Simple PCB testing process

The PCB industry is a B2B industry, and the cooperation between them is often based on trust. Any unhappiness in any link will lead to the collapse of trust between both parties. Therefore, PCB testing is considered an indispensable link. Taking FS Technology PCB testing as an example, we provide a variety of testing processes: manual inspection, AOI testing, assembly inspection, XRAY inspection, etc. In this article, we will discuss the simple PCB testing process, which is suitable for both PCBA processing factories and electronics enthusiasts.

As the most common and cheapest testing equipment, digital multimeters are often used in the testing process of circuit boards. If your board is a simple circuit configuration and can be powered normally, using a digital multimeter to check the rail voltage of the IC, the output of the voltage regulator will be the right choice. An oscilloscope can be used to verify the voltage waveform and communication of the powered board. To check for the presence of a Wi-Fi signal output from the PCBA, even a cell phone can come in handy.

With the assistance of a digital multimeter, we can easily find the leakage capacitor by adjusting the resistor setting. Specific steps: Set the meter to read in the high ohms range and touch the meter leads to the corresponding leads on the capacitor; red is positive and black is negative. The meter should start at zero and slowly move towards infinity. For large capacitor values, the ramp will be very slow.

Before making electrolytic measurements, disconnect the power supply and carefully discharge the capacitor by connecting a resistor across the leads. When the meter is on the ohms setting, it sends some constant current from the positive lead to the negative lead. An open cap will show open; a shorted one will show close to zero ohms.

Checking the operation of HMI interface items such as touch panels and switches may reveal functional issues due to connectivity or component issues.

Signal probing with a DMM or oscilloscope requires some knowledge of circuits to interpret the results, but it becomes much easier if you have a known good board to compare point-to-point results. The DC voltage test is first probed with reference to ground. When checking an IC, test the power pins first.

Most ICs can be identified by their markings, and many can be tested for operation to their published specifications using oscilloscopes and logic analyzers. Comparing an IC's behavior to that of a known good IC is a quick way to identify anomalous behavior.

An engineer's favorite habit of touching low-voltage parts of a circuit changes the impedance, which in turn changes the behavior of the system (or inadvertently overheats!). Used in conjunction with an oscilloscope, for example, this technique can help identify where additional capacitance is needed to eliminate unwanted oscillations.

Intermittent failures are the most challenging and time-consuming aspect of troubleshooting. Common irregular failures can be caused by overheated or degraded components, poor soldering, and loose connections. Long memory in oscilloscopes helps zoom in on signal records to find rare events. Using freeze spray in the right places can sometimes exacerbate and identify intermittent problems.

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