IC Package Connector Height Control for Thermal Fatigue

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Solution Overview

Problem

Integrated circuit packages face thermal cycle-induced fatigue due to differences in thermal expansion between component packages and printed circuit boards, leading to solder connection failures and uneven solder column heights, which reduce thermal cycle life and increase production variability.

Innovation Solution

The integration circuit packages are designed with package connectors that have a solder surface with a shortest distance of at least 6 mils (0.152 mm) to the seating plane, ensuring uniform solder column heights of at least 6 mils (0.152 mm), 8 mils (0.203 mm), or 10 mils (0.254 mm), eliminating gaps between the IC bottom and the PCB and allowing for precise control of solder height.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If package connectors extend below the seating plane to create a gap, then thermal cycle life is improved through longer solder columns, but manufacturing precision deteriorates due to uneven solder column heights and quality variation

Engineering Contradiction:

Improvethermal cycle lifeVSAvoidsolder column height uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

Instead of extending package connectors below the seating plane to create gaps (traditional approach), the invention inverts the approach by ensuring package connectors do not extend below the seating plane. This eliminates the gap and allows the solder paste stencil to define the solder column height directly, achieving both thermal cycle life improvement and manufacturing precision.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention changes the critical parameter from 'solder column height' to 'distance between package connector solder surface and seating plane'. By controlling this distance to be at least 6 mils and ensuring package connectors do not extend below the seating plane, the solder column height is automatically defined by the stencil thickness, achieving uniform heights and improved manufacturing precision while maintaining thermal cycle life.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If solder paste stencil thickness is increased to raise solder column height, then thermal cycle life is improved, but device complexity increases due to additional materials and processes

Engineering Contradiction:

Improvethermal cycle lifeVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The package structure itself serves to define the solder column height through the distance between the package connector solder surface and seating plane. This self-defining mechanism eliminates the need for complex additional processes or materials to control solder height, achieving thermal cycle life improvement without increasing device complexity.

Inventive Principle:

Principle #25Self-service

3Length of stationary object

If package connectors are positioned to create gaps under IC bottom, then solder column height can be extended, but thermal conduction efficiency deteriorates due to reduced thermal path effectiveness

Engineering Contradiction:

Improvesolder column heightVSAvoidthermal conduction efficiency

Core Design Contradiction:

Length of stationary objectVSLoss of energy

Solution Approach 1:

The invention uses a composite approach where the solder column acts as a thermal conductor and the package structure provides mechanical support. By ensuring package connectors do not extend below the seating plane and maintaining a controlled distance of at least 6 mils, the solder column achieves sufficient height for thermal cycle life while remaining an effective thermal conduction path.

Inventive Principle:

Principle #40Composite materials

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 design enhances thermal cycle fatigue life, reduces variability, and improves quality by maintaining consistent solder heights, increasing the number of thermal cycles to failure and enhancing mass production reliability.

Implementation Method 1

Because of a difference in thermal expansion, the solder connections fail by thermal fatigue. The component package may experience a small expansion and the PCB may experience a relatively larger expansion.

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

IC packages are then placed with their package connectors over the solder paste columns and the PCB, IC packages, and solder paste columns are heated until the solder paste columns melt and soften

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS20240244761A1Packages with a shortest distance between package connectors and a seating plane of at least 6 mils

Publication Date: 2024.07.18 MICROCHIP TECHNOLOGY INC

AI summary

An integrated circuit package with a package connector and at least three bottom-most points of the package that define a seating plane, wherein the shortest distance between the seating plane and the package connector solder surface is at least 6 mils (0.152 mm). A printed circuit board comprising a pad; an integrated circuit package comprising a package connector and at least three bottom-most points of the package in contact with the printed circuit board; and a solder column having a height at least 6 mils (0.152 mm) electrically and mechanically connecting the pad to the package connector. Methods for controlling solder column height are disclosed.