What is PCB Electrical Testing? Global Standards

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This International Standard specifies methods for testing printed circuit boards and printed circuit assemblies and their associated materials or the bonding strength of parts, regardless of how they are manufactured.

What is the process of PCB electrical testing?

This standard consists of parts containing information for product designers, technologists, and specialists in the field of test methodology. Each part focuses on a specific main theme; test methods are grouped according to their use and numbered sequentially according to their development and publication.

In some cases, test methods developed by other technical committees (eg TC 50) have been reproduced from existing IEC standards to provide the reader with a complete set of test methods.

In such a situation, the relevant test methods will be noted; if the test method is reproduced with minor modifications, the modified items will also be indicated.

This International Standard contains test methods for printed circuit boards and electronic assemblies. The descriptions shall be complete and contain sufficient detail to ensure uniformity and reproducibility of test methodologies and procedures.

The tests presented in this standard are grouped as follows:

R: preparation/conditioning test methods;

V: visual test methods

D: dimensional test methods;

C: chemical test methods;

M: mechanical test methods;

E: electrical test methods;

N: environmental test methods;

X: other test methods.

In order to create an index of specific types of tests, to maintain the sequence of their presentation, and to allow further expansion of the list of applicable types of tests, each test is identified by a sequential number added to the code letter of the group (for example, P or V, or others) to which the test method belongs.

The numbers of the test methods are irrelevant for the final sequence in which they are carried out; this function is implemented in the corresponding technical description, which provides for the use of a certain method. The relevant datasheet also provides, in most cases, criteria for passing or failing the test results to the specifications.

Accuracy in PCB Electrical Testing

The mode of routine calibration of the test equipment shall be clearly defined in the quality management documentation of the supplier or test organization and shall be following the requirements (ISO 9002 clause 4.11).

Calibration must be carried out by an organization accredited by a national or international metrology body. Calibration should be carried out regularly according to national or international standards.

In cases where calibration under a national or international standard is not possible, interlaboratory verification methods with documented results may be used to increase the reliability of measurement errors.

The Interval Between the Calibration

The interval between calibrations should normally be one year. Equipment that systematically falls outside the margin of error should be calibrated more frequently. Equipment that consistently meets the requirements for error limits may be calibrated at longer intervals.

Calibration and maintenance information must be recorded for each measuring instrument. These records should include the uncertainties of the calibration technology (percentage deviations) in order to gather information about the uncertainties of measurement and from this to determine the accuracy of the instrument.

A procedure shall be in place to deal with situations where the meter reading is outside the calibration range.

PCB

List of approved test methods

This International Standard contains detailed descriptions of the performance of each specific test method with minimal cross-reference to other procedures.

These methods introduce by reference to the use of universal conditioning methods, for example by reference to IEC 61189-1 and IEC 60068, and, where applicable, such use becomes a mandatory part of the test method standards.

Each method has its own name, number, and information about the current revision status of the document, which allows you to quickly update and improve the methods as industry requirements change and the need for a new methodology arises.

The whole complex of test methods consists of methods combined into groups, as well as individual tests.

R: Test methods for preparation/conditioning

Under consideration

: Visual test methods

Test 3V01: Visual inspection, 3x magnification

Purpose

This method describes the procedure for visual inspection of materials and finished printed circuit boards in cases where a 3-fold increase is required by the technical requirements (TT) or partial specifications (PRS).

Finished printed circuit board(s), finished printed circuit board section, or test coupon(s) specified in a specific TT or CTU.

Test equipment and materials

The following materials and test equipment shall be used:

  • an optical device capable of providing 3x magnification.
  • b) a reference optical device capable of 10x magnification.

The following materials and test equipment shall be used:

a) Glow wire consisting of a loop of nickel and chromium (80%/20%) wire 4 mm in diameter (see figure 1). When forming the loop, care must be taken to prevent the formation of a crack at the end;

b) To measure the temperature of the hot wire, use a sheathed thin wire thermocouple having an overall diameter of 0.5 mm and NiCr and NiAl wires with a spot weld located inside the sheath.

c) The sheath consists of metal capable of withstanding a temperature of at least 960°C. The thermocouple is mounted in a 0.6 mm diameter blind hole drilled at the end of the glow wire, node Z.

