Sensitive environment and failure mode of electronic components failure

In this paper, the failure modes and failure mechanisms of electronic components are studied and their sensitive environments are given to provide some reference for the design of electronic products
1. Typical component failure modes
Serial number
Electronic component name
Environment-related failure modes
Environmental stress

1. Electromechanical components
Vibration causes fatigue breakage of coils and loosening of cables.
Vibration, shock

2. Semiconductor microwave devices
High temperature and temperature shock lead to delamination at the interface between the package material and the chip, and between the package material and the chip holder interface of the plastic-sealed microwave monolith.
High temperature, temperature shock

3. Hybrid integrated circuits
Shock leads to ceramic substrate cracking, temperature shock leads to capacitor end electrode cracking, and temperature cycling leads to solder failure.
Shock, temperature cycle

4. Discrete Devices and Integrated Circuits
Thermal breakdown, chip soldering failure, inner lead bonding failure, shock leading to passivation layer rupture.
High temperature, shock, vibration

5. Resistive components
Core substrate rupture, resistive film rupture, lead breakage
Shock, high and low temperature

6. Board level circuit
Cracked solder joints, fractured copper holes.
High temperature

7. Electric vacuum
Fatigue fracture of hot wire.
2, typical component failure mechanism analysis
Failure mode of electronic components is not a single, only a representative part of the typical components sensitive environment tolerance limit analysis, in order to get a more general conclusion.
2.1 Electromechanical components
Typical electromechanical components include electrical connectors, relays, etc. The failure modes are analyzed in depth with the structure of the two types of components respectively.

1) Electrical connectors
Electrical connector by the shell, insulator and contact body of the three basic units, the failure mode is summarized in the contact failure, insulation failure and mechanical failure of the three forms of failure. The main form of failure of the electrical connector for the contact failure, the failure of its performance: contact on the instantaneous break and contact resistance increases. For electrical connectors, due to the existence of contact resistance and material conductor resistance, when there is current flow through the electrical connector, contact resistance and metal material conductor resistance will generate Joule heat, Joule heat will increase heat, resulting in an increase in the temperature of the contact point, too high contact point temperature will make the contact surface of the metal softening, melting or even boiling, but also increase the contact resistance, thus triggering contact failure. . In the role of high temperature environment, the contact parts will also appear creep phenomenon, making the contact pressure between the contact parts decreasing. When the contact pressure is reduced to a certain extent, the contact resistance will increase sharply, and finally cause poor electrical contact, resulting in contact failure.

On the other hand, the electrical connector in storage, transportation and work, will be subject to a variety of vibration loads and impact forces, when the external vibration load excitation frequency and electrical connectors close to the inherent frequency, will make the electrical connector resonance phenomenon, resulting in the gap between the contact pieces become larger, the gap increases to a certain extent, the contact pressure will disappear instantaneously, resulting in electrical contact "instant break ". In the vibration, shock load, the electrical connector will generate internal stress, when the stress exceeds the yield strength of the material, will make the material damage and fracture; in the role of this long-term stress, the material will also occur fatigue damage, and finally cause failure.

2) Relay
Electromagnetic relays are generally composed of cores, coils, armatures, contacts, reeds and so on. As long as a certain voltage is added to both ends of the coil, a certain current will flow in the coil, thus producing an electromagnetic effect, the armature will overcome the electromagnetic force of attraction to return to the spring pull to the core, which in turn drives the armature's moving contacts and static contacts (normally open contacts) to close. When the coil is powered off, the electromagnetic suction force also disappears, the armature will return to the original position under the reaction force of the spring, so that the moving contact and the original static contact (normally closed contact) suction. This suction and release, thus achieving the purpose of conduction and cut off in the circuit.
The main modes of overall failure of electromagnetic relays are: relay normally open, relay normally closed, relay dynamic spring action does not meet the requirements, contact closure after the relay electrical parameters exceed the poor. Due to the shortage of electromagnetic relay production process, many electromagnetic relay failure in the production process to lay the quality of hidden dangers, such as mechanical stress relief period is too short resulting in mechanical structure after the molding parts deformation, residue removal is not exhausted resulting in PIND test failed or even failure, factory testing and use of screening is not strict so that the failure of the device into use, etc.. The impact environment is likely to cause plastic deformation of metal contacts, resulting in relay failure. In the design of equipment containing relays, it is necessary to focus on the impact environment adaptability to consider.

