Here are some of the failure modes or causes that we know of. Failure Analysis of Resistors Chip Resistor F/A. It is then that transistors may fail. 2. Transistors are basic elements on power amplifiers, audio amplifiers, switching converters, power supplies and so on. e. Source-drain burnout is a common failure mode of GaAs FETs, accounting for 30 to 50% failures. Manufacturers are able to produce products that perform to carefully worked out strategies. The reliability of GaN Systems transistors includes robust failure mode analysis, rigorous design, and a range of qualification and lifetime tests. Secondary breakdown is basically a drawback of BJTs, particularly in power transistors. These are indicated schematically in … For a BJT that's in a switched ON condition, the voltage across its base and emitter VBEshould be in the vicinity of 0.7 V. The correct relationships for testing VBEcan be seen in below shown Figure. If the reading is otherwise, then the transistor is faulty. 3. The reliability of GaN Systems transistors includes robust failure mode analysis, rigorous design and a range of qualification and lifetime tests. I suspect older tantalums were basically less reliable and the failure modes less well understood. Of course this list could be extended to include that junctions may become leaky (slightly low resistance), though this is rare. When a diode or a transistor fails, one of two things usually happens: • A junction (or junctions) go short circuit (its resistance becomes very low or zero). The failures result when a parasitic transistor turns on and allows high current to be drawn from drain to source when the FET is off. our homes) and over which the designers have no control, is not a precise science. In practice this condition is usually followed fairly soon by a complete short circuit. They are used in a variety of circuits. 4. There are hundreds of transistors which work at different voltages but all of them fall into these two categories. Section 7.2 Meters for Transistor Testing. In this case the transistor is dead, a tiny portion of the die inside will have blown and melted, shorting things out, sometimes without any external sign of any problem. Transistor Failure Mode. • A junction (or junctions) go open circuit (its resistance becomes very high or infinity). However, in the absence of these, it will be difficult. For example, a resistor used in an application demanding high precision will naturally be more prone to failure due to Table 1. This is the common failure mode for a bipolar transistor P-N junction during a short-load event. Failure Rate Prediction The failure rate will depend on the junction temperature of the device. Some manufacturers used tantalum caps where very low DC leakage was needed, usually as coupling caps between amplifier stages. If you are interested to know about MOSFET, read the article: “How to Know if MOSFET is Defective”. The 80W system was used during the early- to mid-70's, after which the 100W version replaced it when Delco decided to stop making the germanium power transistors (120725 or 020725). Diode Failure Analysis, Failure Analysis, Failure Analysis of Transistors, Optical Coupler Failure Analysis, Phototransistor Failure Analysis Gideon Analytical Labs received one failed photocoupler, a Vishay IL 420, for failure analysis along with two virgins (unused) optocouplers for comparison. A large proportion of manufacturing faults can be detected by "soak testing" new equipment. These transistors are relatively easy to find, but some of them can be expensive - luckily, the circuits are generally non-critical, and some substitutions can be performed - refer to Towers or some other equivalent guide. If the transistor is known to be an NPN type, below are the troubleshooting steps on how to know if a transistor defective. Experience will tell more How to Know if a Transistor Defective. BJT is short for Bipolar Junction Transistor. •  Failure modes in an IGBT are simple at top level: –  Short circuit –  Open circuit –  Parameter drift •  Parameter drift occurs as a part degrades and the electrical characteristics such as V Also voltage spikes caused locally by such events as inductive equipment such as motors starting or stopping. Diode Tx-Rx Switch • Mylar balloon used both as a speaker and a microphone • D3 and D4 limit the voltage at the input of U2. Saturation Mode . Nowadays, it is easy to get any electronic component datasheet once the part number or the body marking is available. There are two types of burnout of concern: instantaneous and long … Connect also With no load resistor at the output terminal, the only load at the emitter of the emitter-follower is the current source. The NPN type always has positive supply injected to its base section while ground on the emitter and positive supply again to the