Resistor buried resistors

Gangqiang, W., Rajagopalan, V., Barlow, F., Elshabini, A., and Ang, S., Effect of design and processing parameters on buried resistors in LTCC systems, 2001 Proceedings of the International Symposium on Microelectronics, Baltimore, MD, October 2001. 

Furthermore, surface resistors can be laser trimmed and thus enable cost-effective implementations for a variety of designs. On the other hand, buried resistors are available today with limited range of resistances from <100 Q to over 100 k l with wider tolerances. 

Resistors buried in LTCC are out of direct access. In general, the following three strategies of embedded resistor trimming are available ([39] Figure 9.37) ... 

Energy of high- Buried resistor trimming High impact on layout. 

Frequency behavior DC to 3 GHz (Locus diagram) of buried resistors (a) 10 Q/n, (b) 100 12/ (trimmed curve after high-voltage pulse trirnming). 

Thust, H., Drue, K.-H., Thelemann, T., Polzer, E., and Muller, J., Is Buried Better — Evaluating the Performance of Buried Resistors in LTCC, Advanced Packaging, March-April 1998, pp. 40-46. 

Muller, J., Thust, H., and SjolLng, B., Trimming of buried resistors in LTCC-Circuits, Proceedings of the ISHM Nordic, Helsingor, Denmark, September 22-24, 1996. 

J.6.5.2 Resistive Foils. Other treatments can also be applied to the base foil for nse in mannfactnring inner-layer circnits with buried resistors. This technology can enable the creation of resistors on internal layers of a mnltilayer circnit, with removal of many of the resistors commonly assembled on the outside of the multilayer circuit. This can improve board reliability and free np space on the outside of the board for active components. These foils typically nse a resistive metal alloy coated onto the base foil. The laminate made with this foil can then be seqnentially imaged and etched to produce the desired circuit pattern along with resistive components. 

With the rapid advance of technology in the PCB industry, data exchange formats must adapt to include new information. For example, none of the CAD formats mentioned here and neither ODB++ nor IPC-2581 support buried resistors and capacitors out of the box, and therefore buried passive technology development is hindered by data communication errors and costs. 

The mentioned methods are not applicable if the elements are buried deep in the circuit (multilayer or LTCC). Alternatively, trimming by high-voltage pulses can be applied. Types of resistor arrangements and trim possibilities are shown in Figure 9.37. 

Ehrhardt, W. and Thust, H., Trimming of buried Thick film resistors by energy of HV pulses. Proceedings of the 38th IMAPS Nordic Conference, Oslo, 2001, pp. 316-321. 

ODB++ version 7 to be released in 2007 supports buried passive resistors and capadtois. 

One advantage that LTCC has over the other multilayer technologies is the ability to print and fire resistors. Where trimming is not required, the resistors can be buried in intermediate layers with a eorresponding saving of space. It is also possible to bury printed capacitors of small value. 

Several measurements can be made after a coupon-type corrosion sensor has been attached to a cathodically protected pipeline. on potentials measured on the coupon are in principle more accurate than those measured on a buried pipe, if a suitable reference electrode is installed in close proximity to the coupon. The potentials recorded with a coupon sensor may still contain a significant IR drop error, but this error is lower than that of surface on potential measurements. Instant-OFF potentials can be measured conveniently by interrupting the coupon bond wire at a test post. Similarly, longer-term depolarization measurements can be performed on the coupon without depolarizing the entire buried structure. Measurement of current flow to or from the coupon and its direction can also be determined, for example, by using a shunt resistor in the bond wire. Importantly, it is also possible to determine corrosion rates from the coupon. Electrical resistance sensors provide an option for in situ corrosion rate measurements as an alternative to weight loss coupons. 

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