Failure analysis of electronic products: what is the cause of component failure?

Date：2021-09-28 18:03:14Views：1619

Electronic components mainly include components and devices. Electronic components are finished products with unchanged molecular components in the production and processing process, such as capacitance, resistance, inductance, etc. Electronic equipment is the finished product whose molecular structure changes in the process of generation and processing, such as electron tube, integrated circuit and so on. Therefore, mastering the effective mechanism and characteristics of various electronic components is an indispensable knowledge for hardware engineers. Next, analyze the failure of various electronic components.

Resistance element

The failure of resistance components accounts for a large proportion in electronic equipment, which can be divided into shunt, step-down, load, impedance matching and other functions. According to different structures, resistance elements can be divided into wire wound resistance and non wire wound resistance.

The main methods of resistance element failure are contact damage, open circuit and lead mechanical damage.

The influence of temperature change on the resistance is that when the temperature increases, the thermal noise of the resistance increases, the resistance value deviates from the nominal value, and the allowable consumption probability decreases. But we can also take advantage of this characteristic of resistance. For example, there is a specially designed resistor: PTC (positive temperature coefficient thermistor) and NTC (negative temperature coefficient thermistor), whose resistance value is greatly affected by temperature.

Mechanical vibration will loosen the solder joint and crimping point, resulting in mechanical damage such as poor contact.

Capacitive element

The main methods of capacitor component failure include breakdown, mechanical damage, electrolyte leakage and so on.

The main causes of capacitor breakdown are:

1. Dielectric defects, impurities and conductive ions;

2. Medium aging;

3. Dielectric materials have electricity Air gap breakdown;

4. The medium has mechanical damage during manufacturing;

5. Change of medium molecular structure;

6. Metal ions migrate to form a conductive groove or edge arc discharge.

Capacitor failure may also be caused by open circuit, low-level open circuit caused by oxidation of contact point between conductor and capacitor, poor contact between conductor and electrode, mechanical fracture of metal foil caused by anode of electrolytic capacitor, resulting in open circuit fault. Therefore, the capacitor may also fail due to the degradation of electrical parameters, such as the migration of metal ions in electrode materials, the self-healing effect of metallized electrodes, electrolytic and chemical corrosion of electrodes, humidity, surface pollution, etc.

Inductive element

Inductive elements involve transformers, inductors, filter coils, oscillation coils, etc. The faults of inductive components are mostly caused by external factors, such as the rise of transformer temperature, the excessive current passing through the coil caused by load short circuit and so on. This can lead to short circuit, short circuit and breakdown of the coil.

In the integrated circuit, no matter which part has problems, the whole can not operate normally, such as electrode short circuit, open circuit, mechanical wear, poor weldability and so on. Failure is mainly divided into complete damage and poor thermal stability. Thermal stability failure mainly occurs at high or low temperature, exceeding the working temperature range of the equipment.

The following methods are generally adopted for fault inspection of inductance and transformer components:

(1) DC resistance measurement method. Measure the quality of inductive components with the resistance block of multimeter. When measuring antenna coil and oscillation coil, the measuring range shall be set at the minimum resistance gear (such as R) × 1 W gear); When measuring the circumference and output input transformer, the measuring range shall be placed at the low barrier (R × 10W or R × 100 W gear), the measured resistance value is compared with the maintenance data or daily accumulated experience data. If it is very close, it indicates that the tested element is normal; If the resistance is much smaller than the empirical data, it indicates that the coil has a local short circuit; If the needle indicates zero, the coil is short circuited. It should be noted that the secondary resistance of oscillation coil, antenna coil and mid circumference is very small, only a few tenths of an ohm. Be especially careful when reading, and do not misjudge it as a short circuit. Block with high × 10kW) when measuring the resistance between the primary coil and the secondary coil, it should be infinite. If there is a certain resistance value between the primary and secondary, it indicates that there is leakage between the primary and secondary.

(2) Power on inspection method. Power on the power transformer to check whether the secondary voltage drops. If the secondary voltage drops, it is suspected that there is a local short circuit in the secondary (or primary). When the transformer burns rapidly or has burning smell and smoke after power on, it can be judged that there must be a local short circuit in the transformer.

(3) Instrument inspection method. The high frequency Q meter can be used to measure the inductance and its Q value, and the inductive short circuit instrument can also be used to judge the local short circuit of the low frequency coil. The megger can be used to measure the insulation resistance between the primary and secondary of the power transformer. If leakage is found in the transformer, it may be caused by poor insulation or moisture. At this time, the transformer can be removed to remove moisture and dry. In addition, various carbon brushes or copper brushes of the voltage regulating transformer are very easy to wear out in case of improper maintenance and use. Their fragments and carbon deposits often burn the transformer due to the burning of the coil of the short-circuit part. Therefore, attention should be paid to maintenance at ordinary times.

Integrated block class

The main causes of open circuit or on-off of electrodes are metal migration between electrodes, electric corrosion and process problems. The main causes of electrode short circuit are metal electric diffusion between electrodes, metallization process defects or foreign matters. The main causes of lead breakage are uneven wire diameter, insufficient lead strength, excessive hot spot stress and mechanical stress, electric corrosion, etc. The main reasons for the drift of electrical parameters are raw material defects, reactions caused by mobile ions and so on. Mechanical wear and packaging cracks are mainly caused by packaging process defects and excessive environmental stress. Poor weldability is mainly caused by lead material defects, poor lead metal coating, lead surface pollution, corrosion and oxidation. Inability to work is generally caused by working environment factors.

To sum up, during debugging, when the circuit cannot work or works abnormally. Firstly, through the dynamic observation method, that is, when the line equipment is powered on, judge the fault of electronic components by listening, looking, touching and smelling. For example, listen to the equipment for abnormal sound, and carefully check whether there are smoke, sparks, etc. in the circuit; Touch the components Whether the circuit is hot; Smell whether there is burnt smell. It can also be judged by measuring the on-off in the circuit with a multimeter and by measuring various values in normal and abnormal circuits. In order to ensure that the equipment or system can work reliably, the reliability requirements of electronic components are very high. Reliability index has become one of the important quality indexes of components. Understanding the failure mode and failure mechanism of components is very important for diagnosing equipment faults and maintaining equipment reliability.