In engineering school, I learned that different laws of physics apply when the widely used electricity with 50/60 Hertz gets into the Gigahertz or even Terahertz range. In the decades since, I have managed to keep a safe distance to this challenging world of radio frequencies (RF) needed for transmitting data wirelessly. With Antenna in Package (AiP) becoming an important topic for advanced packaging, my luck ran finally out. I now find myself studying again RF physics: Insertion loss, modulators, mixers, S-parameter models, impedance matching, attenuators, types and characteristics of filters, etc. – so I can better understand the challenges as well as benefits of AiP for higher levels of integration.
The Evolution Toward Antenna in Package
At the June 17 MEPTEC & iMAPS webinar, Chris Barratt, the co-founder and CTO at Insight SiP, located in Southern France, described their evolution towards AiP (Figure 1). He demonstrated his many years of RF experience, outlined the strengths of the Insight SiP team – pictured above – and explained how easy their FCC approved modules make it to transmit data wirelessly. As a backbone of his presentation and example for their products, Barratt used one of their RF modules, the ISP4520. It’s designed for Bluetooth Low Energy (BLE) and Long Range (LoRa) signaling. The integrated antenna supports 2.4 GHz for BLE, 915 MHz for LoRa and is small enough to fit into the 9.8 x 7.2 x 1.7 mm package.
Benefits of Using RF modules with Integrated Antennas
As Figure 1 shows, modules with integrated antennas reduce a system’s form factor significantly. The shorter interconnections and lower drive I/Os in a module reduces power consumption and extend battery life. Modules with integrated antennas, like the one discussed here, also enable system design experts to quickly incorporate wireless signaling into their systems – reducing system design time and risk. Depending on the country and regulatory agency (e.g. FCC in the U.S.), every radio has to pass a more or less stringent certification process, before the entire system can be operated in their region. RF modules are either fully or mostly pre-certified and eliminate or minimize such time-consuming and costly certification efforts. Last, but not least, modules reduce the number of components on a system’s bill of materials (BOM), simplifying supply, and inventory challenges.
ISP 4520 Block diagram
Figure 2 shows a block diagram with the functions inside baseband SoC and RF transceiver. In addition to the two packaged and fully tested ICs, this figure also shows that a significant number of other parts are needed to complete the module. In response to a question from the audience, Barratt emphasized that he prefers to use fully packaged ICs in a module, because exhaustive testing of bare dice, especially if they contain RF functions, is not (yet) sophisticated enough.
RF Module Design and Verification Flow
Barrett first described the schematic to the layout design process, then extraction and the verification steps. His team uses Altium Designer, Cadence’ Allegro SiP, or Expedition, from Mentor, a Siemens Business, for the design steps. For 3D parasitic extraction, they use Ansys’ HFSS, CST Studio, or ADS’ FEM. They create n-port S-parameter models and feed them, together with the annotated schematics and the models of baseband SoC and RF transceiver, into the Keysight ADS simulator. Then Barrett’s team simulates accurately the interactions between the two ICs, the passive components, the antenna as well as the impact of substrate characteristics on the RF signals. Insight SiP typically uses BT as substrate material. Barrett emphasized: Since using Electronic Design Automation (EDA) tools extensively, they can optimize and verify designs much faster, easier, and more accurately than with traditional prototyping. Also, EDA tools enable them to consider component tolerances, materials characteristics as well as manufacturing variations, to improve manufacturing yields, and performance of their products.
Antenna Integration Challenges
The wavelength of a 915 MHz LoRa signal is 32 cm and a quarter of the wavelength (minimum length the antenna should have) is 8 cm. A 2.4Ghz Bluetooth signal has a wavelength of 12 cm and a ¼ wave is 3cm. Considering that the entire module is less than 1 cm long, it takes RF expertise to “extend electrically” the length of an integrated, in this case, dual-purpose antenna, to meet signal transmission and reception criteria. Figure 3 gives a hint of how extending the length of an antenna works, to fit it into a small package. It also shows the keep-out zone required near an antenna.
Barrett’s presentation gave a perfect example of the benefits of higher levels of integration. While combining packaged ICs in a module is widely used today, Insight SiP’s extensive use of EDA tools surprised me. Their reasons for not using bare dice confirm what I heard from other designers: Wafer-probe needs to improve further! In addition, SoC dice designers need to include more probe pads, loop-back circuitry, built-in self-test (BIST), and even redundant circuitry, to make it easier for manufacturers to achieve high yielding multi-die ICs.
The value of the Internet of Things (IoT) depends significantly on the amount of data the low-power IoT edge nodes can capture and transmit to the cloud, using BLE, WiFi, LoRa, 5G or other standards. As the use of 5G is taking off in mobile phones, RF experts tell me that multiple RF modules, with AiP, will be needed per phone. Phase 1 of 5G deployment, using sub 6 GHz signaling, is ongoing and doesn’t require many changes to the RF modules. However, phase 2 uses Millimeter-wave signaling, will demand big changes, e.g. accurate data about existing materials characteristics at 60+ GHz and new materials that minimize insertion loss at such frequencies.
What MEPTEC & iMAPS Offer Now and Next
If you want to learn more about Barrett’s presentation, you can download his slides and/or listen to the entire presentation, as well as many previous webcasts, here.
On July 1, Stephen M. Rothrock from ATREG will address the U.S. – China trade war. Register here.
On July 15, Jan Vardaman will give her annual IC Packaging update
For Sept 16 the Known-good-die (KGD) workshop is planned. See more about it here. ~Herb