Concave BGA Solder Pad Layout for Thermal Expansion Relief

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Solution Overview

Problem

Differential thermal expansion between circuit board dielectric material and conductive vias leads to cracking or fracturing of BGA connections, particularly pronounced with stacked vias.

Innovation Solution

The use of conductive pads with concave edges that are offset from the conductive vias, creating a gap to accommodate differential thermal expansion, thereby reducing the risk of solder joint cracking or fracturing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional conductive pads with straight edges are used, then manufacturing is simple, but solder joints crack or fracture due to differential thermal expansion

Engineering Contradiction:

Improvesolder joint integrityVSAvoidpad design complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The conductive pad is designed with a concave edge instead of a straight edge, creating a curved geometry that accommodates differential thermal expansion between the circuit board substrate and conductive via. This curvature allows the pad to flex and absorb thermal stress, preventing solder joint cracking while maintaining manufacturing feasibility through standard PCB fabrication processes

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Reliability

If stacked vias are used to connect BGA, then electrical connection is improved, but thermal expansion stress increases causing cracking

Engineering Contradiction:

Improveelectrical connectionVSAvoidthermal expansion stress

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The concave edge of the conductive pad creates a curved interface that distributes and absorbs thermal expansion stress generated by stacked vias. This curvature allows the pad to accommodate the differential expansion between materials without transmitting excessive stress to the solder joints, thereby protecting the electrical connection while using stacked via structures

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 effectively reduces or eliminates solder joint cracking or fracturing due to thermal expansion, maintaining the integrity of BGA connections without requiring changes to the BGA component.

Implementation Method 1

Differential thermal expansion between circuit board dielectric material and conductive vias leads to cracking or fracturing of BGA connections

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS12328826B2Solder pads with concave edges for ball grid arrays

Publication Date: 2025.06.10 MOTOROLA SOLUTIONS INC

AI summary

A device is provided that includes: a substrate including dielectric material and a conductive via extending into the substrate from a surface of the substrate. The device further includes a conductive pad positioned at the surface of the substrate and offset in a plane of the surface from the conductive via, the conductive pad to receive a solder joint connection to an electronic component. The conductive pad includes a concave edge that defines a gap with a convex edge of the conductive via.