Page 291 - System on Package_ Miniaturization of the Entire System

Radio Fr equency System-on-Package (RF SOP) 265

front-end module is the foundation of many applications identified in the beginning of
this chapter, and the integration of its many different components poses rigid challenges.
The SOC concept tries to achieve the integration of all the system components on a
single chip. Such an approach has two major limitations—cost and performance of the
RF system. The high cost is due to the high cost of digital and RF mixed-signal ICs. The
performance limitation is due to poor component properties such as low Q factor
inductors that can be achieved on silicon. The SOP concept addresses both of these. It
allows for diverse ICs, not requiring monolithic integration, and it allows for the best
component properties to be achieved, optimizing between IC and the package. In
addition it allows for miniaturization of the entire RF system. This optimization concept
between the two is illustrated in Figure 5.4, showing the best regimes for each. For
example, package integration, which does not exist in the current manufacturing of cell
phones and PDAs other than through bulky discrete components, can be achieved by
microscale thin-film embedded components such as filters, switches, antennas,
inductors, capacitors, and resistors as described later in this chapter.

5.3 Historical Evolution of RF Packaging Technologies
Historically, wireless communication systems have been on a path of ever-increasing
functionality, lower cost, and smaller size. For example, the first generation (1G) of
cellular telephony used analog modulation techniques and was only capable of voice
communications. The second generation (2G) used digital modulation technologies,
and although limited data communication rates were possible, it was primarily geared
to voice communications. The enhancements brought on by digital technologies allowed
more users to have simultaneous access, and hence a rapid adaptation followed [5]. The
evolution to the third-generation (3G) cellular standards increased the available
bandwidth for data communications, but at a substantial increase in the cost of required
infrastructure. The sales of cell phones is approaching about a billion units and given a
world population of six billion, it is expected to grow at a rate of 20 to 30 percent
annually, thus driving a substantial portion of RF component technology. Moreover,
handsets are evolving beyond the traditional voice services and are rapidly becoming
multimedia terminals with Internet access, and concurrently with “slimmer” size as is
evident from the marketing of the Motorola Razor and Samsung’s latest 11.9-mm thin
ultraslim phone. The latest cell phone that captured the imagination of the consumer
and shocked all the other manufacturers is the iPhone from Apple with the most easy-
to-use user interface.
To keep up with the above trend in miniaturization and functionality, packaging
has gone through dramatic changes in the past three decades from bulky packages to
thin-film components and devices. This historical evolution in packaging technology is
depicted in Figure 5.5. In the 1970s, the components were bulky and the device packaging
was double-sided DIP, which migrated to four-sided quad-flat package (QFP) with
interconnects in the board made of drilled holes followed by printed-through-hole
connections. The next-generation technologies began to implement surface-mount
technologies (SMT) for discrete passive and active components. The next step involved
integration of discrete components themselves into individual prepackages leading to
integrated passive devices (IPDs) that helped reduce the form factor. With the
development of multichip modules (MCMs) in the 1980s with as many as 100 to
144 chips flip-chip bonded onto a single ceramic or thin-film substrate, the package