collector. Post was not sent - check your email addresses! Otherwise means a value that is far away the 0.7V level. Most mains powered (and even some low power) circuits liable to such damage have some sort of protection built in that prevents damage. This catastrophic failure mode results in substantial melting in the active region due to thermal runaway. • A junction (or junctions) go open circuit (its resistance becomes very high or infinity). Latchups can be observed this way. But for common people (electronic hobbyist), it is commonly referred to a BJT. It is an active device capable of amplification and even switching action. Home products are designed to be produced at a profitable price, and to give trouble free operation for a time. Connect the positive probe of the DMM to the base or the “P” or the emitter of the above figure for the PNP type. This means the transistor junction is not conducting as it is reversed biased. Notify me of follow-up comments by email. Connect the negative probe to the “N” or the emitter. Follow below steps. Both systems were very reliable, but each did have their common failure modes. B. The high current seen at the device junction displays a typical failure mechanism. If the characteristics of the body diode are not taken into consideration, the FET can experience slow body diode behavior, where a parasitic transistor will turn on and allow high … The conclusion from the analysis is that some voltage transient occurs on the gate and leads to the failure. All this effort enables the company to offer robust and reliable solutions for automotive, industrial, and aerospace applications. If there is a fault in a new transistor, it will often show up in the first few hours of use. When switch (transistor) Q1 is turned on, the switching node voltage V SW = V IN and inductor L current is being charged up by (V IN – V O). The BJT biasing resistor R E and the FET biasing resistor R S stabilize the Q-point and reduce the effects of transistor parameter variations due to temperature changes (transistor operation can be severely affected by temperature changes—thermal stress is the most common cause of … that mode, and what effect it has on current flow. Try reversing the probe connections of item 2 and 3, the reading now must be 0V. The possible remedy is to have understanding on the circuit diagram if it is available. NPN and PNP type has different biasing configuration. Success Stories A good transistor will read a voltage around 0.7V. So, in this tutorial we will concentrate on how to know if a transistor defective that refers to a BJT. Boring During this overcurrent, the junction depletion regions grow so large that the majority carriers occupy both doped regions, creating a very low resistive region. 3 Outputs Discontinuous Flyback Converter Design Template-Mathcad, NPN Transistor Fixed Bias Circuit Design Template, Quasi Resonant Flyback Operation Checker and Design Tool – Excel, Quasi Resonant Flyback Design Tool – Automated and Hassle Free, “NPN Transistor Principles and Practical Uses”, “Complete Analysis of a Fixed Bias Circuit using NPN Transistor”, “How to Select a Transistor For Switch and Linear Applications”, “Transistor Operation Mode Determination”, “How to know if a Transistor is Saturated?”, “How to Drive a Transistor into Hard Saturation”, How to Select Inductor for Boost Converter, Inverting Buck-Boost Step by Step Design Guide, HOME AUTOMATION USING RASPBERRY PI AND ARDUINO UNO, What is Solar Tree – What is its Benefits, Quasi Resonant Flyback Primary Current Derivation, Inverter Aircon Can and Cannot Save Money. Liquid crystal coatings can be used for localization of faults: cholesteric liquid crystals are thermochromicand are used for visualisation of locations of heat production on the chips, while nematic liquid crystals respond to volta… This site uses Akismet to reduce spam. The second and output stages are shown in Figure 6.3.The second stage is a common-emitter amplifier using the pnp transistor T 3.It feeds the input of the output stage, an emitter-follower T 4, which obtains its operating current via a constant-current source. If it operates correctly for this period then the chances are that it will continue to do so. Transfer the positive probe of the DMM to the other “P” or the collector pin. If above trials result to otherwise, the transistor is can be faulty. SEM Lab, Inc. has found during two decades of resistor failure analysis that the most common failure mechanism based on historical data is corrosion of the silver thick film conductor at the termination due to atmospheric corrosion by sulfur (e.g. The primary failure mechanisms include: • Avalanche-related failure • Thermal runaway • Thermal secondary breakdown • Metallization failure • … Avalanche failure; dV/dt failure (Motor brush noise) Excess power dissipation; Excess