CSP Technology Shrinks RF Component Size

This innovative chip-scale-packaging technology helps cut in half the amount of space occupied by RF/microwave integrated circuits and components on a printed-circuit board.

Components and integrated circuits for RF/microwave applications have traditionally been small in size, although the limit on miniaturization has often been the package. With the announcement of its unique WaferCap chipscale- packaging (CSP) technology, however, Avago Technologies (San Jose, CA) has dramatically shrunk the size of microelectronic packaging, but also the losses that such packaging can inflict on high-frequency circuits. Avago's semiconductor-based CSP technology offers IC, device, and component packages that are the same size as an 0402 component, measuring just 1.0 x 0.5 mm and with a height of only 0.25 mm. In spite of the small size, these packages sacrifice nothing in terms of electrical performance, with the potential of supporting ICs and components operating past 100 GHz.

The fundamental approach of CSP technology is to surround a component or IC device with a housing that is no more than 1.2 times the size of the component to be packaged.

CSP technology is not new with the WaferCap approach, but has been in development for years and driven by research at major semiconductor companies, including National Semiconductor (www.national.com). Avago has built upon earlier work aimed at film-bulk-acoustic-resonator (FBAR) filters and has applied it to analog and RF circuits. WaferCap packaging provides a low-loss, low-impedance signal path through the package/chip combination with significantly reduced parasitic circuit elements compared to conventional SMT packages.

Avago's semiconductor-based CSP technology promises extreme miniaturization while minimizing signal losses for a wide range of RF/microwave components. The small size of CSP components (Fig. 1) can reduce by 50 percent or more the amount of space an RF/microwave component or IC occupies on a printed-circuit board (PCB). For example, at only 0.25 mm high, the use of WaferCap parts can reduce the thickness of any assembly, allowing RF designers to change the way they think about a wide range of commercial and military high-frequency systems.

In addition, the WaferCap CSP technology contributes to lower-cost systems, since the CSP approach allows high-frequency devices to be batch packaged cost effectively using standard semiconductor processing techniques. When a CSP enclosure is added to a component or IC (Fig. 2), an air cavity is created under the "lid" of the package and over the circuit, supporting high-frequency operation through millimeter-wave frequencies. The packaging technology employs viaholes for electrical connections to a PCB, eliminating the need for costly and lossy bond wires. Because a CSP component is directly attached to the circuit traces on a PCB, the length of the RF signal path is minimized providing less parasitic resistance than typical SMT housing approaches. This close contact to the PCB also improves the transfer of heat from the device to the PCB and surrounding system. The combination of eliminating bond wires and the improved thermal dissipation helps enhance the reliability of a WaferCap device.

Because circuits with WaferCap CSP components are assembled with standard SMT methods, CSP devices can be directly soldered onto a PCB with standard soldering techniques. In addition, WaferCap components can be handled with pick-and-place machines the same way that any 0402 components are handled. This minimalization of assembly steps results in lower-cost packaged devices.

In terms of products available now with the WaferCap technology, Avago recently announced its line of VMMK- 12xx discrete field-effect transistors (FETs) in WaferCap form, and introduced the VMMK-2x03 line of RF/ microwave amplifiers, demonstrating the performance of these miniature WaferCap amplifiers during the 2008 IEEE Microwaves Theory & Techniques (MTT-S) event in Atlanta, GA this June.

The VMMK-2x03 amplifier line (see table) is fabricated with Avago's enhancement-mode GaAs pseudomorphic high-electron-mobility-transistor (E-pHEMT) technology. The packaged amplifiers measure just 1.0 x 0.5 x 0.25 mm and can be handled and placed with standard 0402 package pick-and-place assembly equipment and techniques (Fig. 3). The amplifiers are extremely simple to use, matched to 50 ohms and requiring only a DC blocking capacitor, RF choke, and single positive voltage supply for most practical applications. The VMMK-2x03 amplifiers have all input and output ports (I/Os) routed to the backside of the device through viahole connections. Because of this, RF transitions suffer minimal signal losses and parasitics, a significant improvement over conventional, low-cost plastic packages that can limit the operating frequency range.

