How Aging Components Impact Your Servo Amplifier or Drive

Aging of electronic components like resistors, capacitors, and diodes can fault out your drive, bringing your process to a screeching halt.

Aging of electronic components like resistors, capacitors, and diodes can fault out your drive, bringing your process to a screeching halt.

Most Common Reasons for Failure

Industrial electronics such as servo drives, power supplies, amplifiers, HMI displays and any electronic equipment that has printed circuit boards (PCB’s or PWB’s), will potentially fail during their life-time of usage.  No matter how well it can be designed, there are numerous reasons a circuit or components on a PCB will fail.  Some of the most common reasons are over current, over voltage, contamination, corrosion, manufacturing defect, operating environment and aging.  In this article, we will look at aging, and how it affects the electronic boards and components on your unit.

What is Aging?

Circuit aging refers to the deterioration of circuit performance over time.  As an electronic board and its components are used, or by just sitting, aging will occur over time, as chemical reactions reduce the quality of the circuit and its components.  This includes all capacitors, resistors, relays, diodes, microprocessors, chokes, inductors, driver chips, IGBT’s, transistors, rectifiers, transformers, opto-isolators and other components found on a printed circuit board (PCB).  But circuit aging is accelerated by switching activity or voltage cycles.  The more switching activities mean more input and output transitions for the same period of time will dramatically result in more aging.  A spike in voltage or a voltage overshoot can increase aging on a circuit.  The environment and other factors also have an accelerated effect on aging.

What are Age-Related Failures?

Once the initial burn-in phase is over, usually done by the manufacturer to rule out any failure due to defects, a unit’s overall failure rate typically remains low for several years.  But, the useful life ends when the failure rate increases due to age related failures.  These include insulation breakdown, increases in current leakage, loss of resistance and loss of capacitance.

Identifying a Failed Circuit or Component due to Aging

A visual inspection is usually the first method used in determining failed components on an electronic board.  “The most obvious indicator when a specific component has failed is by carefully looking at it,” says Adam, a drive repair specialist.  “You can spot burn-in on a board which indicates a violent voltage spike, so you check all components in the vicinity, as well as a bulging capacitor, or cracked coatings on resistors, processor chips, .  Those are easy ones.”  But to spot signs of aging, “you have to look for other things that aren’t as obvious,” says Jim, an HMI monitor repair specialist.  “The tarnish on leads is a giveaway, markings on the components that are old, as in the company branding has changed and you see an old symbol, the date codes on components are also a way to check for aging.”  Yet, there are still other visual signs to look for as well.  Brad, a Fanuc amplifier repair specialist, says, “I look at corrosion, capacitors for leakage, bad connections and color change due to prolonged heat exposure (thermal).  Also, natural discoloration over time takes place and I change these components out as well as all the others.  Many components still work under these conditions, but need replacement for prolonged life on a servo drive or amplifier.”

Sometimes, aging leaves no clues. Detection by visual inspection is limited to visible anomalies.  Therefore, there are other methods that are used to find age-compromised components that otherwise look totally fine.  One way is to look at historical data of known component failure and look at those for defection.  Furthermore, testing methods are used to find compromised or failed components, such as the frequent use of ocsiliscopes and multi-meters to take readings on components to see if they are out of spec and their electrical characteristics have broken down over time.

Preventative Maintenance Repair: A solution for Aging Electrical Components

servo amplifer and drive repair

Changing out aged components during preventative maintenance can prevent catastrophic breakdown.

 

When an electrical device breaks down, often it is in the circuit board(s).  The quickest way to repair the issue is to replace the whole board with a new one.  But many times a board replacement is not available, or, there are other issues at hand.  So then you are left with repairing the components on the board.  This is time-consuming and can be costly, but necessary to get the device working again.  A preventative maintenance repair on electrical components inside your servo drive or other unit on a critical machine in your process is recommended every 18-24 months of usage.  Many times an electrical component can still work even when compromised, but at some point it will lead to failure and usually at the wrong time and potentially creating more damage to the unit.  Contact a professional industrial electronics repair outfit for further information on an emergency or preventative maintenance repair.

Get Your Repair Started    Or call (989)922-0043 for fast service.

 

Further Reading (Excerpts from ‘Evaluating the Effects of Aging on Electronic Instrument and Control Circuit Boards and Components in Nuclear Power Plants’ – by J. Naser, U.S Department of Energy)

Report Summary

Circuit boards used in the electronic instrument and control (l&C) systems of nuclear power
plants may suffer from aging failures that can cause a plant trip or unavailability of plant
systems. The overall objective of this study was to determine how precursors of failures in I&C
circuit boards can be measured and how these measures can be used to estimate the probability
of failure during the next operational period within a statistical confidence level. The study
provides a framework for the identification of techniques that can be used to monitor circuit
board component aging failure modes that could lead to a failure of the circuit.

