Product category:
Electronics Manufacturing Materials and Consumables
News Release from: Tecan | Subject: Labyrinth RFI screening cans
Edited by the Electronicstalk Editorial
Team on 02 January 2001
Labyrinth RFI screening can brings RFI
benefits
A labyrinth RFI screening can is an effective one-part board-level alternative for PCB designs which would otherwise require solid metal enclosures or multiple screening cans.
A labyrinth RFI screening can has been developed as an effective one-part board level alternative for single or double-sided PCB designs where cast or milled solid metal enclosures or multiple screening cans are traditionally used Conceived by Weymouth based specialist, Tecan Components, the technique can be applied to a wide range of areas, offering many benefits, especially in microwave and telecommunications applications
This article was originally published on Electronicstalk on 24 Oct 2000 at 8.00am (UK)
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One labyrinth from a single source makes procurement easier and a less expensive, the RF design and PCB track layout can be simplified, board sizes can be reduced, assembly simplified and rework minimised.
A development case study cites a specialist microwave engineering company looking for a double-sided board level alternative to expensive cast and milled aluminium housings.
The company had already made some progress, away from the original milled metal housing, by employing a large number of small RFI cans of different sizes and profiles, mounted on both sides of a microwave application PCB, but this was far from ideal, being logistically cumbersome and labour intensive.
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For each side of the board, Tecan suggested a single labyrinth can, with separate lid, replacing the multiple can approach and providing a completely hermetically sealed and EMC sealed low-profile board-level solution.
Along the way to achieving this integrated solution, new techniques were simultaneously established for the reflow operation to ensure consistent electromechanical integrity for the solder joints.
As the labyrinth is a large metal part it retains a lot of heat in the reflow process and so tends to draw more solder than is required for the ideal joint.
To inhibit this Tecan has developed "the Plimsoll line" and a multilevel solder-paste stencil incorporating "lattice bridging" - a combinational solution.
First, a linear break in the plating is produced, horizontally all the way around the walls of the screening can, so that solder can only flow up the wall of the can to a set height - that defined by the Plimsoll line.
Solder will not wick higher than this and therefore remains where it should be - on the pad to ensure a good joint.
Furthermore, the stencil also deposits a lattice bridge across the retention gaps in the RFI screening can track, so that a full solder seam is achieved all around the can.
The multilevel solder paste stencil is important in ensuring a consistent volume of solder paste is deposited for the can tracks, lattice bridging and fine-pitch components simultaneously.
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