Surface-mount BGA reduces MMIC packaging cost

Priced typically at $5.50 each in large quantities, a true surface-mount microwave BGA package overcomes the high cost of packaging GaAs MMICs used in high-frequency commercial applications. The package allows array processing and is compatible with wafer and automated assembly.

To keep up with the falling prices of GaAs-based MMIC, Micro Substrates (Tempe, AZ) has developed a low-cost leadless ceramic package in a true surface-mount configuration. Called the Via/Pak ball grid array (VBGA), the chip-scale microwave package costs well under $10 in high production quantities, far less than conventional microstrip and stripline packages.

Developed specifically for commercial wireless applications such as point-to-point radio, local multichannel distribution systems, ground terminals, and active-array antennas, the VBGA is suited for high-frequency MMICs operating at frequencies from dc to 31.5 GHz. The package is manufactured using semiconductor vacuum deposition and metallization techniques to achieve the cost advantages of array processing.

Because it is a chip-scale package, the VBGA has the smallest possible footprint and offers a known-good MMIC die for multichip modules and other packages. The package allows assembly at the wafer level and is compatible with automatic pick-and-place equipment. It is suited for both wirebond and flip-chip.

The package's base material is Via/Plane, a single-layer, ceramic interconnect substrate with tungsten-copper solid vias for good heat dissipation. One set of wirebonds is used to connect the MMIC to the package, while copper-silver eutectic balls connect the package to the system's pc board. A typical VBGA package accommodates a 2 x 2-mm MMIC and has three RF and five dc ports (see photo ).

The VBGA package from Micro Substrates provides a low-cost
surface-mount ceramic package for MMICs operating over the dc to 31.5-GHz range.

Compared to the VBGA, microstrip and stripline packages not only cost more, but are more cumbersome to assemble onto pc boards. They require two sets of wirebonds –one to connect the device to the package and the other to connect the package to the board. Their leads take up at least 30% more space on the pc board over the package footprint. The microstrip and microline packages are also incompatible with wafer-level and automated assembly equipment.

Specifications for the VBGA package include a return loss of ­15 dB or better, an insertion loss of less than 0.5 dB per port, a thermal conductivity of 200 W/mK, and a thermal shock rating to MIL-STD-883. The package can be customized for single or multiple MMIC modules.

A 0.25-in.-sq.single MMIC package costs about $5.50 each in lots of 100,000, with samples available from stock. NRE and tooling costs for customizing the package to a specific MMIC run about $5,000. For more, contact Ram Panicker of Micro Substrates at 602-731-6230.