Polyimide Resin Adhesive Strength for Flexible PCBs
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Solution Overview
Problem
Flexible copper clad laminates (FCCLs) face issues with adhesive strength when used in multilayer printed circuit boards, as existing methods either compromise heat resistance, flexibility, or lead to curling due to differences in thermal expansion coefficients, making it difficult to adhere them to bonding prepregs effectively.
Innovation Solution
A polyamic acid solution is developed, comprising 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) and pyromellitic dianhydride (PMDA) as aromatic tetracarboxylic acid dianhydrides, mixed with aromatic diamines and an inorganic filler, which forms a polyimide resin with improved adhesive strength through imidization, reducing thermal expansion differences and enhancing properties like heat resistance and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the adhesive method is used to prepare FCCL by attaching copper clad layer on polyimide film via epoxy adhesive, then the bonding is achieved, but the adhesive film is weak to heat and causes copper ion migration under high temperature, leading to circuit shorting
Solution Approach 1:
The invention removes the epoxy adhesive layer from the FCCL structure and replaces it with a polyimide resin layer formed by the cast method. This extraction of the adhesive component eliminates the heat weakness and copper ion migration issues inherent in epoxy adhesives, while maintaining bonding functionality through the polyimide resin's natural adhesive properties to the copper clad layer.
Solution Approach 2:
The invention uses a composite polyimide resin system comprising multiple aromatic diamines (p-phenylenediamine, m-phenylenediamine, 4,4'-oxydianiline) combined with aromatic tetracarboxylic acid dianhydrides (BPDA and PMDA). This composite material approach creates a polyimide resin with enhanced thermal stability, flexibility, and adhesive strength, resolving the contradiction between bonding capability and heat resistance.
2Ease of manufacture
If the cast method is used to prepare FCCL by applying polyimide varnish on copper clad layer, then no adhesive is needed, but curling occurs due to difference in thermal expansion coefficients between polyimide layer and copper clad
Solution Approach 1:
The invention modifies the chemical composition parameters of the polyimide resin by incorporating specific ratios of aromatic diamines and aromatic tetracarboxylic acid dianhydrides. This parameter change in the resin composition allows adjustment of the thermal expansion coefficient to better match that of the copper clad layer, thereby reducing curling while maintaining the manufacturing simplicity of the cast method.
3Reliability
If the polyimide resin layer is improved for heat resistance or flexibility, then curling is prevented, but the adhesive strength of the polyimide resin layer is decreased, making it difficult to adhere to bonding sheet
Solution Approach 1:
The invention employs a composite polyimide resin system that simultaneously achieves enhanced heat resistance, flexibility, and adhesive strength. The combination of multiple aromatic diamines with aromatic tetracarboxylic acid dianhydrides creates a synergistic effect where the resin exhibits both improved thermal stability and maintained bonding capability to bonding sheets, resolving the trade-off between these properties.
Solution Approach 2:
The invention introduces an inorganic filler (such as talc, mica, or silica) into the polyimide resin composition to locally modify specific properties. This filler addition provides thermal stability and controls thermal expansion characteristics while the organic solvent system maintains the resin's adhesive properties, allowing different regions of the resin structure to optimize for different functions.
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 resulting polyimide resin exhibits enhanced adhesive strength to both metal clads and bonding prepregs, maintaining flexibility and heat resistance, enabling effective use in multilayer printed circuit boards without curling issues.
Implementation Method 1
a polyimide resin prepared by imidization of the polyamic acid solution
Implementation Method 2
carrying out heat treatment under an appropriate condition
Data Source
AI summary
Disclosed are a polyamic acid solution, a polyimide resin prepared by imidization of the polyamic acid solution, a flexible metal clad laminate using the polyimide resin, and a printed circuit board including the flexible metal clad laminate, wherein the polyamic acid solution includes (a) 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA), and pyromellitic dianhydride (PMDA) as aromatic tetracarboxylic acid dianhydride; (b) at least one aromatic diamine; (c) an organic solvent; and (d) an inorganic filler.