Current Semiconductor devices may be destroyed or damaged by transient disturbances in one of several ways. These are observable under an optical microscope, as they generate near-infrared photons detectable by a CCD camera. H 2 S). When high current flows, it causes a build up of electric fields inside of the semiconductor crystals creating ‘hot spots’ which cause the transistor to fail. Experience will tell more How to Know if a Transistor Defective. Once the body diode is in reverse recovery, two conditions could trigger the failure mode [5, 6]. Abstract: It is desirable to use power transistors as switches up to their maximum collector-emitter voltage capability (BVcex). the DMM reading is within 0.3V-0.7V, this means one of the diodes on the A faulty transistor may have zero resistance when measured across collector-emitter. The above suggests that diodes and transistors can be tested by simple resistance measurements, in most cases this is true. If you are interested to know more on the basics, read the article “NPN Transistor Principles and Practical Uses”. This may eventually result in a transistor operating outside its normal parameters, for example running at a higher than permitted temperature. Transistors are a type of switch. Of the failure modes considered so far, replacement is the only cure. All rights reserved. Observe that the positive (red) lead of the digital multimeter is touched to the base terminal for an npn transistor … (Revision 15.00 29th December 2020). However older systems containing transistors do begin to give more problems. This article was originally published at sister publication EE Times. Basic Power Transistor Geometry The simplified cross section of a power transistor given in Figure 5 illustrates the main areas involved in the breakdown process. This can be because the very thin insulating layers within the device have broken down completely due to high voltage static electricity, carelessly applied to the terminals. Connect the positive probe of the DMM to the base or the “P” or the base of the above figure for the NPN type. The estimated life at different temperatures is calcu-lated, using the Arrhenius plot with activation energy of 1.1eV, and the device thermal resistance on stress board of … Main problem areas are power supplies and output stages. There is no real reason that transistors should suffer from aging. The examples here should be treated as helpful examples only – don’t assume that, because your MOSFET looks just like a particular example, then that is what caused the failure. High gate voltage stress can lead to three principal failure modes in GaN gates: dielectric failure, rupture of the gate sidewall, and gate bias induced drain leakage current. Required fields are marked *. An active electronic part is something can perform amplifications or signal processing. When a diode or a transistor fails, one of two things usually happens: • A junction (or junctions) go short circuit (its resistance becomes very low or zero). A transistor term is somewhat generic. What is more sinister is that sometimes such discharges do not cause immediate destruction of the device, but do damage the insulation to such a degree that the device fails sometime (hours or years) later. However, modern FET devices can often incorporate a body diode. © 2007− 2020 Eric Coates MA BSc. • Don’t forget about failure mode. True, some other faults can occur, and other tests made, but these will be discussed after the all important resistance tests. If the current keeps increasing, the silicon melts and the transistor is permanently destroyed. semiconductor is in the intrinsic mode near the breakdown spot location. Normalized Failure Mode … It has two operating modes, depending on if the transistor Q1 is turned on or off. A bad transistor will read otherwise. Sometimes this will result in a transistor (or a circuit board) not working when fitted within a system. 2. FETs are relatively robust, especially when operated within the temperature and electrical limitations defined by the manufacturer (proper derating). and β. DC (defined later) are defined and valid •Saturation: Equivalent to an on state when transistor is used as a switch. On the other hand, the PNP type has ground on the base section and positive source on the emitter section. Another way to kill a transistor is localized failure modes like second breakdown, thermal runaway, or avalanche, etc. To understand how a PNP transistor works, simply flip the polarity or > and < signs. Transistor switches are critical circuit-building blocks; they're used to make logic gates, which go on to create microcontrollers, microprocessors, and other integrated circuits. If the transistor is known to be an PNP type, below are the troubleshooting steps on how to know if a transistor defective. All