Off the shelf resistors minimise PCB stress

The Flex Series product line is also now available from Digi-Key, an authorized distributor of VFR products.

"The Flex Series is the future of COTS resistors, providing superior flex performance compared to standard termination systems to isolate the resistor body from harmful PCB stresses due to a difference in the TCE," said Yuval Hernik, senior director of application engineering for VFR. "It is the perfect solution for applications where the PCB will be exposed to high levels of board flexure during assembly or mounting, or where resistors are going to be subjected to heavy shock or vibration."

When mounted on a board that is bent or flexed during the manufacturing process or in the field, resistors can develop cracks that affect their electrical performance and reliability. The VFR Flex Series is a surface-mount precision resistor that incorporates a unique flexible termination system which isolates the resistors from board stresses to help prevent them from reaching the resistance element. Integrated with the latest generation of Bulk Metal Foil technology — Z-Foil — this system is designed to establish pliability while maintaining terminal strength, solderability, stability, and electrical performance.

Flex Series resistors offer low harmonic distortion, power ratings to 600 mW at +70°C, and a PCR (ΔR due to self-heating) of 5 ppm at rated power. The devices feature a resistance range from 1 Ω to 80 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. Featuring a non-inductive (<0.08 μH), non-capacitive design, the resistors offer a thermal stabilisation time of < 1 s (within 10 ppm of steady state value), voltage coefficient of <0.1 ppm/V, and current noise of 0.010 μVRMS/V of applied voltage (<-40 dB). Flex Series devices are designed to withstand ESD spikes to at least 25 kV and are available with lead (Pb)-free and tin/lead alloy terminations.

"The Flex Series resistors are now available from Digi-Key in custom order quantities," continued Hernik. "Through collaboration with VFR, Digi-Key is helping to set a new standard by shipping the exact number of resistors needed of the precise resistance value and tolerances required, such as 120 Ω and 350 Ω for strain-gage applications or 250 Ω for 4 mA to 20 mA current loops. This provides an invaluable source for small-quantity prototype runs and quick changes prior to full production."

Samples and production quantities of the Flex Series are available now, with lead times of five working days for prototype samples and six weeks for standard orders.