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46 FLEX007 MAGAZINE I JULY 2018 roll up like a newspaper due to the structural differences of the opposing sides. IC packages, including wafer level packages, have helped to hold the thickness reduction gains with mini- mal increases in overall thickness. Moreover, wafer stacking has redefined the possible as 3D assemblies become a more prominent solution to the density challenge. Another element in the effort is passive device technology. Embedded passive technology has long been a partner in the creation of lower- profile assemblies, though it was not the original intent. Embedded passives were originally seen as a way to free up circuit real estate on the surface of PCBs. They have proven especially attractive in applications such as analog circuit applications that are often popu- lated with myriad discrete devices. The problem is exacerbated by the fact that the "bleeding edge" devices have become so small as to be virtually indistinguishable from "fly specks." This makes assembly a challenge, relative to both pick- and-place and soldering. Still, discrete devices have an attractive feature that exceeds the limits of most of their embedded brethren alternatives. Specifically, they can be built to better toler - ance and are less prone to drift over time. The result is that there have been a number of efforts to embed discrete passive devices into the circuit board. To date, all known efforts have focused on use of standard devices with traditional planar orientations which increase the need for more exacting place - ment accuracy and more expensive placement equipment, leaving the door open to improvements. One attractive alternative is to create discrete devices, both pas- sive and active, which are thin and have a vertical orientation for con- nection by design. The concept of a vertical orientation for an embedded resistor was envisioned and had been implemented, however a structural variation described in U.S. Patent No. 7,049,929 is arguably more practical. However, an interesting alternative concept involves the creation of vertically-ori - ented discrete components. These prospective alternative devices offer the combined bene- fits of discrete devices along with the surface space savings and a higher degree of flexibility for the design of dense circuit assemblies. Figure 1: Examples of low-profile flex construction and assembly.

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