PCB inspection, these points you must know

It is strictly prohibited to test PCB boardby using grounded test equipment to contact the TV, audio, video and other equipment on the baseboard that is live without isolating transformer

When testing PCB board, we should pay attention to the following 9 tips to ensure the quality of the product.

1.PCB detection

It is strictly prohibited to test PCB board by using grounded test equipment to contact the TV, audio, video and other equipment on the baseboard that is live without isolating transformer

It is strictly prohibited to directly test TV, audio, video and other equipment without power isolation transformer with the instrument whose shell has been grounded. Although the general radio recorder has a power transformer, when exposed to the more special especially large output power or the nature of the power supply is not very familiar with the television or audio equipment, first of all to make clear whether the chassis of the machine is live, otherwise it is easy to and floor live TV, audio and other equipment caused by short circuit, ripple integrated circuit, resulting in further expansion of the fault.

2. Pay attention to the insulation performance of electric soldering iron when detecting PCB board

Do not allow the use of electric soldering iron welding, to confirm that the iron is not charged, the shell of the iron ground. MOS circuit should be more careful, can use 6~8V low voltage circuit iron is safer.

3. Understand the working principle of the integrated circuit and its related circuits before testing the PCB board

Before checking and repairing integrated circuit, we should be familiar with the function, internal circuit, main electrical parameters, the role of each pin, and the normal voltage, waveform and components of the pin circuit. If these conditions are in place, analysis and inspection are much easier.

4. Do not cause short circuit between pins when testing PCB board

When measuring voltage or testing waveform with oscilloscope probe, the stylus or probe should not be short-circuited between the pins of integrated circuit due to sliding, so the measurement should be carried out on the printed circuit directly connected with the pins. Any momentary short circuit can easily damage the IC, and extra care should be taken when testing CMOS integrated circuits in flat packages.

5. The PCB board test instrument should have high internal resistance

When measuring the DC voltage of integrated circuit pins, use a multimeter with an internal resistance greater than 20 kω /V. Otherwise, there will be a large measurement error for some pins.

6. Pay attention to the heat dissipation of power integrated circuit when detecting PCB board

The heat dissipation of the power integrated circuit should be good. It is not allowed to work in a high power state without a radiator.

7. Test the PCB board leads properly

If you need to add components to replace the damaged part of the integrated circuit, small components should be selected, and wiring should be reasonable to avoid unnecessary parasitic coupling, especially to deal with the audio power amplifier integrated circuit and the pre-amplifier circuit between the ground terminal.

8. Check PCB board to ensure welding quality

Welding is really solid, the accumulation of solder, porosity is easy to cause virtual welding. Welding time is generally not more than 3 seconds, the power of the iron should be about 25W internal heat. The soldered integrated circuit should be carefully checked, and the ohmmeter should be used to measure whether there is short circuit between the pins to confirm that there is no solder adhesion phenomenon before switching on the power supply.

9. Detection PCB board do not easily determine the damage of integrated circuit

Do not easily judge the integrated circuit has been damaged, because the vast majority of integrated circuits are direct coupling, once a circuit is abnormal, may lead to multiple voltage changes, and these changes are not necessarily caused by the damage of the integrated circuit. In addition, in some cases, when the pin voltage is consistent with or close to the normal value, it may not be able to show that the integrated circuit is good, because some soft faults will not cause changes in DC voltage.

Control PCB cost, these four points you want to look at

Usually the same area, the more PCB layers, the more expensive the price. The design engineer should use as few layers as possible to complete the PCB design while ensuring the quality of the design signal.

In PCB design, there are four main factors affecting the cost.

PCB layers

Usually the same area, the more PCB layers, the more expensive the price. The design engineer should use as few layers as possible to complete the PCB design while ensuring the quality of the design signal.

PCB size

In the case of a certain number of layers, the smaller the PCB size, the lower the price will be. In PCB design, if the size of PCB can be reduced without affecting the electrical performance, the size can be reduced reasonably and the cost can be reduced.

Manufacturing difficulty

The main parameters affecting PCB manufacturing include small wire width, small wire spacing, small drilling, etc. If these parameters are set too small or the process capacity has reached the small limit of PCB factory, then the PCB yield will be low and the cost of production and manufacturing will increase. Therefore, in the process of PCB design, try to avoid challenging the limits of the factory, set 20 reasonable line width and line spacing, drilling and so on. In the same way, through holes can complete the design. Try not to use the blind buried holes of HDI, because the processing technology of blind buried holes is much more difficult than through holes, which will increase the production cost of PCB.

PCB board material

PCB board classification is many, common paper based printed circuit board, epoxy glass fiber cloth printed circuit board rice composite substrate printed circuit board, special substrate printed circuit board metal substrate, etc. Different materials processing gap is very large, and some special materials processing cycle will be long, so in the design as far as possible to choose both can meet the design requirements, and relatively common affordable materials, such as RF4 materials.