IPC-TM-650 2.5.6.2 Electrical Strength of Printed Wiring Material

The standard “IPC-TM-650 2.5.6.2 Electrical strength of printed wiring material” developed by the Institute of Printed Circuits (IPC) describes a test method to evaluate the ability of an insulating material to resist electrical breakdown perpendicular to the plane of the material when exposed to short-duration, high voltages at standard AC power frequencies of 50-60 Hz.

This method can be used on any material thickness up to approximately 3,175 mm, but for materials above 0,508 mm, other methods, such as dielectric breakdown, are typically used to characterize a material's electrical integrity. The results of this test can be significantly affected by moisture content, and results obtained using different preconditioning methods may not be comparable.

This method uses an oil medium to prevent ignition in a small sample, and the results may not be comparable to tests performed in air. Values ​​obtained using this method should not be used to estimate the insulating ability of ultrathin metal-clad laminates.

Values ​​determined by this method generally decrease with increasing specimen thickness for otherwise identical materials. This method is based on techniques described in ASTM D149, Standard Test Method for Dielectric Strength and Dielectric Breakdown Voltage of Solid Electrical Insulating Materials at Commercial Power Frequencies.

Unless otherwise specified, three samples should be prepared. Sample dimensions should be 10 cm plus/minus 2,5 cm x 10 cm plus/minus 2,5 cm, but size is not critical as long as flashover does not occur at the edges.

Samples should be cut appropriately on both edges1 and from the centre of the laminate, but no sample should be taken closer than 2,5 cm from the edge of full-size boards.

Foil-faced materials must have all metal coatings removed by abrasion and be thoroughly cleaned before conditioning or testing.

Uncured material must be fully cured. Under normal conditions, two-ply laminates are recommended for comparison with prepreg materials. Single-ply laminates are recommended for single-ply cover layers and similar products.

The equipment and materials used in the tests are as follows:

• At least a 25 kV high voltage fault tester with adequate current rating, a motorized control with a 500 volt per second rate of rise, and a meter capable of indicating a 5 percent fault voltage over the full range of actual fault voltages (usually 1 kV to 20 kV)
• Oil tank filled with insulating oil.
• The electrode test set consists of 5 cm diameter electrodes with a 0,64 cm radius on the edge. The electrodes can be made of stainless steel or brass. The electrodes must be free of surface irregularities and can be polished to achieve this.
• Two high voltage test leads (leads rated above the voltage capability of the tester are recommended).
• Micrometer capable of resolving at least 0,0003 cm. For accurate measurement of materials below 0,013 cm, testing accuracy may be severely limited by the ability to accurately measure the sample.
• Constant temperature water bath filled with distilled water, capable of maintaining 50 degrees plus/minus 2 degrees.
• Large beaker or pan filled with distilled water at ambient temperature.
• Rack for supporting and separating samples in a 50°C water bath.
• Lint-free paper towels.

Unless otherwise specified, the sample shall be conditioned in distilled water held at 50°C plus/minus 2°C for 48 hours plus 2 hours and minus 0 hours. Following this, the sample shall be immersed in distilled water at ambient temperature for a minimum of 30 minutes and a maximum of four hours to achieve temperature equilibrium without significant changes in moisture content.

The test should be performed at ambient temperature, 23 degrees Celsius plus/minus 5 degrees Celsius. Relative humidity is not important since the tests are performed under oil.

When testing, the preconditioned sample is removed from the ambient water and dried with a lint-free paper towel. The sample thickness is determined and recorded at four points, 2,5 cm from the edge at the midpoint of each side. The sample is placed in the test fixture and centered to reduce the possibility of flashover. The tester is operated to apply voltage at a rate of 500 volts per second, and the point at which the device indicates a failure is observed. For values ​​above 10 kV, the breakdown voltage is recorded to the nearest 0,1 kV and for all lower values, at least to the nearest 5 percent. The sample is removed from the oil medium, and it is verified that a failure has occurred. If none are visible, the sample is reinserted, carefully centered, and the test is repeated. If flashover occurs, a larger sample or fresh oil is used. The remaining two samples are tested as described above.

The average thickness for each sample is calculated from the four individual measurements. The electrical strength for each sample is determined in volts per mil by dividing the breakdown voltage, expressed in kilovolts, by the thickness. The average electrical strength is determined by averaging the individual values ​​for each sample. The average is rounded to the nearest 10 volts per mil. If any sample falls below the specification minimum, a percentage of the requirement is calculated.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services to businesses in accordance with the "IPC-TM-650 2.5.6.2 Electrical Strength of Printed Wiring Material" standard.