Multilayer Polyimide Film for Flexible PCBs
Solution Overview
Problem
Conventional polyimide films used in flexible printed circuit boards face challenges in achieving a balance between high flexibility and dimensional stability, with existing solutions either compromising on stiffness or experiencing issues during manufacturing and insulating reliability.
Innovation Solution
A multilayer polyimide film structure is developed, comprising a core layer and clad layers with controlled coefficients of linear expansion and modulus of elasticity, where the clad layers have a peeling strength of 3 N/cm or less, and the entire film has a coefficient of linear expansion between 9 ppm/°C to 30 ppm/°C, allowing for high flexibility and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If copolymerization is performed with p-phenylenediamine to improve dimensional stability, then the coefficient of linear expansion decreases (close to copper), but the modulus of elasticity increases causing loss of film flexibility
Solution Approach 1:
The polyimide film is divided into multiple layers with different compositions and properties. The first polyimide layer has a coefficient of linear expansion of 20-40 ppm/°C and lower modulus of elasticity for flexibility, while the second polyimide layer has a coefficient of linear expansion of 0-10 ppm/°C and higher modulus of elasticity for dimensional stability. This segmentation allows each layer to contribute its specific property to the overall film performance.
Solution Approach 2:
The invention uses a composite structure combining two different polyimide materials with distinct thermal expansion characteristics. By laminating these composite layers together, the film achieves a balanced combination of flexibility (from the first layer) and dimensional stability (from the second layer), resolving the contradiction between these two properties.
2Strength
If film thickness is reduced to decrease stiffness value, then flexibility improves, but the film easily tears during manufacture and insulating reliability decreases
Solution Approach 1:
Instead of using a single thin film, the invention segments the film into multiple layers. This allows the total thickness to be sufficient for strength and reliability (e.g., 12.5 μm or more), while the specific structure (with at least one layer having lower modulus of elasticity) provides the needed flexibility. The segmented structure prevents tearing during manufacture while maintaining insulating reliability.
Solution Approach 2:
Different regions (layers) of the film have different local properties. The first polyimide layer has lower modulus of elasticity to provide flexibility, while the second polyimide layer has higher modulus of elasticity to provide strength. This local differentiation of material properties allows the film to simultaneously achieve flexibility and manufacturing reliability without requiring reduced thickness.
Data Source
AI summary
An object of this invention is to provide a polyimide film suitable for use in flexible printed circuit boards and the like which have high flexibility and dimensional stability, and to provide a laminate and metal-clad laminate which uses such a polyimide film. This invention relates to a multilayer polyimide film being a polyimide film having a multilayer structure, including: a core layer; and clad layers provided on each side of the film, which clad layers are exposed, the core layer being a non-thermoplastic polyimide having an average coefficient of linear expansion at a temperature from 100° C. to 200° C. in a range of 5 ppm/° C. to 20 ppm/° C., each of the clad layers being a polyimide having a peeling strength of 3 N/cm or less, the film as a whole having an average coefficient of linear expansion at a temperature range of 100° C. to 200° C. in a range of 9 ppm/° C. to 30 ppm/° C., and (a)>(b), where (a) is an average modulus of elasticity of the core layer and (b) is an average modulus of elasticity of the clad layers.