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PCB-Jun2017

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28 The PCB Magazine • June 2017 a high temperature heater mode. The resistor was powered to reach a steady state tempera- ture of 150°C and periodically measured over a period of 1200 hours to monitor any change in resistance. The change in resistance after the test period was less than 1%. The stability over long term operation validates the use in burn- in applications that require prolonged periods of stress on device under test. Figure 7 shows an example of a burn-in board application. This example placed the heaters in an inner layer under the areas shad- ed in gray. Burn-in boards generally have the added benefit of a more flexible power budget as opposed to battery operated applications. Al- though, the heater areas in both portable and bench type applications will be primarily driv- en by the size of the device to heat. Conclusion Thin-film NiP resistors in heater applica- tions are growing in popularity as they find new ways to provide solutions to the design en- gineer. These heaters can reliably produce tem- perature deltas of 30°C to 200°C+. There are many factors that will contribute to a success- ful heater design. In complex systems with mul- tiple material interfaces it is recommended to employ simulation tools. For less complex sys- tems, ballpark power estimates for desired tem- perature rises will work. PCB References 1. Mahler, Bruce, "New Applications for Em- bedded Thin Film Heaters." Paper presented at BiTS Workshop, March 2017. 2. IPC-4101B "Specification for Base Mate- rials for Rigid and Mulitlayer Printed Boards," IPC-4101B Reference Chart. 3. Brandler, Daniel, "The Performance of Embedded Resistors by Alloy Type and Film Thickness," The PCB Magazine, November 2011. Manuel Herrera is the design and test engineer at Ohmega Technolo- gies Inc., in Culver City, California. THIN FILM NiP EMBEDDED RESISTORS IN HEATER APPLICATIONS The Schweizer p² Pack allowing to embed power electronics semiconductors into the PCB is a preferred solution for future high current mo- tor drives. This embedding technology saves valu- able installation space and offers further system advantages such as: improved conduction losses (RDSon) of the power electronics, improved ther- mal resistance and thermal impedance (RTH und ZTH), a low-inductive design, improved switching characteristics, improved electromagnetic com- patibility (EMC) and higher reliability. Schweizer Electronic AG now takes the next integration step by embed- ding shunts in combination with a half bridge for the first time, so the components 'thermal dissipation is optimised and further installation space can be saved, a considerable technical advantage in today's trend towards miniaturisation. First dem - onstrators of this innovation will be shown at the Schweizer booth (Hall 7, booth 240) on occasion of PCIM, taking place in Nuremberg from May 16– 18, 2017. Many power electronics applications (e.g., mo- tors) use shunts for current measurement. A shunt is a low-resistance precision resistor that is applied for measuring electric currents. The current passing the shunt triggers a proportional voltage drop, which is then measured. Shunts so far have usually been mounted on the PCB. Consequently, the resulting heat has to be conducted through the substrate PCB first before reach- ing the cooling system. Technical details for embedded shunts Resistance values 0.05 up to 0.1 mΩ Currents: 0 – 300 A Voltage drop: 0.5 – 30 mV Dissipation: 4.5 – 9 W Temperature rise: 3 – 5 K Contact resistance: <1% of precision resistor. Schweizer Presents Innovation at PCIM 2017

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