate and attracting corrosive agents away from unintentionally exposed areas, using methods such as laser, chemical, or mechanical processes to form intentionally exposed areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wire is coated with metal layers to prevent corrosion, then corrosion resistance is improved, but unintentional exposure of the wire during bonding leads to rapid corrosion
Solution Approach 1:
The patent applies preliminary action by intentionally exposing additional wire areas before corrosion can occur. This preventive measure creates a controlled electrochemical cell configuration that slows down future corrosion rates. The method proactively prepares the wire surface by removing coating in specific patterns before the wire is exposed to corrosive environments during assembly and field use.
Solution Approach 2:
The patent implements local quality by creating non-uniform coating distribution on the wire surface. Specific areas have coating removed to create intentional exposure zones, while other areas retain the protective coating. This localized variation in coating presence optimizes the electrochemical cell configuration to reduce overall corrosion rate while maintaining protection where needed.
2Reliability
If coating is removed to expose wire areas, then corrosion rate is reduced through increased anode area, but wire integrity may be compromised
Solution Approach 1:
The patent applies parameter changes by carefully controlling the extent, location, and size of coating removal. By adjusting these parameters, the method optimizes the anode-to-cathode area ratio to achieve desired corrosion rate reduction while maintaining sufficient wire integrity. The controlled exposure creates a favorable electrochemical configuration without excessive material removal that would compromise strength.
3Reliability
If additional coating removal is performed to control corrosion, then corrosion distribution is improved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces complex mechanical coating removal methods with alternative approaches such as selective area treatments. This substitution simplifies the manufacturing process by using methods that can achieve the desired coating pattern more efficiently, reducing the need for multiple mechanical steps while maintaining control over corrosion distribution.
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 approach reduces corrosion extent, promoting the reliability and integrity of wire bonds by diffusing corrosive elements over a larger area, thereby minimizing the impact on conductivity and preventing wire breakage.
Implementation Method 1
the metal coating acts as a cathode, and the exposed underlying metal wire portion acts as anode from which portions of the wire metal will be removed, or corrode
Data Source
AI summary
A semiconductor structure includes a bond pad and a wire bond coupled to the bond pad. The wire bond includes a bond in contact with the bond pad. The wire bond includes a coating on a surface of the wire bond, and a first exposed portion of the wire bond in a selected location. The wire bond is devoid of the coating over the selected location of the wire bond, and an area of the first exposed portion is at least one square micron.