When I was reading about counterfeit items in the supply chain, I was dismayed to read that even component manufacturers can outsource manufacturing to subcontractors, or that authorized distributors may get name brand components from other distributors or agents, all vying for lowest price. This has led surprisingly to counterfeit items penetrating the authorized distributors
parts chain, albeit far less than outside it.
http://distributioninsider.electronicproducts.com/articles/counterfeits-continue-flooding.php
"If the supplier knows in advance that the customer has a formal inspection process in place and will not only refuse to pay for, but basically destroy, counterfeit materials, it really removes the motivation that the supplier may have to try to pass off counterfeit goods. If the supplier cannot make money, why do it?" says Hamiter, who also chairs a "Counterfeit Electronic Components Avoidance" workshop series in conjunction with Custom Analytical Services Inc., a failure-analysis lab based in Salem, N.H.Thus, my speculation, its very possible to have quality control problems with say, resistor tolerances, from some makes even if those parts aren't considered counterfeit, if said company oursources their manufacturing. Tolerance is one thing, but what if you need them also to conform to proper wattage, or parasitic inductance or capacitance?
I don't build manufacture in quantity, so I can afford to test every part I use, but if one were to do this for a high volume consumer item, it would lead to higher production cost unless some robot can do the testing. Right now a common tactic is limited to testing batch samples.
Sadly, six sigma is supposed to avoid that. With faults at 3ppm, one can project failure rates and its over all costs more consistently without testing every component used.
I used the Kelvin clips and current reversal because I was also measuring 1K, 100, 10, 1, and 0.1 Ohm resistors. These are 25ppm TC and I did compensate for measuring at 25 deg.C instead of 23 deg.C. For the 10K that were bad that is only 0.5 Ohm correction.
Because of availability I ended up with Bourns, Vishay-Dale, RCD, and Panasonic resistors.
The RCD were crazy accurate with most reading less than .01% off nominal.
Vishay-Dale and Panasonic were next with most using about half of the available tolerance.
Bourns was the worst, even the two values that were in spec. were all over the place and constantly skirting the high low limit.
One thing I learned is that having a good bench meter has its benefits. I didn't think I needed one, I was just lusting after one for for a long time and finally gave in.
If you are using pick and place how would you measure all the resistors on a tape and still be able to use them?