Product category:
Electronics Manufacturing, Tools and Instruments
News Release from: Tecan | Subject: RFI screening
Edited by the Engineeringtalk Editorial
Team on 05 December 2000
Labyrinth screening can bring RFI
benefits
A labyrinth RFI screening can has been developed as an effective one-part board level alternative for single or double-sided PCB designs.
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 Engineeringtalk on 24 Oct 2000 at 8.00am (UK)
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Can-on-board solder migration problems solved
Tecan Components has solved a range of problems associated with automated soldering of RFI screening cans/fences onto PCBs with the introduction of the 'Plimsoll line and lattice bridging stencils'.
The benefits of fabricated labyrinth screening
Tecan Components says electronics designers are increasingly taking advantage of the cost and performance benefits of fabricated labyrinth screening solutions, as opposed to casting and milling
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 re-work 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.
Further reading
Off-the-shelf modular EMI screening system
A wide range of fast and effective EMI/RFI screening products is offered by Dorset based specialist Tecan, with solutions for prototype, development and production needs.
Cans keep interference in check
Standard-pitch screening cans for the most demanding applications are now available off-the-shelf from Tecan.
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 re-flow operation to ensure consistent electromechanical integrity for the solder joints.
Since the labyrinth is a large metal part it retains a lot of heat in the re-flow 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 multi-level solder-paste stencil incorporating 'lattice bridging' - a combinational solution.
Firstly, 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 multi-level 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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