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rlcZONE Products for the week of March 31, 2008
RF Micro Devices Says…
RFMD Introduces MicroShield Integrated RF Shielding
MicroShield Technology Featured in Polaris 3 Total Radio
RF Micro Devices, Inc., a global leader in the design and manufacture of high- performance radio systems and solutions, announced the introduction of its patent pending MicroShield Integrated RF Shielding technology. RFMD's MicroShield Integrated RF Shielding technology can eliminate the need for bulky and costly external shields by integrating RF shielding directly into the RFIC or module. In doing so, RFMD's MicroShield reduces the height and volume requirements for RF sections by up to 25% and 50%, respectively, and provides customers with components that are insensitive to board placement.
RF shielding reduces emissions related to electromagnetic interference (EMI) and radio frequency interference (RFI) and minimizes susceptibility to external fields. Traditional RF shielding is implemented with external metal "cans" that encapsulate and shield the RF section of a circuit board. However, this implementation is costly and time consuming, as the cans used for RF shielding must be customized according to individual circuit boards. Additionally, external RF shields increase the space requirements for RF sections and, more significantly, can degrade the performance of the underlying RF circuitry. This performance degradation leads to a time- consuming retuning process that is necessary to counter the effects of the external shield.
RFMD's MicroShield Integrated RF Shielding reduces the impact of EMI and RFI by minimizing exposure to external fields and preventing energy leakage into unwanted areas of the host device. Also, by eliminating sensitivity to board placement, RFMD's MicroShield eliminates the risk of circuit retuning, thereby accelerating time-to-market and reducing the cost of RF implementation.
In handset applications, sensitivity to board placement is a critical factor as handset designers and manufacturers increasingly rely upon handset platforms to satisfy their time and cost requirements. When these platforms are applied to individual handset designs, performance can suffer, with EMI and RFI emissions often prime contributors to performance inconsistencies. With RFMD's MicroShield, handset manufacturers are able to place highly complex RF modules as they would any component that is insensitive to EMI/RFI, providing a true "plug-and-play" solution that is robust to board design and layout changes.
Handset manufacturers using MicroShield enjoy the benefits of improved RF performance, lower total cost, reduced board space requirements and overall ease of RF implementation. RFMD's MicroShield Integrated RF Shielding technology is applicable to any over-molded packaging technology and is first available in RFMD's Polaris 3 Total Radio solution.
EN-Genius Says…
Metal shields have been used around RF circuits since the days of vacuum tubes. Today's bantam RF circuits are no exception, but formed shielding cans are typically smaller. They're usually stamped from thin sheet metal using high-speed stamping machines. Stamped, formed, and plated cans are, by definition, custom components. Although inexpensive to begin with, that nonetheless makes them more expensive than off-the-shelf parts. Metallic shields also add manufacturing steps, requiring physical placement and soldering.
Of course, you can resort to alternative EMI/RFI suppression techniques such as sputtering or conductive paints. As with everything in engineering, each shielding option has its own set of tradeoffs.
RF Micro Devices's MicroShield Integrated RF Shielding may change this picture. As you read on, keep in mind that it’s essentially a process step, not an off-the-shelf product per se.
Package-Level Plating
MicroShield is plating, applied at the package level. According to a paper recently published by RFMD, the plating comprises about 12 microns of multi-layer copper, topped by a flash of about two microns of nickel.
As the press release notes, RFMD MicroShield Integrated RF Shielding is initially being rolled out in the company's Polaris 3 Total RADIOmodule quad-band EDGE radio. Polaris 3 consists of the company's RF6030 single-chip CMOS radio transceiver module and SAW filters, its RF3251 transmit front-end module, and its matching RF9003 dc-to-dc switch mode power supply. Together, these modules occupy a 200-mm2 footprint.
Obviously, if RFMD can avoid expanding its module set footprint due to relatively-bulky stamped metal shielding, that is an improvement. Indeed, RFMD claims its plating shielding can save 20% to 30% of the real estate of conventionally shielded assemblies. What's more, MicroShield also reduces Z-height. MicroShield's 0.01-mm of plating, rather than the 80 mils or so of height demanded by stamped enclosures with standoffs, lowers RF circuit profiles.
Significantly, the technique is also conformal, which is a way around the need for complex-shaped stampings, and the costlier tooling for them. Re-work may be simpler, too, as there are no metal shields to unsolder before getting to devices hiding under them.
No De-Tuning
Detuning of LC circuits, especially at microwave frequencies where stray capacitance and inductance can wreak havoc, is always a design issue. But, according to Eric Creviston, president of RFMD's Cellular Handset Product Group, “MicroShield eliminates problems associated with de-tuning. It’s quite insensitive to placement. That’s a critical factor in the implementation of high-volume handsets.”
RFMD published attenuation figures also indicate that MicroShield may provide a lot more attenuation than RF cans, and it’s applicable to just about any over-molded packaging technology. Right now, MicroShield is proprietary and used only on the POLARIS 3 product. However, the process may well shape up as a viable alternative to conventional post-design shielding techniques, and its applicability may broaden.
Unfortunately, regardless of numerous telephone calls to RFMD, I could get no further details about the company’s plans for this packaging technology, nor its likely cost. Calls to company CFO Dean Priddy, and publicity manager Doug DeLieto go unanswered. Ditto a query directed to packaging engineering manager Milind Shah. If that’s any indication of RFMD customer service culture, caveat emptor.
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