What is Kelvin Test?
This paper uses data to outline what a 4-wire Kelvin test. Several examples are illustrated of what the 4 wire Kelvin test can and cannot do.
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Authored By:
Rick Meraw and Todd Kolmodin, Gardien Services USA
Manfred Ludwig, Gardien Services China
Holger Kern, Gardien Services Germany
Summary
The PCB industry is ever changing and adapting to new technologies. OEM specifications and requirements have also advanced due to these technologies. In some cases the OEMs are asking for a low resistance test to be performed on some or all electrical test nets of the PCB or on the holes of the PCB. This requirement is typically not well defined on the fabrication drawing and that leads to misleading conclusions by the fabrication house.
4-Wire Kelvin testing has been around for many years but using this type of measurement on bare PCB's is a relatively new requirement. The requirement for PCB 4-Wire Kelvin testing was originally requested by digital commercial OEMs in the US with the aim to set out to improve the overall quality of the products. The first 4-Wire Kelvin test requirement for PCB's were on a limited hole criteria. Since that time automotive companies in Japan have also adopted such requirements. Medical applications are also joining in with their own 4-Wire Kelvin requirement.
This paper will use the data gathered by the company's operations to outline what a 4-wire Kelvin test is and how it can be used. Several examples will be illustrated of what the 4 wire Kelvin test can and cannot do. A clear definition of what limitations are present during the testing operation will be defined. The paper will assist designers in understanding how the low resistance test can assist them and also identify causes that can identify unwanted concerns/issues.
Conclusions
The paper discussed what the 4-wire Kelvin test is, what it can detect on PCBs versus standard flying probe testing such as plugged hole voids and cracks and thin plating as well as best practices when generating programs with the Flying Probe 4-wire Kelvin test. It also discussed some of the drawbacks of the test such as increased test time and cost of equipment.
OEM's are beginning to require more and more from their suppliers and the 4-wire Kelvin test is just one of the requirements on the horizon.
Initially Published in the IPC Proceedings
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