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Next-Generation E-band WLCSP MMICs Enabling Assembly Cost Reduction

The product supports mass communication infrastructures such as mobile phones.

Product data

What is the MMIC?

MMIC is an abbreviation for Monolithic Microwave Integrated Circuit. It integrates plural elements such as transistors and diodes on a semiconductor substrate. This circuit is mounted on a signal amplifier of electronic apparatus including mobile communication devices.
As 4G/LTE*1 smartphones spread rapidly, the capacity demands of the backbone network keeps increasing. Millimeter wave band (E-band) wireless backhaul link is recognized as not only a cost effective solution but also a relatively robust infrastructure in case of potential damage. Wireless communication devices supporting such communication have caused a problem of large increase in mounting cost for telecommunication equipment manufacturers because of precise packaging that MMIC requires.

*1
Long Term Evolution (LTE): A standard of mobile communications

What is the Main Feature of Our MMIC?

The newly developed E-Band MMIC applies wafer level chip scale package (WLCSP) with surface mount technology (SMT). Bonding wire free assembly process enables performance improvement of the circuit as well as reduction in mounting space by a factor of one-third. Downsizing the amplifier contributes to a large cost reduction. The products are already employed in major telecommunication equipment manufacturers since their volume production started in October 2014.

Interview with engineer in charge
Miki Kubota
Electron Device Development Department,
Sumitomo Electric Device Innovations, Inc.
Miki Kubota

What motivated you to develop MMIC?

An MMIC is used in a very high frequency millimeter waveband. Conventionally, wire bonding technique*2 was generally used for wiring MMICs. However, misalignment of a wire by only 50 μm (1 μm = 0.001 millimeter) degraded greatly the performance of the MMIC. A lot of time was consumed to realize the originally intended performance and this increased surface mount cost. To reduce the cost, we came up with an idea of applying a solder mounting technique for producing millimeter band MMICs. A solder mounting technique, which can connect electronic parts in a short period of time, had been widely used for producing general electronic devices. We began to develop a new millimeter band MMIC by applying a solder mounting technique ahead of our competitors with the belief that the new MMIC would become an innovative product that upsets the conventional wisdom in the electronics industry.

What were the difficulties in developing MMIC?

The biggest challenge was how to assure the quality of the new MMICs by preventing performance degradation after they are assembled into electronic devices. Regarding the quality, solder penetrated into the joint between the devices and substrate, and significantly degraded the performance. The development project team members worked together to successfully prevent the penetration of solder through repetitive trial and error processes. Performance-wise, solder itself dramatically degraded the performance. To minimize the degradation of performance, we carried out an accurate simulation analysis of solder joints. As a result, we succeeded in determining a circuit structure that can minimize the degradation of new MMICs’ performance. This new technique is expected to play an important role in the development of Sumitomo Electric’s new products in the future.

*2
A technique for electrically connecting between electronic components and semiconductor substrates using wires with a diameter of several tens of micrometers.

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