Thermal Cushions for Flexible Circuit Bonding Alignment
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Solution Overview
Problem
Conventional ACF bonding methods for flexible printed circuits face misalignment issues due to non-uniform heat distribution, leading to faulty connections, especially at fine interconnection pitches ≤100 μm, as the substrate closer to the bonding head heats and expands more than the substrate further away, causing electrodes to become misaligned.
Innovation Solution
The method involves using thermally resistive and elastic cushions on both substrates to ensure uniform heat and pressure distribution, with cushions formed of materials like silicone rubber, providing identical thickness and thermal conductivity to prevent differential expansion and maintain alignment during the bonding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single cushion is provided between the bonding head and one substrate during ACF bonding, then the bonding process can be simplified, but non-uniform heat distribution causes misalignment of interconnections
Solution Approach 1:
The single cushion is segmented into two separate cushions, each placed between the bonding head and one substrate. This segmentation allows independent thermal management for each substrate, ensuring uniform heat distribution across both substrates and preventing misalignment during the bonding process
Solution Approach 2:
The cushions act as intermediary thermal management components between the bonding head and substrates. By introducing these intermediary elements, uniform thermal energy distribution is achieved across both substrates, preventing differential expansion and maintaining alignment precision
2Ease of manufacture
If heat is applied from a single bonding head to one side of the assembly, then the bonding process is simpler, but the substrate closer to the bonding head heats and expands more causing misalignment
Solution Approach 1:
Instead of applying heat from a single bonding head to one side, the method inverts the approach by placing cushions on both substrates and applying heat uniformly to both sides. This inversion of the thermal application strategy ensures equal heat distribution and prevents differential expansion that would cause misalignment
Solution Approach 2:
The bonding process achieves equipotential thermal distribution by heating both substrates to the same temperature through the intermediary cushions. This creates uniform thermal conditions across the entire assembly, preventing temperature gradients that would lead to misalignment
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 ensures uniform thermal energy distribution across both substrates, preventing misalignment and achieving stable, durable electrical connections by ensuring both substrates expand equally, resulting in improved bonding accuracy and reliability for fine pitch interconnections.
Implementation Method 1
providing a second cushion on the second substrate; wherein the first and second cushions are formed of a thermally resistive and elastic material
Implementation Method 2
the first and second cushions are formed of a thermally resistive and elastic material to enable substantially uniform pressure and heat to be applied
Implementation Method 3
the element closer to the bonding head to heat and expand more than the element further away from the bonding head
Data Source
AI summary
A method for forming electrical connections between electrical conductors is provided. The method includes depositing an anisotropic conductive bonding material (AC bonding material) on a first plurality of electrical conductors, sandwiching the AC bonding material between the first plurality of electrical conductors and a second plurality of electrical conductors, providing first and second cushions formed of a thermally resistive and elastic material, and applying heat and pressure to the second cushion to form the AC bond between the first and second plurality of conductors.