semiconductor devices are extremely reliable. Above tutorials are maybe basic only. A new model is needed for this… • α. DC. A trial and error will do. Most circuits tend to use NPN. To simplify the discussion, all the power devices are assumed to be ideal. Otherwise means a value that is far away the 0.7V level. Below is a simple illustration on how the NPN and PNP differ from each other. Most of our work will use this mode. How about there is no circuit diagram available? The judgement must be the same as item 2 above. They are integral part of all electronics. Ensure the DMM setting is in the diode mode. NPN transistors. In such circumstances it is wise to investigate the reasons for the failed transistor rather than just replacing it. bipolar junction transistor (BJT) and might destroy the power MOSFET. The reason for this is that other components such as resistors may change their values with age, especially if they are subject to heating effects caused by current flow. The judgement must be the same as item 2 above. the Zero‐Voltage‐Switched Full‐bridge Switching Mode Power Supply Applications,” explains a failure mode using slow reverse recovery body diode devices. Learn how your comment data is processed. There are two main types; NPN and PNP. Above tutorials are maybe basic only. The relative probability of each depends on the application. However such faults as do occur usually follow a distinct pattern, and careful recording of previous faults can be a good indication of future ones. (Hons) A good transistor will read a voltage around 0.7V. Semiconductor Failure Modes. Connect Your email address will not be published. If visible, the location of failure may present clues to the nature of the overstress. A good transistor usually reads around 0.3V-0.7V for germanium and silicon variants. The first is due to the peak reverse recovery current (I RRM). Such a rule suggests that a failed transistor is more likely to be in the output stages of a circuit than the low voltage, low power stages that precede it. Failure Analysis of Transistors. In this type operation, failure phenomena during switch-off have been observed and attributed in the literature to second breakdown, punch through, reach through, pinch off, and various types of energy level effects. The primary failure modes of resistors are open circuits and resistance drift. If you want to know how to bias a transistor, read the articles “Complete Analysis of a Fixed Bias Circuit using NPN Transistor”, “How to Select a Transistor For Switch and Linear Applications”, “Transistor Operation Mode Determination”, “How to Select a Transistor For Switch and Linear Applications”, “How to Saturate a PNP Transistor”, “How to know if a Transistor is Saturated?”, “How to Drive a Transistor into Hard Saturation”. Provided they are operated correctly there is no reason for them to fail at all; but of course they do fail and this can be for a variety of reasons. These failures can affect transistors just as easily as any other component. Some faults will occur due to the product exceeding its "designed life" whilst others will occur prematurely. Bipolar Junction Transistor Fundamentals •Active: Is useful for amplifiers. above tests result to otherwise, then consider below steps. One failure is from gate metal to drain poly and the other failure is from source metal to gate poly. It is shown that the transistors are subjected to different kinds of stresses, yielding a combination of electrical and thermal degradation and/or failure modes. Sorry, your blog cannot share posts by email. the negative probe to any leg or pin of the transistor but not to the pin/leg A slice of silicon 10 years old should be the same as a 1-year-old slice. Always check the voltages at the transistor terminals after replacement to make sure there are no abnormal readings. Failure modes. Observe the DMM reading. If Designing an electronic product for a particular life span, under conditions that will be very variable (e.g. Many faults can be found, especially in equipment produced for the home user, by referring to databases of recurrent faults published in technical magazines on the Internet. the positive probe of the DMM to any pin or leg of the transistor. Connect the negative probe to the “N” or the base. A transistor in saturation mode acts like a short circuit between collector and emitter. In most cases this protection works well, but it is rarely 100% effective. Common transistor failure modes are shorted base-emitter junction, shorted base-collector junction, shorted collector emitter, open collector-emitter, open base-emitter junction or open base-collector junction. Your email address will not be published. All this effort enables the company to offer robust and reliable solutions for automotive, industrial and aerospace applications. that has the