Ultrasonic Wire Bonding Transverse Vibration Copper Aluminum Splash
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Solution Overview
Problem
In semiconductor device wire bonding using copper wire, the high hardness of copper causes significant aluminum (AL) splash during ultrasonic bonding, leading to electrical shorts and reduced quality and reliability, especially in fine pad pitch products.
Innovation Solution
The method involves coupling copper wires with aluminum electrode pads while applying ultrasonic waves in a direction transverse to the wave application, minimizing AL splash formation by rubbing the ball against the pads in a second direction, thereby reducing the risk of electrical shorts and improving bonding quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is used for wire bonding to reduce cost and improve electrical conductivity, then cost and electrical characteristics are improved, but aluminum splash becomes severe due to high hardness of copper
Solution Approach 1:
The patent applies ultrasonic vibration in a direction transverse (perpendicular) to the wire bonding direction. This dimensional change in vibration application prevents aluminum splash from occurring in the bonding direction while maintaining effective bonding, thus resolving the contradiction between using hard copper wire and preventing aluminum splash.
Solution Approach 2:
The patent utilizes ultrasonic vibration to modify the bonding process. By applying high-frequency mechanical vibration transverse to the bonding direction, the copper wire can effectively bond to the aluminum pad without causing severe aluminum splash, thus enabling the use of hard copper wire while preventing the harmful effect.
2Strength
If ultrasonic wave application is increased to improve bonding strength, then bonding strength is improved, but aluminum splash increases leading to electrical shorts
Solution Approach 1:
The patent applies ultrasonic vibration in a direction transverse to the wire bonding direction. This dimensional change allows sufficient ultrasonic energy to be applied for strong bonding while preventing aluminum material from being pushed in the bonding direction, thus achieving both strong bonding and preventing electrical shorts.
Solution Approach 2:
The patent creates an asymmetric vibration application where ultrasonic energy is applied perpendicular to the bonding direction rather than parallel to it. This asymmetric approach allows the bonding interface to receive sufficient mechanical energy for strong adhesion while the aluminum pad is not subjected to directional pressure that would cause splash.
3Ease of manufacture
If copper wire is used instead of gold wire, then cost is reduced, but aluminum splash occurs due to hardness difference
Solution Approach 1:
The patent employs ultrasonic vibration transverse to the bonding direction to enable the use of copper wire. The mechanical vibration facilitates bonding between the hard copper wire and aluminum pad without causing severe aluminum splash, thus making copper wire viable as a cost-effective alternative to gold wire.
Solution Approach 2:
The patent changes the parameters of the bonding process by applying ultrasonic vibration in a transverse direction rather than the conventional parallel direction. This parameter change allows copper wire with its high hardness to bond effectively without generating harmful aluminum splash, enabling cost reduction through copper wire usage.
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 risk of electrical shorts and enhances the quality and reliability of semiconductor devices by minimizing AL splash, particularly in fine pad pitch products, while maintaining the cost benefits of using copper wire.
Implementation Method 1
a bonding head 6b of a wire bonder 20 used for ball bonding is provided with an ultrasonic horn 6d that excites ultrasonic wave
Data Source
AI summary
A risk of an electrical short between electrode pads of a semiconductor device can be reduced to thereby improve quality of the semiconductor device. During ball bonding in wire bonding, in each of the electrode pads of a semiconductor chip which are arrayed along an ultrasonic wave application direction (ultrasonic vibration direction), a ball at the tip of a copper wire and the electrode pad are coupled to each other while being rubbed against each other in a direction intersecting the ultrasonic wave application direction. Thus, the amount of AL splash formed on the electrode pad can be minimized to make the AL splash smaller. As a result, the quality of the semiconductor device assembled by the above-mentioned ball bonding can be improved.