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Avago Technologies of San Jose, CA, USA claims that its new WaferCap technology uses the industry’s first wafer-level chip-scale packaging (CSP) for RF devices, creating the world’s smallest RF amplifier. The VMMK-2x03 series, in a 0402-size package - more familiar as the form factor for surface-mount technology (SMT) capacitors - is currently sampling and will be generally available in Q4/2008.

Avago has previously fabricated three-quarters of a billion 0402-packaged discrete devices for its line of thin-film bulk acoustic resonator (FBAR) RF filters for cell-phone handsets by using a micro-electro-mechanical system-like (MEMS-like) wafer-level capping technique. Avago has now adapted the technique to enable RF amplifier chips to be batch packaged cost effectively using standard semiconductor processing techniques at its 6-inch GaAs wafer fab in Fort Collins, CO, USA.

To adapt the devices to the 0402 package, Avago lays down a wafer-scale gasket that isolates each chip en masse while still on the wafer, then bonds a second blank GaAs capping wafer on top, effectively encapsulating each chip.

Creating an air cavity above the chip’s circuitry (rather than a layer of traditional dielectric material) enables higher-frequency operation. Also, via-holes through each chip route all I/Os (inputs-outputs) to contacts on the backside of the GaAs device wafer. As well as removing the need for costly wire bonding, the RF transitions suffer almost no signal loss and minimal parasitic capacitance. This improves performance over conventional plastic-packaged amplifiers, where substantial parasitics from bond wires limit the operating frequency.

RF performance is also improved by direct contact between the chip and the package substrate, and because it reduces the RF signal path length and hence electrical resistance compared to typical SMT designs. It also improves heat transfer from the device to the assembly by removing the intervening package. The improved thermal condition and reduced number of bond wires greatly increase reliability.

After capping, the bonded wafers can be diced and the chips are ready to use, without a lead frame. WaferCap CSP therefore allows packaging of RF chips in a leadless 0402-size package (thinner than standard plastic packaging).

The VMMK-2x03 measures just 1mm x 0.5mm by just 0.25mm high, occupying just 10% of the board area and 5% of the volume of a standard SOT-343 package. In some cases, it can more than halve the PCB area occupied by an RF device.

Also, instead of using a flip-chip and solder-bump technique (which would invert the ground plane of chips on a PCB, interfering with the chip’s RF properties) the wafer-level CSP technique enables the chip to remain right-side-up on the PC board. The chips can then be used directly in an SMT asssembly using standard equipment to mount and solder the devices directly onto a board.

The elimination of wire bonding gives the flexibility and simplicity to fit a WaferCap packaged device using t raditional mass-production pick & place or chip shooter machines in a variety of positions in a wide range of RF architectures . The dimensions and performance levels provide a new level of design flexibility in device placement that will change the way RF designers think about wireless product designs, reckons Bryan Ingram, senior VP and general manager for Avago’s wireless semiconductors division.

With miniature package dimensions and no wire bonds, the VMMK-2x03 series’ fully matched SMT design is optimized for 500MHz to 12GHz frequencies (with potential to reach the 100GHz frequency range), suiting a variety of radio designs.

The family provides high gain, high IP3, low NF and integrated 50-ohm I/O matching networks to simplify system design. Covering five frequencies from 500MHz to 12GHz, the amplifiers can be used in many roles in a radio systems, such as mobile devices, radios, sensors and military communication applications. Their flexibility in size and high-frequency performance also suit applications such as wireline, fiber-optic, base-station, CATV, and instrumentation.

The family includes:

• VMMK-2103: a 0.5-6GHz broadband matched LNA with bypass/shutdown mode using a single control pin;
• VMMK-2203: a 1.0-10GHz broadband matched LNA with high gain of 15dB at 5GHz;
• VMMK-2303: a 0.5-6GHz low-voltage broadband matched LNA supporting 1.8-3.3V;
• VMMK-2403: a 2.0-4GHz high-linearity matched amplifier with 2.5dB NF;
• VMMK-2503: a 1.0-12GHz broadband high-linearity matched gain block with flat gain performance of up to 8GHz.

Pricing is less than $1 in volume. Avago will demonstrate the amplifiers at the 2008 MTT-S International Microwave Symposium in Atlanta, GA, USA (15-20 June).

Avago is also planning for WaferCap CSP 0402 - packaged products with higher levels of integration in the future, according to marketing manager Titus Wandinger.

See related items:

High-linearity 1W and 2W amplifiers for WiMAX and next-generation cellular networks

Avago introduces PAs for WiMAX and next-generation cellular applications

Avago launches LNAs for cellular and WiMAX base-stations

Search: Avago Technologies RF amplifier GaAs

Visit: www.avagotech.com/rf