Capillary Inner Chamfer Angle for Copper Wire Bonding
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Solution Overview
Problem
The use of copper wires in semiconductor devices leads to increased damage on pads due to copper's hardness and oxidation, requiring higher loads and ultrasonic vibrations for bonding, which can cause pad peeling during the wire bonding process.
Innovation Solution
A method involving a capillary with a tapered inner chamfer angle less than 90 degrees is used to minimize the ultrasonic conversion load perpendicular to the pad surface, reducing the compressive load on the press-bonded ball and the frictional force between the capillary and the press-bonded ball, thereby preventing pad peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is used instead of gold wire, then cost and electric resistivity are improved, but pad damage increases due to copper's hardness and oxidation
Solution Approach 1:
The patent changes the geometric parameters of the capillary, specifically setting the inner chamfer angle to 60 degrees or 120 degrees. This parameter modification allows the capillary to effectively control the press-bonded ball formation process, reducing the load and ultrasonic vibration required for bonding copper wires to pads, thereby minimizing pad damage while maintaining electrical connectivity
Solution Approach 2:
The capillary serves as an intermediary tool between the bonding head and the pad. By designing the capillary with specific chamfer angles, it mediates the bonding process to reduce direct harmful effects on the pad. The capillary controls the deformation of the copper wire and distributes the bonding load, protecting the pad from excessive stress
2Strength
If higher load and ultrasonic vibration are applied to deform copper initial ball, then bonding strength is improved, but pad peeling increases
Solution Approach 1:
The patent modifies the capillary geometry by setting the inner chamfer angle to specific values (60 or 120 degrees). This changes how the load and ultrasonic vibration are transmitted during bonding, enabling effective copper wire deformation and bonding without requiring excessively high forces that would cause pad peeling
Solution Approach 2:
The patent utilizes ultrasonic vibration applied through the capillary to facilitate the bonding process. The vibration helps deform the copper initial ball and remove oxide films with reduced mechanical load, preventing pad damage while achieving sufficient bonding strength
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 effectively reduces the likelihood of pad peeling by minimizing the compressive load and frictional force, ensuring reliable bonding of copper wires to semiconductor pads without causing damage.
Implementation Method 1
an ultrasonic vibration is supplied through the capillary in the direction in parallel with the surface of the bonding pad
Implementation Method 2
a bonding load is applied thereto, and an ultrasonic vibration is supplied through the capillary
Data Source
AI summary
There is provided a technology capable of suppressing the damage applied to a pad. When the divergence angle of an inner chamfer part is smaller than 90 degrees, the ultrasonic conversion load in a direction perpendicular to the surface of the pad is very small in magnitude. In other words, the ultrasonic conversion load in a direction perpendicular to the surface of the pad is sufficiently smaller in magnitude than the ultrasonic conversion load in a direction in parallel with the surface of the pad. Consequently, when the divergence angle of the inner chamfer part is smaller than 90 degrees, the ultrasonic conversion load in a direction perpendicular to the surface of the pad can be sufficiently reduced in magnitude, which can prevent pad peeling.