2.2 Semiconductor microwave components
Microwave semiconductor devices are components made of Ge, Si and III ~ V compound semiconductor materials that operate in the microwave band. They are used in electronic equipment such as radar, electronic warfare systems and microwave communication systems. Microwave discrete device packaging in addition to providing electrical connections and mechanical and chemical protection for the core and pins, the design and selection of the housing should also consider the impact of the housing parasitic parameters on the microwave transmission characteristics of the device. The microwave housing is also a part of the circuit, which itself constitutes a complete input and output circuit. Therefore, the shape and structure of the housing, size, dielectric material, conductor configuration, etc. should match the microwave characteristics of the components and circuit application aspects. These factors determine parameters such as capacitance, electrical lead resistance, characteristic impedance, and conductor and dielectric losses of the tube housing.

Environmentally relevant failure modes and mechanisms of microwave semiconductor components mainly include gate metal sink and degradation of resistive properties. Gate metal sink is due to the thermally accelerated diffusion of gate metal (Au) into GaAs, so this failure mechanism occurs mainly during accelerated life tests or extremely high temperature operation. The rate of gate metal (Au) diffusion into GaAs is a function of the diffusion coefficient of the gate metal material, temperature, and material concentration gradient. For a perfect lattice structure, the device performance is not affected by a very slow diffusion rate at normal operating temperatures, however, the diffusion rate can be significant when the particle boundaries are large or there are many surface defects. Resistors are commonly used in microwave monolithic integrated circuits for feedback circuits, setting the bias point of active devices, isolation, power synthesis or the end of coupling, there are two structures of resistance: metal film resistance (TaN, NiCr) and lightly doped GaAs thin layer resistance. Tests show that the degradation of NiCr resistance caused by humidity is the main mechanism of its failure.

2.3 Hybrid integrated circuits
Traditional hybrid integrated circuits, according to the substrate surface of the thick film guide tape, thin film guide tape process is divided into two categories of thick film hybrid integrated circuits and thin film hybrid integrated circuits: certain small printed circuit board (PCB) circuit, due to the printed circuit is in the form of film in the flat board surface to form a conductive pattern, also classified as a hybrid integrated circuits. With the emergence of multi-chip components this advanced hybrid integrated circuit, its substrate unique multi-layer wiring structure and through-hole process technology, has made the components become a hybrid integrated circuit in a high-density interconnect structure synonymous with the substrate used in multi-chip components and include: thin film multilayer, thick film multilayer, high-temperature co-fired, low-temperature co-fired, silicon-based, PCB multilayer substrate, etc..

Hybrid integrated circuit environmental stress failure modes mainly include electrical open circuit failure caused by substrate cracking and welding failure between components and thick film conductors, components and thin film conductors, substrate and housing. Mechanical impact from product drop, thermal shock from soldering operation, additional stress caused by substrate warpage unevenness, lateral tensile stress from thermal mismatch between substrate and metal housing and bonding material, mechanical stress or thermal stress concentration caused by internal defects of substrate, potential damage caused by substrate drilling and substrate cutting local micro cracks, eventually lead to external mechanical stress greater than the inherent mechanical strength of ceramic substrate that The result is failure.

