Low-Temperature Bonding for Flexible Substrate Connection Integrity
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Solution Overview
Problem
Flexible substrates with thermoplastic resins used in electronic devices are prone to connection failures when adhered together via thermocompression bonding, as the heat softens the substrates, causing wiring patterns and electrodes to shift or sink.
Innovation Solution
A connection structure is developed where each substrate is adhered using a conductive bonding material with a lower bonding temperature than the thermoplastic resins, and an insulating adhesive with a lower adhesion temperature, ensuring the substrates remain rigid during bonding and adherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermocompression bonding is used to adhere flexible substrates together, then the substrates can be connected, but the heat softens the substrates causing wiring patterns and electrodes to shift or sink leading to connection failure
Solution Approach 1:
The patent changes the temperature parameter of the bonding process by using a bonding material with a melting point below the glass transition temperature of the thermoplastic resin. This allows bonding to occur at low temperature without softening the substrate, thereby preventing wiring pattern shift and sinking while ensuring reliable connections
Solution Approach 2:
The patent introduces a bonding material as an intermediary substance between the substrates. This bonding material has specific thermal properties (melting point below substrate glass transition temperature) that enable it to facilitate bonding without transferring excessive heat to the substrate, thus avoiding softening and dimensional changes
2Reliability
If thermocompression bonding is used to adhere substrates together, then the substrates can be connected, but the heat causes the substrates to soften leading to connection failure
Solution Approach 1:
The patent fundamentally changes the temperature parameter by selecting a bonding material with a melting point significantly below the glass transition temperature of the thermoplastic resin. This parameter change enables bonding at low temperatures that do not soften the substrate, resolving the contradiction between achieving connection and avoiding thermal softening
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 significantly reduces connection failures among substrate electrodes by maintaining the structural integrity of the substrates during the bonding process, resulting in a highly reliable connection structure.
Implementation Method 1
a bonding material which is conductive and bonds the first substrate electrode and the second substrate electrode together; a bonding temperature of the bonding material is lower than a melting point or a glass transition temperature of the first thermoplastic resin and lower than a melting point or a glass transition temperature of the second thermoplastic resin
Implementation Method 2
an adhesive which has insulating properties and adheres the first principal surface other than a portion where the first substrate electrode is arranged and the fourth principal surface other than a portion where the second substrate electrode is arranged together; an adhesion temperature of the adhesive is lower than the melting point or the glass transition temperature of the first thermoplastic resin and lower than the melting point or the glass transition temperature of the second thermoplastic resin
Data Source
AI summary
A connection structure includes a first substrate having first and second principal surfaces opposed to each other and includes a first thermoplastic resin; a first substrate electrode on the first principal surface; a second substrate which has a third principal surface and a fourth principal surface opposed to the third principal surface and facing the first principal surface and includes a second thermoplastic resin; a second substrate electrode on the fourth principal surface; a conductive bonding material which bonds the first and second substrate electrodes together; and an insulating adhesive which adheres the first principal surface other than a portion where the first substrate electrode is and the fourth principal surface other than a portion where the second substrate electrode is together. A bonding temperature of the bonding material is lower than a respective melting point or a respective glass transition temperature of the first and second thermoplastic resins.