Nanotwin-Plated Lead Stitch Bonding for Stronger Wirebond Joints
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Solution Overview
Problem
The low strength connection between a bond wire/stitch bond and a lead frame affects bondability and reliability, and existing techniques to enhance this connection, such as ball bump over stitch bond and stitch bond over ball bump, increase manufacturing cost and complexity.
Innovation Solution
A nanotwin plated layer is applied to the conductive terminal, enhancing the bond strength between the bond wire and lead frame through improved mechanical stability and resistance to electromigration, allowing for cost-effective and efficient wire bonding processes without added complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ball bump over stitch bond or stitch bond over ball bump techniques are used, then connection strength between bond wire and lead frame is improved, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent changes the surface parameters of the lead frame by applying a nanotwin plated layer, which modifies the crystalline structure at the nanoscale. This parameter change enables strong stitch bonding without requiring complex multi-step bonding processes like ball bump over stitch bond, thus improving connection strength while maintaining process simplicity
Solution Approach 2:
The patent uses a composite structure consisting of a nanotwin plated layer on the lead frame surface. This composite material approach, where the nanotwin layer is deposited on the base metal, provides enhanced bonding characteristics that achieve strong connections through simple stitch bonding without the need for complex process sequences
2Ease of manufacture
If bare copper to copper bonding is used, then manufacturing cost is reduced, but surface granularity increases causing delamination between lead frame and mold compound
Solution Approach 1:
The patent applies a nanotwin plated layer that modifies the surface parameters of the copper lead frame. This nanoscale structural modification reduces surface granularity while maintaining copper-copper bonding compatibility, thereby preventing delamination between the lead frame and mold compound while keeping manufacturing costs low
Solution Approach 2:
The patent applies the nanotwin plated layer selectively on the bonding surface of the lead frame where wire bonding occurs. This local quality enhancement provides the necessary surface characteristics for reliable bonding and adhesion only where needed, maintaining cost-effectiveness while improving reliability at critical interfaces
3Strength
If ultrasonic wire bonding is used, then bond strength is enhanced through copper atom diffusion, but manufacturing cost increases
Solution Approach 1:
The patent changes the surface parameters of the lead frame by introducing a nanotwin plated layer, which enhances copper atom diffusion and bond strength through simple thermo-compression stitch bonding. This parameter modification eliminates the need for expensive ultrasonic bonding equipment and processes while achieving comparable or superior bond strength
4Productivity
If higher wirebonding process temperature is used, then bonding process is accelerated, but oxidation occurs impacting manufacturability and reliability
Solution Approach 1:
The nanotwin plated layer modifies the thermal and oxidative parameters of the lead frame surface. This nanoscale structural change enables the material to withstand higher bonding temperatures without oxidizing, thus allowing faster bonding processes while maintaining reliability by preventing oxidation at the bonding interface
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
The nanotwin plated layer provides superior mechanical and electrical properties, enabling high-strength stitch bonding with reduced manufacturing costs and process complexity, while mitigating oxidation and improving reliability.
Implementation Method 1
Ultrasonic wire bonding can enhance bond strength compared with thermo-compression by increasing copper atom diffusion
Implementation Method 2
performing a plating process that forms a nanotwin plated layer on a conductive terminal
Data Source
AI summary
An electronic device includes a package structure, a conductive terminal exposed outside the package structure and having a nanotwin plated layer, a semiconductor die in the package structure, and a bond wire enclosed by the package structure and having a first end and a second end, the first end connected to the semiconductor die by a first bond, and the second end connected to the nanotwin plated layer by a second bond. A method includes performing a plating process that forms a nanotwin plated layer on a conductive terminal, and performing a wirebonding process that forms a bond wire having a first end connected to a semiconductor die by a first bond, and a second end connected to the nanotwin plated layer by a second bond.