Passive Integration - Seminar Report

 Passive Integration

Miniaturization has been a key contributor to advances in electronic technology. Many electronics applications have serious space considerations that are pressuring manufacturers to reduce component size. Much of the motivation for this Certainly, miniaturization has been made possible mostly through remarkable breakthroughs in reducing the size of active components. But as integrated circuits get smaller and more complex, there is an increasing need to also reduce the space required for the supporting passive components.
     Passive integration suggests that if the passives were so small and flat, then they could be inserted between layers of the circuit board itself, rather than taking space on top of it. The integrated passives would be a part of the circuit board itself, formed when the board was, so odds are good that their overall cost could eventually be less than what manufacturers pay today to buy and solder on discrete devices. Advantages of this technology point to a potentially huge shift for the electronics industry. Passive component integration is and will continue to be an important contribution in the development of electronic technology.


Miniaturization has been a key contributor to advances in electronic technology. Certainly, miniaturization has been made possible mostly through remarkable breakthroughs in reducing the size of active components. But as integrated circuits get smaller and more complex, there is an increasing need to also reduce the space required for the supporting passive components. If any of the electronic devices such as cellphone, camcorder, computer, or other consumer electronics system is opened, one or two circuit boards on which are mounted a few integrated circuits and dozens and dozens of tiny discrete devices-resistors, capacitors, inductors etc can be seen. It is those so-called passive devices that dominate the board’s real estate.
Passive integration suggests that if the passives were so small and flat, then they could be inserted between layers of the circuit board itself, rather than taking space on top of it. The electronic devices could be thinner and sleeker than they are today, or they could contain more electronics, or if it is a phone can have much larger batteries and therefore longer talk time and brighter color screens. The  same goes for almost every device from PDAs to portable DVD players.

The integrated passives would be a part of the circuit board itself, formed when the board was, so odds are good that their overall cost could eventually be less than what manufacturers pay today to buy and solder on discrete devices. Speaking of solder, eliminating it is another advantage of integration, because bad solder joints are one of the most common reasons electronic gear fails. Less solder also means less harm from lead waste.
Advantages like these point to a potentially huge shift for the electronics industry. Over a trillion passive components were bonded to boards last year, according to the National Electronics Manufacturing Initiative's road map. These devices are minuscule, and that makes putting them in place a chore. The smallest discrete passives today measure 0.50 mm by 0.25 mm; spread on a sheet of paper, they'd look like ground pepper. Such compact components are difficult to handle and attach, even for automated assembly equipment. And though the total cost of each part—including capital, assembly, and the prorated cost of the underlying board—is less than two cents on average, collectively the impact of integrated passives on system cost, reliability, and, most of all, size, could be enormous.
In a sense, the situation with passive components today is a lot like that of active devices 40 years ago, when Intel, Fairchild, and others had just introduced ICs that combined active devices like transistors and diodes on a single substrate. But don't expect Moore's Law to apply to passives. These components cannot be scaled down into the submicron realm occupied by active devices. The reason, of course, is that passive components have to handle signals whose amplitude cannot be reduced arbitrarily—say, microwave signals going to a cellphone antenna or inputs for analog-to-digital conversion. Despite this fundamental limit, passive integration will make for much more miniaturization.


     Passive components refer to such kind of electrical components that cannot generate power. Typical components are resistors, capacitors and inductors. The primary functions of passive components are to manage buses, bias, decouple Ics, by-pass, filter, tune, convert, and sense and protect. It is a huge, multi-billion business, supporting the various electronic products in automotive, telecommunications, computer and consumer industries, both for digital and analog-digital applications. There are a large number of passive components that are used in consumer electronic products such as VCRs, camcorders, television tuners, and other communication devices. Most of the passive components nowadays are discrete surface mount passive components that directly mount on the surface of the printed circuit board. It is called as discrete passive component-a singular component enclosed in a single case that must be mounted to an interconnecting substrate. Passive components are commonly referred to as “glue components” since they “glue” integrated circuits together to make the system.

