Polyimide Film CTE Control for Flexible Substrate Warpage
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Solution Overview
Problem
Polyimide films used in flexible display boards face warpage issues due to differences in coefficient of thermal expansion (CTE) between the polyimide film and glass substrates during high-temperature heat treatment, making subsequent processes difficult.
Innovation Solution
A polyimide precursor composition is developed with a specific structure, including a diamine or acid dianhydride derived from Formula 1, dissolved in a solvent mixture with a positive partition coefficient, which forms a polyimide film with a modulus of 4 GPa or less and a CTE of 30-200 ppm, reducing stress on the substrate during heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a polyimide film is formed on a glass substrate through high-temperature heat treatment, then the polyimide film achieves heat resistance and curing, but the difference in coefficient of thermal expansion (CTE) between the glass substrate and polyimide film causes warpage of the glass substrate
Solution Approach 1:
The patent modifies the chemical structure of the polyimide precursor by introducing specific molecular configurations (Formula 1 with defined R groups and m values) to control the coefficient of thermal expansion. By changing the molecular parameters of the polyimide resin, the CTE is adjusted to be closer to that of the glass substrate, thereby reducing thermal expansion mismatch and preventing substrate warpage during high-temperature heat treatment.
Solution Approach 2:
The patent employs a composite approach by formulating a polyimide precursor composition with specific solvent systems (positive partition coefficient solvents) and additive packages. This composite material system ensures uniform film formation and controlled curing behavior, allowing the polyimide film to achieve heat resistance while maintaining dimensional compatibility with the glass substrate during thermal processing.
2Reliability
If the polyimide film has high heat resistance through high-temperature curing, then the film achieves desired thermal properties, but the stress difference causes difficulty in laminating devices on the film
Solution Approach 1:
The patent optimizes the polyimide precursor molecular structure (Formula 1 parameters) to achieve a balance between heat resistance and flexibility. By adjusting the molecular weight, chain flexibility, and cross-linking density through precise chemical structure control, the film attains sufficient thermal stability while maintaining adequate stress flexibility to accommodate device lamination processes without compromising bonding strength.
Solution Approach 2:
The patent creates different functional zones within the polyimide film structure. The bulk of the film provides heat resistance through high-temperature curing, while the interface regions maintain controlled stress properties that facilitate device lamination. This local differentiation of material properties allows simultaneous achievement of thermal reliability and bonding capability.
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 polyimide film exhibits high transparency, heat resistance, and dimensional stability, preventing substrate warpage and enabling the production of flexible boards for electronic devices like OLEDs and LCDs.
Implementation Method 1
followed by dehydration ring closure at a high temperature to imidize the polyamic acid derivative
Implementation Method 2
a difference in coefficient of thermal expansion (CTE) between the underlying glass substrate and the polyimide film layer causes warpage of the glass substrate after formation of the film
Data Source
Figure 1
Figure 2
AI summary
Disclosed is a polyimide precursor composition for the production of a flexible board of a photoelectronic device. The polyimide precursor composition includes a polyimide precursor derived from a diamine or acid dianhydride including a structure of Formula 1: wherein R1 to R8, m1, m2, and m3 are as defined in the specification. Also disclosed is a polyimide film produced from the polyimide precursor composition. The polyimide film is obtained by applying the precursor composition to a substrate and curing the composition. The polyimide film has high transparency and good heat resistance. In addition, the polyimide film exhibits good dimensional stability because the substrate does not undergo an increase in stress even during high-temperature heat treatment.