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Manufacturers of electronic devices employ electromagnetic interference (EMI) and radio-frequency interference (RFI) shielding to protect sensitive digital circuits from external emissions that can impair product performance, as well as to contain the potentially harmful emissions that come from their products (see “The Dark Force Of Evil In Electronics: Electromagnetic Interference”).

But these manufacturers face critical challenges in complying with EMI/RFI shielding requirements, such as material selection and converting chosen materials into effective shielding components. To meet these challenges, many OEMs turn to outside firms who specialize in the conversion of flexible materials.

In the early stages of a project, top firms provide critical engineering support to improve product design and manufacturability. Leading converters also have the automated equipment and trained personnel necessary to perform the breadth of converting operations required in this industry.

SHIELDING BASICS
EMI/RFI shielding is required in consumer electronics such as televisions, radios, cell phones, and computers, as well as devices used in medical and aerospace applications. Shielding for these devices is provided by Faraday cages that surround components and serve as barriers to electronic emissions.

Faraday cages are made of a number of flexible materials supplied by manufacturers such as 3M, Parker Chomerics, Laird Technologies, Saint-Gobain, Permacel, and Intertape Polymer Group (see the figure). Common EMI/RFI materials include:

• Foil tapes: Relatively easy to fabricate, tapes with aluminum- and copper-foil backings eliminate the need for costly metal plating of enclosures to provide shielding properties.
• Metal-filled elastomers: These materials suit shielding applications that require gap-filling and cushioning.
• Wire mesh: Used for EMI gaskets, mesh materials handle heat better than foils but are also heavier and take up more space.

HELP FROM CONVERTERS
Converters need a comprehensive selection of flexible shielding materials provided by leading suppliers. At the outset of a project, converters with engineering teams help OEMs select materials that are best suited for a particular shielding application. Material selection by a converter is based on reference data from material suppliers and their deep experience in shielding applications.

To get an idea of the potential value of this input, consider a situation where an OEM specifies a copper EMI/RFI material as a shielding strategy. Copper provides excellent shielding properties and is heavy enough to withstand soldering for the attachment of wires. But it is also relatively expensive. In a case like this, a converter might determine that aluminum foil tape, which is much less costly than copper alternatives, will do the trick.

In other cases, a converter’s engineering team might recommend concurrent testing of more and less robust shielding options. This gives customers the option of going with the less robust (and less expensive) option if tests show that it meets the shielding requirements of the application.

At the request of a customer, a converter can arrange with the material supplier to provide EMI/RFI testing services. Sometimes, such testing might show that the customer’s original design provides inadequate shielding. When this happens, a converter’s engineers might assist by recommending a foil tape to enhance the shielding.

OTHER DESIGN SERVICES
Using well-known 2D and 3D solidmodeling software, engineers at converting firms can work with the OEM’s electronic designs and also generate their own drawings. These capabilities allow converters to help customers turn concepts into actual products and easily point out problems with proposed shielding configurations.

Sometimes, OEMs with little or no shielding experience will come up with designs that are difficult and/or expensive to manufacture in volume because of overly tight tolerances, an impractical configuration, or some other reason. With their engineering resources and manufacturing expertise, leading converters can quickly spot such problems and suggest alternative manufacturing strategies that still meet the OEM’s shielding requirements.

Also critical are quick-turnaround sampling and rapid prototyping of shielding designs at no charge to customers. This service helps OEMs develop better shielding solutions. It also gives their converting partners a chance to test the manufacturing processes required to support full-scale production.

Engineers at converting firms work with customer samples, hand sketches, or full engineering drawings to provide samples for testing and evaluation. Equipped with stateof- the-art devices such as lasers, water jets, and Zund flatbed prototyping machines, small numbers of prototypes are produced without tooling in 48 hours or less.

Many prototyping processes require several iterations to produce final designs that meet all requirements. Throughout such processes, the converter’s engineers help OEMs adjust their designs until they are satisfied with form, fit, and function.

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TURNING DESIGNS INTO PRODUCTS
Once a design is completed, converters procure the necessary materials and turn them into shielding products. Common converting processes produce slit rolls of foil tapes and die-cut parts of various shapes. In addition, some converters have advanced production machines such as lasers and water jets, which can cut intricate designs into a variety of materials.

Converters can also laminate multiple materials together to produce finished products. Leading firms are equipped with wide- and narrow-width machines that allow them to laminate a variety of materials with different adhesives. Laminating capabilities range from one-step processes to multiple-material operations incorporating final finishing such as punching and cutting. Some converters can laminate up to five individual materials together in one pass. Laminated products can include one material for EMI/RFI shielding and another that provides electrical insulation or some other necessary property.

In some applications, very close-tolerance die-cut parts and complex shielding configurations are required, such as a composite consisting of an insulator like Mylar with a die-cut shielding patch “island” placed on it. Or, a multilayer product comprising a foil, an adhesive, and a specialty liner could allow easy removal by the OEM’s pick-and-place machine during final assembly. The converter would laminate these three elements together and then die cut the lamination to produce the finished product.

When a shielding application calls for a box-shaped part, converters can provide customers with creased or scored materials. This allows OEMs to easily produce the needed shape by folding flat materials along the crease or score lines.

Leading converters also offer printing capabilities that can handle everything from basic one-color applications to intricate multicolor designs. They can print on a variety of shielding materials using both water-based and ultraviolet-cured inks.

CONCLUSION
Firms that specialize in the conversion of flexible materials can make the multifaceted task of shielding sensitive components from EMI and RFI easier. Leading converters have the in-house engineering resources to help electronics manufacturers choose the best materials and designs for shielding applications.

After procuring the raw materials from a network of leading suppliers, converters use a variety of manufacturing processes to turn them into shielding products. In many cases, converters use multiple materials and techniques to produce effective solutions for the toughest shielding problems posed by a variety of industries.

CRAIG McCLENACHAN, VP of the fabrication and assembly business, graduated from St. Lawrence University in Canton, N.Y., and holds a post-graduate degree from the University of Virginia. He has also completed the Management Development Program at Genuine Parts Company, parent company to EIS and Fabrico, as well as the leadership program at Emory University in Atlanta, Ga.