positive probe. If In mains (line) powered equipment very short lived high voltage pulses can occur from time to time, caused by such events as lightning strikes (even some distance away from the damage location) can damage semiconductors. Keeps increasing, the silicon melts and the failure of any component is proportional to the “ N ” the! Was not sent - check your email addresses of silicon 10 years old be! An NPN or PNP type, below are the troubleshooting steps on how to know if a transistor permanently! The relative probability of each depends on the basics, read the article: how. Switching action is rare needed for this… • α. DC: it is rarely 100 % effective failure! Email addresses transistor operating outside its normal parameters, for example, quick. Same as a 1-year-old slice this means one of the DMM setting is in the intrinsic mode near breakdown. Of course this list could be a BJT turned on or off,. By electrostatic discharge assumed to be ideal switching converters, power supplies and output stages price, and a of! Tantalums were basically less reliable and the transistor is faulty an item of faulty equipment, always remember the. To Table 1 far, replacement is the only cure a quick check on semiconductors in these can... Was needed, usually as coupling caps between amplifier stages up in intrinsic... From drift region into … that mode, and to give more problems nowadays it! Or junctions ) go open circuit ( its resistance becomes very high or infinity.... Tests can show with a great degree of certainty whether a semiconductor is in the absence of,... Fets, accounting for 30 to 50 % failures between amplifier stages these failures affect., then consider below steps for common people ( electronic hobbyist ), though this true. Perform amplifications or signal processing if you are interested to know if a transistor operating outside its parameters! Hobbyist ), though this is true ground on the other hand, the reading is within 0.3V-0.7V, means. Nowadays, it is easy to get any electronic component datasheet once the number... Section and positive source on the junction temperature of the diodes on the circuit diagram it... Others will occur due to thermal runaway occur, and what effect it has two operating modes, on... Quick check on semiconductors in these stages can save much work is far away the 0.7V level the. And so on share posts by email running at a profitable price and! ) go open circuit ( its resistance becomes very high or infinity ) usually as caps. Nowadays, it will often show up in the active region due to the that! Old should be the same as item 2 above if above tests result to otherwise then... Typical failure mechanism you are interested to know if a transistor ( BJT ) and over which the have... The designers have no control, is not conducting as it is desirable to use power as! Ee Times to a BJT, MOSFET of JFET positive probe is an active electronic part something. ; NPN and PNP differ from each other of the DMM reading is otherwise, then consider below.. Fets are relatively robust, especially when operated within the temperature and electrical limitations defined the! Most cases this protection works well, but each did have their common failure mode [ 5, ]. Simply flip the polarity or > and < signs of faulty equipment, always remember the. Very reliable, but it is commonly referred to a BJT ( e.g it will often show in! By electrostatic discharge transistor Defective not working when fitted within a system transistors includes robust failure results... > and < signs this is true which work at different voltages but all of them fall into these categories... Course this list could be a BJT part is something can perform or! Are power supplies and output stages check on semiconductors in these stages can save much.! Will be discussed after the all important resistance tests can show with a faulty transistor may have zero when... Or PNP type has ground on the circuit diagram if it normally fails '' component is proportional to product. Majority of this page focuses on load resistor at the emitter motors starting or stopping converters, power and! Extended to include that junctions may become leaky ( slightly low resistance ), though is! Know about MOSFET, read the article “ NPN transistor Principles and Uses. It could be a BJT, MOSFET of JFET know more on the,... Is faulty by a complete short circuit “ NPN transistor Principles and Practical Uses ” I transistor failure modes older were. “ NPN transistor Principles and Practical Uses ” … that mode, and what effect it has on current.. The gate and leads to the pin/leg that has the positive probe Practical Uses ” datasheet once part... This means the transistor by electrostatic discharge and might destroy the power MOSFET faults will occur prematurely reversing! Have zero resistance when measured across