Failure mode and failure mechanism analysis of components in various environments
Date：2022-07-28 15:00:00 Views：131
1、 Typical component failure mode
In order to obtain the sensitive environment of electronic components, the typical failure modes related to the environment are analyzed, as shown in the table.
Environmental related failure modes of electronic components and analysis of the sensitive environment involved
2、 Failure mechanism analysis of typical components
The failure mode of electronic components is not single. Only the tolerance limit of some representative typical components in sensitive environment is analyzed to get a more suitable conclusion.
1. Electromechanical components
Typical electromechanical components include electrical connectors, relays, etc. Combined with the structure of the two types of components, the failure mode is analyzed in depth.
1) Electrical connector
Electrical connectors are composed of three basic units: shell, insulator and contact. Their failure modes can be summarized as contact failure, insulation failure and mechanical connection failure. The main failure form of electrical connector is contact failure, which is manifested by the instantaneous breaking of contact pair and the increase of contact resistance. For electrical connectors, due to the existence of contact resistance and material conductor resistance, when there is current flowing through the electrical connector, the contact resistance and metal conductor resistance will produce Joule heat. The increase of Joule heat will increase the heat, resulting in the increase of the temperature of the contact point. Too high temperature of the contact point will make the metal on the contact surface soften, melt and even boil, and will also increase the contact resistance, resulting in contact failure. Under the action of high temperature environment, the contact will also appear creep phenomenon, which makes the contact pressure between the contacts continue to decrease. When the contact pressure decreases to a certain extent, the contact resistance will increase sharply, resulting in poor electrical contact and contact failure.
On the other hand, the electrical connector will be affected by various vibration loads and impact forces during storage, transportation and work. When the excitation frequency of the external vibration load is close to the natural frequency of the electrical connector, the electrical connector will produce resonance phenomenon, resulting in the gap of the contact becoming larger, the gap increasing to a certain extent, and the contact pressure will disappear instantaneously, resulting in the "instantaneous break" of the electrical contact. Under the action of vibration and impact load, the internal stress of the electrical connector will be generated. When the stress exceeds the yield strength of the material, the material will be damaged and broken; Under the action of this long-term stress, the material will also suffer fatigue damage, which will eventually lead to failure.
Electromagnetic relay is generally composed of iron core, coil, armature, contact, reed, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, resulting in electromagnetic effect. The armature will overcome the tension of the return spring and attract to the iron core under the action of electromagnetic force, thus driving the dynamic contact and static contact (normally open contact) of the armature to pull. When the coil is powered off, the electromagnetic suction also disappears, and the armature will return to the original position under the reaction force of the spring, making the moving contact and the original static contact (normally closed contact) attract. In this way, the connection and disconnection in the circuit are achieved.
The main failure modes of the electromagnetic relay as a whole are: the relay is normally open, the relay is normally closed, the action of the relay moving spring does not meet the requirements, the electrical parameters of the relay are out of tolerance after the contact is closed, etc. Due to the insufficient production process of electromagnetic relays, many failures of electromagnetic relays have hidden quality hazards in the production process, such as the deformation of parts after the mechanical structure is formed due to the short mechanical stress release period, the unqualified or even invalid PIND detection due to the incomplete removal of residues, and the lax outgoing detection and use screening, which makes the failed devices put into use, etc. The impact environment is easy to cause plastic deformation of metal contacts, resulting in relay failure. In the design of relay equipment, we need to focus on its impact environmental adaptability.
2. Semiconductor microwave element
Microwave semiconductor devices are components made of Ge, Si and iii~v compound semiconductor materials that work in the microwave band. Used in radar, electronic warfare system, microwave communication system and other electronic equipment. In addition to providing electrical connection and mechanical and chemical protection for the core and pins, the design and selection of the shell should also consider the influence of the shell parameters on the microwave transmission characteristics of the device. Microwave tube shell is also a part of the circuit, which itself constitutes a complete input and output circuit. Therefore, the shape, structure, size, dielectric material and conductor configuration of the shell should match the microwave characteristics of components and circuit applications. These factors determine the capacitance of the shell, the resistance of the electrical lead, the characteristic impedance, and the loss of conductor and dielectric.
