Test and analysis of electrical stress failure of electrical devices

Date：2021-12-15 15:09:56 Views：1630

Due to the continuous improvement of science and technology in modern society, the application scope of electronic devices is expanding. Electronic devices can be seen everywhere in our life and work. Due to the wide range of applications of electronic devices, the failure phenomena of electronic devices are also diverse and can be seen everywhere. Electrical stress failure is an important aspect of electronic device failure. The analysis and research of electrical stress failure of electrical devices is of far-reaching significance to the production, use and R & D of electronic devices.

First, the failure phenomenon and characteristics of electrical stress

1. Electrical stress failure refers to the failure of packaged devices due to the use of electrical stress that exceeds or violates the voltage and current specified in the device specification. The main forms of electrical stress failure are ESD electrostatic damage, EOS over-current damage and electromigration.

2. The main characteristics of electrostatic (ESD) damage are: lattice melting or co melting of metal and silicon, resulting in damage and short circuit of p-n junction; The oxide layer vaporizes and creates a cavity, which shortens and opens the device; The volatilization of metal wires causes short circuit and open circuit between devices.

3. Main characteristics of over electric stress (EOS) failure: in the practice of failure analysis, over electric stress damage often refers to the damage with obvious visible melting traces, especially the carbonization of packaging materials: generally, the bonding wire is blown, resulting in an open circuit; The metal wiring on the chip surface melts and evaporates, resulting in open circuit, short circuit or leakage; The fusing of silicon melt evaporation bonding wire can occur on any pin.

4. Main failure characteristics of electromigration: silver ions climb into dendritic or flocculent crystals, resulting in wafer short circuit or leakage; When the components work, a certain strength of current passes through the aluminum strip of the metal interconnection line. Under the action of the current, the metal ions move along the conductor to produce mass transmission, resulting in cavities or whiskers in some parts of the body, resulting in open circuit or leakage.

Second, failure mechanism characteristics

1、ESD

(1) ESD generation mode: 1) human body mode: human body model of electrostatic discharge (HBM for short). It is mainly the effect of human electrostatic discharge on sensitive electronic devices, which leads to the failure of packaging devices; 2) Machine mode: machine model (mm for short). It is mainly the effect of conductor with static electricity on the device, which leads to the failure of packaged devices. For example, the components on the automatic assembly line suffer from electrostatic discharge caused by charged metal objects on the components, or the effect of charged tools and test fixtures on the components; 3) Charged device mode: charged device model (CDM for short). It is mainly used to describe the electrostatic discharge phenomenon of charged devices.

(2) Investigate the failure background of the sample to be inspected, including service environment, service time, material selection, failure, etc., and compare it with the characteristics of ESD failure mechanism. The characteristics of ESD failure mechanism include but are not limited to the following: (a) ESD shall meet the comprehensive characteristics of ESD failure mechanism; (b) Failure (including short circuit, open circuit and leakage) may be found in the electrical test of the test material; (c) Failure is found in the function test of the tested material; (d) Delamination may occur in acoustic scanning detection of test materials; (e) Lead fracture may occur in X-ray detection of test materials; (f) The opening test found that there was electric breakdown on the wafer surface: lattice melting or co melting of metal and silicon, and cavitation caused by the vaporization of oxide layer.

2、EOS

Investigate the failure background of the sample to be inspected, including the service environment, service time, material selection, failure, etc., and compare it with the characteristics of EOS failure mechanism. The characteristics of EOS failure mechanism include but are not limited to the following: (1) EOS shall be able to meet the comprehensive characteristics of EOS failure mechanism; (2) The appearance of the tested material may be burnt yellow; (3) Failure (including short circuit, open circuit and leakage) is found in the electrical property test of the test material; (4) Failure is found in the function test of the tested materials; (5) Delamination may occur in acoustic scanning detection of test materials; (6) Lead fracture, solder cavity and wafer crack may occur in X-ray detection of inspection materials; (7) It is found that there are over electric melting marks on the wafer surface: grid open circuit and wafer crack; There is sintering inside the chip; There is carbonization on the wafer surface; The lead wire is fused.

3. Electromigration

(1) Electromigration usually refers to the failure of components or circuits caused by the movement of conductive ions under the action of electric field. They are the common silver ion migration on the surface of adjacent conductors and the metallized electron migration inside metal conductors.

(2) Investigate the failure background of the sample to be tested, including the service environment, service time, material selection, failure, etc., and compare it with the characteristics of electromigration failure mechanism. The characteristics of electromigration failure mechanism include but are not limited to the following: 1) electromigration should conform to the comprehensive characteristics of electromigration failure mechanism, and the test material has failed after being used in high temperature and humidity; 2) The high failure rate of inspection materials gradually appears after being used for a period of time (several months); 3) The failure phenomenon of the sample to be tested may disappear temporarily in dry environment and reappear in hot and humid environment; 4) Failure (including short circuit, open circuit and leakage) is found in the electrical property test of the test material; 5) Failure is found in the function test of the tested material; 6) Lead breakage may occur in X-ray detection of test materials; 7) The surface of the wafer is found to have corrosion traces during the unsealing test: there are holes on the wafer surface or leads; There are dendritic crystals on the wafer surface and corrosion traces on the wafer surface.

