Multi-Stepped Wire Bonding Capillary for Sensitive Metallization
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Solution Overview
Problem
Conventional wire bonding tools struggle to form reliable bonds with substrates having sensitive metallization, such as low-K value materials, and 'bonding over active circuitry,' often causing damage due to inadequate ultrasonic energy transfer and mechanical stress.
Innovation Solution
A wire bonding tool with a cylindrical portion that decreases in diameter at multiple discrete intervals along its length, enhancing ultrasonic energy transfer and impedance, allowing for more efficient bonding with sensitive metallization and active circuitry while being cost-effective and easily integratable into existing facilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wire bonding tools are used, then the bonding process can be performed, but reliable bonds cannot be formed with sensitive metallization such as low-K value materials
Solution Approach 1:
The patent modifies the physical parameters of the bonding tool by incorporating multiple outer steps with varying diameters along the cylindrical portion. This changes the mechanical and acoustic properties of the tool, enabling it to transfer ultrasonic energy more effectively to sensitive metallization without causing damage, thus improving bond reliability while adapting to low-K value materials and active circuitry.
Solution Approach 2:
The bonding tool is segmented into multiple sections with different diameters through the inclusion of multiple outer steps. This segmentation allows different portions of the tool to serve specific functions: the larger diameter portions provide structural support and impedance matching, while the smaller diameter portions near the working tip concentrate ultrasonic energy. This segmented structure enables reliable bonding with sensitive metallization that conventional uniform-diameter tools cannot achieve.
2Reliability
If higher ultrasonic energy is applied to bond sensitive metallization, then bond reliability may improve, but damage such as metal peel-off, cratering, and oxide cracks increases
Solution Approach 1:
The bonding tool features local quality variations through its multiple outer steps, where each section has a specific diameter optimized for its location. The working tip has a smaller diameter to concentrate ultrasonic energy precisely where needed, while larger diameter sections provide impedance matching and reduce overall energy requirements. This localized optimization allows effective bonding without excessive energy that would cause damage to sensitive metallization.
Solution Approach 2:
The patent utilizes mechanical vibration in the form of ultrasonic energy transferred through the multi-stepped bonding tool. The specific geometry of the outer steps is designed to resonate and amplify vibrations at the working tip, enabling effective bonding of sensitive metallization with lower overall energy input, thereby avoiding damage such as metal peel-off, cratering, and oxide cracks while maintaining bond reliability.
3Use of energy by moving object
If conventional bonding tools are used, then the bonding process is simple, but ultrasonic energy transfer is inadequate
Solution Approach 1:
The bonding tool employs segmentation with multiple outer steps of different diameters along its length. This segmented structure improves ultrasonic energy transfer efficiency by creating impedance gradients that facilitate energy transmission from the transducer to the working tip. Although this increases structural complexity compared to conventional uniform tools, the segmentation is achieved through a single monolithic body, keeping manufacturing feasible.
Solution Approach 2:
The patent changes the geometric parameters of the bonding tool by incorporating multiple outer steps with progressively varying diameters. This parameter variation optimizes ultrasonic energy transfer through impedance matching, allowing more efficient energy transmission. The design balances the increased structural complexity with improved energy efficiency, enabling reliable bonding of sensitive metallization that conventional tools cannot achieve.
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 tool achieves reliable wire bonds with reduced risk of metal peel-off, cratering, and oxide cracks by amplifying ultrasonic displacement, allowing lower energy input for effective bonding, thus improving bond reliability and reducing damage to sensitive substrates.
Implementation Method 1
The bonding tool supplies the fine wire and employs a method known as ball bonding to electrically connect the electrical leads of the IC to the bond pads of the substrate. The free end of the wire at the working tip is the end that forms the ball for ball bonding... adequate amounts of pressure, heat, and ultrasonic forces are then applied to the ball bond
Implementation Method 2
When the free-air ball contacts the bond pad, for example, adequate amounts of pressure, heat, and ultrasonic forces are then applied to the ball bond for a specific amount of time, thus forming the initial metallurgical weld between the ball and the bond pad
Implementation Method 3
forming the initial metallurgical weld between the ball and the bond pad
Implementation Method 4
a gold ball is first formed by melting the end of the wire at the capillary tip through electronic flame-off (EFO)
Implementation Method 5
Pressure and ultrasonic forces are applied to the wire to form the second bond (known as a wedge bond, or stitch bond) with the electrical lead in order to complete one bonding cycle
Data Source
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AI summary
A bonding tool for bonding a fine wire to a substrate, said bonding tool comprising an at least substantially cylindrical portion having a concentric capillary therein through which the fine wire runs; a working tip portion formed at an end of the cylindrical portion being tapered towards the tip thereof, said working tip portion having an annular chamfer at the tip thereof; wherein the concentric capillary opens into the annular chamfer of the working tip, and wherein the diameter of the cylindrical portion decreases consecutively at a plurality of discrete intervals along the length of the cylindrical portion towards the working tip portion.