Cause Analysis And Solution Strategy of False Open Circuit in Flying Probe Test

Printed Board Product Questions:

If the test equipment and process data are excluded, another situation should belong to the problem of the PCB product itself, which is mainly manifested in warpage, solder mask, and irregular characters.

(1) Warpage:

Some production planners often omit the hot air leveling process and send it directly to the final inspection. If it is not heated, the warpage of the product is greater than the allowable warpage range of the testing equipment. Therefore, the process of heat leveling is indispensable, and it also requires inspection testers to add warpage measurement before testing.

(2) Soldering Mask:

Products with more open circuits are often unsatisfactory because some of the via holes are blocked by the solder mask layer. During the test, try to avoid the transfer hole (or ensure that the hole guide pass without error) test.

(3) Characters:

Many PCB manufacturers will print the characters first and then measure them electrically. As long as the printed position of the characters is slightly offset or the accuracy of the character film is not enough, the fine surface stickers and small holes may be partially covered by the characters. Therefore, in order to avoid the open circuit caused by the characters, it is more reasonable that the printed boards with thin surface mounts, small holes (Φ<0.5) and high density of thin lines should be electrically measured first and then the characters.

The difference between flying probe test and fixture test:

◆ A flying probe tester is a typical test equipment using capacitance method. The test probe moves quickly point by point on the circuit board to complete the test.

◆ The standard board learning must be carried out first, and the standard value of the capacitance of each network must be read in.

◆ Use the capacitance method to test first, and then use the resistance method for accurate confirmation when the measured capacitance is not within the qualified range.

◆ Four-wire measurement is possible.

◆ Due to the slow test speed, it is only suitable for testing samples with small batches.

Advantages and disadvantages:

◆ Test pins are easily damaged

◆ The test speed is slow

◆ High test density, the minimum pitch can reach 0.05mm or even smaller

◆ No fixture cost

◆ The withstand voltage cannot be tested, and the high-level high-density board test has a greater risk.