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Labyrinth RFI screening at design stage pays dividends

Tecan : 24 June, 2006  (Company News)
Increasing demand on design and development teams associated with the screening of RF and microwave circuitry has led to the development of labyrinth and lid RFI screening, a board-level multi-cavity shielding concept developed and produced by Tecan.
With electronic equipment getting smaller, operational frequencies and digital clock speeds increasing, there is more pressure on equipment designers to come up with new solutions. With its many advantages, the photo chemically machined labyrinth RFI screen meets these needs. The technique successfully resolves issues relating to EMC, cross talk, PCB real estate, overall product size, access for rework and production cost.

The need for multi-cavity screening can be fulfilled by a number of methods, some of which can be time-consuming and expensive. However, if RFI needs are considered at the outset of a design, the end result is simpler to achieve as it can be treated as just another component in the assembly process rather than a cumbersome add-on or afterthought. Thus, the labyrinth solution becomes an integral cost-efficiently produced part of the printed circuit board assembly.

During assembly, labyrinths are hand placed on to the PCB as a one-piece assembly between the electronic component pick and place operation and reflow soldering, affording a seam soldered joint all around any cavity requiring to be shielded. The lid can then be fitted following any further production processes, such as visual inspection, in-circuit testing or subsequent rework.

Prior to the development of PCM labyrinths, traditional options were either a multitude of individual shielding cans or a labyrinth milled from solid, generally in aluminium. The disadvantages of multiple cans, even if these are able to be machine placed from tape and reel, are a considerable increase in the PCB real estate, due to double tracks for the individual cans and the space required between the cans for adjacent spring finger or other lid fixings. Similarly, if the Labyrinth is machined from solid, then inevitably the walls are thicker than with a PCM labyrinth, in this case connection to the PCB is generally not as effective as the seam-soldered joint of a PCM labyrinth.

Labyrinth screening delivers a host of advantages, which include: Low-cost tooling; Fast turnaround of initial design and changes; High-quality finish; Half-Etched bend lines for easy assembly; Different metals can be processed with the same tooling; Low cost of modifications; Burr and stress free fabrications; Magnetic and other material properties unaffected; Complex designs are easy to tool; Different options can be contained on the same tooling for development trials (depending on size and complexity); High or low manufacturing quantities (from one to several thousand); and Company logos, part numbers and indents of all kinds can easily be etched-in during manufacture.

The company has brought together a number of facilities and developed proprietary processes over recent years, which are used to provide cost-effective and electronically proven labyrinth solutions. To take full advantage of these developments the company advises initial discussions with customer development teams as early as possible in the design process, preferably at the concept stage and before the final PCB layout is considered. To assist in this process it offers a complete screening enclosure process from initial concept through to volume production using its Design, Develop and Draw (3D) service, affording PCB assemblers and designers the opportunity to optimise product designs at the outset. Additionally, the company's SMT stencil division can also provide multi-level stencils, which facilitate effective application of the solder paste volumes required by labyrinths and other large components during PCB assembly.
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