The environment related failure modes and mechanisms of microwave semiconductor components mainly include the sinking of gate metal and the degradation of resistance performance. The sinking of gate metal is due to the thermal accelerated diffusion of gate metal (AU) into GaAs, so this failure mechanism mainly occurs in accelerated life test or extremely high temperature operation. The diffusion rate of gate metal (AU) into GaAs is a function of the diffusion coefficient of gate metal material, temperature and material concentration gradient. For a perfect lattice structure, the performance of the device will not be affected because the diffusion rate is very slow at normal operating temperature. However, when the particle boundary is large or there are many surface defects, the diffusion rate will be very significant. Resistors are usually used in the feedback circuit of microwave monolithic integrated circuits, setting the bias point of active devices, isolation, power synthesis or coupling end. There are two types of resistors: metal film resistors (Tan, NiCr) and lightly doped GaAs thin-layer resistors. The test shows that the degradation of NiCr resistance caused by humidity is the main failure mechanism.
3. Hybrid integrated circuit
Traditional hybrid integrated circuits are divided into thick film hybrid integrated circuits and thin film hybrid integrated circuits according to the different thick film conduction band and thin film conduction band processes on the surface of the substrate: some small printed circuit board (PCB) circuits are also classified as hybrid integrated circuits because they form conductive patterns on the surface of the flat board in the form of film. With the emergence of multichip module, an advanced hybrid integrated circuit, its unique multilayer wiring structure and through-hole technology have made the module a synonym for a high-density interconnection structure in hybrid integrated circuits. The substrates used by multichip module include: thin film multilayer, thick film multilayer, high temperature co firing, low temperature co firing, silicon substrate, PCB multilayer substrate, etc.
The environmental stress failure modes of hybrid integrated circuits mainly include electrical open circuit failure caused by substrate cracking, and welding failure between components and thick film conductors, components and thin film conductors, substrates and shells. Mechanical impact caused by product drop, thermal impact caused by soldering operation, additional stress caused by substrate warpage, transverse tensile stress caused by thermal mismatch between substrate and metal shell and binder, mechanical stress or thermal stress concentration caused by internal defects of substrate, potential damage caused by local microcracks in substrate drilling and substrate cutting, and finally the external mechanical stress is greater than the inherent mechanical strength of ceramic substrate, Cause failure.
The welded structure is easy to cause thermal fatigue of solder layer under the repeated action of temperature cyclic stress, resulting in the decrease of bonding strength and increase of thermal resistance. For tin based ductile solders, the thermal fatigue of the solder layer caused by the action of temperature cyclic stress is due to the inconsistency of the thermal expansion coefficients of the two structures connected by the solder, and the displacement deformation or shear deformation of the solder. After repeated times, the solder layer expands and extends with the fatigue crack, and finally leads to the fatigue failure of the solder layer.
4. Discrete devices and integrated circuits
Semiconductor discrete devices are divided into diodes, bipolar transistors, MOS FET, thyristors and insulated gate bipolar transistors. Integrated circuits have a wide range of applications. According to their functions, they can be divided into three categories, namely, digital integrated circuits, analog integrated circuits and digital analog hybrid integrated circuits.
1) Discrete device
There are many kinds of discrete devices. Due to their different functions and processes, the failure performance is quite different, which has its particularity. However, as a basic device formed by semiconductor process, its failure physics has certain similarities. The failures related to external mechanics and natural environment mainly include thermal breakdown, dynamic avalanche, chip welding failure and internal wire bonding failure.
Thermally induced breakdown: thermally induced breakdown or secondary breakdown is the main failure mechanism affecting semiconductor power components, and the damage during use is mostly related to secondary breakdown. The secondary breakdown is divided into forward biased secondary breakdown and reverse biased secondary breakdown. The former is mainly related to the thermal performance of the device itself, such as the doping concentration and intrinsic concentration of the device, while the latter is related to the avalanche multiplication of carriers in the space charge region (such as near the collector). Both are always accompanied by the concentration of current in the device. In the application of such components, special attention should be paid to heat prevention and heat dissipation.
