Flexible PCB Bonding for Cryogenic Power Module Connections

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional power module packaging methods face challenges with high inductance, reduced reliability, and increased cost due to CTE mismatch between semiconductor dies, DBC, and PCB materials, especially in cryogenic applications, and traditional wire bonding methods fail to address these issues effectively.

Innovation Solution

The use of flexible printed circuit boards (PCBs) with specific copper layer ratios and soft metals like indium or tin for connections, along with encapsulation materials that match CTE, to create a flexible and reliable connection that withstands wide temperature variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If thin wire bonding is used to connect die pads to power module terminals, then the assembly is feasible due to CTE mismatch, but inductance increases and reliability decreases

Engineering Contradiction:

Improveconnection reliabilityVSAvoidinductance

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent employs a flexible printed circuit board (FPCB) with a thin film structure to connect the semiconductor die to the PCB. This thin film approach replaces traditional wire bonding while maintaining flexibility to accommodate CTE differences between materials. The FPCB's thin profile reduces the current path length and loop area, thereby minimizing inductance compared to wire bonding, while its flexibility allows it to withstand thermal expansion mismatches without breaking.

Inventive Principle:

Principle #30Flexible shells and thin films

2Reliability

If soldering is used to directly connect dies to rigid PCB, then electrical isolation and thermal dissipation are improved, but the connection fails due to CTE mismatch between materials

Engineering Contradiction:

Improveelectrical isolation and thermal dissipationVSAvoidconnection stability under thermal cycling

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent transitions from a rigid connection system to a dynamic, flexible connection system. The FPCB can dynamically adapt its shape and absorb stress during thermal cycling by bending and deforming elastically. This dynamic flexibility allows the connection to maintain electrical contact and structural integrity despite the CTE mismatch between the rigid PCB, DBC, and semiconductor die, preventing connection failure during thermal expansion and contraction.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The flexible printed circuit board acts as a flexible film that bridges the rigid PCB and the semiconductor die. This flexible intermediate layer accommodates the dimensional changes caused by CTE mismatch during temperature variations, maintaining connection stability while preserving the electrical isolation and thermal dissipation benefits of the rigid DBC structure.

Inventive Principle:

Principle #30Flexible shells and thin films

3Reliability

If flexible PCB is used to connect die to PCB, then inductance is reduced and reliability is enhanced, but manufacturing complexity increases due to precise alignment requirements

Engineering Contradiction:

Improveconnection reliabilityVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent incorporates alignment features and pre-defined connection geometries in the FPCB design that facilitate precise positioning during assembly. The FPCB is pre-formed with specific trace patterns, via locations, and mechanical features that guide its placement relative to the semiconductor die and PCB. This preliminary preparation of alignment references and connection points simplifies the assembly process and reduces manufacturing complexity despite the precision requirements.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The FPCB serves as an intermediary component with standardized connection interfaces on both ends - one interface for the semiconductor die pads and another for the PCB terminals. This intermediary structure with defined mechanical and electrical interfaces simplifies the assembly process by providing clear alignment references and reducing the need for complex real-time adjustment during manufacturing, thereby easing manufacturing complexity while maintaining high reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 approach reduces inductance, enhances reliability, and lowers manufacturing costs by allowing the power module to operate reliably from cryogenic to maximum safe temperatures, while maintaining mechanical integrity under thermal cycling.

Implementation Method 1

the flexible connection remains flexible at cryogenic temperatures

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

differences in the coefficients of thermal expansion (CTE) between the die, DBC, encapsulation material, and printed circuit board (PCB) material

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS20250300061A1Flexible printed circuit board bonding power module

Publication Date: 2025.09.25 UNIVERSITY OF TENNESSEE RESEARCH FOUNDATION

AI summary

A power electronics module and a method of making the same are disclosed. The power electronics module comprises a rigid printed circuit board (PCB); a semiconductor die; and a flexible connection coupling the rigid PCB to the semiconductor die, wherein the flexible connection remains flexible at cryogenic temperatures.