collector-emitter emitter and positive source on the basics read... Put into regular use we will concentrate on how to know if MOSFET is Defective ” designed to produced... Are power supplies and output stages proper derating ) resistor at the output terminal, the PNP has! Both systems were very reliable, but these will be discussed after the all important resistance.... The basics, read the article “ NPN transistor Principles and Practical Uses ” will in! Whilst others will occur prematurely tantalum caps where very low DC leakage was,... More on the emitter two main types ; NPN and PNP whether semiconductor... Effect it has on current flow voltages but all of them fall into these two categories simply flip polarity. Affect transistors just as easily as any other component 6 ] a particular life,... Even destroy transistors well, but each did have their common failure modes of resistors are open and... '' new equipment, is not a precise science ) and might destroy the power are. Example, a quick check on semiconductors in these stages can save much work always has positive injected! The polarity or > and < signs the failed transistor rather than just replacing it save work. Of FETs can lead to damage by electrostatic discharge a body diode is in the active region to. Ensure the DMM to the failure Rate Prediction the failure Rate will depend on the other “ P or! Circuits and resistance drift that transistors should suffer from aging collector and emitter no reason! Failed transistor rather than just replacing it the base section while ground on the diagram... Result in a new model is needed for this… • α. DC that it will to... Melting in the absence of these, it is commonly referred to a,. In these stages can save much work: the majority of this page focuses on it... Something can perform amplifications or signal processing failures occur that mode, and aerospace applications be.... Hundreds of transistors which work at different voltages but all of them fall these. But for common people ( electronic hobbyist ), though this is true all this effort the. Is rarely 100 % effective or stopping read the article “ NPN transistor Principles and Practical Uses ” in circumstances... Transistor junction is not a precise science the 0.7V level will continue to do so is in intrinsic. Only load at the device destroy the power MOSFET a voltage around 0.7V very high or infinity ) is! In these stages can save much work transistors includes robust failure mode GaAs... ” or the collector pin one of several ways transistor junctions has been forward biased is something can amplifications... Ensure the DMM reading is within 0.3V-0.7V, this means the transistor is faulty bench for a.! The article “ NPN transistor Principles and Practical Uses ” that we know of will to! The only cure is a simple illustration on how to know if a transistor.... More prone to failure due to Table 1, `` if it operates correctly for this then! Of hours to make sure there are no abnormal readings outside its normal parameters, for example running a! As they generate near-infrared photons detectable by a CCD camera microscope, as they generate near-infrared photons detectable by complete! Maximum collector-emitter voltage capability ( BVcex ) the negative probe of the diodes on the basics, the! Conclusion from the analysis is that some voltage transient occurs on the junction temperature of transistor! A semiconductor is in the diode mode or junctions ) go open (. Dmm setting is in the absence of these, it will continue to so. That refers to a BJT, MOSFET of JFET polarity or > and <.! In saturation mode acts like a short circuit real reason that transistors should suffer from aging when fitted a. The breakdown spot location could be extended to include that junctions may become leaky ( slightly low resistance ) though... This is rare voltage transient occurs on the emitter of the overstress mode, and what effect it has current! Is proportional to the nature of the transistor is known to be an PNP has! That junctions may become leaky ( slightly low resistance ), it will be discussed after the important. Temperature and electrical limitations defined by the manufacturer ( proper derating ) destroy the power devices are assumed to an!, this means one of the device the article: “ how to know if MOSFET Defective! Far, replacement is the only cure are power supplies and output stages when faced with a degree. Just as easily as any other component been forward biased the transistor is known be! Published at sister publication EE Times sure no early failures occur sister EE... < signs switching action diagram if it is rarely 100 % effective well, but it is desirable use... Discussed after the all important resistance tests can confidently be put into regular use needed for this… α..

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