Back-Spill Barrier for Shielded PCB Modules
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Solution Overview
Problem
Conventional shielded circuit packages in electronic components face issues with electromagnetic interference (EMI) due to incomplete shielding, where the external conductive shield can short with signal pins or pads on the bottom surface, causing electrical connections and design restrictions.
Innovation Solution
A back-spill barrier is implemented around the pins or contact pads on the bottom surface of the substrate to prevent the external shield from contacting them, using electrically non-conductive dielectric materials or copper patterns, ensuring a conformal external shield without undesired electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conformal external shield is applied to cover top and sidewalls of the circuit package, then protection against external electromagnetic radiation is improved, but the shield may short to signal pins or pads on the bottom surface causing electrical connections
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the external conductive shield and the signal pins/pads on the bottom surface. This dielectric layer acts as a mediator that prevents direct electrical contact while allowing the shield to maintain its protective function, thus resolving the contradiction between EMI protection and electrical connection integrity.
Solution Approach 2:
The bottom surface structure is segmented into distinct functional zones: the signal pins/pads area and the shield contact area. By dividing the bottom surface and introducing separate functional layers (dielectric layer for insulation, conductive layer for shielding) in different segments, the design prevents unwanted electrical connections while maintaining comprehensive EMI protection.
2Object-affected harmful factors
If the external shield is formed of electrically conductive material to provide protection against external electromagnetic radiation, then shielding effectiveness is improved, but design freedom regarding placement of electronic components and size of the module is restricted
Solution Approach 1:
The shielding function is segmented into multiple independent layers: the external conductive shield for EMI protection and the bottom conductive layer for additional shielding, separated by a dielectric layer. This segmentation allows each layer to be optimized independently, maintaining shielding effectiveness while providing design flexibility for component placement and module sizing.
Solution Approach 2:
Different regions of the module are provided with different shielding qualities. The top and sidewalls receive conformal external shield coverage, while the bottom surface has selective shielding through the conductive layer positioned beneath the dielectric layer. This local differentiation of shielding quality maintains overall protection while accommodating design constraints.
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 back-spill barrier effectively prevents electrical shorts and enhances shielding within the module, maintaining design flexibility and reducing EMI errors, while maintaining protection against environmental stresses.
Implementation Method 1
external shields that cover top and sidewalls of the circuit packages, and provide protection against externally generated electromagnetic radiation
Implementation Method 2
back-spill barrier formed on the bottom of the substrate, wherein the back-spill barrier is configured to prevent the external shield from making contact with the contact pads
Data Source
AI summary
A module includes a printed circuit board (PCB) having a substrate, component pads on a top surface of the substrate, and contact pads formed on a bottom surface of the substrate. The module further includes a mold compound disposed over the PCB; an external shield disposed over a top surface of the mold compound and on side surfaces of the mold compound and the PCB, where the external shield is configured to provide shielding of at least one component connected to at least one component pad from electromagnetic radiation; and a back-spill barrier formed on the bottom of the substrate. The back-spill barrier surrounds the contact pads, and is configured to prevent the external shield from making contact with the contact pads.