RF and Microwave Microelectronics Packaging II

Electronic packaging at radio frequency (RF) and microwave frequency has become an important part of engineering development for a wide variety of products. Mobile phones, for instance, integrate processors, RF amplifiers, antennas, and passive components into a compact and robust form factor. The processors and amplifiers can dissipate significant heat, which requires proper heat transfer design. In addition, the high-speed digital signal lines, microwave transmission lines, and interconnects must be designed to maintain the integrity of the signal. The antennas in mobile phones are often integrated into the case or circuit boards and radiate not only away from the phone but also into the phone circuits. This means that sensitive circuits in the phone must be designed to minimize coupling of the phone’s wireless signals that can cause undesirable effects such as oscillations or resonances in the circuits. Passive components must be carefully chosen and implemented because their physical size is a significant fraction of a wavelength at the operating frequency. As a result, the passive components may no longer function as ideal capacitors, inductors, or resistors. Rather, they may have distributed effects that must be taken into account to achieve desired performance. For these reasons, and others, the task of electronic packaging is widely recognized as a critically important task for development of products operating at microwave and millimeter-wave frequencies.

Transmit/Receive (T/R) modules were initially developed as the key component in phased array radar systems, which allowed the antenna beam to be scanned electronically. This was an important innovation over mechanically scanned arrays since it improved reliability, decreased beam scan time, and allowed other functionality. T/R modules are now used or are planned for use in satellites, wireless backhaul communication, mobile phones, Wi-Fi, and 5G mobile communication systems. As a result, development of T/R modules is expanding and shows no signs of slowing. A key to successful T/R modules is the use of the correct electronic packaging.

In this chapter, we will consider four types of 3D transitions. Each transition type has its own challenges, but each follows the design principles of keeping the transition as compact as possible and using transmission lines as the transition element. The transitions considered here are: 1. Vertical Transitions Between Planar Transmission Lines: We will consider the microstrip to stripline transition in co-fired ceramic substrates. 2.Vertical Transitions Using Stacked Die and Through Silicon Vias: In this approach, integrated circuits are stacked on top of each other and interconnects are made between them. 3. 3D Transitions Using Connectors: Transition connectors transfer the RF signal from one layer to another layer in the packaging. The fuzz button connector and elastomeric connectors were mentioned in the previous chapter. In this chapter, the SMP connector is described. 4. Vertical Transition Using Balls or Bumps: These vertical interconnects are sued with flip chip ICs.

Antennas and electromagnetic radiation helped mankind to invent radio, TV, GPS, wireless communication, and many other advanced and convenient technologies that are taken for granted in daily life. Just for a moment, imagine the world without radiation phenomena, a world without antennas and wireless communication. It would be a world without cellphones, TVs, radios, radar and satellite communication to assist in navigating the sky and oceans, a world in the 1800s. Intentional radiation is necessary to make mobile communication possible; however, unintentional radiation is an obstacle to wireless and wired communications, destructive to electronic systems, and harmful to health.

The microwave transceiver is an important module in the communication system, it can convert the high microwave carrier frequency and a low intermediate frequency. This paper mainly studies the filter circuit of the C-band transceiver modules. We design the interdigital filter circuits and hairpin filter on the basis of microstrip technology, and conduct the simulation by means of the electromagnetic simulation software. The results show that the insertion loss and the out of band rejection conform to the requirements of the indicator, and the filter circuits meet the requirements of the system.

The compositions and technology for high-reliable low-loss HTCC technology were discussed in this chapter. Low-loss ceramic was prepared by Al₂O₃ powder and some additives, MgO, SiO₂, Cr₂O₃, MoO₃, for example. The additives were deposited on Al₂O₃ powder in liquid solution, enwrapping the surface of Al₂O₃ powder uniformly to make composite powder. The compact ceramic was prepared by two-sinter technology to ensure densification and perfect microstructure. Bending strength, phase composition, micro-morphology, and dielectric loss of the low-loss ceramic sample were measurement. The dielectric loss of the ceramic is (8.0–10.0)×10⁻⁴. Techniques of manufacturing high temperature co-fired tungsten conductor pastes were researched in this chapter, and also the effects of microstructure and distribution of tungsten powders, the content of nonmetallic in slurry, metallization combination strength, and sheet resistance of the paste were analyzed. The resistance of tungsten paste sheet is 6 mΩ/□; the metallization combination strength to alumina co-fire ceramic substrate is 54 Mpa. This tungsten slurry can be used in fine line printing of 100 μm line wide on thick film integrated circuits process. Tungsten paste was applied on insulator of microwave and millimeter wave package as conductor material connected the devices in the shell and the module out of the shell. The result of microwave test on the SMT package prepared by the high-reliable low-loss HTCC technology showed that the insert loss of single RF signal transmission channel in 8 mm frequency range was less than 0.8 dB, the return loss was larger than 10 dB and the isolation was larger than 20 dB. This research work supported the application of low-loss ceramic in microwave and millimeter-wave medium.