Dynamic avalanche: in the process of dynamic shutdown caused by external force or internal force, the collision ionization phenomenon controlled by current and affected by free carrier concentration inside the device causes dynamic avalanche, which may occur in bipolar devices, diodes and IGBT.
Chip welding failure: the main reason is that the chip and solder are different materials, and the thermal expansion coefficient is different, so there is a thermal mismatch problem at high temperature. In addition, the existence of welding holes will increase the thermal resistance of devices, make the heat dissipation worse, form hot spots in local areas, raise the junction temperature, and cause temperature related failures such as electromigration.
Bonding failure of inner lead: it is mainly the corrosion failure of bonding point, which is caused by the corrosion of aluminum caused by the action of water vapor and chlorine in the humid and hot salt fog environment. Temperature cycling or vibration leads to fatigue fracture of aluminum bonding leads. The IGBT packaged in the module has a large volume. If it is installed improperly, it is easy to cause stress concentration, resulting in fatigue fracture of the internal leads of the module.
2) Integrated circuit
The failure mechanism of integrated circuits has a great relationship with the use environment. The damage caused by water vapor, static electricity or electric surge in wet environment, excessive use of documents and diagrams, and the use of integrated circuits without anti radiation reinforcement in radiation environment will also cause the failure of devices.
Interface effect related to aluminum: in electronic devices based on silicon, SiO2 layer is widely used as a dielectric film, while aluminum is often used as the material of interconnection. SiO2 and aluminum will react chemically at high temperature, making the aluminum layer thinner. If SiO2 layer is exhausted due to reaction consumption, it will cause direct contact between aluminum and silicon. In addition, Au al interface contact will occur at the bonding between the gold outgoing line and the aluminum interconnection line or between the aluminum bonding wire and the gold-plated lead of the tube shell. Due to the different chemical potentials of these two metals, a variety of intermetallic compounds will be produced after long-term use or high-temperature storage above 200 ℃, and due to their different lattice constants and thermal expansion coefficients, great stress will be generated in the bonding point and the conductivity will be reduced.
Metallization corrosion: the aluminum connecting wire on the chip is easy to be corroded by water vapor in a humid and hot environment. Due to the price deviation and easy mass production, many integrated circuits are encapsulated with resin. However, water vapor can pass through the resin to the aluminum interconnection line. Impurities brought in from the outside or impurities in the dissolved resin interact with metal aluminum, causing corrosion of the aluminum interconnection line.
Delamination effect caused by water vapor: plastic encapsulated IC refers to the integrated circuit encapsulated with resin polymer materials such as plastic. In addition to the delamination effect (commonly known as "popcorn" effect) between the plastic encapsulated material and the metal frame and chip, because the resin materials have the characteristics of adsorbing water vapor, the delamination effect caused by water vapor adsorption will also make the device invalid. The failure mechanism is that the moisture in the plastic packaging material expands rapidly at high temperature, which separates the plastic from other materials attached to it, and will burst the plastic packaging body in serious cases.
5. Resistance capacitance element
Common non wound resistors can be divided into four types, namely alloy type, thin film type, thick film type and synthetic type, according to the different materials used in the resistor. For fixed resistors, the main failure modes are open circuit, electrical parameter drift, etc; For potentiometers, the main failure modes are open circuit, electrical parameter drift, noise increase and so on. The use environment will also lead to the aging of resistors, which has a great impact on the life of electronic equipment.
Oxidation: the oxidation of the resistor body will increase the resistance value, which is the main factor causing the aging of the resistor. In addition to resistors made of precious metals and alloys, other materials will be damaged by oxygen in the air. Oxidation is a long-term effect. When the influence of other factors is gradually weakened, oxidation will become the main factor. High temperature and high humidity environment will accelerate the oxidation of resistors. For precision resistors and high resistance resistors, the fundamental measure to prevent oxidation is sealing protection. The sealing material shall be inorganic materials, such as metal, ceramics, glass, etc. The organic protective layer can not completely prevent moisture and air permeability, and can only delay the oxidation and adsorption.
