Diode Failure Analysis

Gideon Analytical Laboratories received two 1N645 silicon rectifier diodes for failure analysis. One was bad and the other was a quality diode to be used for comparison. A rectifier is an electrical device that converts alternating current(AC), which periodically reverses direction, to direct current(DC), which flows in only one direction. Rectifiers are used inside the power supplies of virtually all electronic equipment. AC/DC power supplies may be broadly divided into linear power supplies ands witched-mode power supplies. The 1N645 silicon rectifier diode has 225V 400mA ratings. It can handle a maximum of 5 Amps surge current and at 25 Degrees Celsius has an average maximum rectified current of 0.4 Amps. The goal was to determine why these diodes were failing.

Gideon Analytical Laboratories received two On Semiconductor SS16 rectifier for failure analysis. The On Semiconductor SS16 Schottky Rectifier features glass-passivated junctions and a high-current capacity. Their applications include low voltage, high-frequency inverters, freewheeling, and polarity protection. Their storage temperature range is between -65 and 150 Degrees Celsius and the operating junction temperature is between -65 and 125 Degrees Celsius. Along with the two failed rectifiers, several good devices were also supplied for comparison. The goal was to determine why the On Semiconductor SS16 Schottky rectifiers were failing.

Gideon Analytical Laboratories received two LUMEX SSL-LX093UWC/Gc LEDs for failure analysis. A LED (Light Emitting Diode), is a semiconductor light source that emits light when current flows through it. LEDs can be used in many different applications. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. Some of the more creative uses include creating an LED virtual sky, LED bionic contact lenses, and LED wallpaper. Both of the LUMEX SSL-LX093UWC/Gc LEDs were intermittent; one was mounted to a PCB and the other was loose. The goal was to determine the cause of these failing LEDs.

Gideon Analytical Laboratories received four Vishay SS26 Surface Mount Schottky Barrier Rectifiers for possible premature conditions to failure. A Schottky barrier is a potential energy barrier for electrons formed at a metal-semiconductor junction. Schottky barriers have rectifying characteristics, suitable for use as a diode. These Vishay SS26 Surface Mount Schottky Barrier Rectifiers feature a low profile package, high surge capability, and are RoHS compliant. The diodes came from PCB P/N 170310142001 Rev A03 S/N 051208-231. Positions D8, D9, D18, and D27 were identified as possible trouble spots. The goal was to determine the cause of failure.

Gideon received several Vishay SS26 Schottky rectifiers for failure analysis. It was thought something within the manufacturing process caused the devices to have a premature end of life in what would be considered a non-stressful application.

The Schottky diode is what is called a majority carrier device. It has advantages in terms of speed because it does not rely on holes or electrons recombining when they enter the opposite type of region as in the case of a conventional diode. When making the devices small, the normal RC type time constants can be reduced, making these diodes an order of magnitude faster than the conventional PN diodes. This is the prime reason why they are used in radio frequency applications.

Gideon Analytical Laboratories received several electronic metal-halide (MH) ballast black semiconductor diode, but it also permits current to flow in the reverse direction when its “Zener voltage” is reached. The goal was to expose the circuitry and reverse engineer the cause of failure of the three components that were failing at a high rate.

Failure analysis ensued. First, the zener diodes and fuses were exposed and potting material removed so that the circuitry was revealed. After analysis of the circuitry, a notable problem stood out. The configuration had no “soft” current limiting impedance for input line spikes. Input utility power has common surges and spikes. In a regular household, this sudden inrush of electrical current exposes unprotected equipment to damaging voltages. It can overheat motors, burn out lights and damage electronic components. In order to mitigate this potential threat, a surge protector is a good idea. However, all electronics should have some inrush limiting device to prevent these input power voltage spikes from damaging equipment.

Gideon Analytical Laboratories received two Fairchild transient voltage suppressors (TVS) SMBJ5V0CA. Both diodes were identified as having failed.Transient Voltage Suppressors (TVS’s) are devices used to protect vulnerable circuits from electrical overstress such as that caused by electrostatic discharge, inductive load switching, and induced lightning. Within the TVS, damaging voltage spikes are limited by clamping or avalanche action of a rugged silicon pn junction which reduces the amplitude of the transient to a nondestructive level. All semiconductors have to be confirmed failure and in what sense they have failed. The diode gave an abnormal curve trace in which the surface is inverted.

