Dummy Core Restrict Resin Process for Rigid-Flex PCB
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Solution Overview
Problem
Current processes for manufacturing rigid-flex printed circuit boards face challenges such as high costs, limited supply of low flow prepreg, difficulty in controlling resin squeeze out, and irregular rigid-flex boundaries, leading to panel distortion and impedance control issues.
Innovation Solution
The use of a dummy core and coverlay process to protect and expose select inner core circuitry, allowing for the formation of a flexible PCB portion with a smooth and regular rigid-flex boundary, eliminating the need for low flow prepreg and lamination accessories, and enabling standard lamination pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If low flow prepreg is used to control resin squeeze out, then resin flow is reduced, but cost increases and supply is limited
Solution Approach 1:
A conformal film is introduced as an intermediary layer between the prepreg and the rigid portion. This thermoplastic film softens under lamination temperature to conform to the prepreg shape, thereby controlling resin flow into the rigid portion without requiring expensive low flow prepreg
Solution Approach 2:
The invention changes the physical state of the conformal film from solid to softened state under lamination temperature, allowing it to adapt to the prepreg contour and control resin flow dynamically during the lamination process
2Manufacturing precision
If conformal film is used to control resin flow, then resin squeeze out is reduced, but lamination pressure increases causing panel distortion
Solution Approach 1:
The conformal film acts as a flexible thermoplastic layer that softens under lamination temperature to conform to the prepreg contour. This flexibility allows it to control resin flow while distributing lamination pressure evenly, preventing panel distortion
3Manufacturing precision
If high pressure lamination is applied, then resin flow is controlled, but panel distortion increases
Solution Approach 1:
The conformal film serves as a compliant layer that softens under heat to match the prepreg contour, enabling effective resin flow control while distributing pressure uniformly across the panel to maintain flatness and prevent distortion
4Manufacturing precision
If release film and conformal film are used as lamination accessories, then resin squeeze out is controlled, but production cost increases
Solution Approach 1:
The conformal film performs multiple functions: it controls resin flow into the rigid portion, maintains panel flatness during lamination, and eliminates the need for separate release films, thereby reducing overall production costs while achieving the desired precision
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 results in a printed circuit board with a flat exterior surface, improved reliability of surface mounted components, and enhanced yield in fine line etching and soldermask imaging, while reducing production costs and panel distortion.
Implementation Method 1
a coverlay is applied over the select inner core circuitry
Implementation Method 2
a dummy core is applied over the coverlay
Implementation Method 3
The non-conductive layers can be made of prepreg or base material that is part of a core structure
Data Source
AI summary
A printed circuit board (PCB) has multiple layers, where select portions of inner layer circuitry, referred to as inner core circuitry, are covered by a coverlay material and the covered inner core circuitry is exposed from the remaining layers of the PCB. The PCB having covered inner core circuitry is formed using a dummy core plus coverlay process. The select inner core circuitry is part of an inner core. The inner core corresponding to the covered inner core circuitry forms a flexible PCB portion. The flexible PCB portion is an extension of the remaining adjacent multiple layer PCB. The remaining portion of the multiple layer PCB is rigid. The inner core is common to both the flexible PCB portion and the remaining rigid PCB portion.