Shield Frame with Overmolded Elastomer for Narrow RF Tracks
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Solution Overview
Problem
Traditional RF shielding approaches, such as soldered sheet metal cans and overmolded conductive elastomer methods, are inefficient in terms of space usage, especially in miniaturized designs, due to the need for significant board space and high compressive loads, which limits their applicability in communications products with tight space requirements.
Innovation Solution
A shield frame comprising a sheet metal frame overmolded with a conductive elastomer, providing compliance in the z-axis direction and stiffness in the x-axis and y-axis directions, allowing for narrower shield tracks and reduced clamping loads, thereby optimizing ground contact and space efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sheet metal cans with side by side solder tracks are used, then complete perimeter ground contact is achieved, but board space in the x-y plane is significantly increased
Solution Approach 1:
The shield frame is divided into multiple compartments separated by walls, with each compartment providing ground contact through its own solder track. This segmentation allows ground contact to be achieved in a distributed manner, reducing the total width of solder tracks required compared to traditional side-by-side cans while maintaining complete perimeter ground contact.
2Length of stationary object
If dispensed conductive elastomer beads are used, then z-height is reduced, but compressive loads become excessively high
Solution Approach 1:
The shield frame combines sheet metal walls with overmolded conductive elastomer to create a composite structure. The sheet metal provides structural strength to distribute and reduce compressive loads, while the conductive elastomer maintains electrical compliance and ground contact. This composite approach allows reduced z-height compared to traditional cans while avoiding the excessively high compressive loads that would result from using only dispensed elastomer beads.
3Reliability
If overmolded conductive elastomer is used directly over sheet metal can, then ground contact is improved, but z-space efficiency is reduced in stacked board assemblies
Solution Approach 1:
The conductive elastomer is overmolded as a thin compliant layer onto the sheet metal walls of the shield frame. This thin film approach provides the necessary electrical compliance and ground contact while minimizing the z-height occupation, thereby improving z-space efficiency in stacked board assemblies compared to traditional overmolded can approaches.
4Length of stationary object
If spacer gasket approach with plastic gasket and overmolded elastomer is used, then z-space is minimized, but track widths must be large (2 mm) requiring significant board space
Solution Approach 1:
The shield frame uses compartmentalized walls with integrated solder tracks, eliminating the need for wide spacer gaskets. Each compartment wall provides its own ground contact path, allowing narrow track widths that fit within tight board space requirements while maintaining adequate z-height minimization.
5Reliability
If traditional sheet metal cans are used, then shielding effectiveness is achieved, but space in the z-plane is increased due to sheet metal thickness and clearance gap
Solution Approach 1:
The conductive elastomer overmold forms a thin compliant shielding layer on the sheet metal walls, providing RF shielding effectiveness while minimizing the additional z-height that would be required by traditional clearance gaps between sheet metal cans and the board.
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 enables RF isolation with reduced shield track area and minimum clamping load, facilitating miniaturization and cost-effective design flexibility by allowing thinner ground runners and eliminating the need for separate solder cans and complex tooling.
Implementation Method 1
a sheet metal frame overmolded with a conductive elastomer to provide compliance in a z-axis direction and stiffness in x-axis and y-axis directions
Implementation Method 2
a sheet metal frame overmolded with a conductive elastomer to provide compliance in a z-axis direction and stiffness in x-axis and y-axis directions
Implementation Method 3
The compliant nature of the frame provides optimum ground contact with a reduced shield track area
Data Source
AI summary
A shield frame (800) is provided that allows for narrow width tracks to be used in a radio frequency (RF) shielding apparatus (900). The shield frame (800) is formed of a sheet metal frame (700) overmolded with a conductive elastomer (802) to form narrow edges (808, 810) that provide compliance in a +/−z-axis (814) directions while thicker portions of the overmolded conductive elastomer prevent buckling of the elastomer. The shield frame (800) can be sandwiched between two substrates (902, 908) of a communication device (900) having components (904) requiring RF shielding. Narrowing of the conductive elastomer overmold (802) allows ground tracks/runners (906) to be used on a substrate (902) which are narrower in width (912) than the shield frame width (702) thereby providing increased area for component placement.