Surface mount technology was starting to take deep root in our industry in early 80’s and is fully developed till today. In the early days, surface mount components were many times more expensive than through hole components and new surface mount assembly equipment costs were off the charts. As time went on, the cost of the components, assembly equipment and all of the other infrastructure came down, today it is less expensive to build a surface mount assembly than a through hole assembly. However, the faster bus speeds required new technology. PCB traces have always had transmission line characteristics and are more sensitive at subnano-second rise times. The package lead inductance and line capacitance have greater impact on signal integrity. The integrated circuit industry is achieving faster speeds by shrinking technology; it follows that the passive solution must also shrink. In addition to these, the need to drive out every cent of costs, miniaturization, improved product reliability and the passive to active ratios have caused to seriously consider much higher levels of passive integration than in the past. Then comes the idea of integral passives.

Integral passives are noted as passive components embedded within or on the surface of a substrate. These are distinguished from discrete chips and also from integrated(multiple passive functionality within a single package).It is a part of the printed circuit board using some type of material to make resistors, capacitors or inductors. The requirement for integral resistors, capacitors and inductors are:

       A primary requirement for integral resistors is that they be size competitive with the chip resistor. It dictates that the largest dimension be of the order of 1.0mm.Cost considerations dictate that trimming should not be required to obtain a 5%-10%  tolerance. The range of values used,from one ohm to one mega-ohm dictates that if that  range was implemented there would be insufficient numbers in the tails of the value distribution to justify integrating the full range.

       Discrete capacitors are used in larger number and greater density than any other discrete passive component. There are atleast two distinct application potentials for integration, one in which the polymer or ceramic board itself provides dielectric and capacitor plates within the interconnection; and the second, wherein progressively higher dielectric constant materials make increasingly larger capacitance feasible. There is a possibility to eliminate about 40% of the discrete capacitors in a hand held product by simply designing low value capacitors into one or more of the two level interconnection patterns normally used.

    Inductors are currently used in such low quantities,that the equivalent per part cost will probably be too high to incorporate any special processes or materials. High values are best attained with conventional discrete parts.However,about 80% of the inductors used in a hand held product are low enough in value, that they can be incorporated directly into wiring of a suitable substrate.They require fine line capability small vias and thin dielectrics.Careful attention to design will be necessary due to coupling to nearby metal..

Integrated passive components (RC circuits) and passive component arrays (MLC capacitors, MLV transient suppressors, and thick-film resistors) used in medical electronics