Solder structures are susceptible to repeated temperature cycling stresses, which can lead to thermal fatigue of the solder layer, resulting in reduced bonding strength and increased thermal resistance. For tin-based class of ductile solder, the role of temperature cyclic stress leads to thermal fatigue of the solder layer is due to the thermal expansion coefficient of the two structures connected by the solder is inconsistent, is the solder displacement deformation or shear deformation, after repeatedly, the solder layer with fatigue crack expansion and extension, eventually leading to fatigue failure of the solder layer.
2.4 Discrete devices and integrated circuits
Semiconductor discrete devices are divided into diodes, bipolar transistors, MOS field effect tubes, thyristors and insulated gate bipolar transistors by broad categories. Integrated circuits have a wide range of applications and can be divided into three categories according to their functions, namely digital integrated circuits, analog integrated circuits and mixed digital-analog integrated circuits.

1) Discrete devices
Discrete devices are of various types and have their own specificity due to their different functions and processes, with significant differences in failure performance. However, as the basic devices formed by semiconductor processes, there are certain similarities in their failure physics. The main failures related to external mechanics and natural environment are thermal breakdown, dynamic avalanche, chip soldering failure and internal lead bonding failure.

Thermal breakdown: Thermal breakdown or secondary breakdown is the main failure mechanism affecting semiconductor power components, and most of the damage during use is related to the secondary breakdown phenomenon. Secondary breakdown is divided into forward bias secondary breakdown and reverse bias secondary breakdown. The former is mainly related to the device's own thermal properties, such as the device's doping concentration, intrinsic concentration, etc., while the latter is related to the avalanche multiplication of carriers in the space charge region (such as near the collector), both of which are always accompanied by the concentration of current inside the device. In the application of such components, special attention should be paid to thermal protection and heat dissipation.

Dynamic avalanche: During dynamic shutdown due to external or internal forces, the current-controlled collisional ionization phenomenon that occurs inside the device influenced by the free carrier concentration causes a dynamic avalanche, which can occur in bipolar devices, diodes and IGBTs.

Chip solder failure: The main reason is that the chip and the solder are different materials with different coefficients of thermal expansion, so there is a thermal mismatch at high temperatures. In addition, the presence of solder voids increases the thermal resistance of the device, making heat dissipation worse and forming hot spots in the local area, raising the junction temperature and causing temperature-related failures such as electromigration to occur.

Inner lead bonding failure: mainly corrosion failure at the bonding point, triggered by the corrosion of aluminum caused by the action of water vapor, chlorine elements, etc. in a hot and humid salt spray environment. Fatigue fracture of aluminum bonding leads caused by temperature cycle or vibration. The IGBT in module package is large in size, and if it is installed in an improper way, it is very 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 and the use of the environment has a great relationship, moisture in a humid environment, damage generated by static electricity or electrical surges, too high use of the text and the use of integrated circuits in a radiation environment without radiation resistance reinforcement can also cause the failure of the device.

Interface effects related to aluminum: In the electronic devices with silicon-based materials, SiO2 layer as a dielectric film is widely used, and aluminum is often used as a material for interconnection lines, SiO2 and aluminum at high temperatures will be a chemical reaction, so that the aluminum layer becomes thin, if the SiO2 layer is depleted due to reaction consumption, will cause direct contact between aluminum and silicon. In addition, the gold lead wire and aluminum interconnection line or aluminum bonding wire and the bonding of the gold-plated lead wire of the tube shell, will produce Au-Al interface contact. Due to the different chemical potential of these two metals, after long-term use or storage at high temperatures above 200 ℃ will produce a variety of intermetallic compounds, and due to their lattice constants and thermal expansion coefficients are different, in the bonding point within a large stress, the conductivity becomes small.

Metallization corrosion: The aluminum connection line on the chip is susceptible to corrosion by water vapor in a hot and humid environment. Due to the price offset and easy mass production, many integrated circuits are encapsulated with resin, however, water vapor can pass through the resin to reach the aluminum interconnects, and impurities brought in from outside or dissolved in the resin act with metallic aluminum to cause corrosion of the aluminum interconnects.

