Copper Ball Bond Interface for Thermal Cycling Reliability
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Solution Overview
Problem
Conventional ball bonding processes in semiconductor packaging face mechanical integrity issues due to stressors like temperature cycling, leading to aluminum cracking beneath copper ball bonds, especially on low-k dielectric layers with active circuits, where large ball bond structures are difficult to implement effectively.
Innovation Solution
The method involves controlling bonding parameters to form copper ball bonds on aluminum pads with specific structural and geometric features, such as minimizing aluminum remnant thickness, ensuring symmetry, and extending the intermetallic contact area, to prevent cracking and enhance thermal cycling reliability, using a combination of heat, pressure, and ultrasonic energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ball bonding processes are used with large ball bond structures, then thermal cycling reliability is improved, but device complexity and practical applicability to state of the art devices deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling bonding parameters (temperature, pressure, ultrasonic energy, time) to form copper ball bonds with specific geometric features (aluminum minima feature location, thickness, symmetry) that prevent cracking. This allows achieving thermal cycling reliability without requiring excessively large ball bond structures, thus resolving the contradiction between reliability and device complexity.
2Productivity
If copper ball bonds are formed on low-k dielectric layers with active circuits, then integration density is improved, but mechanical integrity deteriorates due to aluminum cracking
Solution Approach 1:
The patent applies local quality by creating specific geometric features (aluminum minima) at precise locations (outer half of chamfer-squeezed region) under the copper ball bond. This localized structural modification prevents aluminum cracking at critical stress points while maintaining overall bond integrity, enabling reliable copper ball bonds on low-k dielectric layers with active circuits.
3Reliability
If bonding parameters are controlled to form specific structural features, then thermal cycling reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by establishing specific ranges for bonding parameters (temperature: 150-200°C, pressure: 1-10 kgf, ultrasonic energy: 10-100 W, time: 1-10 seconds) that produce the desired aluminum minima features. By defining these parameter ranges, the patent achieves thermal cycling reliability while providing practical manufacturing guidance, balancing reliability improvement with manufacturability.
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 results in reliable copper ball bonds that meet or exceed minimum ball shear strength thresholds, ensuring thermal cycling reliability and compatibility with AEC Q100 Grade standards, even for smaller ball bond structures on low-k dielectric layers over active circuits.
Implementation Method 1
Conventional ball bonding processes use a combination of heat, pressure and ultrasonic energy to form an intermetallic connection or weld between a wire and a connection pad
Implementation Method 2
Conventional ball bonding processes use a combination of heat, pressure and ultrasonic energy to form an intermetallic connection or weld between a wire and a connection pad
Implementation Method 3
Conventional ball bonding processes use a combination of heat, pressure and ultrasonic energy to form an intermetallic connection or weld between a wire and a connection pad
Data Source
AI summary
An integrated circuit copper wire bond connection is provided having a copper ball (32) bonded directly to an aluminum bond pad (31) formed on a low-k dielectric layer (30) to form a bond interface structure for the copper ball characterized by a first plurality of geometric features to provide thermal cycling reliability, including an aluminum minima feature (Z1, Z2) located at an outer peripheral location (42) under the copper ball to prevent formation and/or propagation of cracks in the aluminum bond pad.