The technologies  available for the  packaging of microelectronics at that time were generally thick film and thin film circuits hermetically sealed in a package made of ceramic or metal with glass to metal feed-throughs. The need for a package, interconnect board plus discrete components complicated the assembly of the hybrid microcircuit and increased volume and weight requirement.A new technology that could integrate these three functions would dramatically reduce size and assembly complexity with concurrent improvements in cost and reliability.
None of then existing technologies were suitable for all three functions. The cofired ceramic could provide a durable hermetic package but was limited to refractory metal systems due to the high firing temperatures. There are several disadvantages: high trace resistances, a requirement of plating for all exposed metal to provide for corrosion resistance and subsequent metallurgical connections, and firing in a reducing atmosphere which limited the range of cofirable film components which could be included.
Thick and thin films use gold, silver or copper metallurgy which  have excellent conductivity and do not require plating  while being, except for copper. Thick films, however, were not in general dense or strong enough for use in building hermetic packages  and were  expensive when used for high count multiplayer interconnect structures.
Low Temperature Cofired Ceramics(LTTC) was seen as a potential  solution for achieving a new integrated packaging technology from a combination  of thick film and low temperature cofired dielectrics .LTTC has many advantages such as it allows high density of lines throughout the part, be able to construct  various geometries of interconnects  by layer cut outs, good heat transfer ability, etc. In addition to offering competitive capabilities in packaging and interconnection, LTTC has a clear advantage over other technologies in the area of  integral passive components. They are
·        Reduction in the number of contacts and transitions:  traditional assembly has the internal contacts of the components themselves, the transition to the attachment material  and  then to the interconnect. By integrating these transitions, the associated losses are reduced dramatically.
·        Increasing reliability : Failures occur primarily at transitions or interfaces between materials. Reducing the number of transitions increase the reliability.
·        Cost saving : Few additional steps are required for component integration  and a large number of assembly steps are eliminated.
·        Density saving : Component size and component count are the typical drivers for assembly size. The same components can be effectively spread ”two dimensionally” within the package substrate or the package itself in traditionally unused or waste  area.
·        LTTC provides wider components value range compare to other technologies.0.1W to 10 MW for resistors under the tolerance of 25%, 4pF to 0.04mF for capacitors with the typical tolerance  from 5 to 10%, 15nH to over three order of magnitude inductors with the tolerance around 5%.
Integrated passive technologies are not exactly new. They have been used for decades in the ceramic substrates that underlie circuits in military, microwave, and mainframe computer systems. But those represent a specialty within the electronics market. The vast majority of circuit boards today are made using FR4, the ubiquitous green epoxy insulator reinforced with glass fiber. FR4 boards are formed by sandwiching alternating layers of insulator with etched copper circuit traces and laminating them under heat and pressure. Drilled  holes, or vias, plated with copper, connect conductor segments on different layers to form circuit interconnects.
A smaller but growing portion of the circuit board market has been going to "flex," which are laminated stacks of unreinforced polyimide (Kapton), polyester, or layers of other polymer film, each 25 to 125 µm thick, with copper traces on one or both sides. Because the polymer layers can be thinner, enabling smaller vias, flex allows more interconnects to be crammed into a given area than is possible with FR4. But flex costs more per square centimeter than FR4.
In both FR4 and flex, the presence of organic material limits their processing temperatures to about 250 °C, far below the 800 to 1200 °C used in processing ceramic substrates. So to put passives within the layers of FR4 and flex boards, engineers had to come up with new techniques.
The components in these boards can be no thicker than a single layer of the board, maybe only a few micrometers. So for all intents and purposes, the devices are planar rather than three-dimensional. Manufacturers are using several different techniques, including sputtering, plating, chemical vapor deposition, screen-printing, and anodization, to deposit various film materials to produce the passives. All of those deposition methods are compatible with the 250 °C limit for FR4 and flex. Depending on the process, technicians can add material just where it is needed, or cover an entire board layer with it and then subtract material where it is not wanted.
The average value of cellphone capacitors is typically 1 to 10 nanofarads and there can be hundreds of capacitors in each board; a manufacturer would have to pack hundreds or even thousands of nanofarads of capacitance into the board. For contrast, most current products for making integrated capacitors are limited to polymer-based low-capacitance density materials good for only about 5 nF/cm2. A new company, Xanodics  is commercializing a capacitor process,
called Stealth, that is based on tantalum (common in cellphone capacitors).. We anodize it at room temperature to create tantalum pentoxide in a solution that is benign to the board and its copper conductors. This forms devices with capacitance to be sure that the integration would reduce the board's size. DuPont and others are developing processes that should yield over 100 nF/cm2, a value good enough to replace many of a cellphone's surface-mounted capacitors with integrated ones.

Size matters
            Integrating passives can drastically reduce the size of an ordinary circuit board.Here, four capacitors and six resistors have been removed from the surface and put into an extra layer of circuit board [bottom]. Resistors are copper connection points bridged by a resistive film, and capacitors are conductive plates separated by a thin film of dielectric material.
After the board is laminated, holes are drilled and plated to form vias that connect the integrated components to other board wiring. An integrated one can replace not every value of passive; two remain on the surface. Some commercial processes would require separate capacitor and resistor layers.
In contrast to capacitors, integrated inductors are a snap to fabricate. They are nothing but spirals of interconnect metal. The challenge is not in the materials or process technology but in their design. The main problem is that any nearby metallic structures, such as interconnects or other inductors, will interfere with their magnetic fields and change their performance. The dielectric material is FR4 and the conductor material is Aluminium. At low frequency, the reactive inductance is smaller than the series resistance, therefore, the resistance dominates the impedence. The resonant frequency is determined by the parasitic capacitance of the inductors.
            Inductors are angled away from each other to avoid crosstalk in this low-pass filter that fits between the layers of a circuit board. Designed by one of the authors, and built by Integral Wave Technologies for NASA's Langley Research Center, the thickest part of this filter is less than 6 µm. Capacitors are made from a thin-film oxide, inductors from copper.