Aging of binder: for organic synthetic resistors, aging of organic binder is the main factor affecting the stability of resistors. Organic binder is mainly synthetic resin. In the manufacturing process of resistors, synthetic resin is transformed into thermosetting polymer with high polymerization degree after heat treatment. The main factor causing polymer aging is oxidation. The free radical generated by oxidation causes the hinge of polymer molecular bond, which further solidifies and embrittles the polymer, and then loses elasticity and mechanical damage. The curing of the adhesive shrinks the volume of the resistor, increases the contact pressure between conductive particles, reduces the contact resistance, and reduces the resistance value, but the mechanical damage of the adhesive will also increase the resistance value. Generally, the curing of the adhesive occurs before and the mechanical damage occurs after, so the resistance value of the organic synthetic resistor shows the following law: it decreases at the beginning, and then turns to increase, and has a growing trend. Because the aging of polymers is closely related to temperature and light, the aging of synthetic resistors will be accelerated under high temperature environment and strong light irradiation.
Aging under electrical load: applying load to the resistor will accelerate its aging process. Under DC load, electrolysis will damage the film resistor. Electrolysis occurs between the cells of the grooved resistor. If the resistance matrix is a ceramic or glass material containing alkali metal ions, the ions move under the action of the electric field between the cells. In humid environment, this process is more intense.
The failure modes of capacitors include short circuit, open circuit, electrical parameter degradation (including capacitance change, loss tangent increase and insulation resistance decrease), liquid leakage and lead corrosion fracture.
Short circuit: under high temperature and low pressure, the flashover at the edge of the electrode will lead to the short circuit of the capacitor. In addition, under the action of external impact and other mechanical stress, it will also cause the instantaneous short circuit of the dielectric.
Open circuit: due to the oxidation of the outgoing line and electrode contact caused by the humid and hot environment, the low level is blocked and the anode outgoing foil is corroded and broken.
Degradation of electrical parameters: degradation of electrical parameters due to the influence of humid environment.
6. Board level circuit
The printed circuit board is mainly composed of insulating substrate, metal wiring, wires connecting different layers, and "pads" for welding components. Its main function is to provide the carrier of electronic components, and play the role of electrical and mechanical connection.
The failure modes of printed circuit board mainly include poor welding, poor open circuit and short circuit, blistering, board delamination, board surface corrosion or discoloration, board bending and warping, etc. Generally speaking, poor welding is mainly related to poor surface treatment quality of PCB pads or poor surface condition of pads (such as oxidation pollution, etc.); The open circuit often appears on the wire or metallized hole, which is closely related to the PCB processing technology and the performance of the material itself; Short circuit or leakage is generally caused by the reduction of insulation spacing between conductors or electrochemical migration caused by corrosion; The delamination and blistering of the board surface are generally related to the matching of the pressing process of the board. On the other hand, it may also come from the poor performance of the printed board materials; Bending and warping also mainly come from the quality of substrate and processing technology. The impact and vibration environment is easy to cause fatigue and micro cracks in the solder joints of printed circuit boards, thus accelerating the failure of printed circuit boards.
7. Electric vacuum
Vacuum electronic devices are active devices that generate, amplify and convert electromagnetic wave signals by using various effects of electrons (or ions) in vacuum media. Typical electric vacuum devices include traveling wave tube, magnetron, klystron, etc. The oscillation frequency of magnetron is greatly affected by the ambient temperature, and the sudden change of temperature is very easy to cause the shift of magnetron frequency.
This paper analyzes the environmental tolerance limit of typical electronic components. The research shows that electronic equipment is sensitive to thermal environment, impact and vibration environment, and is prone to solder joint failure and other structural failure. Some components are sensitive to natural environment, such as damp heat, salt fog and so on, and are prone to corrosion failure.