PCB Technical - 10 PCB repair inspection methods and storage methods

10 kinds of circuit board repair and detection methods

Circuit board maintenance and inspection methods are mainly divided into the following ten types:

1. Offline measurement

When the circuit board is not soldered into the circuit, compare the DC resistance value between the pins with the known normal DC resistance value between the pins of the circuit board of the same model to determine whether it is normal.

2. Online measurement

Measure whether the voltage value, resistance value and current value of each pin of the circuit board are normal on the circuit to determine whether the circuit board is damaged.

3. Substitution method

Replace the circuit board under test with a well-known circuit board of the same model and specification. It can be judged whether there is a problem with the circuit board, and the circuit board can be repaired.

4. Separation test

A fault checking method that separates the circuit parts related to the fault in the electronic equipment in order to clarify the range of the circuit where the fault is located. This method is to pass multiple separate inspections to confirm part of the circuit and negate part of the circuit, so that the range of the circuit where the fault may occur is narrowed step by step, until the fault location is found, and the circuit board is repaired.

5. Signal injection

Use the different output signals of the external signal source as known test signals, and use the terminal indicator of the tested electronic device to show the test result. During the inspection, select the corresponding signal source according to the specific requirements to obtain the known signals of different indicators; check from the latter stage to the previous stage, that is, to inject the known signals from the input terminal of the terminal indicator of the tested equipment, and then sequentially The subsequent stage circuit moves to the previous stage circuit. In the industrial circuit board maintenance, inject the known and different test signals into the input terminals of each level of the circuit, and observe whether the reaction of the terminal surface indicator of the tested equipment is normal, and use this to determine the location of the fault and analyze the occurrence of the fault The basis of the reason.

6. Intuition check

Without using any equipment or soldering any circuit components, it is a method to check the fault of the PCB circuit board to be repaired based on human intuition-sight, smell, hearing, and touch. Intuitive inspection is the simplest method of equipment failure.

7. Signal tracking method

Use a single test signal, with the help of an oscilloscope, an electronic voltmeter, etc., to check step by step from front to back. This method can in-depth quantitative inspection of all levels of circuits, and can quickly determine the location of the fault.

8. AC short circuit method

A method of bypassing a certain part of the electronic equipment circuit under test by using capacitors of appropriate capacity and withstand voltage. It is suitable for judging the circuit parts that produce power interference and parasitic oscillation in the circuit of electronic equipment.

9. Parametric test

An electronic equipment fault inspection method that uses instruments to test the voltage value, current value, component value, device parameter, etc. in the electronic equipment circuit. Generally, the resistance value is measured when the power is not applied; the voltage value and current value are measured when the power is applied; or the components are removed to measure the related parameters.

10. Waveform Observation Method

Use an oscilloscope to observe the waveforms of the faulty parts and related parts of the electronic equipment; and analyze the cause of the fault and take the circuit board repair measures based on the difference between the waveform shape, amplitude parameters, time parameters and the normal waveform parameters of the electronic equipment obtained from the test.

PCB circuit board storage method

A PCB board undergoes the final finished product inspection. While waiting for shipment or is not in a hurry to assemble the finished product, the PCB board needs to be stored at this time. Prevent the storage time from being too long, which will affect the performance of the product.

Vacuum packaging storage

The PCB board cannot be in direct contact with water, nor can it be exposed to humid air for a long time. At this time, we need to vacuum bag the PCB board, and the packaging needs to be surrounded by bubble film around the box and put on moisture-proof Beads. Then label and classify. Store in a dry and ventilated place, avoid direct sunlight.

Brush with three anti-paint

PCB boards with surface treatment such as immersion gold, electro-gold, spray tin, and silver plating can generally be stored for 6 months, and PCB boards with surface treatment such as immersion silver, tin, and OSP can generally be stored for 3 months. It is recommended to apply a layer of conformal paint to PCB boards that have not been used for a long time. In this way, the storage life of the PCB will increase to about 9 months.

Temperature and humidity control

The temperature of the warehouse where PCBA is stored should be controlled at 23±3°C, 55±10%RH, the temperature under good storage conditions should be less than 25 degrees, the relative humidity should be less than 65%, and the indoor environment should be free of corrosive gases.