PCB Disconnect Cavity via Plating Resist Process
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Solution Overview
Problem
The existing methods for forming recessed cavities in printed circuit boards (PCBs) face challenges such as high cost, limited supply of low flow prepreg, difficulty in controlling resin squeeze out, and increased panel distortion due to high lamination pressure, which complicates the formation of disconnect cavities required for radio frequency applications.
Innovation Solution
A plating resist process is used to form a disconnect cavity within a PCB, where the plating resist is printed on a core structure, and after lamination, depth control milling and electroless copper plating are performed, followed by stripping to create a cavity that is electrically disconnected from the PCB landing layer, allowing the use of regular flow prepreg and avoiding the need for selective copper etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If low flow prepreg is used to form recessed cavity, then resin squeeze out is controlled, but cost increases and supply is limited
Solution Approach 1:
The patent changes the flow characteristics of prepreg by applying a resist coating to the cavity area, transforming regular flow prepreg into a localized low-flow region during lamination. This allows control of resin squeeze out without using expensive low flow prepreg materials throughout the entire board.
Solution Approach 2:
The resist coating acts as an intermediary material applied to the cavity area that temporarily modifies the flow properties of prepreg resin during lamination. The resist prevents resin from entering the cavity area, enabling precise control of resin distribution without requiring special low flow prepreg.
2Ease of manufacture
If lamination accessories (release film and conformal film) are used, then cavity formation is enabled, but cost increases and panel distortion increases
Solution Approach 1:
The patent removes the need for conformal film and release film by applying resist directly to the cavity area on the copper foil. This extraction of unnecessary accessories simplifies the lamination process and reduces cost while maintaining cavity formation capability.
Solution Approach 2:
Instead of using conformal film that covers the entire panel, the resist is applied only to the specific cavity area where cavity formation is needed. This localized approach maintains the necessary cavity formation function while eliminating unnecessary materials and reducing panel distortion.
3Manufacturing precision
If high lamination pressure is applied, then low flow prepreg performs well, but panel distortion increases and flat surface is difficult to achieve
Solution Approach 1:
The resist coating changes the local flow parameters of prepreg resin in the cavity area, allowing regular flow prepreg to behave like low flow prepreg only where needed. This enables cavity formation with good quality at normal lamination pressure without the panel distortion caused by high pressure.
4Reliability
If selective copper etching is used to disconnect transmission cavity wall, then electrical disconnection is achieved, but control precision is poor
Solution Approach 1:
The resist coating is applied to the cavity area before lamination, preliminarily defining the cavity boundaries and preventing resin infiltration. This preliminary action ensures that the cavity walls are properly formed and electrically disconnected from the landing layer without requiring subsequent selective copper etching, thereby improving control 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 process eliminates the need for low flow prepreg and lamination accessories, reduces lamination pressure, and ensures a flat surface, improving board flatness, impedance control, and reliability of surface-mounted component connections, while simplifying the manufacturing process and reducing costs.
Implementation Method 1
plating resist is printed on a core structure selectively positioned within a PCB stack-up... the process steps of depth control milling, drilling and electroless copper plating are performed, followed by a plating resist stripping process to substantially remove the plating resist and all electroless copper plating to the plating resist
Implementation Method 2
the process steps of depth control milling, drilling and electroless copper plating are performed
Data Source
AI summary
A disconnect cavity is formed within a PCB, where the disconnect cavity is electrically disconnected from a PCB landing layer. The disconnect cavity is formed using a plating resist process which does not require low flow prepreg nor selective copper etching. Plating resist is printed on a core structure selectively positioned within a PCB stack-up. The volume occupied by the plating resist forms a subsequently formed disconnect cavity. After lamination of the PCB stack-up, depth control milling, drilling and electroless copper plating are performed, followed by a plating resist stripping process to substantially remove the plating resist and all electroless copper plated to the plating resist, thereby forming the disconnect cavity. In a subsequent copper plating process, without electric connectivity copper cannot be plated to the side walls and bottom surface of the disconnect cavity, resulting in the disconnect cavity wall being electrically disconnected from the PCB landing layer.