It may seem unlikely given their relatively low value compared to other components but counterfeit resistors continue to be a problem in the electronic component supply chain. Failure to spot a counterfeit resistor device, before it is installed in the end equipment, can have catastrophic consequences.
Resistors in high reliability applications and those designed and manufactured to address the specific requirements of a particular application tend to be higher value devices and prime candidates for counterfeiting. Resistors may be a fraction of the price of a semiconductor integrated circuit but they tend to be used in much higher volume making them a viable target for those looking to make a quick profit.
Faced with the prospect of production delays and unhappy end customers the natural choice for many businesses with an obsolescence issue is to look for a residual stock at distributors or stockists. Failing that, the next point of call tends to be the dealer channel or grey market. This approach significantly increases the chances of encountering counterfeit resistors.
When accepting a batch of resistors, a sensible approach is to try to minimise the resources needed to identify counterfeits by taking a multi stage approach (from least to most expensive). A review of paperwork and the traceability trail can pick up the less sophisticated counterfeit resistor devices at minimal cost but it is important to remember paperwork can also be forged.
Visual inspection can identify some counterfeit devices but it is often necessary to inspect on a 100% basis. A standard trick of counterfeit component suppliers is to add a number of genuine devices to the counterfeit batch.
If paperwork analysis and visual inspection are insufficient then electrical, mechanical and/or stress testing may be employed on the resistor batch. The cost of such testing can be significant so it is important the test flow is carefully designed to ensure suspect devices are clearly identified.
If the risk of taking components from sources other than the original manufacturer is just too high one potential solution is to obtain a form fit and function replacement for the obsolete resistor device. Specialist resistor manufacturers can often manufacture equivalents to obsolete devices in the low to medium quantities required to keep production running until a long-term replacement can be found.