One of the most critical elements of producing any cable assembly or harness is the amount of cable assemblies testing that is done when the product is completed in manufacturing. There are many methods and levels for testing cable assemblies, but all testing has one goal – to ensure that the product meets or exceeds its specifications.
Cable assemblies can be built to one or multiple specifications. For example, an assembly may be produced to a customer specification with regards to the color of the jacket and over mold material used, among other customer centric requirements, but from an electrical standpoint the assembly may be required to meet an industry standard. Based on the specifications and standards the assembly was produced to, a final test plan is constructed that the assembly will be tested to. The test plan states the pass/fail criteria and the assembly is deemed serviceable if it meets, at a minimum, the pass criteria.
Cable Assembly Electrical Testing
At a bare minimum, cable assembly testing must include complete electrical tests for shorts, opens, or incorrect wiring. The proper method to electrically test an assembly is to attach the connector at each end of the assembly to a mating connector. The mating connector will be attached to a fixture that will check for opens in the assembly, shorts between the conductors or the conductors and shields if any are present, and the proper pin placement for all the components of the assembly. This setup puts the assembly into a test situation that fully replicates the installation that the assembly was built for.
Additional Cable Assembly Tests
Additional testing may be considered from a visual, environmental, mechanical, and signal integrity standpoint. The use of EIA Standard 364, IPC/WHMA-A-620B, and any other relevant industry standards documents should be used as guidelines for this testing. These additional tests may not be necessary on all assemblies and the below information is presented as guidelines to consider.
Cable Assembly Signal Integrity Analysis
- The connectors and/or sockets will be inspected to assess workmanship, proper markings, correct finish, appropriate materials, and design and construction.
- The entire assembly will be inspected dimensional to ensure compliance to the specification it was built to. The visual inspection will also check for any defects present such as deformation or blistering of the outer covering of the cable or the connector.
- High Temperature Aging – The assembly will be subjected to an elevated temperature to see what impact it will have on either the electrical or mechanical attributes of the connectors or cable used in the assembly.
- Low Temperature Aging - The assembly will be subjected to a decreased temperature to see what impact it will have on either the electrical or mechanical attributes of the connectors or cable used in the assembly.
- Thermal Shock/Thermal Cycling – The assembly will be subjected to high and low temperatures to evaluate what impact the temperature fluctuation will have on the connectors, cable, and termination points.
- Humidity – The assembly will be exposed to high levels of humidity to evaluate what effect the raised humidity will have of the connector, cable, or termination points
- Salt Spray - The assembly is exposed to a salt spray or fog to check for corrosion resistance of the materials and coatings used in the construction of both the connectors and the cable.
- Vibration Testing – The assembly is subjected to repeated and constant vibration to evaluate the impact on the connector interface and the terminations.
- Industrial Corrosion – The assembly is exposed to different climates as a method of accelerating in use corrosion failures to estimate service life of the assembly.
- Mating and Unmating – The connectors will be mated and unmated to determine the force needed to engage and disengage the assembly.
- Durability – The assembly will be subjected to repeated flexing at a set angle for a set number of repetitions determining the approximate life expectancy of the assembly.
Signal Integrity Test
- Eye Diagram Analysis – Data eye diagrams are used in high speed signal analysis to show the key parameters of the electrical quality of a signal by using bit error testing.
- Time Domain Measurements – Time domain measurements will test the assembly for Intra-pair skew, inter-pair skew, and differential impedance.
- Frequency Domain Measurements – Frequency domain measurements will test the assembly for far end crosstalk and attenuation.
- Insertion Loss – The assembly will be tested for a loss in signal power which results from the inclusion of a component into the circuit. The components typically inserted into the circuit would be connectors, splices, or filters.
The above list is by no means meant to be totally inclusive of the testing that is to be considered for cable assemblies. Additional testing such as insulation resistance tests, Hi-Pot testing, Safety certifications, and numerous other customer and industry requirements should be considered as potential testing areas.
Cable assemblies and wire harness production should be entrusted to reputable manufacturers that have the means to do a complete testing plan and perform all tests documented within the plan. As you can see, the list of testing can be quite extensive, all of which is designed to deliver the best possible product to customers.