Z-Foil Surface-Mount Flip Chip Voltage Divider

Vishay has announced that it has enhanced its VFCD1505 surface-mount flip chip voltage divider with an almost instantaneous thermal stabilization time of < 1 second. The device provides a low absolute TCR of ±0.05 ppm/°C from 0°C to +60°C and ±0.2 ppm/°C from −55°C to +125°C, +25°C Ref., an excellent PCR tracking (ΔR due to self heating) of ±5 ppm at rated power, and a load life stability ratio of ±0.005% (50 ppm).

The VFCD1505 provides tight tolerance matching of ±0.01% (available down to ±0.005 %) and TCR tracking of 0.1 ppm/°C between two resistors simultaneously etched on one piece of foil on a common substrate. For designers, the electrical specifications of this integrated construction offer improved performances and better real estate utilization over discrete resistors and matched pairs.

The flip chip termination of the VFCD1505 minimizes the board space required, as the terminal pad is under the resistor and not out to the side, as it is in with a wraparound termination. In dividers that are comprised of two resistors and three terminations, the flip chip divider has three pads under the resistor rather than four to the side. An early disadvantage of flip chips was thought to be the hindrance to inspection for solder flow, but this has subsequently been overcome by X-ray and other more advanced techniques.

The VFCD1505 offers the utmost in ESD immunity, withstanding electrostatic discharges up to 25 kV, for increased reliability. Either side of the divider can have a resistance specified from 1 kΩ to 10 kΩ. Like all Vishay Foil resistors, the VFCD1505 is not restricted to standard values, and can be supplied with as required values (e.g., 7 kΩ vs. 7.6543 kΩ) at no extra cost or delivery time.

Applications for the device include high-precision instrumentation amplifiers, bridge networks, differential amplifiers, and ratio arms in bridge circuits for ultra-stable and high-reliability products, such as medical, test, and military equipment. Screening in accordance with EEE-INST-002 is available (MIL-PRF 55342). The VFCD1505 has a load-life stability ratio of ±0.005% for 2000 hours at +70°C; a power rating of 0.1 W at +70°C (divided between the two resistors proportionally to their value); a low voltage coefficient of < 0.1 PPM/V; current noise of < -40 dB; and thermal EMF of 0.05 µV/°C. It offers a fast rise time of 1.0 ns, effectively without ringing, and features a non-inductive (< 0.08 µH), non-capacitive design.

In spite of a low TCR tracking, a resistance ratio may change considerably based on the absolute TCR. To assure good ratio stability, designers should utilize resistors with the lowest absolute TCR possible, such as the VFCD1505, which is built on Vishay's breakthrough Z- foil technology that provides a significant reduction of the resistive component's sensitivity to ambient applied power changes.

In other technologies, such as thin and thick film, even if the resistance ratio is 1:1, there will be a temperature difference between the resistors in a pair under identical power loading conditions. This is due to the self-heating in each resistor as a result of the design and/or manufacturing tolerances, and the dissymmetry of heat transfer due to differences in thermal resistance within the package, even when applied power is extremely small (close to zero).

Samples and production quantities of the VFCD1505 voltage divider are available now, with lead times of 72 hours for samples, and three weeks for standard orders.