Influence of selected constructional and technological factors on tolerance and stability of thin-film resistors embedded in PCBs (original) (raw)
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In this work environmental behavior of resistors embedded into Printed Circuit Boards (PCBs) and discrete chip resistors assembled to standard PCBs are co mpared. The investigations were based on the thin-film resistors made of NiP alloy, thick-film resistors made of carbon or carbon-silver inks as well as chip resistors in 0402 and 0603 packages. Thin-and thickfilm resistors were made in the bar form. In addition, poly mer thick-film resistive films were screen-printed on the several types finishing materials of contact terminations such as copper, silver, and gold. To determine the sensitivity of embedded resistors versus s tandard assembled chip resistors on environmental exposure the climatic chamber was used. The measurements of resistance were carried out periodically during the tests, and after the exposure cycles.
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Long-term stability of embedded passives is very important issue. To determine this matter an aging process can be used, where test samples are exposed to environmental conditions. Objecti ve of this research was analyzing reliability of thin-fil m resistors based on Ohmega-Ply® technol ogy. Resistive material was a nickelphosphorus (Ni-P) alloy (wi th sheet resistance 25 Ω/sq or 100 Ω/sq) on FR-4 substrate. A number of vari ables were considered in this study (sheet resistance, geometry of resistor, type of cl adding, l aser trimming, pulse stress and environmental conditi ons). Two di fferent accelerated ageing processes-Ex-Situ (samples exposed to elevated temperature and/or rel ati ve humi di ty but resistance measurements made at room temperature) and In-Situ (resistance of test samples performed directly at the ageing condi tions) were carried out to perform long-term behavior analysis. The results revealed a significant influence of thickness of resistor, type of cladding and temperature on stability of investigated structures. Signification of other factors was negligible.
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In this work environmental behavior of resistors embedded into Printed Circuit Boards (PCBs) and discrete chip resistors assembled to standard PCBs are co mpared. The investigations were based on the thin-film resistors made of NiP alloy, thick-film resistors made of carbon or carbon-silver inks as well as chip resistors in 0402 and 0603 packages. Thin-and thickfilm resistors were made in the bar form. In addition, poly mer thick-film resistive films were screen-printed on the several types finishing materials of contact terminations such as copper, silver, and gold. To determine the sensitivity of embedded resistors versus s tandard assembled chip resistors on environmental exposure the climatic chamber was used. The measurements of resistance were carried out periodically during the tests, and after the exposure cycles.
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Modern electronic devices are more and more complex and multifunctional. It could be done by producing faster and more reliable active components and increasing number of passives and interconnections' density. To form such complex devices one can embed components in substrate of printed circuit board (PCB) or build multilayer boards. The other way is to form multi-terminal passive components to spare free surface and decrease number of interconnections. Authors created three-terminal thin-film (TF) resistors embedded in PCBs and investigated their selected properties such as resistance repeatability, long term stability, pulse durability and thermal characteristics.
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