Electrical testing

A material s behaviour in the proximity of electrical fields or discharges and the static build-up and dicharge behaviour of a material are tested. Tests include volume and surface resistivity, permittivity, breakdown strength, insulation resistance, power (or loss) factor and tracking resistance. 

If a released part does not move as expected it is possible to poke the part with the probe, often times without breaking the part. If the release step was not carried through to completion, sometimes the remaining residual sacrificial films that have been partially etched can be broken by mechanical probing without destroying the part that is to be released. Also, if the part moves sluggishly it can be an indication that there is a residual contaminant film or absorbed water layers between the released part and the substrate if the released parts have not been stored in a dry environment such as a storage cabinet with desiccant. 

In addition to mechanical test structure it is good practice to include electrical test structures. Simple structures like electrical bond pads that 

As described in Chapter 2, the M-Test structures are useful for determining thin film properties as well as testing electrical functionality. By applying increasing voltages to the M-Test structures, they can be optically inspected to determine the voltage that is required for pull-in. These simple test structures enable a rapid assessment to determine quickly if released parts are able to be actuated as expected using electrostatic forces. 

Often the supplier will include one of their own test structures in the customer s layout space. For example the PolyMUMPs die will have a comb-drive resonator added into the layout after the customer turns it in, so long as they have followed the design guidelines that specify leaving a space on the layout for the inclusion of the comb-drive resonator. The comb-drive can be inspected for the fidelity of the patterning since the combs of the comb-drive use the minimum space to achieve the maximum force. The comb-drive can also be driven into electrical resonance by the application of the appropriate biasing conditions [3]. 

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Fig. 1. Volume change in anisotiopic giaphite during General Electric Test Reactor (GETR) irradiations. Courtesy of Oak Ridge National Laboratory, managed by Martin Marietta Energy Systems, Inc. for the U.S. Department of Energy under Contract No. DE-AC05-840R21400.

HS(Gjl3 Electrical testing safety m chemical testing... 

The performance of organic finishes on test is evaluated by visual observation and by physical tests made upon coated specimens that have been exposed for various periods of time to natural or accelerated weathering conditions. Electrical tests are sometimes used on immersed specimens. 

After obtaining the prototypes, tests must be made to determine the utility. Generally these include a short time destructive test to determine the strength and to check out the basic design. Another test that is done is to use the product in the projected environment with stress levels increased in a rational manner to make for an accelerated life test. Other tests may include consumer acceptance tests to determine what instructions in proper use are required, tests for potential safety hazards, electrical tests, self-extinguishing tests, and any others that the product requires. In the case of high risk products, the test program is continued even after the product enters service. 

An electrical testing load system was prepared as shown below using two variable resistance potentiometers rated at 0 to 1.0 ohm at 25 watts, a current measuring shunt, and two digital multimeters. 

Above Electrical test system. The four fixed resistors... 

Electrical tests shall be made periodically to determine that the piping system is protected in accordance with the applicable criteria. 

In both mechanical and electrical testing, the frequency of dynamic stress application can be increased, although heating effects and time for relaxation processes have to be considered. For some products it is appropriate to simply use them more often, for example where in service the use is intermittent or there is normally downtime. 

Fig. 18 shows a tank cell of the International >xygen Company, which is not unlike the diagrammatic 11 which has just been explained. Tests on four of lese cells by the Electrical Testing Laboratories of lew York give the following figures —... 

FM Data Sheet 5-20. 2001. Electrical Testing. Factory Mutual EngineeringCorporation, Norwood, MA. 

Figure 5. Triple-track resistor electrical testing performance of crown ethers in commercial RTV silicon encapsulants. Conditions bias, 180 V relative humidity, 96% temperature, 100°C.

Pyro-electric and piezo-electric tests. When a crystal belonging to one of the non-centrosymmetric classes is heated or cooled, it develops electric charges and becomes positive at one end and negative at the other end of each polar axis. Therefore, if a crystal is found to be pyro electric, it must belong to one of the classes which lack a centre of symmetry. Various qualitative tests for pyro-electric character have been used. The three most suitable for small crystals are the following ... 

In the electrical field the International Electrotechnical Commission (IEC) performs the same function as ISO. The work of this body is of interest where rubbers are used in electrical insulation, etc. As regards electrical test methods for rubber, ISO and BSI have tended to adapt the basic procedures and principles standardised by IEC or to rely on the IEC standards. 

Physical testing of rubbers is the concern of PRI/22 which has a panel to deal with electrical tests. Until recently, there were 4 other active panels to split the detailed work on test methods but, as a result of the drive to economise effort and the effects of virtually all test methods coming from ISO, they were disbanded. Other committees which should be mentioned in the context of testing are PRI/71 which deals with flexible cellular materials, PRI/20 for accuracy of test machines, PRI 26 for burning behaviour of plastics and rubber and PRI/23 for chemical testing. Unfortunately, systems are never as simple as we would like specialised tests may be considered in product committees and not all products containing rubber are covered in PRI committees... 

Details are given for the press and mould construction and for the vulcanisation procedure. The most important parameters are the time and temperature of moulding and ISO 2393 specifies close limits, 0.5°C, on the latter. ISO 2393 requires only that the mould is loaded and unloaded as quickly as possible but the mouldings are to be cooled in water, or on metal plates if intended for electrical tests, on removal. One has to assume that cure time is derived from curemeter measurements. 

It is generally assumed that humidity is not important in most rubber tests and, hence, conditioning in an atmosphere with control of temperature only is usually specified. However, control of humidity is considered necessary in certain cases, for example testing latex rubber and electrical tests. In many instances the 16h minimum conditioning period will not be sufficient for equilibrium to have been reached, especially with relatively thick test pieces. Hence, all that this conditioning can hope to achieve is to bring test pieces having similar dimensions into more nearly comparable conditions than they would otherwise be. To reach complete moisture equilibrium would in many cases take several days and for thicker test pieces probably weeks. 

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