IC chip detection method: how to judge the quality of IC chip?

Date：2021-10-20 14:10:57Views：2042

Many components such as resistors, diodes and triodes are made on semiconductor silicon wafer in the form of circuit, and then the pins are connected and encapsulated to form an integrated circuit. How to accurately judge whether the IC in the circuit is in working state? If the judgment is not accurate, it often takes great efforts to replace the new integrated circuit, and the fault still exists. Next, let's look at how to judge the quality of integrated circuit IC chip?

1. First, master the purpose, internal structure principle and main electrical characteristics of the IC in the circuit, and analyze the internal electrical schematic diagram if necessary. In addition to these, if there are DC voltage, waveform and forward and reverse DC resistance to ground of each pin, it provides more favorable conditions for judgment before inspection.

2. Then judge the position according to the fault phenomenon, and then find the fault element according to the position. Sometimes a variety of judgment methods are needed to prove whether the device is indeed damaged.

3. Generally, there are two methods to check and judge the IC in the circuit: one is off-line judgment, that is, the judgment that the IC in the circuit is not welded into the printed circuit board. In this method, it is very difficult to determine the quality of IC in the circuit without special instruments and equipment. Generally, the DC resistance method can be used to measure the forward and reverse resistance between each pin corresponding to the grounding pin, and compare it with the intact integrated circuit, The replacement method can also be used to insert the suspicious integrated circuit into the position of the integrated circuit of the same model of normal equipment to determine its quality. Of course, if possible, the integrated circuit tester can be used to quantitatively test the main parameters, so the use is more guaranteed.

4. There is also online inspection and judgment, that is, the judgment method of integrated circuit connected to printed circuit board. On line judgment is the most practical method to repair integrated circuits in TV, audio and video equipment. The following situations are described:

DC working voltage measurement method: mainly measure the DC working voltage value of each pin to the ground; Then compare with the nominal value to judge the quality of the integrated circuit. Using voltage measurement method to judge the quality of integrated circuits is one of the most commonly used methods in maintenance, but we should pay attention to distinguish non fault voltage errors. When measuring the DC working voltage of each pin of the integrated circuit, if the voltage of individual pins is inconsistent with the voltage value marked in the schematic diagram or maintenance technical data, do not rush to conclude that the integrated circuit has been damaged. The following factors should be eliminated before determining.

(1) Whether the nominal voltage provided is reliable, because the values marked on some instructions, schematic diagrams and other data are quite different from the actual voltage, sometimes even wrong. At this time, more relevant data should be found for comparison. If necessary, analyze the internal schematic diagram and peripheral circuit, and then conduct theoretical calculation or estimation to prove whether the voltage is wrong.

(2) To distinguish the nature of the nominal voltage provided, the voltage belongs to which working state. Because individual pins of the integrated block obviously change with different injection signals, you can change the band or the position of the recording and playback switch at this time, and then observe whether the voltage is normal. If the latter is normal, it means that the nominal voltage belongs to a certain working voltage, and this working voltage refers to that under a specific condition, that is, the measured voltage is different under different working conditions.

(3) Pay attention to the pin voltage change caused by the variable elements of the peripheral circuit. When the measured voltage is inconsistent with the nominal voltage, a potentiometer or switch with variable resistance (such as volume potentiometer, brightness, contrast, video recording, fast forward, fast reverse, video recording and playback switch, audio frequency amplitude modulation switch, etc.) may be connected to an individual pin or the peripheral circuit related to this pin. The position of these potentiometers and switches is different, and the pin voltage will be significantly different. Therefore, when the voltage of a certain pin is inconsistent, the position change of the pin or the potentiometer and switch associated with the pin should be considered. You can rotate or pull it at the beginning to see whether the pin voltage is near the nominal value.

(4) Errors caused by measurement shall be prevented. Due to the different internal resistance of the multimeter head or different DC voltage gears, errors will be caused. In general, the marked DC voltage is tested with the internal resistance of the test instrument greater than 20K Ω / v. When the multimeter with internal resistance less than 20K Ω / V is tested, the measured result will be lower than the original target voltage. In addition, it should also be noted that the voltage measured on different voltage levels will be different, especially with a large number of ranges, the reading deviation will have a more significant impact.

(5) When the measured voltage of a pin is inconsistent with the normal value, it shall be analyzed according to whether the pin voltage has an important impact on the normal operation of the IC and the corresponding changes of other pin voltages, so as to judge the quality of the IC.

(6) If the voltage of each IC pin is normal, the IC is generally considered normal; If the pin voltage of IC part is abnormal, start from the maximum deviation from the normal value, and check whether the peripheral components are faulty. If there is no fault, the IC is likely to be damaged.

(7) For dynamic receiving devices, such as TV sets, the voltage of each pin of IC is different when there is no signal. If it is found that the pin voltage should not change, but does not change with the signal size and different positions of adjustable components, it can be determined that the IC is damaged.

(8) For devices with multiple working modes, such as video recorders, the voltage of each IC pin is also different under different working modes.

The above is that when the IC in the circuit has no fault, the measured result is different from the nominal value for some reason. Therefore, in general, a test condition should be specified when testing the DC voltage or DC resistance of the integrated block, especially when recording as the measured empirical data. Usually turn each potentiometer to the middle position of the machine, and the signal source adopts the standard signal under a certain field strength. Of course, if the position of each function switch can be recorded again, it will be more representative. If the measured voltage of individual pins still does not conform to the nominal value after excluding the above factors, further analysis is required, but there are no more than two possibilities. One is caused by the failure of the integrated circuit itself; The second is caused by the peripheral circuit of the integrated block. Distinguishing these two fault sources is also the key to repairing integrated circuit household appliances.

AC working voltage measurement method: in order to master the changes of IC AC signal, a multimeter with DB jack can be used to approximately measure the AC working voltage of IC.

During detection, the multimeter is placed in the AC voltage gear, and the positive probe is inserted into the DB jack; For a multimeter without DB jack, a 0.1 ~ 0.5uf DC isolation capacitor shall be connected in series with the positive probe. This method is suitable for IC with low working frequency, such as video amplification stage of TV, field scanning circuit, etc.

Because the natural frequencies and waveforms of these circuits are different, the measured data are approximate or whether they are present or not.

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