Copper Wire Bonding With Withdrawn Surface To Prevent Pad Damage
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Solution Overview
Problem
The use of copper wires in electronic devices poses a risk of damaging semiconductor devices due to the hardness of copper wires, which can apply excessive force when pressed against electrode pads, leading to potential damage during the wire bonding process.
Innovation Solution
A manufacturing method that involves forming a withdrawn surface on the copper wire, which is then pressed against the electrode pad using ultrasonic vibration, allowing for a controlled and reduced force application, thereby preventing damage to the semiconductor device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If copper wire is used instead of aluminum wire, then electrical resistance and thermal resistance are reduced, but the wire hardness increases causing excessive force on electrode pads
Solution Approach 1:
A flattened portion is formed on the copper wire surface before the bonding process. This preliminary structural modification reduces the wire's effective hardness at the bonding interface, allowing the wire to be pressed against the electrode pad with reduced force while still maintaining the electrical and thermal benefits of copper material
Solution Approach 2:
The wire structure is made non-uniform by creating a localized flattened portion at the bonding end. The flattened portion has different mechanical properties (reduced hardness, increased compliance) compared to the rest of the wire, allowing the bonding area to be softer while the wire body remains strong for current carrying
2Reliability
If copper wire is pressed against electrode pad, then reliable electrical connection is achieved, but semiconductor device may be damaged due to wire hardness
Solution Approach 1:
The flattened portion is created in advance on the copper wire, preparing a compliant bonding surface that will naturally conform to the electrode pad geometry during bonding. This preliminary preparation ensures reliable electrical contact while controlling the pressing force to prevent device damage
Solution Approach 2:
The mechanical parameters of the wire at the bonding interface are changed by flattening, which modifies the wire's effective hardness and compliance. This parameter change allows the wire to deform more easily under pressing force, ensuring good electrical contact without transmitting excessive force to the semiconductor device
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 effectively joins copper wires to electrode pads without damaging the semiconductor devices, ensuring reliable electrical connections while managing the force applied during the bonding process.
Implementation Method 1
in the joining step, ultrasonic vibration is applied to the wire, in a state in which the withdrawn surface is pressed against the first joining target
Data Source
AI summary
A manufacturing method for a wire bonding structure of the present invention includes a step of preparing a wire made of Cu and a step of joining the wire to a first joining target formed on an electronic device. Before the joining step, the wire has an outer circumferential surface and a withdrawn surface. The withdrawn surface is withdrawn toward a central axis of the wire from the outer circumferential surface. In the joining step, ultrasonic vibration is applied to the wire in a state in which the withdrawn surface is pressed against the first joining target.