Flexible Substrate Microelectronic Package Thermal Stress

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Solution Overview

Problem

Microelectronic packages face challenges in handling differential thermal expansion and contraction between semiconductor chips and circuit boards, leading to stress on solder connections, and testing is complicated by non-planarity of terminals and test fixtures, which increases costs and reduces reliability.

Innovation Solution

A microelectronic package design featuring a flexible substrate with conductive posts that can move relative to the chip, allowing them to engage contact pads despite irregularities, and a method of encapsulating these posts with an encapsulant material while maintaining accessibility, facilitating reliable connections and high-frequency signal transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If terminals are fixed relative to the chip using solder, then electrical connection is established, but differential thermal expansion and contraction cause stress on the solder connections

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidstress on solder connections

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent employs a flexible substrate that can dynamically deform to accommodate differential thermal expansion between the chip and circuit board. The substrate transitions from a rigid fixed connection to a flexible dynamic connection that absorbs thermal stress through elastic deformation, preventing stress concentration on solder joints while maintaining electrical connectivity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the mechanical parameters of the substrate by using a flexible material with specific elastic properties. This allows the substrate to change its shape and accommodate dimensional changes during thermal cycling, transforming the connection from a rigid fixed-state to a flexible adaptive-state that responds to thermal parameters.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If non-planar terminals are pressed against a test fixture, then testing can be performed, but the non-planarity causes difficulty in making reliable connections

Engineering Contradiction:

Improvetesting capabilityVSAvoidconnection reliability during testing

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The flexible substrate enables dynamic adaptation during testing by deforming to match the test fixture surface. The substrate's elasticity allows it to conform to non-planar contact surfaces, ensuring all terminals make reliable contact with the test fixture simultaneously, thereby enabling efficient testing without compromising connection reliability.

Inventive Principle:

Principle #15Dynamics

3Volume of moving object

If the package is made compact to reduce assembly size, then space is saved, but heat dissipation becomes more difficult

Engineering Contradiction:

Improvepackage sizeVSAvoidheat dissipation

Core Design Contradiction:

Volume of moving objectVSTemperature

Solution Approach 1:

The flexible substrate acts as a thin film that provides both mechanical support and thermal management. Its flexibility allows it to maintain compact packaging while its large surface area in contact with the chip enables efficient heat transfer. The substrate can be designed with optimized thickness and material properties to conduct heat away from the chip effectively despite the compact form factor.

Inventive Principle:

Principle #30Flexible shells and thin films

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 the reliability and compactness of microelectronic assemblies by accommodating thermal expansion and contraction while enabling reliable testing and high-frequency signal transmission without the need for specialized test fixtures.

Implementation Method 1

providing an encapsulant material around the at least one conductive element for supporting the microelectronic package and so that the remote surfaces of the at least one conductive element remains accessible at an exterior surface of the encapsulant material

Methodology Applied

Scientific EffectEncapsulation:

Implementation Method 2

Assemblies including packages can suffer from stresses imposed by differential thermal expansion and contraction of the device and the substrate

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

compressing the at least one conductive element so that the remote surface thereof lies in a common plane

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentUS8728865B2Microelectronic packages and methods therefor

Publication Date: 2014.05.20 ADEIA SEMICONDUCTOR SOLUTIONS LLC

AI summary

A method of making a microelectronic assembly can include molding a dielectric material around at least two conductive elements which project above a height of a substrate having a microelectronic element mounted thereon, so that remote surfaces of the conductive elements remain accessible and exposed within openings extending from an exterior surface of the molded dielectric material. The remote surfaces can be disposed at heights from said surface of said substrate which are lower or higher than a height of the exterior surface of the molded dielectric material from the substrate surface. The conductive elements can be arranged to simultaneously carry first and second different electric potentials: e.g., power, ground or signal potentials.