Interposer Au-Sn Bonding Bumps With Shared Gold Pad Fabrication
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Solution Overview
Problem
Existing methods for manufacturing interposers with both wire-bonding and bump-bonding electrodes on the same side are inefficient, requiring numerous steps, compromising material characteristics, and facing issues like oxidation and contact resistance, especially when using Au-Sn solder bumps.
Innovation Solution
A method involving forming a first gold layer with separate portions for wire-bonding pads and bonding bumps, depositing Au-Sn solder with a lower gold content, merging it through reflow to achieve the eutectic composition, and planarizing to form flat bumps, which reduces process steps, adjusts gold content, and minimizes environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple separate processes are used to form wire-bonding electrodes and bump-bonding electrodes with different material characteristics, then the electrical connection quality is optimized, but the manufacturing process complexity and number of steps increases
Solution Approach 1:
The patent segments the manufacturing process into distinct phases: forming a common metal layer, selectively removing portions, and separately treating remaining portions for wire-bonding or bump-bonding. This allows different material characteristics to be achieved for different electrode types while maintaining a unified base structure, thus optimizing electrical connections without proportionally increasing overall process complexity.
Solution Approach 2:
The patent applies local quality by providing different surface treatments and material compositions at different locations on the interposer. Wire-bonding electrodes receive one type of surface treatment while bump-bonding electrodes receive another, allowing each to be optimized for its specific bonding method while sharing a common manufacturing foundation.
2Productivity
If the number of manufacturing steps is reduced by using a common process for both electrode types, then manufacturing efficiency improves, but the ability to provide optimal material characteristics for each electrode type deteriorates
Solution Approach 1:
The patent performs preliminary actions by forming a common metal layer with uniform properties that serves as the base for both wire-bonding and bump-bonding electrodes. This common layer is prepared in advance using a single process, improving manufacturing efficiency, while subsequent selective treatments are applied to achieve optimal local material characteristics for each electrode type.
3Strength
If Au-Sn solder is used for bump-bonding electrodes, then bonding strength is improved, but oxidation occurs on the electrode surface requiring additional cleaning steps
Solution Approach 1:
The patent applies preliminary protective action by forming a barrier layer or applying a protective coating to the Au-Sn solder bumps before they are exposed to oxidizing environments. This prevents oxidation from occurring in the first place, eliminating the need for subsequent cleaning steps while maintaining the bonding strength benefits of Au-Sn solder.
Solution Approach 2:
The patent converts the potential harm of oxidation into a benefit by using the oxidation resistance as a means to reduce overall process complexity. By preventing oxidation through preliminary protective measures, the method eliminates the need for separate cleaning steps, thus transforming what would be a harmful effect into a process simplification opportunity.
4Reliability
If contact resistance is minimized by using specific materials and processes, then electrical connection reliability is improved, but chemical consumption and environmental impact increase
Solution Approach 1:
The patent changes material parameters by selecting specific metal compositions and surface treatment parameters that inherently provide low contact resistance without requiring excessive chemical processing. By optimizing the base metal layer composition and thickness, the method achieves reliable electrical connections while minimizing the need for additional chemical cleaning or treatment steps.
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 method simplifies the manufacturing process, reduces chemical consumption, ensures high-quality bonds, and allows precise adjustment of bump height for improved alignment and reliability, particularly in photonics modules.
Implementation Method 1
the first composition comprises a smaller proportion of gold than is in the eutectic composition of gold-tin alloy; merging the deposited Au-Sn solder with the second portion of the first gold layer by performing a reflow process to form said at least one bonding bump, wherein the majority of the bonding bump is made of gold-tin alloy having the eutectic composition of gold-tin alloy
Implementation Method 2
merging the deposited Au-Sn solder with the second portion of the first gold layer by performing a reflow process to form said at least one bonding bump
Data Source
Figure 1~2
Figure 3A~3D
Figure 3E~3G
AI summary
A method of manufacturing an interposer product (10) comprises the formation, on the same side of an interposer substrate (2), of at least one wire-bonding pad (12) and at least one bonding bump (14). The method comprises the formation on the substrate (2), by a common process, of first and second portions (6a,6b) of a gold layer. The first portion (6a) of the gold layer constitutes the wire-bonding pad. Then a layer (7) of solder paste comprising gold-tin alloy having a first composition, with less gold than the eutectic composition, is deposited on the second portion (6b) of the gold layer. A reflow process merges the deposited layer (7) of gold-tin solder with the underlying portion of the gold layer, to form a bonding bump (8/14). The bonding bump is planarized to a target thickness. The majority of the bonding bump (8) is made of gold-tin alloy having the eutectic composition.