Low-Profile Interconnects Using Indium Discs and Prepreg for Thermal Compliance

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Solution Overview

Problem

Conventional frame attachment interconnects, such as pigtail connectors, face limitations in pin-out, placement difficulty via soldering, and require increased board surface area, while failing to provide a reliable and compliant connection between substrates and frames, especially under thermal and vibration stresses.

Innovation Solution

A method involving copper pads on both the substrate and frame, with epoxy glass prepreg material and metal discs (indium or indium-lead alloy) to form a metallurgical connection, cured in a controlled atmosphere, creating a low-profile, fluid-tight, and thermally compliant joint.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If pigtail connectors are used for frame attachment, then compliancy is achieved, but pin-out is limited and placement via soldering is difficult

Engineering Contradiction:

ImprovecomplianceVSAvoidplacement difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent introduces an intermediary component (the frame attachment interconnect assembly with copper pads and prepreg material) that mediates between the rigid frame and the flexible PCB, enabling both reliable compliance and ease of soldering placement. The intermediary structure allows the PCB to flex while providing a stable soldering surface.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The interconnect assembly is segmented into distinct functional layers: copper pads for electrical connection, prepreg material for mechanical compliance and soldering, and frame attachment components. This segmentation allows each layer to optimize its specific function while working together to solve the overall problem.

Inventive Principle:

Principle #1Segmentation

2Reliability

If pigtail connectors are used for frame attachment, then compliancy is achieved, but board surface area is increased

Engineering Contradiction:

ImprovecomplianceVSAvoidboard surface area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent transitions from a two-dimensional surface mounting approach to a three-dimensional vertical integration approach. The copper pads and prepreg material are layered vertically beneath the frame attachment points, eliminating the need for large horizontal surface area while maintaining compliance functionality.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of manufacture

If conventional interconnects are used, then assembly is simple, but thermal and vibration reliability is insufficient

Engineering Contradiction:

Improveassembly simplicityVSAvoidthermal-cycle and vibration reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs composite materials including copper pads for electrical conductivity, prepreg material for mechanical compliance and thermal management, and metal discs for structural integrity. This composite structure provides both assembly simplicity and superior thermal-cycle and vibration reliability through the synergistic properties of the material layers.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The interconnect design incorporates parameter changes in material properties - using materials with appropriate coefficients of thermal expansion, conductivity, and mechanical flexibility to withstand thermal cycling and vibration while maintaining electrical and mechanical performance.

Inventive Principle:

Principle #35Parameter changes

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 solution provides a reliable, electrically conductive, and thermally compliant interconnect that withstands thermal cycles and vibrations, ensuring a secure and fluid-tight seal between the frame and substrate, suitable for harsh environments like military systems.

Implementation Method 1

The assembly is cured in a controlled atmosphere that can include a vacuum and a temperature of about 125 degrees Celsius to form an electrically conductive metallic joint between adjacent pads

Methodology Applied

Scientific EffectMetallurgical connection: Welding

Implementation Method 2

The prepreg material can include a composite material of fiber cloth impregnated with a rubberized epoxy

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS8878072B2High reliability fluid-tight low-profile electrically conductive interconnects for large scale frame attachment

Publication Date: 2014.11.04 LOCKHEED MARTIN CORP

AI summary

A method for forming a frame attachment interconnect between a substrate and a frame is disclosed. The method can include applying a composite material (e.g., epoxy-glass prepreg) to a surface of a substrate. The composite material can have one or more holes disposed to substantially align with a corresponding pad on the surface of the substrate. A metal disc is placed in each hole of the composite material on top of the corresponding pad. A frame member can be placed on top of the composite material and the metal discs. The frame member can have one or more pads disposed to substantially align with the metal discs. The substrate, composite material, metal discs and frame combination can be cured in a controlled atmosphere that can include a vacuum and a predetermined temperature to create discrete electrical connections between adjacent pads but with each encapsulated and electrically isolated.