Gideon Analytical Laboratories received two failed AUIRF7648M2 MOSFETs. These are rather new on the market and specifically designed for the automotive industry. Typically, when a MOSFET fails, all terminals short. It is the failure analyst’s job to discover how the MOSFET failed in the application by combining the schematics, clues found in the failure analysis, and clues found on the PCB to give a complete picture to help resolve the client’s problem.

Gideon Analytical Laboratories, Inc. received on Vishay ES2D rectifier on a PCB. The initial condition and observation were that the diode had a conformal coating on a small circuit board in which when tested on a curve tracer had excessive leakage current across the junction and caused the PCB to fail in the application.

Rectifiers are primarily used for conducting in one direction and blocking in the other. The Vishay ES2D is an ultra-fast rectifier, which means the reverse recovery time should be less than 100 ns. Rectifiers are primarily used for power or signal conditioning in a variety of applications. This can range from high power output rectifier applications to low power switching rectifier requirements. They can be used for clamping networks on SMPS, dampening and modulating diodes on deflection circuits in CRTs, or freewheeling diodes on inductive loads etc.

Gideon Analytical Laboratories received several rectifier assembly rotors for failure analysis. A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The simplest kind of rectifier circuit is the half-wave rectifier. It only allows one half of an AC waveform to pass through to the load. Rectifiers are used as components of power supplies and as detectors of radio signals. Rectifiers may be of solid state diodes, vacuum tube diodes, mercury arc valves, and more. Each rectifier assembly rotor had three DO-5 type package in a standard configuration (stud is the cathode ). At least one of the three power rectifiers had failed in the assembly. The goal was to find the cause of these failures.

Gideon Analytical Laboratories received a JanTXV1N821 Zener diode for electronic failure analysis. A diode is a two-terminal electronic component with asymmetric conductance; it has low (ideally zero) resistance to current in one direction and high (ideally infinite) resistance in the other. A semiconductor diode is the most common type of diode; it is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode but also permits it to flow in the reverse direction when the voltage is above a certain value, known as the breakdown voltage. Zener diodes are semiconductor diodes which have been manufactured to have their reverse breakdown occur at a specific, well-defined voltage. The JanTXV1N821 diode is a surface mounted diode with a voltage selection range between 6.2 and 6.55 V. Its operating temperatures are between -65° C and 175º C, has tin-lead plated leads and comes in a hermetically sealed glass case. The JanTXV1N821 diode tested open. The goal was to identify the cause of the failure.

Gideon Analytical Laboratories received two Microsemi JanTX1N649-1 diodes for electronic failure analysis. A diode is a two-terminal electronic component with asymmetric conductance. It has low resistance to current flow in one direction, and high resistance in the other direction. There are various kinds of diodes, including vacuum tube diodes and solid state diodes. The most used and ubiquitous diode is the semiconductor. The JanTX1N649-1 is a voltage regulator diode is ideal for high-reliability applications where a failure cannot be tolerated. They are 1.5-watt voltage regulators that are hermetically sealed with a void-less glass construction using an internal metallurgical bond.

Gideon Analytical Laboratories received a failed Microsemi DZ771215A 10 watt diode for failure analysis. Two working devices were provided for comparison. A diode is an electric device that has two electrodes (anode and cathode) and that only allows current to flow in one direction, resisting current in the other direction. Diodes are used copiously as rectifiers, which convert alternating current (AC) to direct current (DC) to change the amplitude of the signal in proportion to its voltage in the circuit. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. The Microsemi DZ771215A semiconductor is made with silicon, has a 6.8-volt maximum regulator voltage rating, and is in a hermetically sealed case. The goal was to identify the cause of the failure.

Gideon Analytical Laboratories received several photodiodes to examine for possible contamination. A diode is a two-terminal electronic component with asymmetric conductance. It has low resistance to current flow in one direction, and high resistance in the other direction. There are various kinds of diodes, including vacuum tube diodes and solid state diodes. The most used and ubiquitous diode is the semiconductor. A photodiode is a type of device capable of converting light into either current or voltage. Gideon Analytical Laboratories was requested specifically to examine the gold bond pads for possible contamination.

Gideon Analytical Laboratories received several components for failure analysis: two Fairchild FDC6324L integrated load switches and two Fairchild BAV99 small signal diodes. Integrated load switches are designed for power management to minimize power loss by reducing current leakages; the FDC6324L is ideal for compact computer peripheral switching applications where 3V to 20V input and 0.6A output current capability are needed. Small signal diodes are small non-linear semiconductors that are often used in electronics where high frequencies or small currents are involved.

