EMBEDDED PASSIVES -- UNIFORMITY AND RELIABILITYAuthors: Tom Clifford and Melissa Lau
Date Published: 1/24/2008 Conference: Pan Pacific Symposium
This paper describes 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 provides information on the two critical uncertainties: uniformity as-received and longterm environmental reliability or stability.
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: values as a function of temperature; values measured after longterm storage at elevated humidity and temperature; vibration stability; stability after long-term thermal-cycling; stability after water immersion, stability after molten-solder-dip thermal-shock; and stability after surface over-heating.
Uniformity results show substantial and varied 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. Results depend on type of element. This is before any cherry-picking or screening. Environmental stability amongst the specimens and types of materials is discussed. Most exposures cause relatively little change: these embedded passives are reassuringly robust. Stability depends on materials, processes and geometries.
This data is offered to help guide procurement specs and SOWs, 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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