Third, analysis steps

1. Inspection principle

(1) Comprehensively understand the background of the tested material, the temperature and humidity of the use environment, the length of use, whether there is excessive stress, etc., and compare it with the characteristics of failure phenomenon;

(2) Failure of electrical verification;

(3) First conduct non-destructive test, and then conduct destructive test;

(4) First conduct failure isolation and positioning, then conduct physical verification, and compare with good products;

(5) Simulation verification confirms the failure phenomenon, which shall be adopted when appropriate.

2. Electrical location of failure point

The electrical measurement, analysis and inspection methods are comprehensively used to locate the failure point of the test material. The electrical performance analysis methods include: testing the functions, parameters, lead to lead characteristics and junction characteristics of components. Electrical positioning failure point: use volt ampere characteristic curve instrument, probe table and other electrical performance measuring instruments to isolate and locate the failure part of the sample in sections, and find out the physical failure point causing abnormal electrical performance of the sample.

According to the analysis of the circuit schematic diagram, multiple failure points that may lead to failure are listed respectively, and the volt ampere characteristics of the target failure circuit are measured. It is found that the current voltage curve (I-V curve) of the target failure circuit shows a straight line along the X axis or the resistance value is infinite, which may be caused by open circuit (high resistance) failure, If it is found that the current voltage curve (I-U curve) of the target failure circuit presents a straight line across the first and third quadrants across the origin, and the resistance value is zero or much lower than the original resistance value, it may be caused by short circuit or leakage failure. The failure location point can be found by this method.

Measure the volt ampere characteristics at the failure position of good products and bad products. If the volt ampere characteristics at the same position of good products are found to be the normal set value, it can be confirmed that the cause is caused by abnormal circuit (open circuit, short circuit and leakage) between failure points.

(1) According to the characteristics and failure phenomenon of the test material, isolate the failure parts in sections and comprehensively verify the electrical failure point of the test material.

(2) If there is a standard sample, comprehensively evaluate the similarities and differences between the electrical characteristics of the test material and the standard sample through the comparative test of the electrical characteristics of the test material and the standard sample.

(3) Some failure phenomena are related to environmental conditions. Therefore, according to the actual situation of the analysis object, temperature cycle, vibration or impact, damp heat and other tests can be selected to reproduce and observe the failure phenomenon.

(4) The failure point shall be located in a nondestructive manner first, and the failure point of the tested material shall be located by using the above electrical measurement, analysis and inspection method.

3. Electrical verification of failure point

Select appropriate inspection methods to conduct electrical verification for failure points. It can measure the current voltage curve of the tested material at the failure point and the standard sample for comparative analysis.

4. Physical verification of failure point

According to the electrical failure points detected in 3.3, nondestructive testing methods are used to carry out nondestructive testing on the failure points. The specific inspection methods include optical microscope analysis, transmission ray analysis and ultrasonic scanning analysis.

1) Optical microscope analysis.Visual inspection on the periphery of optical microscope to check the overall situation and observe whether there are serious mechanical and physical damage defects, such as device packaging cracking, incomplete plastic packaging, substrate fracture, pin damage and falling off, tin ball falling off, false soldering and obvious abnormalities, which can lead to open circuit or high resistance failure; Device package cracking, incomplete plastic packaging, substrate fracture, abnormal pins, bridging between pins, abnormal tin balls, bridging between tin balls, dendritic crystals of copper pins on the substrate, obvious abnormalities, etc. can lead to short circuit or leakage failure.

2) Transmission ray analysis.Using the principle of transmission ray, check the internal circuit connection of the target device package, such as the solder joint of gold wire or copper wire falls off, and the absence of defects such as gold wire or copper wire welding can lead to open circuit or high resistance failure; Defects such as dislocation of gold wire or copper wire solder joint or its sagging deformation can lead to short circuit or leakage failure. At the same time, check the obvious defects inside the printed circuit board (PCB), such as broken copper wiring and broken through-hole copper wire, which can lead to open circuit or high resistance failure; Bridging between copper wires and dislocation of through-hole copper wires can lead to short circuit or leakage failure.

3) Ultrasonic scanning analysis.For the complementarity of X-ray detection, ultrasonic scanning is used to check whether there are serious defects in the package of the target device. Different working modes can be selected: A-scan, B-scan, C-sam, t-sam and tami-scan. For example, serious delamination cracking, solder joint separation, serious cavities or bubbles, chip cracking, chip fragmentation, etc. can lead to open circuit or high resistance failure. Serious delamination cracking leads to gold wire deformation and short circuit, serious cavity or bubble leads to short circuit, chip cracking and chip fragmentation can lead to short circuit or leakage failure. If the mechanical and physical damage or defect is found through the nondestructive failure analysis method, and it can be proved that the damage or defect is the direct and only cause of open circuit (high resistance) or short circuit and leakage, the failure point can be found.