- Buyers Guide
Vishay Precision Group Inc. announced that its Vishay Foil Resistors brand (VFR) has enhanced its VFCP series of Bulk Metal® Z-Foil ultra-high-precision flip chip resistors with an extended resistance range down to 5 Ω. The devices feature ultra-low TCR of ±0.05 ppm/°C nominal (0°C to +60°C) and ±0.2 ppm/°C typical (-55°C to +125°C, +25°C ref.) and load-life stability of ±0.005% at 70°C for 2,000 hours at rated power and ±0.01% at 70°C for 10,000 hours.
Available in five chip sizes ranging from 0805 to 2512, the VFCP series offers high power ratings up to 600 mW at +70°C and an excellent power coefficient (ΔR due to self-heating) of ±5 ppm at rated power. The devices feature a wide resistance range from 5 Ω to 125 kΩ, with tight resistance tolerance to ±0.01%. Any conceivable ohmic value within this range, to six digits, is available with no additional cost or lead time effect. Matched resistor sets are available by request.
The extremely low TCR of VFCP resistors over a wide temperature range makes them suitable for the high demands of cryogenic applications. The flip chip devices are qualified as anti-sulfurated resistors for use in environments with high levels of contamination. In addition, the devices are ideal for use in many alternative energy, RTD, Li-ion battery, 4 mA to 20 mA current loops, and smart grid applications in which analog circuitry operates under severe environmental, thermal, and mechanical conditions. Designing and manufacturing equipment for these applications involves extreme challenges that seemed insurmountable until a few years ago. These challenges have an impact on the design of analog circuits and the role and expectations of precision resistors, which must be ultra-stable, ultra-reliable devices with an extremely low total error budgets.
"Many designers use a resistor's TCR as a shorthand index to its relative level of precision. And while it is generally true that a better TCR does correspond to higher precision, this degree of precision does not maintain the same TCR/precision proportion across all technologies," said Yuval Hernik, senior director of application engineering for VFR. "For Bulk Metal Foil resistors, the stress/strain balance throughout the temperature and power application ranges ensures that none exceeds the elastic limit (Hooke's law) for any material used and that all performance criteria are repeatable and reliable."
Harmonic distortion is an important consideration in the choice of precision resistor. A significant signal voltage across the resistor may change the resistance value depending on the device's construction, material, and size. Under these conditions, Bulk Metal Foil resistors behave more linearly than other resistor types. Featuring a non-inductive (< 0.08 μH), non-capacitive design, VFCP devices offer a rise time of 1.0 ns with effectively no ringing, a thermal stabilization time of <1 s (within 10 ppm of steady-state value), current noise of 0.010 µVrms per volt of applied voltage (< -40 dB), and a voltage coefficient of <0.1 ppm/V. The resistors are immune to extraordinary incidents such as radiation exposure and withstand ESD spikes to at least 25 kV.
The VFCP resistors' one-side terminations ensure secure contact during the manufacturing process and save up to 35% PCB space compared with a surface-mount chip with wraparound terminations while also providing better strain relief to eliminate cracked substrates and board delamination. The devices are available with both lead (Pb)-free and tin/lead alloy terminal finishes.
Samples and production quantities of the Z-Foil resistors are available now, with lead times of five days for prototype samples and two days to six weeks for standard orders from VPG's Precision Centers and catalog houses around the world. Pricing for U.S. delivery only starts at $2.93 per piece.