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PCBD-June2017

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42 The PCB Design Magazine • June 2017 by Dora Yang PCBCART Thin-film microstrip circuits have been widely applied in microwave communications, electronic countermeasures (ECM), and aero- space applications, etc. When manufacturing thin-film ICs, it is very important to apply de- posited thin-film resistor material to fabricate high-accuracy and highly stable thin-film em- bedded resistors. Thin-film ICs call for thin-film resistors that meet these stringent requirements: a. Square resistance should be wide enough b. Temperature coefficient of resistance should be small c. Adhesive force with substrate should be strong enough d. Thin-film resistors should feature a stable and reliable performance e. Filming should be easy and convenient f. Should be capable of handling high- temperature processing, high power and relatively wide application range. A Brief Introduction of Embedded PCBs The first IC invented by Jack Kilby in 1959 contained only two transistors and a resistor. Nowadays, multiple complex techniques are applied to combine tens of millions of transis- tors into one single PC chip. With electronic products stepping towards miniaturization and multifunction, a type of embedded passive component technology occurred to meet the in- creasingly higher demands. The ratio between passive components and active components is approximately 20:1, density has been gradually going up with the ratio rising. With so many passive components embedded in PCBs, the area of an SMT circuit board shrinks by 40% compared to board fabricated through embed- ded technology. The early 1980s saw the starting of embed- ded passive component technology that is usu- ally achieved in a planar form. Based on pas- sive component classification, embedded PCBs can be further classified into embedded resistor PCBs, embedded capacitor PCBs and embedded inductor PCBs. Resistors, capacitors and induc- tors can be nearly seen in all electronic systems, providing impedance and storing energy for the system. Among those embedded passive com- ponents, capacitors and resistors account for the majority, at least 80% of all altogether. Embedded passive components have been widely applied in filters, attenuators, baluns, Bluetooth applications, power amplifiers, and ore. Furthermore, some trends, including high- speed and high-frequency digital signals, con- stantly decreasing voltage of passive compo- FEATURE

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