Gideon Analytical Laboratories received 10 parts each of Everlight and Nichia, respectively, LED components to on which to perform a moisture ingress comparison. An LED (light-emitting diode) is a semiconductor light source that uses an anode, a cathode, and a die to direct electrons to release energy in the form of protons.  A moisture ingress test is to determine the protection and susceptibility level of a device to moisture. Moisture ingress tests are conducted for all kinds of electronics equipment. The devices tested were an Everlight  67-23SDRSUGSUBC/TR8 and a Nichia NSCM315CT. These experiments were run to determine if these LEDs were compatible with their own production process, and then also to compare them with each other in their ability to resist moisture.

Gideon Analytical Laboratories received a Unity PLCC LED and was asked to perform FTIR analysis for the purpose of materials compatibility. Fourier transform infrared spectroscopy (FTIR) is a process used to acquire an infrared spectrum of absorption, emission, or photoconductivity of some substance. It can work with solids, liquids, or gasses, and can reveal the chemical composition of numerous materials. Gideon Analytical Laboratories was asked specifically to utilize FTIR on two substances: a white encapsulate and a clear/colorless material.

Gideon Analytical Laboratories received several VCSELs (vertical cavity surface emitting laser" with diminished light capacity over time for failure analysis. VCSELs are a type of semiconductor laser diode with laser beam emission perpendicular from the chip surface. The VCSEL has become of great importance in the optical communications field. Gideon Analytical Laboratories was tasked to diagnose the failing VCSELs.

Failure analysis commenced. The devices were tested on a curve tracer to determine whether any junction problems (junction inversion, leakage current, facet oxidation, etc.) were present; there was no leakage current detected by the curve tracer. The VCSELs were then enclosed in a hermetic T0-46 can with a slanted anti-reflective glass coating radiating in the region of 795 nanometers, which is pictured below.

Gideon Analytical Laboratories received three failed Vishay MOC8101 isolating photocouplers for failure analysis. These photocouplers are components that transfer electrical signals between two isolated circuits by using light. Like the MOC8102, MOC8103, MOC8104, and MOC8105, the MOC8101 consists of a consisting of gallium arsenide infrared emitting diode optically coupled to a silicon planar phototransistor detector in a plastic plug-in DIP-6 package (http://www.vishay.com/docs/83660/moc8101.pdf) The MOC8101 were reported to have intermittent function, it was the goal of Gideon Analytical Laboratories to diagnose the cause of these failures.

Gideon Analytical Laboratories received several GVD30601-001 super hyperabrupt junction tuning varactor diodes with a latent failure mechanism over time. A varactor diode is a P-N junction diode that changes its capacitance and the series resistance as the bias applied to the diode is varied. Hyperabrupt tuning varactor diodes offer a large change in junction capacitance over a small tuning voltage range. Varactors are operated in a reverse-bias state, like a Zener diode. Thus, no current flows, but since the thickness of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. The depletion region thickness is proportional to the square root of the applied voltage; capacitance is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of the applied voltage. The goal was to find the cause if the GVD30601-001 varactor failures.

Gideon Analytical Laboratories received one failed 1N5626GP diode and several good ones for comparison.  According to a Wikipedia post, a p–n junction diode is made of a crystal of a semiconductor, usually silicon, but germanium href=“https://en.wikipedia.org/wiki/Gallium_arsenide">gallium arsenide are also used. Impurities are added to it to create a region on one side that contains negative charge carriers (electrons), called an n-type semiconductor, and a region on the other side that contains positive charge carriers (holes), called a p-type semiconductor. When the n-type and p-type materials are attached together, a momentary flow of electrons occurs from the n to the p side resulting in a third region between the two where no charge carriers are present. This region is called the depletion region because there are no charge carriers (neither electrons nor holes) in it. The diode’s terminals are attached to the n-type and p-type regions. The boundary between these two regions called a p–n junction is where the action of the diode takes place. When a sufficiently higher electrical potential is applied to the P side (the anode) than to the N side (the cathode), it allows electrons to flow through the depletion region from the N-type side to the P-type side. The junction does not allow the flow of electrons in the opposite direction when the potential is applied in reverse, creating, in a sense, an electrical check valve.

Gideon Analytical Laboratories received one failed photocoupler, a Vishay IL 420, for failure analysis along with two virgins (unused) optocouplers for comparison.

