Antenna-in-Package Technology and Applications. Duixian Liu
for fabrication, and Duixian Liu did the evaluation and feedback.
In June 2005, Naoyuki Shino, Hiroshi Uchimura, and Kentaro Miyazato from the Kyocera research and development center reported the unification of antenna with a package based on laminated waveguides, coupling slots, and open cavity radiating elements in LTCC for short‐range car radar operating in the 77‐GHz band [25].
Even after all of the early attempts at integration of antennas onto or into packages, there is not yet an all‐encompassing term to describe this process. Inspired by SiP, Zhang coined the term AiP to promote the idea [26]. In early March 2006, Zhang attended the Second International Workshop on Small Antenna Technology in New York and visited the IBM Thomas J. Watson Research Center. The visit strengthened the collaboration for integrating antennas in packages and accelerated AiP development. Figure 1.6 shows images captured in the design stage and photos of fabricated AiP samples for IBM 60‐GHz SiGe transmitter and receiver dies. The AiPs for the transmitter and receiver dies measured 12.5 × 8.6 × 1.265 mm3 and 12.5 × 8 × 1.265 mm3, respectively. The transmitter AiP integrated a Yagi‐Uda antenna and the receiver AiP a novel coplanar waveguide (CPW)‐fed quasi‐cavity‐backed, guard‐ring‐directed, substrate‐material‐modulated slot antenna. The measured antenna results were promising and were recognized with the Best Paper Award in the third International Workshop on Small Antenna Technology held on 21–23 March 2007 in Cambridge, UK [27].
In August 2007, Sibeam put the first CMOS 60‐GHz phased array radio in an LTCC AiP [28]. It made board and system design much easier by containing all high‐frequency routing within the CMOS die and chip package, and enabled products in the market for wireless transmission of high‐definition video content. It is worthwhile mentioning that after Zhang's keynote address at the Antenna Systems and Short‐Range Wireless Conference 2005 held on 22–23 September in Santa Clara, California, USA, in the break Zhang enthusiastically discussed some issues about integration of antennas in LTCC with Doan, one of founders of SiBeam and pioneers in mmWave CMOS [29].
1.4 Developing the Idea into a Mainstream Technology
The success of the idea of AiP is largely due to the renewed interest in 60‐GHz radios. In 2007 a new phase of 60‐GHz radios began as the Institute of Electrical and Electronics Engineers (IEEE) initiated development of a new standard for the unlicensed 60‐GHz band and many companies started to get involved in the development of 60‐GHz radio chipsets with multiple antennas in chip packages. Since then, there have been numerous AiP designs reported by industry for applications at 60 GHz and other mmWave frequencies. Clearly, the idea of AiP has been developed into a mainstream antenna and packaging technology. The milestones in the development are described here.
The first and perhaps most important milestone was to break the boundaries between antenna and circuit fields, and to implement the design considerations for both antenna and circuit in a single design platform. It was stressed by the design strategy that the AiP should be co‐simulated with the radio frequency integrated circuit (RFIC) in a circuit simulator with compact models extracted from full‐wave electromagnetic simulations of the antenna and package for optimum results. The co‐design platform with software tools from different vendors had been built before Cadence released the RF‐SiP methodology kit in 2006 [30]. It runs the Advanced Design System from Agilent for two‐dimensional (2D) electromagnetic simulation, the High Frequency Structure Simulator (HFSS) and ePhysics from Ansoft for three‐dimensional (3D) electromagnetic simulation as well as 3D steady‐state thermal, transient thermal and linear stress analyses coupling to HFSS.
The mass production of AiP began with LTCC technology. In 2005, the non‐standard process to embed an air cavity in LTCC was developed to improve antenna performance [31] and an open cavity radiating element was created to relax LTCC fabrication tolerance. In 2008, a grid array antenna and patterned mesh ground plane were devised to enhance reliability and avoid warpage for AiP in LTCC [32]. In 2012, a paper entitled “Dual grid array antennas in a thin‐profile package for flip‐chip interconnection to highly‐integrated 60‐GHz radios” won the IEEE AP‐S Sergei A. Schelkunoff Transactions Prize Paper Award [33]. In 2013, a step‐profiled corrugated horn antenna was realized in LTCC for AiP to operate at 300 GHz [34]. High‐density interconnect (HDI) technologies were developed specifically for the low‐cost production of AiP. In 2012, Samsung developed FR4‐based HDI technology for 60‐GHz radios. Despite the relatively high loss tangent of the FR4, Samsung confirmed that unit loss was comparable with the LTCC‐based AiP at 60 GHz [35]. In 2015, Intel developed liquid crystal polymer (LCP)‐based HDI technology for 60‐GHz radios. By limiting the number of metal layers to four, with the 60‐GHz routing on the same layer as the die pads, Intel demonstrated that AiP achieved an ultra‐thin profile at 60 GHz [36]. Unlike LTCC and HDI, the embedded wafer‐level ball grid array (eWLB) technology eliminates the need for a laminate substrate and replaces it with a copper redistribution layer. It was developed by Infineon in 2006 and proved to be an alternative approach to fabricating AiP in high volume with low cost [37]. However, eWLB technology only produces a single redistribution layer (RDL), which limits the realization of antennas. To overcome this limitation, the Taiwan Semiconductor Manufacturing Company (TSMC) developed the InFO‐AIP technology in 2018, which places the feeding line in the RDL at the bottom of the package, coupled to the patch antenna on the top side of the package. As a result, InFO‐AIP yields a smaller form factor and a higher gain for 5G mmWave system applications [38]. In addition, a major concern with AiP is the risk of electromagnetic interference (EMI). In 2014, Advanced Semiconductor Engineering, Inc. (ASE) developed package‐level conformal and compartment shielding techniques with metal coating to suppress EMI [39].
Accurate characterization of AiP was first made possible with a probe‐based antenna measurement setup built by IBM in 2004 [40]. It used a ground‐signal‐ground (GSG) probe connected to one port of a vector network analyzer with a coaxial cable to feed the AiP. A special waveguide arm with a standard gain born antenna could be rotated around the AiP at a distance to ensure a far‐field condition for radiation pattern measurement. In 2009, Toshiba built a setup to measure the radiation pattern of differential AiP with a ground‐signal‐ground‐signal‐ground (GSGSG) probe [41]. In 2011, Karim et al. introduced a setup to minimize the effect of the probe radiation and to enhance the dynamic range by implementing a backside probing technique [42]. In 2012, Diane et al. demonstrated a setup to measure 3D radiation patterns [43]. In 2015, Reniers et al. developed a bended probe to reduce both the blockage and the interference due to reflections from a conventional probe [44]. In 2018, fast testing of AiP for a production line was proved feasible with over‐the‐air (OTA) contactors [45]. An OTA patch antenna was embedded into the lead backer of a production pick and place handler, which offers a unique and reliable production solution testing an AiP device with 60‐GHz RF signals both radiating out of an antenna array in the lid and connected through the ball grid array. OTA contactors have also been used for testing of 76–81‐GHz AiP automotive radar devices and are being designed for 5G applications at 28 and 39 GHz.
A large number of