The circuit board factory introduces 9 common sense for testing flexible circuit boards
It is strictly prohibited to directly test TV, audio, video and other equipment without power isolation transformer with grounded shell. Although general radio recorders have power transformers, when touching special TV or audio equipment, especially those with large output power or little understanding of the nature of the power used, it is necessary to first find out whether the chassis of the recorder is charged, otherwise it is very easy to cause power short circuit with TV, audio and other equipment charged on the backplane, affecting the integrated circuit, causing further expansion of the fault.
2. Pay attention to the insulation performance of the electric soldering iron when testing the flexible circuit board.
It is not allowed to use a soldering iron for welding with electricity. Make sure that the soldering iron is not charged. It is better to ground the shell of the soldering iron. Be more careful with MOS circuits. It is safer to use a 6-8V low-voltage electric soldering iron.
3. Before testing FPCs, it is necessary to understand the working principles of integrated circuits and related circuits.
Before checking and repairing the integrated circuit, it is necessary to be familiar with the function, internal circuit, main electrical parameters, the role of each pin, the normal voltage of the pin, the working principle of the circuit composed of the waveform and peripheral components. If the above conditions are met, the analysis and inspection will be much easier.
4. Test the FPC to avoid short circuit between pins.
When measuring the voltage or testing the waveform with the oscilloscope probe, the probe or probe shall not cause short circuit between the pins of the integrated circuit due to sliding, and it is better to measure on the peripheral printed circuit directly connected with the pins. Any transient short circuit is easy to damage the integrated circuit, so you should be more careful when testing CMOS integrated circuits in flat package.
5. The internal resistance of FPC testing instrument shall be large.
When measuring DC voltage of integrated circuit pins, a multimeter with internal resistance greater than 20K Ω/V shall be selected, otherwise there will be large measurement error for some pin voltages.
6. The heat dissipation of power integrated circuit shall be paid attention to when detecting FPC.
The power integrated circuit shall have good heat dissipation, and it is not allowed to work in a high-power state without a radiator.
7. The detection of FPC leads shall be reasonable.
If it is necessary to add peripheral components to replace the damaged parts inside the integrated circuit, SMAll components shall be selected, and the wiring shall be reasonable to avoid unnecessary parasitic coupling, especially the grounding terminal between the audio power amplifier integrated circuit and the preamplifier circuit.
8. Welding quality shall be guaranteed when testing FPC.
When welding, it is sure to weld firmly, and the accumulation and porosity of solder are easy to cause false soldering. The welding time is generally no more than 3 seconds, and the power of the soldering iron should be about 25W of internal heating type. The soldered integrated circuit should be carefully checked. It is better to use an ohmmeter to measure whether there is a short circuit between the pins, and then turn on the power after confirming that there is no solder adhesion.
9. Do not easily judge the damage of the integrated circuit when detecting the FPC.
Do not easily judge whether the integrated circuit is damaged. Because the vast majority of integrated circuits are directly coupLED, once a circuit is abnormal, it may lead to multiple voltage changes, which may not be caused by the damage of the integrated circuit. In addition, in some cases, when the measured voltage of each pin is consistent with or close to the normal value, it does not necessarily mean that the integrated circuit is good. Because some soft faults will not cause changes in DC voltage. circuit board manufacturers, circuit board designers and PCBA manufacturers will explain to you: circuit board manufacturers will introduce 9 common knowledge about testing Flexible circuit boards.