Capillary Height Control for Wire Bonding Reliability
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Solution Overview
Problem
The existing wire bonding technologies face challenges in achieving sufficient bonding strength and reliability, especially when using copper wires, which are prone to oxidation and have a weaker bonding force compared to gold wires, leading to issues like wire cutting and high costs associated with gold usage.
Innovation Solution
A method involving height control and load control during the stitch bonding process using a capillary, where the capillary presses the wire in a stepwise fashion, applying a first ultrasonic wave for initial bonding and a second, larger ultrasonic wave for load control to ensure a thick bonding region, thereby enhancing bonding strength and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wires are used instead of gold wires, then cost is reduced and electric conductivity is improved, but bonding strength deteriorates due to oxidation and harder material properties
Solution Approach 1:
The patent applies preliminary action by performing oxide layer removal before bonding through mechanical amplitude operation. The wire bonding method includes a preliminary mechanical amplitude operation that removes oxide layers from copper wire surfaces before the actual bonding process, ensuring clean surfaces for strong bonding while allowing the use of cost-effective copper instead of gold
Solution Approach 2:
The patent utilizes mechanical vibration through ultrasonic waves during the bonding process. The ultrasonic vibration helps break through oxide layers and facilitates bonding of copper wires by providing mechanical energy that overcomes the oxidation barrier, enabling reliable bonding of copper wires without requiring expensive gold materials
2Reliability
If large load and ultrasonic waves are applied to copper wires to break oxide layers, then bonding strength is improved, but stitch portion thickness becomes too thin causing wire cutting
Solution Approach 1:
The patent applies segmentation by dividing the bonding process into distinct phases: a preliminary mechanical amplitude operation phase for oxide removal, followed by a bonding phase. This segmentation allows the wire to receive targeted oxide layer removal without excessive force that would thin the stitch portion, preventing wire cutting while ensuring strong bonding
Solution Approach 2:
The patent uses dynamics by adjusting the mechanical amplitude operation parameters based on wire material type. The system dynamically adapts the bonding conditions - applying mechanical amplitude operation for copper wires to remove oxides, while using conventional methods for gold wires that do not require oxide removal, thus optimizing both bonding strength and wire thickness preservation
3Object-generated harmful factors
If mechanical amplitude operation is applied during stitch bonding, then oxide layer removal is improved, but stitch portion thickness is reduced leading to wire cutting
Solution Approach 1:
The patent applies preliminary action by performing the mechanical amplitude operation as a preliminary step before the main bonding process. This preliminary oxide removal step is followed by a bonding step that rebuilds or maintains stitch portion thickness, ensuring that oxide layers are removed without permanently thinning the wire to a cutting-prone state
Solution Approach 2:
The patent uses dynamics by conditionally applying mechanical amplitude operation only to copper wires that require oxide removal, while excluding gold wires from this operation. This dynamic adjustment prevents unnecessary mechanical stress on gold wires and optimizes the process for each material type, maintaining stitch portion thickness while achieving effective oxide removal when needed
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 ensures a sufficient bonding strength and improved reliability in wire bonding, allowing the use of copper wires for cost reduction while maintaining high conductivity, and can also apply to gold wires for increased bonding strength at wire bonding portions.
Implementation Method 1
a first ultrasonic wave is applied to the wire in the height control step, and a second ultrasonic wave larger than the first ultrasonic wave is applied to the wire in the load-control step
Data Source
AI summary
Height control of a capillary is performed in a stitch bonding (2nd bond) in a wire bonding, so that a thickness of a stitch portion can be controlled, thereby ensuring a bonding strength at the stitch portion and achieving an improvement in a bonding reliability. Also, the stitch portion has a thick portion, and a wire and a part (α portion) of a bonding region of an inner lead is formed to a lower portion of the thick portion, thereby sufficiently ensuring a thickness of the stitch portion and a bonding region.