Platinum Temperature Sensor Element Crack Prevention

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Solution Overview

Problem

Conventional platinum temperature sensor elements face issues with stress-induced cracks due to thermal expansion differences between glass reinforcement materials and lead wires, leading to unreliable connections and potential damage, and the use of gold for reinforcement is costly.

Innovation Solution

A platinum temperature sensor element with a configuration that includes an insulating substrate, platinum resistance film, electrodes, lead wires, and a protective film, where only one side surface of the lead wires and internal electrodes are covered with a reinforcement paste made of a common precious metal material, such as platinum, to reduce thermal stress and prevent cracks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If glass paste material is used as connection reinforcing material between electrode pads and lead wires, then connection strength is improved, but thermal expansion difference causes compressive and tensile stress leading to cracks

Engineering Contradiction:

Improveconnection strengthVSAvoidelectrical reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent uses a composite material consisting of precious metal powder (such as platinum) dispersed in a glass paste matrix. This composite structure combines the low thermal expansion coefficient of precious metals with the bonding properties of glass paste, creating a reinforcement material that reduces thermal stress while maintaining connection strength. The precious metal particles form a network structure that compensates for thermal expansion differences between the glass and lead wires.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the composition parameters of the glass paste by adding precious metal powder with specific particle sizes and concentrations. By controlling the metal content (typically 30-70 wt%) and particle size distribution, the thermal expansion coefficient of the paste is adjusted to better match that of the lead wires, thereby reducing thermal stress during temperature cycling.

Inventive Principle:

Principle #35Parameter changes

2Strength

If entire lead wires are covered with reinforcement paste to ensure complete adhesion, then connection strength is improved, but spaces form due to viscosity and supply method issues preventing sufficient joining

Engineering Contradiction:

Improvejoining strengthVSAvoidadhesion quality

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent applies the reinforcement paste selectively at critical locations rather than uniformly covering entire lead wires. The paste is concentrated at the welding interfaces between lead wires and electrode pads where mechanical and electrical connection is most critical. This localized application ensures adequate adhesion quality while avoiding the formation of spaces that would occur with complete coverage.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If gold is used as protective film material for low temperature calcination and easy bonding, then ease of manufacture is improved, but cost increases due to expensive material

Engineering Contradiction:

Improvebonding easeVSAvoidcost

Core Design Contradiction:

Ease of manufactureVSQuantity of substance

Solution Approach 1:

The patent replaces expensive gold with cheaper precious metals such as platinum, palladium, or their alloys that can also be calcined at low temperatures. While these materials are still precious metals, they offer comparable bonding properties at lower cost. The protective film uses glass paste containing these alternative precious metals, achieving similar manufacturing ease without the high cost of gold.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 configuration enhances the joining strength and conductivity between lead wires and internal electrodes while minimizing thermal stress and the risk of cracks, providing a reliable and cost-effective solution.

Implementation Method 1

stress is applied on the welded parts through compressive stress and tensile stress due to difference in thermal expansion of the glass, thereby generating cracks

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

a hot type (also called a hot wire type) that utilizes change in resistance of a heated wire as a result of current flowing through a platinum element (platinum hot wire) so as to increase the temperature through self-heating

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 3

losing heat as the air hits its heating portion

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS10488270B2Platinum temperature sensor element

Publication Date: 2019.11.26 KOA CORP

AI summary

A temperature sensor element has such a structure as, when reinforcing lead wires on internal electrodes with a paste, one side surface of each of the lead wires is covered with a reinforcement paste and the other side surface is not covered with the reinforcement paste without covering the entire lead wires welded and connected to the internal electrodes. This allows elimination of cause of cracks generating, thereby securing sufficient joining strength and reinforcement of conductivity of the internal electrodes and the lead wires, and securing connection strength between the lead wires and the internal electrodes.