The delamination effect caused by water vapor: plastic IC is the integrated circuit encapsulated with plastic and other resin polymer materials, in addition to the delamination effect between the plastic material and the metal frame and chip (commonly known as the "popcorn" effect), because the resin material has the characteristics of adsorption of water vapor, the delamination effect caused by the adsorption of water vapor will also cause the device to fail. . Failure mechanism is the rapid expansion of water in the plastic sealing material at high temperatures, so that the separation between the plastic and its attachment of other materials, and in serious cases, the plastic sealing body will burst.

2.5 Capacitive resistive components
1) Resistors
Common non-winding resistors can be divided into four types according to the different materials used in the resistor body, namely alloy type, film type, thick film type and synthetic type. For fixed resistors, the main failure modes are open circuit, electrical parameter drift, etc.; while for potentiometers, the main failure modes are open circuit, electrical parameter drift, noise increase, etc. The use environment will also lead to resistor aging, which has a great impact on the life of electronic equipment.

Oxidation: Oxidation of the resistor body will increase the resistance value and is the most important factor causing resistor aging. Except for resistor bodies made of precious metals and alloys, all other materials will be damaged by oxygen in the air. Oxidation is a long-term effect, and when the influence of other factors gradually diminishes, oxidation will become the main factor, and high temperature and high humidity environments will accelerate the oxidation of resistors. For precision resistors and high resistance value resistors, the fundamental measure to prevent oxidation is sealing protection. Sealing materials should be inorganic materials, such as metal, ceramic, glass, etc. The organic protective layer cannot completely prevent moisture permeability and air permeability, and can only play a delaying role in oxidation and adsorption.

Aging of the binder: For organic synthetic resistors, aging of the organic binder is the main factor affecting the stability of the resistor. The organic binder is mainly a synthetic resin, which is transformed into a highly polymerized thermosetting polymer by heat treatment during the manufacturing process of the resistor. The main factor causing polymer aging is oxidation. The free radicals generated by oxidation cause the hinging of the polymer molecular bonds, which further cures the polymer and makes it brittle, resulting in loss of elasticity and mechanical damage. The curing of the binder causes the resistor to shrink in volume, increasing the contact pressure between the conductive particles and decreasing the contact resistance, resulting in a decrease in resistance, but the mechanical damage to the binder also increases the resistance. Usually the curing of the binder occurs before, mechanical damage occurs after, so the resistance value of organic synthetic resistors shows the following pattern: some decline in the beginning of the stage, then turn to increase, and there is a trend of increasing. Since the aging of polymers is closely related to temperature and light, synthetic resistors will accelerate aging under high temperature environment and strong light exposure.

Aging under electrical load: Applying a load to a resistor will accelerate its aging process. Under DC load, electrolytic action can damage thin film resistors. Electrolysis occurs between the slots of a slotted resistor, and if the resistor substrate is a ceramic or glass material containing alkali metal ions, the ions move under the action of the electric field between the slots. In a humid environment, this process proceeds more violently.

2) Capacitors
The failure modes of capacitors are short circuit, open circuit, degradation of electrical parameters (including change of capacity, increase of loss angle tangent and decrease of insulation resistance), liquid leakage and lead corrosion breakage.

Short circuit: The flying arc at the edge between poles at high temperature and low air pressure will lead to short circuit of capacitors, in addition, the mechanical stress such as external shock will also cause transient short circuit of dielectric.

Open circuit: Oxidation of lead wires and electrode contacts caused by humid and hot environment, resulting in low level inaccessibility and corrosion fracture of anode lead foil.
Degradation of electrical parameters: Degradation of electrical parameters due to the influence of humid environment.

2.6 Board-level circuitry
Printed circuit board is mainly composed of insulating substrate, metal wiring and connecting different layers of wires, solder components "pads". Its main role is to provide a carrier for electronic components, and to play the role of electrical and mechanical connections.

The failure mode of the printed circuit board mainly includes poor soldering, open and short circuit, blistering, burst board delamination, board surface corrosion or discoloration, board bending

Post time: Nov-21-2022