Stepped Capillary Tool for Ultrasonic Wire Bonding
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Solution Overview
Problem
Conventional wire bonding tools struggle to form reliable bonds with substrates having sensitive metallization, particularly low-K value materials, and are inadequate for 'bonding over active circuitry', often causing metal peel-off, cratering, and oxide cracks due to insufficient ultrasonic energy transfer and mechanical stress.
Innovation Solution
A wire bonding tool with a tapered working tip and concentric capillary that decreases in diameter at discrete intervals, combined with a nano-scale ultrasonic energy source, enhances ultrasonic energy transfer and displacement amplification, allowing for more efficient bonding without damaging sensitive metallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wire bonding tools are used with standard cylindrical capillaries, then the bonding process can be performed with simple tool structure, but insufficient ultrasonic energy transfer causes unreliable bonds with sensitive metallization and low-K substrates
Solution Approach 1:
The capillary is segmented into multiple sections with different diameters (first, second, and third sections) rather than using a uniform cylindrical structure. This segmentation allows each section to serve a specific function in ultrasonic energy transmission, improving bond reliability with sensitive metallization while maintaining a manageable structural complexity through systematic design.
Solution Approach 2:
Different sections of the capillary have different diameters tailored to specific functional requirements. The first section has a larger diameter for ultrasonic energy input, the second section has a reduced diameter for energy concentration, and the third section has yet another diameter for optimal tip performance. This local variation in geometry optimizes ultrasonic energy transfer at each location, enabling reliable bonding with low-K substrates and sensitive metallization.
2Strength
If high ultrasonic energy is applied to form reliable bonds, then bond strength is improved, but metal peel-off, cratering, and oxide cracks occur on sensitive metallization
Solution Approach 1:
The capillary's geometric parameters (diameters of different sections) are changed to optimize ultrasonic energy transmission. By adjusting the diameter ratios between sections, the tool achieves more efficient energy transfer that produces reliable bonds at lower overall energy levels, preventing metal peel-off, cratering, and oxide cracks on sensitive metallization while maintaining adequate bond strength.
Solution Approach 2:
The tapered geometry of the capillary sections is designed to amplify and concentrate ultrasonic vibrations at the working tip. This mechanical vibration concentration allows effective bonding with reduced overall energy input, preventing harmful effects like metal peel-off and cratering on sensitive low-K substrates and metallization while still achieving reliable bond strength.
3Ease of manufacture
If standard capillary geometry is used, then manufacturing is simple, but ultrasonic energy transfer efficiency is insufficient for bonding over active circuitry
Solution Approach 1:
The capillary is divided into three distinct sections with different diameters, creating a stepped or tapered structure that improves ultrasonic energy transfer efficiency. This segmented design enables effective bonding over active circuitry by concentrating energy where needed, while still being manufacturable using standard ceramic processing techniques and sintering methods.
Solution Approach 2:
The capillary geometry parameters (section diameters, lengths, and transitions) are optimized to maximize ultrasonic energy transfer efficiency. These parameter changes enable reliable bonding over active circuitry by improving energy delivery to the bonding interface, while the overall design remains compatible with conventional ceramic capillary manufacturing processes.
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 low-K value substrates and active circuitry by reducing the need for high ultrasonic energy, minimizing metal peel-off, cratering, and oxide cracks, while maintaining bond reliability and intermetallic coverage.
Implementation Method 1
a nano-scale ultrasonic energy source connected to said bonding tool such that said source is capable of transmitting ultrasonic energy to said bonding tool
Implementation Method 2
The diameter of the substantially cylindrical portion decreases consecutively at a plurality of discrete intervals along the length of the substantially cylindrical portion towards the working tip portion
Data Source
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.