Summary on the judgment and detection methods of integrated circuits

Date：2022-01-05 15:46:13Views：1458

Nowadays, due to the damage of an integrated circuit, some or several parts of electronic products can not work often, which affects the normal use of equipment. So how to detect the quality of integrated circuits? The detection methods of integrated circuits mainly include visual method, sensory method, voltage detection method, resistance detection method, current detection method, signal injection method, substitution method, heating and cooling method, step-up or step-down method and comprehensive method. Let's take a look at the summary of the judgment and detection methods of integrated circuits!

Usually, there are many integrated circuits in a device. When getting a faulty integrated circuit device, first judge the general part of the fault according to the fault phenomenon, then gradually reduce the possible part of the fault through measurement, and finally find the fault.

Visual inspectionIt is to observe whether the appearance of the integrated circuit is different from the normal one through the eyes, so as to judge whether the integrated circuit is damaged. Its main maintenance skill is to see which appearance is damaged. The appearance of the normal integrated circuit is clear handwriting, non-destructive material, smooth surface and no rust on the pins. The appearance of the damaged integrated circuit is cracked, cracked or scratched on the surface and small holes on the surface. Lack of angle, block, etc.

Sensory methodIt is to experience whether the integrated circuit is normal through the feeling of the human body. Senses mainly include touch, hearing and smell. The feeling method includes whether the surface temperature of the integrated circuit is overheated, whether the heat sink is overheated, whether it is loose, and whether it makes abnormal sound. It is the fragrance that produces abnormal taste. The touch is mainly to touch the temperature by hand and broadcast the perceived firmness of the integrated circuit by hand. Sensing temperature is to judge whether the heating of integrated circuit is abnormal according to the thermal effect of current, that is, whether it is overheated. The normal temperature of integrated circuit is - 30-85 ℃, and the installation is generally far away from heat source. The factors affecting the temperature of integrated circuit include working environment temperature, working time, chip area, integrated circuit structure, storage temperature, material and area with heat sink, etc. overheating is often considered from the speed of temperature rise, persistence of temperature and peak temperature.

Voltage detection methodBy detecting the pin voltage value of the integrated circuit and comparing it with the relevant reference value, we can get whether the integrated circuit has fault and the cause of the fault. There are two kinds of data in voltage detection method, namely reference data and detection data.Resistance detection methodIt is a method to judge the quality of the integrated circuit by measuring the positive and negative DC resistance of each pin of the integrated circuit to the ground and comparing it with the normal reference value. This method includes on-line resistance detection method and off-line resistance detection method.

(1) On line resistance detection method refers to the DC resistance detection method when the integrated circuit is electrically connected with the peripheral components. Its biggest advantage is that there is no need to solder the integrated circuit from the circuit board.

(2) The off-line resistance detection method is to measure the resistance between the bare integrated circuit pins, especially between other pins and their grounding pins. Its biggest advantage is that the influence of peripheral components on the measurement can be eliminated

Current detection methodIt is a measurement method that measures the current of each pin of the integrated circuit, mainly to detect the current value of the power supply end of the integrated circuit. Because the measuring instrument needs to be connected in series with the circuit to measure the current, it is not widely used.

At the same time, the current can be measured by measuring the resistance and voltage, and then calculated by Ohm's law. The current value signal injection method refers to a method to judge the fault through the reflection of voltage, current and waveform by injecting the test signal (including interference signal) into the IC pin. One of the keys of this method is to use an appropriate signal source. Signal sources can be divided into special signal sources and non special signal sources. For maintenance personnel, non dedicated signal source has strong practicability. Non dedicated signal sources can be multimeter signal sources and human signal sources.

Substitution methodIt is a maintenance method to replace the suspected bad integrated circuit with a good integrated circuit. Its biggest advantage is that it is clean and easy. When using this method, we should pay attention to the following problems.

(1) Substitution method is divided into direct substitution method and indirect substitution method.

(2) Try to replace the original model of integrated circuit

(3) Replacing integrated circuits sometimes needs to pay attention to the meaning represented by different tail numbers.

(4) Alternative integrated circuits need to pay attention to the packaging form.

(5) The heat sink to be installed for the replacement IC is installed correctly.

(6) Before judging whether the peripheral circuit components of the integrated circuit are damaged, do not rush to replace the integrated circuit, otherwise the replaced integrated circuit will be damaged again.

(7) The replaced integrated circuit is guaranteed to be good, otherwise the detection work will fall into a dead end.

(8) If tentative substitution is carried out, it is better to have a protection circuit.

(9) Remove the bad integrated circuit and operate it correctly. When taking a new integrated circuit, pay attention to eliminate static electricity on people. The heating method is to suspect that the temperature of the integrated circuit is obviously abnormal shortly after normal operation due to poor thermal stability, but it is not fully sure. At this time, an object with a certain temperature radiates heat to it, resulting in obvious failure, so as to judge the damage of the integrated circuit. The heating tools can be baked with an electric soldering iron or blown with an electric fan. The baking and blowing time can not be too long, But don't test every integrated circuit like this. In addition, if the suspected integrated circuit is heated and no fault occurs, it should be considered to stop heating.

Cooling methodIt is a maintenance method to cool the temperature of the integrated circuit so that the fault disappears, so as to judge the damage of the cooled integrated circuit. The cooled substances or tools can be cooled with 95% alcohol and cold blower, and can not be cooled with water or oil. The increase of the power supply voltage of the IC is the boost method. Boost method is generally used when the power supply of integrated circuit is connected low due to fault (the resistance value of a component becomes larger), otherwise it is rarely used. Moreover, the boost voltage should not be too high and should be within the allowable range of integrated circuit power supply.

When the value of the power supply voltage of the integrated circuit is reduced, it isDepressurization method。 Integrated circuits generally work at low voltage. If inferior integrated circuits are used or other reasons cause high working voltage of integrated circuits and self excitation of integrated circuits, step-down method can be used to eliminate faults. The step-down method generally adopts the series resistance method at the power end, the series diode method at the power end, and the method of increasing the power supply voltage. Increasing the power supply voltage is rarely used in the actual maintenance process. The reason is that this method is labor-consuming and time-consuming whether it is external power supply or changing the introduction path of integrated circuit power line, but the voltage of step-up method or step-down method should be within the limit voltage.

According to the actual maintenance experience, when detecting the internal DC equivalent resistance of the integrated circuit in the circuit, it is not necessary to weld the integrated block from the circuit. Just disconnect the pin with abnormal voltage or circuit resistance from the circuit, and disconnect the grounding pin from the circuit board at the same time. Keep the other pins in their original state, and measure the positive and negative resistance value in R between the test pin and the grounding pin. However, it should be noted that safe, simple, easy, economical, reliable and fast methods and the combination of these methods should be used as much as possible. During testing, we should carefully analyze, flexibly use various methods, explore the law, and find out the problem quickly and accurately.