Currently, there are two types of CSP packaging techniques: Flip-chip CSP (FC-CSP) [1] and Wafer-level CSP packaging (WLCSP) [2, 3]. FC packaging technology has been in use for over 40 years. It was first introduced by IBM in the 1970s and was subsequently adopted by other chip makers. The main advantage of FC-CSP packaging is its small size. Although there is no definite rule for how small the package should be, a typical FC-CSP packaged device is 50–100% larger than its original die (chip) size. It is a significant improvement from the traditional wire-bonding-based (SMD and QFN) packaging technologies [4].

Transistors have been widely employed in the areas of power amplifiers and power electronics. Packaging and assembly technologies become critical to the success of such applications where high power dissipation (in the form of heat) is involved while operating the transistors. With the ever increasing output power of such applications, heat dissipated from the transistors needs to be more effectively transferred out of the package so that the junction temperature in the transistors can be maintained at a reasonable low level. This is necessary in order to prolong the life time of the transistor devices. Fig. 8.1 shows the predicted device life time versus the junction temperature for typical Si-based transistors as stress tested at 150 °C.

The superior heat dissipation characteristic of diamond reinforced metal matrix composites has started to demonstrate significant performance advantages in RF Amplifier designs especially when heat dissipation from GaN on SiC and GaN on Diamond devices is a concern. This paper outlines some of the benefits of replacing traditional heatsinks/heat spreaders such as CuW, CuMo and CMC with Diamond Copper and Diamond Aluminum in these RF Amplifier designs. Fabrication process of aluminum based diamond and SiC reinforced metal matrix composites is also reported.

Thermal management is an increasingly critical problem in today’s microelectronics industry. As power increases and size decreases, innovative materials with high thermal conductivity (TC), lightweight, and many times low coefficient of thermal expansion (CTE) are desired to solve these thermal challenges. Thermal Pyrolytic Graphite (TPG*), a unique synthetic material produced via chemical vapor deposition, consists of layers of highly oriented stacked graphene planes and exhibits excellent in-plane thermal conductivity (>1500 W/mK) and very low density (2.25 g/cm³). In order to take advantage of its superior properties for thermal management, various forms of TPG-metal composite products were developed since 1990s. TPG composite with metal encapsulation simultaneously achieves high thermal conductivity from the TPG core and mechanical integrity from the metal shell. Multiple proprietary bonding technologies enable an intimate and strong joint between TPG and dissimilar metals, including Al, Cu, Sn, WCu, MoCu, AlSiC, and AlBe. In addition, the variety of compatible metals adds new functionalities to the composite, such as platability and solderability for direct die attachment, CTE matching to semiconductor, and flexibility for off-plane connectivity. The design guidance, property, and reliability of the TPG-metal composites are reviewed in detail. Tailored TPG-metal composites, i.e., TC1050* heat spreader for board level, TMP-EX heat sink for chip level, and TMP-FX thermal strap for tight space, were developed to tackle specific thermal management challenges. Individually, their performance and application examples are discussed. Great benefits from the integrated TPG solutions are anticipated to a broad range of high power electronics applications, including RF/MW, laser, LED, power management, etc.

With the development of microelectronic processing technologies, electronic devices are constantly scaled down with better performance and lower cost. Further advance in scaling down below current 10nm is very challenging and almost approaching theoretical limit. For example, electrical resistivity of copper interconnects increases with the shrinkage of dimension due to grain-boundary and surface scattering. Electromigration and hot spot of metal interconnects would also become big problems. With the most recent development of three-dimensional (3D) integration, vertical dimension is expected to dramatically promote the integration density. Effective thermal management and heat dissipation is becoming a more and more important topic in developing high performance and reliability semiconductor devices, especially for microwave/RF microelectronics which have high power consumption and heat generation during operation. To address these issues, carbon nanotubes (CNTs) and graphene have been proposed and extensively studied as potential candidate materials for RF electronic packaging because of their ultra-high electrical conductivity, thermal conductivity and stability, resistance to electromigration, and mechanical strength. This chapter is going to present a comprehensive review of CNTs and graphene advanced materials properties, potential applications and challenges in RF microelectronic packaging.