With the explosive growth in wireless communications over the past 10 years, today’s high-volume manufacturing presents many difficult challenges to shielding designers. No longer are a few hand-placed grounding clips sufficient to provide the high levels of shielding required in modern cell phones. Instead, the need for automating the assembly of EMI shielding solutions is rapidly growing.
The general trend in the electronics industry is toward smaller devices, and designers must package more components into less space on the PCB. Factoring in today’s high frequencies leaves little opportunity to reduce interference by simply separating the radiating and affected devices.
At the same time, designers are pressured to hold down the cost of their products. This sometimes leads to compromises. For example, flatness tolerances on plastic phone covers sometimes are quite loose, making it difficult to design shielding so the phone meets the applicable EMC specifications. Also, the costs of shielding installation are becoming an increasingly large part of the overall manufacturing expense. Finally, the dynamic consumer market means rapid ramps in production rates as well as frequent model changes.
The Need for Automatic Assembly
To deal with these challenges, automation systems that install shielding products onto wireless packages can have a significant impact on current market success. The automation process for applying shielding follows the nature of the shielding product. For example, solderable shields such as metal cans are integrated into surface-mount technology assembly lines and mounted directly to the PCB by the original equipment manufacturer or contract electronics manufacturer.
Typically, form-in-place gaskets such as conductive silicone are dispensed onto a metallized plastic shield at an injection-molding integrator, and the automation of this process is traced back to the sealant-dispensing industry. Peel-and-stick gaskets such as soft die-cut laminates also are installed at the integrator using derivatives of label-application equipment.
Peel-and-stick gaskets have particular advantages when considered as a complete shielding solution. As opposed to being formed on-site, these products are manufactured under stringent quality control before shipping to the customer. There are no special storage or handling requirements for preformed die-cut gaskets, which helps reduce work-in-process inventory costs. The absence of toxic outgassing eliminates the need for special ventilation, and all waste is solid and easily handled for disposal.
The flexible assembly techniques range from the simplest hand fixtures for making prototypes to full lights-out automatic assembly of millions of pieces per month. In addition, the floor space and facility infrastructure requirements for the systems are minimal, making setup quick and easy at any location.
The assembly process for the peel-and-stick gaskets can be batched or fully integrated into an assembly line with few compromises. Also, there are no oven-cure cycles required.
The high throughput of the peel-and-stick gasket assembly process—greater than 300,000 parts per month at a five-days × 24-hours/day operation—allows it to be synchronized with other operations such as screw inserting. Product changeover and setup can be accomplished with simple hand tools and basic technical skills.
Example of Automatic Assembly
The wireless phone market now favors multiple outsourcing. This imposes special demands on shielding solutions. A phone manufacturer may buy essentially identical molded frames with identical EMI shields from many different molders.
As a result, it now is commonplace for the shielding automation solution to deal with product streams from dozens of dissimilar molding tools in widely differing manufacturing environments. Such a solution must be globalized without compromising throughput, quality, or reliability. The automation also must be compatible with other assembly processes since today’s integrator often adds value with secondary operations.
This means that shielding suppliers cannot just sell shielding materials but also must deliver a fully integrated solution, ready for installation at an integrator’s site, wherever that may be. But perhaps the subtlest challenge is with delivery: the company delivering the automation solution has to link seamlessly with the designers of the shielding solution to preempt production problems.
An Automatic Assembler
The optimum automation system, such as the CRESCENDO™ Installation System, is a standard element of a complete shielding solution. It can install a family of peel-and-stick EMI gaskets as well as a line of acoustic, thermal, and venting materials.
Several thousand die-cut EMI gaskets are delivered to the assembly area on each reel. The installation system can apply the product directly from the spool, using a combination of modified label-dispensing technology and vacuum tooling to separate the die-cut gaskets from the carrier web as each is needed.
The target assembly, such as a wireless phone, is positioned in a fixture on a rotating dial. After removing the gasket from the web, a vacuum chuck tamps the gasket to the assembly to activate the pressure-sensitive adhesive.
The multistation dial allows efficient hand loading, permitting the operator to work safely behind a guard during the assembly process. The spare stations on the dial are used for secondary operations or optical inspection with no loss of throughput. This concept easily adapts to linear conveyor lines or other layouts without any process compromises.
About the Author
Ashwath Nityanandan is an automation engineer for Wireless Products at W. L. Gore & Associates. He received an M.S. in controls and robotics from Clemson University and has worked in the development of special machines for several years. W. L. Gore & Associates, 750 Ott’s Chapel Rd., Newark, DE 19714, 800-445-4673, e-mail: [email protected].
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May 2001