Electronic Design

Paper-Thin Components Prepare To Enter Mainstream

Like a Bugs Bunny-driven steamroller bearing down on Elmer Fudd, the relentless quest for portability is overtaking electronics technology and flattening just about every component in its path. Parts that once stood noticeably off the circuit board have been mowed down to 1-mm or shorter profiles. These advances have given us the shirt-pocket compactness we relish in the latest portable devices. But as component packaging continues to thin and shrink further, we may start to see a new generation of mobile products thin enough to slip into your wallet, be woven into clothing, and be flexed or folded into unexpected shapes.

As progress continues, the shrinking and thinning of component and packaging technology will let us add sensing, signal and data processing, and communication functions to many everyday items, making them effectively "smart products." Juergen Wolf described some of these products at the hd International conference on high-density interconnect in Santa Clara, Calif., where he presented his and H. Reichl's paper, "Microelectronic Packaging—Ready for the Next Product Generation."

According to Wolf, new applications of microelectronics and microsystems technology will include everything from voice-controlled computers, electronic notepads and work surfaces, electronic newspapers on flat-panel displays that can be rolled or folded up, and the smallest mobile health and diagnostic tools, to the videophone inside your smart watch. Novelties like the smart clothing label that transmits cleaning instructions to the washing machine may put intelligence where we least expect it—and possibly sooner than we anticipate. Many underlying technologies required to build these futuristic products are already here, and some products have already been prototyped.

Advanced packaging and assembly techniques are among the tools now available for device miniaturization. One is chip thinning. Either by mechanical grinding and polishing, or by chemical etching, it's possible to strip unnecessary silicon away from the die. Thinning enables stacking of multiple die in tiny packages, and if extended close to its present limits, produces flexible chips that can be mounted to flexible or curved substrates. Wolf notes that silicon wafers have been thinned to less than 20 µm, with 10 µm being the current practical limit. At around 30 µm, chips become flexible.

Along with chip thinning, a number of other semiconductor-related factors, such as continual die shrinks and reduction in I/O pitches, contribute to miniaturization. Advances in passive component and interconnect technology help further.

Lately, even some usually bulky parts, like batteries and displays, are becoming thinner. Li-polymer cells housed in foil pouches can be less than 0.5-mm thick. Similar thinness has been achieved with lithium coin cells and with novel battery types like those introduced by Power Paper, which silkscreens ink-like electrode materials onto paper.

Ink-like materials are being tried in displays as well. In this area, heat-activated pigments, light-emitting polymers, electrostatically controlled toner, and plastic substrates are some of the ingredients for display technologies that may soon appear in mobile products.

As components continue shrinking, the "paper-thin" description will become increasingly common as parts approach the 100-µm thickness that puts them on par with an ordinary sheet of printer paper. How fitting that paper—which for so long has been the medium for conceptualizing visionary product ideas—will also serve as a yardstick for their implementation.

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