Flexible Solder Bridge for Vehicle Windscreen Thermal Stress
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Solution Overview
Problem
Existing electrical connectors for motor vehicle windshields face challenges in withstanding thermal and mechanical stresses, leading to potential damage of the fragile substrate and failure of the electrical connection due to mismatched coefficients of thermal expansion between materials, especially when using lead-free solders.
Innovation Solution
A flexible electrically conductive solder bridge with a thickness of less than 100 microns, comprising a first and second foot portion interconnected by a flexible body, which is capable of bending without breaking, and is fabricated from materials like copper with encompassing insulation to reduce residual stress and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid solder bridge of 0.8-1.0mm thickness is used to provide structural strength, then mechanical strength is improved, but thermal stress resistance deteriorates due to mismatched coefficient of thermal expansion with the fragile substrate
Solution Approach 1:
The patent applies this principle by using a thin film flexible circuit board (less than 100 microns thick) instead of a rigid solder bridge. The flexible circuit board can bend and deform to accommodate thermal expansion differences between the connector and the fragile substrate (e.g., glass windscreen), thereby reducing thermal stress while maintaining electrical connectivity and mechanical strength through its flexible nature.
Solution Approach 2:
The patent changes the key parameter of thickness from 0.8-1.0mm (rigid) to less than 100 microns (flexible). This parameter change transforms the mechanical properties of the connector body, enabling it to be flexible rather than rigid, which resolves the contradiction between needing mechanical strength and avoiding thermal stress damage to the fragile substrate.
2Reliability
If exact tolerances are maintained for contact surface and dimple height to ensure proper electrical connection, then connection reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The flexible circuit board inherently provides compliance through its flexibility, eliminating the need for precisely engineered dimples and contact surfaces. The flexible board can adapt to variations in substrate surface geometry, allowing for simpler manufacturing processes while maintaining reliable electrical connections without requiring exact tolerances.
3Adaptability or versatility
If lead-free solder is used to meet environmental requirements, then environmental compliance is improved, but thermal stress resistance deteriorates due to higher CTE mismatch
Solution Approach 1:
The flexible circuit board acts as a stress-absorbing element that compensates for the higher CTE mismatch inherent in lead-free solder joints. Its flexibility allows it to deform under thermal stress, protecting the lead-free solder connections from failure while maintaining environmental compliance.
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 flexible solder bridge provides a robust electrical connection with significantly reduced residual stress between the windscreen and the connector, preventing damage and failure, while being more compact and cost-effective for mass production.
Implementation Method 1
a flexible electrically conductive body
Implementation Method 2
the flexible electrically conductive body is capable of bending without breaking
Data Source
AI summary
A solder bridge (1) for a vehicle windscreen, the solder bridge (1) comprises a first foot portion (11A) for connection to a vehicle windscreen and a second foot portion (11B) for connection to a vehicle windscreen, the first foot portion (11A) and second foot portion (11B) being interconnected by a flexible electrically conductive body (12).