Embedded Resistors and Capacitors in Organic and Inorganic Substrates

Abstract

Embedded resistors and capacitors were purchased from two technologies; organic PWB and inorganic low temperature co-fired ceramic (LTCC). Small groups of each substrate were exposed to four environmental tests and several characterization tests to evaluate their performance and reliability. Even though all passive components maintained electrical performance throughout environmental testing, differences between the two technologies were observed. Environmental testing was taken beyond manufacturers' reported testing, but generally not taken to failure. When possible, data was quantitatively compared to manufacturer's data. Both technologies performed favorably with some nuances noted for each material set. The resistors were not embedded deep into the substrate structures but were placed on the surface and coated. This served two purposes: the first was that resistors could later be trimmed if they reside on the surface and the second was that it represented worst case for protection of the resistive elements for the reliability testing, mainly moisture exposure. Typically, the PC board solder resist is sufficient to protect the resistors in the PWB resistors. Should there be a pin-hole or damaged area, the environmental protection could be compromised. During the moisture environmental testing, a resistor in the PWB technology failed due to corrosion. The level of concern for this failure mechanism is elevated only for laser trimmed resistors where the coating would be opened and an additional coating is applied following the adjustment. The failed resistor in this study failed at the 1000 hour readpoint of 85%RH/85/spl deg/C and the failure was not an open but an increase in resistance. The capacitors exhibited a size relationship to reliability where small capacitors varied in capacitance more than large capacitor sizes selected in this study. The best physical size for the capacitors was found to be between 1 and 2 cm on a side.