Just as the early time of the surface mount components,integrated passive components is a fairly new technology and there are several inhibitors keep embedded passives from reaching their market potential.
There are three main barriers to bringing integrated passives into the market: too few design tools, inadequate computer models for predicting costs, and insufficient infrastructure. Better design tools are crucial because taking passives off the surface of a board and burying them generally means that more board layers are required, complicating circuit trace routing. A few design tools can take this complication into account when producing automated layouts; a couple is just now becoming available from Zuken Inc. and Ohmega Technologies Inc.
The lack of software to analyze costs is also a problem. Before board fabricators will get into the business of manufacturing passive components, they will want to have a pretty good idea of how it would affect their bottom lines. And cost calculations are tricky: unlike discrete, integrated  passives cannot be sorted for yield and value precision; one bad component may scrap the entire board. And although most analyses suggest that passive integration can save money, the analyses are very application-specific. For instance, while there is probably a cost advantage to integrating cell phones and other small devices having a high density of components, it may not be cheaper to integrate larger boards, such as those in desktop computers, where size is not a concern. Complicating matters is the fact that the surface-mount world is not standing still; discrete components are getting smaller, cheaper, and more closely packed every year.
The blem of infrastructure is the usual chicken-and-egg story. When plotted against time, technology adoption typically takes the form of an S curve, meaning prothat little happens at first but eventually everyone gets on board.We are at the bottom of the curve now, but there is evidence that adoption is increasing. About a dozen products for integrating capacitors are on the market now, which is double the number a year ago. Still, board manufacturers may be squeamish until there are enough vendors in the business to guarantee a second source for their materials and processes should their first choice fail.
The other inhibitors are:
·        Need to demonstrate the technical viability of integral substrates,including materials,processes,design and test system.
·        Need to demonstrate the value or economic justification for substituting discrete capacitor and resistors with integral technology.
·        Potential delay to the product development cycle. These passives are usually designed in the final stages of a product.The economic impact of a product delay could easily out way any cost saving in size reduction or conversion costs.
·        Integral passives reduce engineering and manufacturing flexibility.The ability to apply engineering changes to an integral substrate without delaying the schedule is critical.
·        Qualification-most of the processes, materials, vendors and products in this space are not qualified.
·        Lack of availability from multiple suppliers.
·        Industry standards are required to capture the true market potential for this technology.

Decoupling may be considered as a killer application of integrated passives. Decoupling is used in high-frequency digital logic circuits, such as in the motherboards of laptop computers. These circuits place severe demands on power-distribution systems to supply stable, noise-free power during the clock-driven simultaneous switching of millions of transistor gates.
Decoupling capacitors help supply these large current surges, ramping as fast as 500 A/ns, to high-power microprocessor and logic ICs during the switching portions of clock cycles. This technique ensures that the logic voltage levels do not drop unacceptably as a result of the high current demands on the power supply, which may be many centimeters away and connected by unavoidably resistive and inductive conductor planes.Between cycles of current demand, the power-distribution system recharges these capacitors in preparation for the next switching cycle. With ever-increasing clock speeds, decreasing power supply voltage, and increasing current demand, designers are finding it harder and harder to supply low-impedance, noise-free power to ICs. The main problem is that decoupling capacitors can't deliver charge quickly, because of their intrinsic inductance.
Decoupling is an obvious first application for integrated capacitors for two reasons: they won't take up valuable real estate near the power-hungry microprocessor, and their electrical performance is superior in this application by virtue of their extremely low parasitic inductance. Especially on digital circuit boards, surface-mounted capacitors surround the big ICs, often on both sides of the board. Since the speed of the system is often limited by memory access times, eliminating the capacitors from the surface and moving memory closer to the microprocessors would result in a smaller and faster system.
Though special discrete capacitors are being built with fairly low inductance, none of them can compare with an integrated parallel-plate capacitor using a thin dielectric located between the power and ground planes (conductor coated layers of the board dedicated to either the ground or power supply). For example, thin-film devices that we built on flex at the University of Arkansas (Fayetteville) and Xanodics deliver several hundred nanofarads with less than 3 picohenrys of inductance and a trifling 10 milliohms of resistance. In comparison, a typical surface-mounted capacitor would have several hundred picohenrys of inductance. Integrated decoupling will likely first appear not in the circuit board itself, but in the small piece of substrate included in the so called ball-grid-array packaging of high-performance microprocessors.Putting the capacitance layer within the package avoids the intervening inductance of the package-to-board connection.


