Lead Frame Interconnect with Gold Bumps for High Power Density

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Solution Overview

Problem

Current lead frame packages face issues with high manufacturing costs and electromigration-related failures due to current crowding and high current densities, particularly in high-power semiconductor devices, where existing solutions like gold-on-gold technologies are expensive and complex to integrate.

Innovation Solution

The use of gold bumps bonded between aluminum bond pads on integrated circuit dies and silver bond pads on lead frames, with a thermosonic bonding process to form an encapsulated semiconductor package that reduces electromigration and lowers manufacturing costs by enabling high current capacity with low impedance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If solder balls are used to connect die to lead frame, then electrical connections are established, but current crowding occurs leading to electromigration-related failures

Engineering Contradiction:

Improveelectromigration resistanceVSAvoidcurrent crowding

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The electrical connection is segmented into multiple parallel interconnect paths within the lead frame bond pad structure. Instead of relying on a single solder ball path, the current is distributed across multiple conductive pathways formed by the laminated copper layers and vias, reducing current density in any single path and mitigating electromigration effects

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The interconnect structure transitions from a two-dimensional surface connection (solder ball bonding) to a three-dimensional laminated structure with multiple conductive layers and vertical via paths. This adds depth dimension to the current flow paths, creating multiple parallel routes that reduce current crowding and improve electromigration resistance

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If gold-on-gold technology is used to form bond pads, then electromigration resistance is improved, but manufacturing cost and process complexity increase significantly

Engineering Contradiction:

Improveelectromigration resistanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The material composition parameters of the bond pad are changed from pure gold to a laminated structure of copper layers with nickel barriers. This parameter change maintains the electrical and mechanical performance needed for electromigration resistance while dramatically reducing material cost and simplifying the manufacturing process by using standard copper lead frames and aluminum-compatible bonding

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces expensive gold materials with cheaper copper-based laminated structures that achieve similar reliability performance. The copper layers with nickel barriers provide sufficient electromigration resistance at a fraction of the cost of gold-on-gold technology, making the solution economically viable for mass production

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of manufacture

If copper lead frame with lead-free solder balls is used, then low cost is achieved, but electromigration-related failures occur due to high current densities

Engineering Contradiction:

Improvemanufacturing costVSAvoidelectromigration resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The bond pad structure uses a composite laminated design with multiple copper layers separated by nickel barrier layers. This composite structure combines the low cost and good conductivity of copper with the electromigration resistance of nickel barriers, achieving both cost-effectiveness and high reliability under high current density conditions

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The current path is segmented into multiple parallel pathways through the laminated copper layers and vertical vias. This segmentation distributes the high current density across multiple routes, preventing localized electromigration failures while maintaining the low-cost copper lead frame architecture

Inventive Principle:

Principle #1Segmentation

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 solution provides a cost-effective and electromigration-resistant interconnect structure that increases current carrying capacity while maintaining low impedance, eliminating the need for underfill materials and integrating seamlessly into standard process flows.

Implementation Method 1

The balls can be thermosonically bonded to the bond pads

Methodology Applied

Scientific EffectThermosonic bonding:

Data Source

PatentUS8283760B1Lead frame interconnect scheme with high power density

Publication Date: 2012.10.09 NAT SEMICON CORP

AI summary

An integrated circuit package configured to incorporate a lead frame and methods for its making are is described. The package comprising an IC with aluminum bond pads in communication with circuitry of the die with lead frame with silver bond pads. The package having gold bumps bonded between the aluminum bond pad of the die and the silver bond pad of the lead frame. The package including an encapsulant envelope and including various materials and bond pad structures and constructed in a manner formed by thermosonically or thermocompressionally bonding the gold balls to the bond pads. Also, disclosed are methods of making the package.