The temperature/voltage characteristics shall be per IEC 60584-1; The characteristics given in this International Standard are essentially linear. If a reliable reference temperature cannot be obtained by other means, the cold joint must be located in melting ice;

d) The temperature/voltage measuring instrument shall have an accuracy of 1% (class 0.5 according to IEC 60051);

e) A hot wire is heated by electricity. The current required to heat the end of the wire to a temperature of 960°C lies in the range of 120-150 A, depending on the type of wire;

f) The test apparatus shall be designed so that the glow-wire is horizontal and a force of 0.8 to 1.2 N is applied to the specimen. The force shall be maintained at this value for as long as the glow-wire or test specimen is moved relative to each other in a horizontal direction at a distance of at least 7 mm;

Perform the following steps in PCB Electrical Testing:

a) Precondition the test specimen in an air circulation oven for 24 h at (124 ± 2)°C. Then, the test specimens for stabilization are kept in a desiccator over anhydrous calcium chloride at room temperature for 4 hours;

b) If the orientation of the test specimen is other than vertical, it shall be specified in the specific specifications.

c) The thermocouple should be calibrated at 960°C. The standard calibration method should be to place silver foil (99.8% purity, 2 mm, 0.6 mm thick) on the upper surface of the end of the glow wire. The hot wire is heated by an increase in the current while melting the silver foil reaches a temperature of 960 ° C;

d) To compensate for changes in the thermocouple and connections, the thermocouple should be recalibrated every five measurements;

e) It must be ensured that the thermocouple can follow the movement of the end of the hot wire caused by thermal expansion;

f) The test piece should be mounted in such a way as to minimize heat loss due to transfer to the test fixture;
How to use glow wire in PCB electrical testing?

The end of the glow wire should be applied to that part of the test specimen which, in normal use, is more likely to be subjected to thermal stress and/or which is the largest combination of base material and coating(s). 

The end shall be applied at least 15 mm below the top edge of the test piece. The glow wire must be heated by an electric heater to one of the preferred temperatures specified in the specification. The temperature should be measured with a calibrated thermometer. 

It must be ensured that the temperature and heating current are stable for at least 60 s before starting the test and that no heat radiation is applied to the specimen during this period or during calibration (e.g.

h) The end of the glow-wire shall be brought into contact with the test specimen for (30 ± 1) s, or for the time specified in the NC.

 The heating current must remain constant during this time. After this time, the glow-wire and the test piece shall be slowly separated, avoiding further heating of the test piece and air movement that could affect the test results;

i) Before each test and calibration, remove material residues from the end of the glow wire (with a brush).

Protocol to follow in Printed circuit board inspection

In addition to the general protocol requirements, the protocol must contain:

a) The number of samples, if other than five;

b) The length of time from the beginning of the application of the end of the wire until the time when the test specimen or the tissue paper underneath is ignited;

c) The length of time from the start of application of the end of the wire until the time the flame is extinguished (during or after the application of the glow wire);

d) The maximum flame height at any given time and place. Flame height is the vertical distance measured between the top edge of the glowing wire when applied to the test specimen and the visible end of the flame. The height of the flame at ignition lasting about 1 s shall not be taken into account;

e) Information on whether the test specimen burns or smolders and to what extent the test specimen or tissue paper has been engulfed in flames;

f) Whether the burning or smoldering ceased within 30 s after the glow wire was removed from the test piece. This refers to the test specimen and/or tissue paper.

Additional information about PCB testing

a) There is a clear hazard in the flammability test. Training of testers and knowledge of laboratory safety procedures is essential. For safety purposes, all combustion products should be considered toxic, even if they are not.

b) Small flammability tests, such as those given in this International Standard, provide information on the properties of the materials tested. The fire resistance of equipment in which printed circuit boards are used can only be assessed by testing the level of the equipment.

c) Test methods under development in IEC technical committees include the use of cone calorimeter materials in determining fire resistance.

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