The basic function of a Photo Coupler is to have electronic isolation, including potential isolation (as in the case of the transformer) in an electrical circuit. Devices of the Photo Coupler family include Photo Transistor, Photo Darlington Transistor, Photo Triac and OPIC. These devices have the characteristics of excellent isolation, high CTR, compact package, high-speed operation, low decay and unit control function not being influenced by field effects.

Gideon Analytical Laboratories received several Fairchild QTC H11N1s, a high-speed logic optocoupler, in 6-pin plastic DIPs. The devices were reported as some good, some intermittent and some not working in the application.

The main function of an opto-isolator is to block high voltages and voltage transients, so that a surge in one part of the system will not disrupt or destroy another part of the circuit. Opto-couplers allow a signal to be sent in digital (some analog) between circuits. This isolation used to take place using isolation transformers via inductive coupling between input and out sides separated by a dielectric. Four of the date codes were 9607E and one 9942K. All the optocouplers were tested under conditions that corresponded to the application; these failed, however, when the current was increased, the output received the signal. Several of the failed devices had reverse leakage current on the diode (input) as measured on a curve tracer.

Gideon Analytical Laboratories received several VCSELs (vertical-cavity surface-emitting laser) with diminished light capacity were submitted for failure analysis. A VCSEL is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers which emit from surfaces formed by cleaving the individual chip out of a wafer. Thus, all the light is emitted from one spot, the laser aperture. The devices were tested on a curve tracer to determine whether any junction problems (junction inversion, leakage current, facet oxidation, etc.) were present. There was no difference in the curve trace of a good and a failed device.

Gideon Analytical Laboratories received Wamco Display Socket 4160001-1 for failure analysis. The device had a reported open diode on pin G.

This display socket is encapsulated in a plastic housing filled with a silicone rubber filler to stabilize movement of the diodes. The diodes are hermetically sealed in glass and position via plastic at one end and a socket located at the bifurcation line. The electrical data indicated the diode was open when initially measured but was intermittent when moved.

Gideon Analytical Laboratories received two integrated load switches and two small signal diodes for analysis. The integrated load switches are particularly suited for compact power management in portable electronic equipment where 2.5V to 8V input and 2.8A output current capability are needed. They have an operating voltage range 1.2V-20.V. The signal diodes are non-linear semiconductor devices generally used in electronic circuits, where small currents or high frequencies are involved such as in radio, television and digital logic circuits. The goal was to diagnose the cause of failure for all of these devices.

Gideon Analytical Laboratories performed failure analysis on several BZT52B5V6-V Zener diodes with dead shorts. The most common function of a diode is to allow an electric current to pass in one direction (forward direction) while blocking current in the opposite direction (reverse direction). Thus, the diode can be viewed as an electronic version of a check valve with current passing in only one direction and blocked in the opposite direction. This unidirectional behavior is called rectification and allows one to convert alternating current to direct current.

Gideon Analytical Laboratories received two failed photocouplers for failure analysis. These photocouplers feature a high isolation voltage, high-speed switching, and high collector to emitter voltage. They are used in many types of applications, including power supply, telephones, and fax machines. The optocoupler was electrically tested; there was a short on both input diodes. The goal was to determine the cause of this failure.

After curve trace tests were performed, both failed devices were immersed in a low surface tension dye penetrant This is a modified Mil-Std 1014.2 with alterations reflecting current processing. After several other tests, these were confirmed as hard shorts. Any dye penetration constitutes a failure and demonstrates that moisture could have ingress the package of these failures.

Gideon Analytical Laboratories received several printed circuit boards (PCB) with fire damage on one and electrical overstress on the LTC4258CGW module when received. One good unit was provided for comparison. The objective was to find the cause and access the risk to the customer.

The LTC4258 can operate autonomously or be controlled by an I2C serial interface. Fault conditions are optionally signaled with the INT pin to eliminate software polling. External power MOSFETs, current sense resistors and diodes allow easy scaling of current and power dissipation levels and provide protection against voltage and current spikes and ESD events.

Gideon Analytical Laboratories received several intermittent diodes failures and two good ones for comparison. The failed devices were checked for intermittent operation. The three diodes open-circuited between 65 and 80C. The lead frame makes contact with a solderable copper-clad steel plug under the glass.

This picture shows the lead frame to plug interconnect. If the solder fails to wet sufficiently the lead frame to plug interconnect, then intermittent opens can occur. This is also true of cold solder joints at this juncture.