How to test the pcba to see if it works?


After the circuit board  completed, it generally needs to undergo a variety of tests, such as short-circuit test and open-circuit test. Due to the complexity of the circuit board production process, there are a variety of defects , such as residual glue and line over-etching. Residual glue usually refers to the bottom of the blind holes left behind glue.

Line over-etching means that for various reasons caused by the original line part of the copper is etched away. These defects usually lead to a decrease in the reliability of the conductive circuit. Therefore, these defects must be found when the board is testing. These defects can lead to a more significant change in the resistance of the conductive lines. So in theory, you can measure the resistance value of the conductive lines to measure the presence of defects.


Existing technology for electrical testing of circuit boards are generally in accordance with the International Standards for Circuit Boards (IPC specification). However, in the IPC specification, the circuit board conductive line path resistance standard for 10Q. That is, the conductive line between the two ends of the resistance is less than IOQ that is normal. So for the circuit board resistance measurement methods and standards are only applicable to the IOQ level of resistance, and the current circuit board.  Such as flexible Circuit boards, such as flexible circuit boards in the conductive line between the two ends of the resistance between 0.01Q to 2Q. So far less than 10Q, can not be fully in accordance with the IPC specifications for electrical testing of circuit boards.


Usually circuit boards have the following two methods of board testing.

The first: flying probe test


Flying probe tester is an instrument for testing PCB boards  with high density of component arrangement, many layers. High wiring density and small distance between test points, mainly for testing insulation and conduction values of circuit boards. Not dependent on mounting on a fixture or stand, based on this system, two or more probes are mounted on tiny heads that can move freely in the x-y plane, and the test points are directly controll by CADI Gerber data.

The dual probes can  move within 4 mil of each other. The probes can move independently and there is no real limit to how close they can be to each other. The tester with two arms that move back and forth  based on the measurement of capacitance. The circuit board place firmly pressed against the insulation on a metal plate, which serves as the other metal plate for the capacitor. If there is a short circuit between the lines, the capacitance will be larger than at a defined point. If there is a broken circuit, the capacitance will become smaller.


The second: open the test rack.


Test rack is a test die, circuit board test rack is an important tool to check whether there is a problem with the circuit board. Open test rack is to detect whether the circuit board is open short-circuit phenomenon, over-hole inaccessible phenomenon. It is to ensure the quality of the board.


Open test rack and a benefit is: if the test rack on that board to return the number of orders. The follow-up will not have to pay the cost of testing. And flying probe test is different, the next time to do this single or to pay the flying probe test fee.


Detection of circuit boards can  use signal injection method, substitution method, non-online measurement method. And online measurement method, parameter testing method, waveform observation method, intuitive inspection method signal tracing method. AC short-circuit method, etc., of which the substitution method is relatively simple, the use of known intact with the same model, specifications of the circuit board to repair. it can  substitute for the circuit board under test repair, to determine whether the circuit board is damage.


Second, how to maintain the circuit board in use




Circuit board in use, must  regularly maintaine to do so, which can ensure that the circuit board in good working condition. But also reduce the failure rate of the circuit board. Semi-maintenance  is very necessary, mainly refers to each quarter on the circuit board dust is clean-up work. You can use a special cleaning solution for cleaning. After the dust cleaning, but also need to use the hair dryer to dry it.


2. Annual maintenance


Every year the circuit board needs annual maintenance work, including cleaning dust, electrolytic capacitor capacity sampling, etc. If the electrolytic capacitor capacity will  lower than 20% of the nominal capacity, it should  replace immediately. Generally speaking, the life of electrolytic capacitors in about ten years, so it needs to  replace once a decade.


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