Thin PCB Dielectrics Using Non-Woven Inorganic Reinforcement
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Solution Overview
Problem
Conventional dielectric materials in printed circuit boards face challenges such as high thickness, high coefficient of thermal expansion (CTE), low glass transition temperature (Tg), and high dielectric constant (DK), leading to poor thermal reliability, manufacturability issues, and high insertion loss, especially in thin and high-density applications.
Innovation Solution
The use of non-woven, inorganic fabric reinforcement impregnated with a crosslinked thermosetting polymer resin, which is low density and low filler content, to create dielectric layers with thicknesses below 125 microns, achieving low CTE, high Tg, and low DK, suitable for high-density interconnect (HDI) boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If unreinforced films are used as dielectrics, then the dielectric thickness can be reduced, but the mechanical stiffness and thickness control capability deteriorate
Solution Approach 1:
The patent uses a composite structure combining unreinforced dielectric film with carrier films and adhesive layers. The unreinforced film provides low dielectric constant and thin profile, while the carrier films provide mechanical support and handling capability, and the adhesive layers provide bonding strength. This composite approach allows achieving both thin thickness and adequate mechanical stiffness.
2Length of stationary object
If unreinforced films are used as dielectrics, then the dielectric thickness can be reduced, but the thickness control precision deteriorates
Solution Approach 1:
The patent introduces carrier films as intermediary elements that enable precise thickness control. The carrier films have controlled thicknesses (e.g., 12.5 microns, 25 microns, 50 microns) and serve as stable substrates for building the dielectric structure. This intermediary layer provides a reference plane and mechanical stability that facilitates precise thickness control during manufacturing processes.
3Strength
If conventional woven glass reinforced dielectrics are used, then the mechanical strength is improved, but the thickness reduction capability deteriorates
Solution Approach 1:
The patent extracts the reinforcement function from the dielectric material itself and separates it into distinct carrier film components. Instead of using woven glass reinforcement within the dielectric layer, the design uses separate carrier films that provide mechanical strength while allowing the dielectric film to remain thin and unreinforced. This separation allows independent optimization of mechanical properties and dielectric properties.
4Productivity
If thin dielectric materials are used to reduce feature size, then the circuit density is improved, but the coefficient of thermal expansion mismatch increases
Solution Approach 1:
The patent changes the material parameters of the carrier films and adhesive layers to achieve CTE matching. The carrier films are selected with specific CTE values that match the substrate and IC materials. The adhesive layers are formulated with appropriate CTE characteristics. By carefully selecting and controlling these material parameters, the overall structure achieves thermal expansion compatibility even with thin dielectric layers, maintaining thermal reliability while enabling high circuit density.
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 solution provides printed circuit boards with improved mechanical stiffness, thermal stability, reduced insertion loss, and lower CTE, making them suitable for high-speed and high-frequency applications with reduced feature sizes and improved reliability.
Implementation Method 1
The non-woven, inorganic fabric reinforcement may be impregnated with a crosslinked thermosetting polymer resin
Data Source
AI summary
Dielectric materials including non-woven inorganic fabrics impregnated with a low-density resin are disclosed. The dielectric materials may have a thickness in a range of about 5 to about 125 microns for use in printed circuit boards.