Avago claims smallest RF amplifier package
Avago Technologies says it is producing the first chip-scale packaging for RF devices, beating off rivals with a process that bonds two GaAs wafers.
The company says that the resulting VMMK 2x03 series packages, which measure 1 mm x 0.5 mm x 0.2 mm, are also the world's smallest RF amplifiers. VMMK 2x03 products are already available as engineering samples and will on be general release in the fourth quarter of 2008.
“It s a true chip-scale package,“ Titus Wandringer, Avago s director of multi-market marketing told compoundsemiconductor.net. “It s a simple three-terminal transistor device and we build circuits around that - you re really making the package as small as you can possibly make it because it's the size of that circuit.”
Wandringer says that the “WaferCap” method involves sealing a cover wafer onto a device wafer, using a proprietary gasket seal to hold the two together. The final step is dicing of the bonded wafers, meaning the complete package can be made at Avago s Fort Collins, Colorado, 6-inch GaAs fab, without needing further assembly elsewhere.
Via holes through the GaAs wafer connect the amplifier's PHEMT to input-output contacts on the device wafer s backside. Wandringer says the composition of these backside contacts is important, as they need to accommodate solder attachment used in high-volume surface mount assembly that Avago is targeting the product at.
“Solder typically leaches gold, so that was a terrible incompatibility,” he said. “We really worked on the metallurgy - you won't be able to tell any difference between this part and any other surface mount part running through your line.”
The VMMK 2x03 series packages are currently covered with scrap GaAs wafers but Wandringer says Avago is developing alternative cover materials, such as glass, to help reduce costs.
Alongside the WaferCap package's suitability for mass manufacture, it has also been designed for use in particularly high-frequency and microwave applications. Packages containing air gaps are used to reduce undesirable parasitic capacitance and dielectric loading effects in such circuits, rather than conventional plastic packages. Thanks to its sealing process, the WaferCap method contains an air gap that Wandringer says makes it suitable for high-volume manufacture of MMICs.
WaferCap has been in development since before Avago span out of Agilent in 2005 and the company is also is using the method in RF filters. For its GaAs amplifiers, Wandringer says that the next stage is to increase the number of input-output connections, so that more complex products can use the packaging technology.