The new VMMK-2x0 CSP amplifiers take up only 5 percent of the volume and use only 10 percent of the PCB space of an SOT-343 package. In some cases, using one of these amplifiers can reduce PCB area by more than 50 percent. As Bryan Ingram, senior vice-president and general manager for Avago Technologies' Wireless Semiconductor Division, comments, "Our new VMMK- 2x03 encapsulates the breakthrough we have achieved in chip scale packaging. We've raised the bar for miniaturization and high-frequency performance and this innovation will change the way RF designers think about wireless product development. The flexibility this product offers opens up new avenues for placement in RF designs. It's really up to the imagination of designers to determine how to best leverage the size and performance of this product."

The VMMK-2x03 family features models covering a total frequency range from 0.5 to 12.0 GHz. For example, model VMMK-2103 offers available gain of 14 dB with typical noise figure of 2.4 dB from 0.5 to 6.0 GHz (Fig. 4). It achieves a third-order intercept of +22 dBm at 3 GHz when operating from +5 VDC and 25 mA. The amplifier suffers only 5.5 dB loss when used in bypass operation (no power). The VMMK-2203 exhibits 10 dB input and output return loss. As with the other VMMK-2x03 WaferCap amplifiers, it is ideal for WiMAX and wireless-localare- network (WLAN) systems as well as military radios, radars, and electroniccountermeasure (ECM) systems.

The more broadband model VMMK-2203 WaferCap amplifier provides typical gain of 16 dB and noise figure of 2.4 dB from 1 to 10 GHz. It achieves a third-order intercept of +15 dBm at 5 GHz when operating from +5 VDC and 28 mA. As with the VMMK-2103, it exhibits input and output return loss of 10 dB. For extremely low-voltage applications, model VMMK-2303 operates from 0.5 to 6.0 GHz with a positive voltage of +1.8 VDC and only 20 mA current. It provides 13 dB small-signal gain over that range, with typical noise figure of 2.2 dB. The VMMK-2303 delivers +10 dBm output power at 1-dB compression with a third-order intercept point of +24 dBm. With its low-voltage capability, it can be powered by standard +1.8-VDC CMOS supplies or +3.3-VDC battery power.

For somewhat higher output power, particularly remarkable from a package measuring just 1.0 x 0.5 x 0.25 mm, model VMMK-2403 operates from 2 to 4 GHz with typical output power at 1-dB compression of +20 dBm and third-order intercept of +32 dBm. The WaferCap amplifier features small-signal gain of 15 dB and typical noise figure of 2.5 dB when operating from a +5-VDC, 50-mA supply.

Model VMMK-2503 is the highestfrequency unit in the WaferCap amplifier family, with a bandwidth of 1 to 12 GHz. Over that range, it provides typical gain of 14 dB with typical noise figure of 3.7 dB (Fig. 5). It delivers +17 dBm output power at 1-dB compression and achieves at third-order intercept of +28 dBm at 6 GHz when operating from +5 VDC and 60 mA. The VMMK-2503 exhibits input and output return loss of 10 dB. The miniature VMMK-2x03 series of broadband amplifiers are fully matched for 50-ohm systems and are suitable for commercial and military applications, in mobile telephones, ultrawideband (UWB), infrastructure equipment, and military radios. They are just one early example of the potential for Avago's WaferCap CSP technology and what it may yet contribute to the miniaturization of RF/microwave commercial and military circuits operating through millimeter- wave frequencies. The VMMK- 2x03 amplifiers sell for less than $1.00 (USD) each in volume quantities. Avago Technologies, 350 W. Trimble Road, Building 90, San Jose, CA 95131; (408) 435- 7400, (877) 673-9442, Internet: www.avagotechwireless.com.

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