Driven by portable-appliance designers' miserly space allotments for electronics, component suppliers are integrating capacitors and resistors into arrays and networks and are increasingly turning to chip-scale and ball-grid-array packaging. The advantages, aside from the obvious space savings, are assembly cost reductions as well as faster throughput.
The packaging approaches can lower the parasitic inductance, equivalent series resistance (ESR) and stray capacitance that are typically introduced through the lead frames of traditional plastic packages.
The parasitic inductance between solder bumps for an on-chip filter capacitor, for example, is 100 picohenries-about five times lower than for standard packaged filter capacitors.
Lowering the components count-even when it ratchets up the per-device cost-are part and parcel of the drive toward smaller electronic assemblies. Makers of handsets, MP3 players, digital cameras and PDAs have pushed hard over the past two years to rein in parts tallies, said Kyle Baker, vice president of marketing for California Micro Devices (Milpitas, Calif.). "There has been a realization that while discrete passives, such as resistors and capacitors, are inexpensive-oftentimes, they're priced to the hundreds of a penny-there are real costs that can add up as a result of having to procure, qualify, inventory and place the component at the manufacturing level for so many different components," Baker said.
For a high-volume manufacturer, the average placement cost is approximately a half a cent per discrete, and the number of discrete passives employed in telephone designs can range anywhere from an average of 300 passives for a very efficient GSM design to as many as 1,000 for a 3G code-division multiple-access design that combines the telephone with a digital still camera or FM receiver, according to Baker.
"From the perspective of the passive function design, the vendors' interest is skewing toward arrays," Baker said-from a device as simple as a four-pack resistor to a mixed-function device that might include perhaps four dozen passives, including resistors, capacitors and diodes, in a single package.
Going standard helps
Designers initially must invest some time to research the types of parts available for integrated arrays and networks. Ultimately, the opportunity to choose among standard integrated solutions that are proven to work well in given applications should simplify the designer's life. Instead of building a custom passives function from scratch by hand-picking discrete capacitors, resistors and diodes separately for each handset design, the engineer can simply specify a previously defined standard integrated part. That can reduce design time and product form factor, as well as parts count.
Vendors are further interested in these solutions because the approaches enable performance levels that aren't achievable with plastic packages, Baker said.
In addition to the space savings, there are total cost benefits, said Mark Obuszewski, senior marketing manager for AVX Corp. (Myrtle Beach, S.C.).
"If you compare the total price of two to four discretes vs. the cost of an array, the cost savings may not be evident. But [with an array] your pick-and-place, manufacturing and inventory costs are all reduced, resulting in a total-cost savings," he said. Obuszewski said the construction of the array might also provide slightly better inductance than a collection of discrete components.
AVX's capacitor array family includes two-element 0405 and 0508 devices and four-element 0508 and 0612 devices. The capacitors are available in X5R, X7R and NPO (COG) ceramic dielectrics for a broad range of capacitance values, down to the low-picofarad range and up to 1 microfarad, with voltage ratings from 6 volts to 16 volts for portable electronics applications. The arrays can be used in a variety of space-constrained applications but are particularly suited to cell phones, where they have found broad use, Obuszewski said.
AVX has also developed a specialty line of passive components in array packaging. The LICA family of capacitor arrays features low inductance to enable high-speed decoupling of multiple signal paths in high-frequency switching applications. To achieve the low inductance and small size, AVX uses a controlled-collapse chip connection (C4) flip-chip technology. The capacitors, available in single, double and quad configurations, offer inductance values from 15 to 120 picohenries, depending on the design.
Combining chip-scale packaging-which also lowers inductance-with a proprietary zener technology, California Micro Devices offers an EMI filter array, the CSPEMI608, with low-capacitance ESD protection for color LCD data lines in clamshell-type wireless handsets. The company says the integrated application specific integrated passive (ASIP) solution offers simplified design layout and an 89 percent board space savings compared with discrete solutions. The CSPEMI608 can also be used for filtering and ESD protection in other handset applications, such as high-speed I/O interface ports, where the cutoff frequency needs to be as high as 118 MHz.
The challenge for handset manufacturers, said the company, is to design with larger, higher-resolution color displays without affecting overall handset size.
Using the new, proprietary Centurion advanced zener process technology, the CSPEMI608 integrates eight pi filters (replacing 40 discrete resistors, capacitors and diodes) while providing a low-capacitance solution. The device offers a 15-pF output capacitance per channel, or 50 percent lower output capacitance than competing solutions, according to the company. The ESD protection diodes on each channel are specified to dissipate ESD strikes of plus/minus 15-kV contact discharge, which is greater than the maximum IEC61000-4-2, Level 4 standard requirement. The high level of attenuation-greater than 30 dB and 40 dB at 1 GHz and 3 GHz, respectively-also removes high-frequency noise while providing immunity from ESD strikes.
"What makes [the device] unique, over and above the level of integration, are the specifications," Baker said. "It not only provides IEC61000 ESD protection and effective filtering up to 6 GHz but does so with about half the capacitance level per output channel of the existing solutions for that application."
"Most ESD and filter applications designed for color LCDs tend to use zener diode technology. Zeners are very good at providing high levels of ESD, but they also tend to have high capacitance levels in terms of output capacitance per channel-often as much as 25 to 35 picofarads," Baker said. "That's fine for a lot of applications, such as standard data ports and even standard LCD interfaces. But with the increased adoption of higher-resolution displays with greater color depths-particularly in a clamshell design, where you're running a flex cable or interface through the clamshell hinge-that flex acts as an antenna and can create some EMI problems."
Effective EMI filtering is thus required; but because of the speed of the data coming across the interface, the capacitance level must be managed. In many cases, levels as high as 25 to 35 pF will interfere with the display interface, Baker added.
Performance improvements are also achieved with BGA resistor networks. Typically resistor nets are offered in molded packages, but in higher-speed applications there is a need to eliminate the leads and wire bonds, said Brian Kane, director of product development for BI Technologies Corp. (Fullerton, Calif.) "We place the resistors between the solder balls, which places the resistors very close to the circuits that they're terminating, so there is very low capacitance and very low inductance while achieving high-density resistors," Kane said. "Using BGA packaging is more of a performance issue, but it also provides a little bit of space and cost savings because you eliminate wire bonds for certain types of arrays and molded packages."
A lot of terminations are done with 0603 or 0805 chip resistors, but by pulling them into a network designers can reduce solder joints and board area and gain in performance advantages, Kane added.
Two of BI's most recent BGA resistor network introductions are the BB110B (27 balls, 18 resistors) and BB110DI (36 balls, 18 resistors), both for DDR SDRAM termination.
The resistors are integrated onto a ceramic substrate between the solder balls to minimize signal paths and eliminate via connections to the device. According to the company, the result is the virtual elimination of stray capacitance and inductance.
Yageo USA (Addison, Texas) also integrates resistors, capacitors and resistor/capacitor (RC) networks and arrays for a variety of applications, including notebook computers, mobile phones and digital consumer products.
The Yageo lineup includes capacitor arrays that integrate four 0402 or four 0603 isolated multilayer ceramic capacitors in a single package and resistor arrays that integrate two, four, or eight 0402 or four 0603 isolated thick-film resistors in a single package. The RC networks combine four 0402 isolated thick-film resistors and four isolated monolayer ceramic capacitors in a single network package. The devices are also available with a concave termination for easy alignment, greater termination strength and improved soldering.
BI Technologies Corp.
California Micro Devices