Conductive Stress-Relief Washers for Microelectronic Assemblies

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Metal screws used in electronic computing devices can cause damage to IC modules due to over-torqueing and fail to yield under thermal cycling stress, leading to mechanical failures at the interface of ICs and PCBs.

Innovation Solution

Conductive stress-relief pads with a low modulus and high thermal and electrical conductivity are used to distribute and alleviate the stress applied by screws, acting as both a thermal and electrical interface material, and deforming elastically to reduce the load on other components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a metal screw is used to fasten IC modules, then the assembly strength is improved, but the IC module is damaged due to over-torqueing

Engineering Contradiction:

Improveassembly strengthVSAvoiddamage to IC module

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

A compliant washer is introduced as an intermediary component between the screw head and the PCB/IC module. This washer acts as a mediator that absorbs excess mechanical stress and torque, preventing direct transmission of damaging forces to the IC module while still maintaining secure fastening. The washer's compliant material properties allow it to deform and cushion the connection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The mechanical properties of the fastening system are changed by replacing the rigid screw-head-to-PCB interface with a compliant interface. The washer's compliance parameter (elastic modulus) is specifically selected to be lower than both the screw and PCB, creating a progressive deformation sequence that protects the IC module from high-stress concentration during tightening.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If a metal screw with high modulus is used, then the assembly stability is improved, but the screw fails to yield under thermal cycling stress, leading to mechanical failures

Engineering Contradiction:

Improveassembly stabilityVSAvoidreliability under thermal cycling

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The elastic modulus parameter of the fastening system is modified by introducing a compliant washer with lower modulus between the high-modulus screw and the PCB. This creates a compliant interface that can yield and deform under thermal expansion/contraction stresses, allowing the assembly to accommodate thermal cycling without generating excessive stress concentrations that would lead to solder joint failures.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The compliant washer serves as a pre-positioned cushioning element that anticipates and absorbs thermal expansion stresses before they can transmit through the rigid screw-PCB interface. By placing this compliant element in advance at the stress transmission path, the system is prepared to yield safely under thermal cycling conditions, protecting the solder joints from stress-induced failures.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 stress-relief pads effectively mitigate the risk of damage from over-torqueing and thermal cycling, reducing mechanical failures and maintaining electrical and thermal contact between components.

Implementation Method 1

a low modulus to yield under stress associated with thermal cycling of the assembly. For example, screw elongation will typically not occur before the stress is concentrated and relieved by mechanical failures at the microscale

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

Conductive stress-relief washers in microelectronic assemblies... high thermal and electrical conductivity are used to distribute and alleviate the stress

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 3

electrically conductive pad between a head of the screw and a metal feature on the first or second substrate

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS10120424B2Conductive stress-relief washers in microelectronic assemblies

Publication Date: 2018.11.06 SK HYNIX NAND PRODUCT SOLUTIONS CORP

AI summary

Microelectronic device assembly including a component attached to substrate by at least a screw. The screw applies compressive force against a pad of a thermally and electrically conductive material having sufficiently low modulus to mitigate stress in addition to providing a thermal and electrical path between the component and the substrate. In some embodiments, the screw affixes a printed circuit board hosting one or more integrated circuit components to a motherboard, or passive heat sink. The pad may be deformed to assuage stress applied through the screw during assembly of the device and/or as the device experiences thermal cycling, for example associated with intermittent operation.