Embedded resistors and capacitors provide high-density high-performance solutions, freeing up the surface for other components and enabling tailored interconnect topology. This technology needs exploration and characterization before it can become a routine resource in high-reliability, harsh-environment and aerospace applications. This paper discusses two critical factors, a) uniformity as-received from the fabricator, and b) long-term stability under extreme environmental conditions. PWB specimens spanned a range of embedded resistors and embedded (distributed and discrete) capacitors, several values of each, from several suppliers, using a variety of materials and processes. Data on as-received boards and coupons includes: Comparisons between target vs. measured values; comparisons between "expected" vs. measured values; comparison of board-to-board uniformity of equivalent features, uniformity of nominally identical features at various spots on the same PWB; comparison edge-to-edge of the same board; and comparisons between coupon feature vs. equivalent PWB feature, to document how representative the coupon is. Environmental stability. Performance data includes: resistance and capacitance values as a function of temperature; values measured after long-term storage at elevated humidity and temperature; stability after vibration; stability after long-term thermal-cycling; stability after water immersion, stability after molten-solder-dip thermal-shock; and stability after surface over-heating. Results are interesting. As-received uniformity data reveals substantial differences (up to 20-40%) between the target value and the actual value, as well as among nominally equivalent features, and between coupon and board. Differences depend on type of element. This is before any of the cherry-picking or screening by the supplier that could happen in typical jobs. Environmental stability is reassuringly robust. Most exposures cause relatively little change. Stability depends on materials, processes and geometries. This information could help guide procurement documents, to provide realistic expectations regarding tolerances and yield, as well as to develop QC sampling and acceptance protocols. It also should provide guidance to designers and users towards qualification and performance expectations, under nominal and adverse in-service conditions.
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