Interposer Au-Sn Bonding Bumps With Flat Height Control
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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 complex, often requiring multiple steps and compromising on material characteristics, leading to suboptimal performance and contact-resistance issues, especially when using Au—Sn solder bumps.
Innovation Solution
A method involving forming a gold layer on the interposer substrate, depositing Au—Sn solder with a lower gold content than the eutectic composition, merging it with the gold layer through reflow to create a gold-tin alloy bump, and planarizing to achieve a flat bonding bump with precise height control, using a common process to reduce steps and 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, then the characteristics of each electrode type can be optimized, but the manufacturing complexity and number of process steps increase significantly
Solution Approach 1:
The patent combines the formation of wire-bonding electrodes and bump-bonding electrodes into a single electroplating process. A patterned Cu seed layer is electroplated to form both types of electrodes simultaneously, eliminating the need for separate plating processes. This reduces manufacturing complexity while maintaining the ability to optimize each electrode type through selective masking and plating parameters.
Solution Approach 2:
The patent segments the electrode formation process into distinct stages within a unified electroplating approach. Different regions of the substrate receive different electrode structures through selective masking, allowing optimization of each electrode type (wire-bonding vs. bump-bonding) while using a common plating process. This enables tailored electrode characteristics without requiring entirely separate manufacturing lines.
2Reliability
If a protective layer is applied to shield bump-bonding electrodes during wire-bonding electrode formation, then wire-bonding electrodes can be formed with appropriate characteristics, but additional process steps and cleaning operations are required
Solution Approach 1:
The patent applies masking layers to specific regions before the electroplating process begins, pre-defining where wire-bonding and bump-bonding electrodes will be formed. This preliminary segmentation allows both electrode types to be formed in a single plating step without requiring protective layers during the process, eliminating subsequent cleaning steps and reducing overall cycle time.
3Reliability
If the surface of bump-bonding electrodes oxidizes during the manufacturing process, then contact-resistance issues arise, but avoiding oxidation requires additional protective measures and cleaning steps
Solution Approach 1:
The patent employs an electroplating process that occurs in a controlled environment where the electrolyte solution prevents oxidation of the Cu seed layer and formed electrodes. The aqueous plating bath creates a protective environment that eliminates oxidation issues entirely, removing the need for additional protective atmospheric measures or cleaning operations to remove oxidized surfaces.
4Reliability
If Ni and Au layers are plated to optimal thickness for wire-bonding electrodes, then wire-bonding performance is optimized, but this interferes with the ability to form solder bumps on bump-bonding electrodes
Solution Approach 1:
The patent applies local quality by forming different electrode structures in different regions of the substrate using selective masking during electroplating. Wire-bonding electrode regions receive plating optimized for wire bonding characteristics, while bump-bonding electrode regions receive plating optimized for solder bump formation. This localized differentiation allows both electrode types to have optimal characteristics without requiring compromise thicknesses across the entire substrate.
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, allows precise adjustment of gold content, and ensures high-quality bonds by maintaining the eutectic composition of the bonding bumps, even after height reduction, thereby improving reliability and alignment in applications like photonics modules.
Implementation Method 1
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
Implementation Method 2
a Cu layer is electroplated on a patterned Cu seed layer to form bump-bonding electrodes
Data Source
AI summary
A method of manufacturing an interposer product that includes: forming on a same side of an interposer substrate, by a common process, first and second portions of a gold layer, wherein the first portion of the gold layer constitutes a wire-bonding pad; depositing a Au—Sn solder on the second portion of the gold layer, the Au—Sn solder comprising a gold-tin alloy having a first composition; merging the deposited Au—Sn solder with the second portion of the gold layer by performing a reflow process to form at least one bonding bump, wherein a majority of the bonding bump is made of a eutectic composition of the gold-tin alloy, and wherein the first composition has a smaller proportion of gold than is in the eutectic composition of the gold-tin alloy; and planarizing the bonding bump to form a flat bonding bump having a selected height.