PCB Technical - PCB considerations and damage to electronic components

Things to consider when making PCB circuit boards

At this stage, in the field of electronic product processing, PCB boards are indispensable as one of the most important electronic components. At this stage, there are various types of PCB boards, such as high-frequency PCB boards, microwave PCB boards, and other types of printed circuit boards that have achieved corresponding recognition in the market. PCB board manufacturers have specific production processes for various types of boards. But in general, the production and processing of PCB boards need to consider several three aspects

1. Consider the choice of substrate

The base material of PCB board can be divided into two categories: organic material and inorganic material. Each material has its own unique advantages. For this reason, the choice of substrate type takes into account various properties such as dielectric properties, copper foil type, base groove thickness, and production and processing characteristics. Among them, the thickness of the surface copper foil is a key factor affecting the performance of this printed circuit board. Generally, the thinner the thickness, the more convenient the etching and the improvement of the precision of the graphics are advantageous.

2. Consider the setting of the production environment

The indoor environment of the PCB board production and processing workshop is also a very important aspect. The control of the working environment temperature and the relative humidity of the air are particularly important factors. If the temperature of the working environment changes too much, it may cause the holes on the base plate to break.

If the relative humidity of the air is too large, the humidity will have an adverse effect on the performance of the substrate with strong water absorption, mainly in terms of dielectric properties. For this reason, it is extremely important to maintain appropriate indoor environmental conditions during PCB production and processing.

3. Consider the choice of technological process

The production of PCB is susceptible to many factors. The number of layers of production and processing, punching process, surface coating treatment and other processes will all affect the quality of the finished PCB board. For this reason, the indoor environment of these technological processes, PCB board production and processing are fully considered in combination with the characteristics of the production equipment, and can be flexibly adjusted according to the types of PCB boards and production and processing requirements.

In summary from the above description, PCB production and processing need to consider the choice of substrate, the setting of the production environment, and the choice of process flow. At the same time, the processing and blanking methods of the engineering materials of the PCB board are also an aspect that needs to be carefully selected, which is closely related to the smoothness of the printed circuit board.

The damage characteristics of the electronic components of the PCB circuit board

Resistance damage

Resistance is the component with the largest total amount of electrical equipment, but it is not the component with the highest damage rate. Open circuit is the most common type of resistance damage. It is rare for the resistance value to become larger, and it is very rare for the resistance value to become smaller. Common types include carbon film resistors, metal film resistors, wire wound resistors and insurance resistors.

The first two types of resistors are the most widely used. One of the characteristics of their damage is the high damage rate of low resistance (below 100Ω) and high resistance (above 100kΩ). ) Is rarely damaged; second, when low-resistance resistors are damaged, they are often burnt and blackened, which is easier to detect, while high-resistance resistors are rarely damaged. Wirewound resistors are generally used for high current limiting, and the resistance is not large. When cylindrical wire wound resistors are burnt, some will turn black or the surface will burst or crack, and some will have no traces. Cement resistors are a type of wire wound resistors, which may break when burned out, otherwise there will be no visible traces. When the fuse resistor burns out, a piece of skin will be blown off on the surface, and some have no traces, but generally it will not burn or turn black. According to the above characteristics, there can be a certain focus when checking the resistance, and the damaged resistance can be found quickly.

Electrolytic capacitor is damaged

Electrolytic capacitors are widely used in electrical equipment and have a high failure rate. Electrolytic capacitor damage has the following types of manifestations: one is complete loss of capacity or reduced capacity; the second is mild or severe leakage; the third is loss of capacity or reduced capacity and leakage. Methods to find damaged electrolytic capacitors are:

(1) Look: some capacitors will leak when damaged, and there will be a layer of oil on the surface of the circuit board under the capacitor or even on the surface of the capacitor. This type of capacitor must never be used anymore; some capacitors will bulge after damage, and this type of capacitor cannot continue to use;

(2) Touch: After starting, some electrolytic capacitors with serious leakage will be hot, and even hot when touched with fingers, this type of capacitor must be replaced;

(3) There is electrolyte inside the electrolytic capacitor. Long-time baking will cause the electrolyte to dry out and reduce the capacitance. Therefore, it is important to check the capacitors near the heat sink and high-power components. The closer they are, the damage may be possible. The greater the sex.

Damaged semiconductor devices such as diodes and triodes

The damage of diodes and triodes is usually PN junction breakdown or open circuit, among which breakdown short circuits account for the majority. In addition, there are two kinds of damage performance: one is the deterioration of thermal stability, which is no problem when starting up, and soft breakdown occurs after working for a period of time; the other is that the characteristics of the PN junction deteriorate, use a multimeter R* In 1k measurement, all PN junctions are okay, but they can't work normally after using the computer. If you use R*10 or R*1 low-range measurement, you will find that the forward resistance of the PN junction is larger than the normal value. The second and triode can be measured on the road with a pointer multimeter. The more accurate method is: set the multimeter to R*10 or R*1 (usually use R*10, and then use R*1 when it is not obvious). 2. The forward and reverse resistance of the PN junction of the triode. If the forward resistance is not too large (relative to the normal value) and the reverse resistance is large enough (relative to the forward value), it indicates that the PN junction is okay. Otherwise, it is worth noting. Test after welding. This is because the peripheral resistance of the diodes and triodes of the usual circuits is mostly over several hundred or several thousand ohms. When measuring on the road with a low resistance value of a multimeter, the influence of the peripheral resistance on the PN junction resistance can be basically ignored.

Damaged integrated circuits

The internal structure of the PCB integrated circuit is complex, with many functions, and any part of it cannot work without problems. There are also two types of damage to integrated circuits: complete damage and poor thermal stability. When it is completely damaged, you can remove it and compare the forward and reverse resistance of each pin to ground with the same model integrated circuit, and you can always find one or several pins with abnormal resistance. For poor thermal stability, you can use absolute alcohol to cool the detected integrated circuit when the device is working. If the failure occurs later or the failure no longer occurs, it can be determined. Usually it can only be ruled out by replacing the new integrated circuit.