Planar Solder Joint Layout for Electromigration-Resistant Tin-Bismuth

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Solution Overview

Problem

Existing technologies fail to effectively prevent electromigration in low-melting temperature tin-bismuth solder joints, leading to bismuth atom migration and increased electrical resistance, which can cause physical damage and affect the operation of connected components.

Innovation Solution

A planar solder joint structure is designed with a diagonal trace that bisects the joint into two identical triangles, allowing for the gradual reduction of length to identify a critical length where electromigration is prevented, maintaining uniform current density and visually observing the electromigration process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electron current flows through solder joints, then electrical connection is achieved, but electromigration occurs causing bismuth atom migration and increased electrical resistance

Engineering Contradiction:

Improvesolder joint reliabilityVSAvoidelectromigration

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The solder joint is divided into multiple segments by introducing intermediate conductive traces that create separate solder joint portions. This segmentation allows each portion to have optimized dimensions that prevent electromigration while maintaining electrical connectivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the solder joint structure are given different properties - the intermediate conductive traces have specific widths and spacing designed to create uniform current density in critical areas, while maintaining overall electrical connectivity. The diagonal trace configuration creates localized regions with enhanced electromigration resistance.

Inventive Principle:

Principle #3Local quality

2Reliability

If solder joint length is reduced to prevent electromigration, then electrical resistance decreases, but current density uniformity becomes difficult to maintain

Engineering Contradiction:

Improveelectromigration resistanceVSAvoidcurrent density uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The problem is solved by transitioning from a simple linear solder joint to a two-dimensional configuration with diagonal traces. This dimensional change allows the creation of multiple solder joint portions arranged geometrically to achieve both compact size and uniform current density distribution through careful geometric design.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

Specific geometric parameters are optimized - the intermediate conductive traces have widths between 0.5-2.0 times the original trace width, and spacing of 0.5-2.0 times the original spacing. These parameter changes create the desired uniform current density while maintaining electromigration resistance.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If complex solder joint structures are used to prevent electromigration, then electromigration resistance improves, but device complexity increases

Engineering Contradiction:

Improveelectromigration resistanceVSAvoidsolder joint structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The intermediate conductive traces serve multiple functions simultaneously: they segment the solder joint to prevent electromigration, they act as additional electrical connection paths, and they provide structural support. This multi-functionality reduces the need for separate components and simplifies the overall design.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The electrical connection function and electromigration prevention function are merged into a single integrated structure. The intermediate conductive traces are formed using the same fabrication processes as the original traces, combining multiple benefits into one design element rather than requiring separate prevention mechanisms.

Inventive Principle:

Principle #5Merging (Combining)

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 structure enables the determination of a critical length below which electromigration does not occur, reducing bismuth atom migration and maintaining uniform current density, thus preventing physical and electrical damage to the solder joint.

Implementation Method 1

The solder joints may be subjected to electromigration as a result of electron current flowing through the solder joints

Methodology Applied

Scientific EffectElectromigration:

Implementation Method 2

electron current flowing through the solder joints

Methodology Applied

Scientific EffectElectron current flow:

Data Source

PatentUS20260068036A1Planar solder joint with diagonal trace for determining solder dimension to prevent electromigration

Publication Date: 2026.03.05 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A substrate may comprise a first conductive trace over a substrate and a second conductive trace over the substrate. The first conductive trace and the second conductive trace may be separated by a length. The substrate may include a solder joint bridging the first conductive trace and the second conductive trace and a third conductive trace diagonally bisecting the solder joint to form a first solder joint portion and a second solder joint portion. A first length of the first solder joint portion may taper to zero from the length. A second length of the second solder joint portion may taper to zero from the length.