Before true integrated passives take hold, widespread use of passive arrays can be seen, in which multiple similar components (capacitors, say) are formed on the surface of a substrate and packaged into a single surface mounted device like an IC. We'll also see more passive networks, which combine different kinds of passives in one package. These networks include devices internally connected to form simple circuits such as filters, terminators, or voltage dividers. In either case, one mounting operation replaces many and the overall footprint of the circuit is much smaller. These arrays and networks are a middle ground—not fully discrete but not fully integrated within a circuit board. They bring some of the advantages of full integration such as a reduced number of placement operations, fewer solder joints, and less board space. Many configurations of arrays and networks are now available in quantity from California Micro Devices, AVX, and other companies, and custom arrangements are also possible. Devices from these companies are typically fabricated on a silicon or other substrate using tried-and-true chip-making processes so the yields are high and the prices reasonable.
The technique raises some interesting possibilities. If ICs or other active devices are mounted atop a passive network, they may form so-called functional modules, such as Bluetooth or GPS subsystems. For example, a GPS module would include passives and antennas integrated on a substrate and one or more ICs bound to it, all in a single chip-scale package. The manufacturer would not have to worry about learning to design and manufacture GPS systems and could also easily upgrade or switch vendors.


            Less than 5 percent of the trillion-plus passive devices mounted on FR4 and flex boards this year will be surface-mounted passive arrays and passive networks, and hardly any passives will be fully integrated into the circuit board.
The circuit board business, in the United States, at least, is largely a contract industry, with much of it removed from the designers of circuits and equipment makers. This gulf makes board makers a bit conservative and slow to change relative to, say, the chip industry, where all aspects of development, design, and manufacture are often in the same company. Still, integrated resistor and capacitor layers are starting to become available from reputable suppliers and a few consumer products are showing up with at least some of the passives integrated, and these should lead the way for significant market penetration in the near future. It is hard to say when, if ever, will more than half the passives be integrated. The microelectronics industry is full of cautionary tales. But some new manufacturing technologies do prove their economic viability and become industry standards, such as surface mounting.
Whether or not passive integration becomes an industry standard will depend on its economic viability. Certainly, it is viable for decoupling and, in fact, may be the only way to handle the future generations of high-power, high-frequency microprocessors. For discrete replacement in general, though, the best processes and materials are still being identified. If we find suitable technologies, then passive integration will probably show a long, steady climb in use the way surface mounting supplanted through-hole mounting in the 1980s. As the infrastructure, supply chain, and industry acceptance grow simultaneously, eventually integration will gain some significant fraction of the total market and put passives in their place: hidden, ubiquitous, and cheap.

The need for increased product miniaturization and increased product function will eventually drive the electronic product to increase their use of integral passive components.Embedded passives offer increased component density beyond the physical capability of discrete-like devices.They also offer high product reliability and eventually lower overall system costs via decreased conversion costs.
Although severely lagging behind developments in active components, passive component integration is allowing the development of an assortment of new product offerings. Some of these items have been possible for several years, but lack of widespread customer acceptance and high costs have slowed their introduction into the general marketplace. Some items are yet to be developed. For example, because several manufacturers can perform both thick- and thin-film manufacturing, hybrid components combining both technologies may be forthcoming. Passive component integration is and will continue to be an important contribution in the development of increasingly smaller medical electronics.
Resistors, inductors, and capacitors are disappearing from view, integrated into the circuit board itself. Passive integration may be the only way to handle the future generations of high-power, high-frequency microprocessors.

No comments:

Post a Comment

leave your opinion