Background
The nuclear power industry is currently facing increasing obsolescence issues with original
equipment installed for instrumentation, control, and safety system applications. These systems,
frequently more than thirty years old, are experiencing aging-induced failures in electronic
boards and components. These failures can cause plant trips and reduce the reliability and
availability of systems. Most plants take a policy of running to failure and/or periodic
replacement-frequently without a good technical basis. Both of these approaches can be very
costly. The industry needs a better understanding of the aging mechanisms and observable
precursors to failure along with more cost-effective aging inspection, mitigation, and other aging
management technologies.

Results
The report describes potentially useful techniques for monitoring the aging of l&C boards. The
techniques have been grouped into six methods: periodic testing, reliability modeling, resistance
measures, signal comparison, external (passive) measures, and internal (active) measures, each
representing distinct theoretical approaches to detection and evaluation. Each technique has
significant advantages and disadvantages. The design of hardware and software monitoring
systems increases in complexity as the methods become more precise in their ability to measure
aging factors, but the technical tools that can be applied to monitoring within the methods have
also clearly improved within the last few years as computers and networks have been enhanced
to rapidly process large amounts of data.

The report provides a decision process for selecting those circuits and components that could
benefit from an upgraded approach for monitoring the effects of aging and highlights areas
where future R&D is needed to establish firm recommendations for I&C systems. The report
also assesses the relative costs and technical benefits of upgrading circuit-monitoring systems.

EPRI Perspective
As the nuclear power industry is facing increasing aging and obsolescence issues, one area that
needs attention is the aging of electronic boards and components used in l&C systems. Existing
methods of functional testing of l&C systems typically detect circuit failures after they occur
whereas the new monitoring techniques provide indications of failure while the circuit is still
functional. This information will make it possible to maximize the operating life of components
without suffering circuit failure.
This report presents a number of specific techniques for improving the ability to monitor aging
induced changes in circuits and board components that could lead to board failure. Some
promising techniques are discussed that have been used in applications outside of electronic
circuit board monitoring. Additional R&D efforts are needed to test, confirm, and demonstrate
the viability of circuit board monitoring techniques for use as a predictive tool to detect aging
induced changes that can lead to circuit failure. Additional engineering studies need to be
completed to better quantify the implementation and operational costs and benefits of the viable
techniques and to provide sufficient justification for their implementation.

Many causes of l&C circuit board failure progress slowly. This opens the possibility for
measuring the impacts of aging progression prior to complete failure. Measures of changes in
electrical characteristics provide a basis for estimating the probability of failure during the next
operational period. Simulation of the aging process can be used to produce a statistical
confidence in the probability estimate. Such information can be used to support optimized
maintenance planning and decisions

The ideal result of this project is to define a framework for selecting techniques for aging
management that can be applied to any circuit. The techniques should be easy to use and
account for various modes of circuit component aging.  Hardwired electric relays have become obsolete, as
electronic circuits rely on integrated circuits and software controls to accomplish the same
functions. Current technology permits software logic to replace relay logic and analog controls
to activate safety and control circuits. Therefore, circuit boards can become obsolete in less than
a decade and as this older equipment fails, the spare parts inventories become depleted and
failures can’t be easily repaired. Then there is an increasing need for older technology l&C
systems to be upgraded or replaced.

In an absolute sense the rate of failure and replacement for electronic circuit boards may not be
considered high. However, from a regulatory point of view, and also relative to other major
plant systems, the I&C system repair and replacement rates are relatively high. For example,
individual circuit boards are typically repaired or replaced several times during the life of a plant.
Therefore, this higher rate of circuit board replacements makes them of low concern as an aging
issue in plant license extension, whereas, insulation on the wires connecting the I&C systems is a
required aging issue that must be addressed in license extension applications.

Reviewing the descriptions of aging failures in circuit boards provides some very valuable
insights. For example, a conclusion from review of information from EPRI (EPRI 2002, EPRI
2003 and EPRI 2004) is that the failure end state of most electronic components is either an open
or short circuit. These findings help simplify the design of potential measurement systems by
permitting the monitoring of each board circuit to be treated as an equivalent circuit with
measurable electronic parameters such as voltage, impedance, resistance, current, and ground
resistance. Changes in these parameters become precursor indications of degradation that could
lead to a complete failure.

Aging induced failures (due to temperature, operating stress, quality of components, corrosion,
and environment) are slow and many intermediate states of partial failure exist. Changes in the
electrical parameter signals from the circuit can be measured before an inoperable condition is
reached. In the case of a rapid shock induced failure (e.g., high voltage spikes, rapid corrosion or
high temperature effects from fire, etc.) the time between the triggering condition and the
component failure would be too short for corrective action to be taken before a failure.

A variety of technology and software methods can be used to develop improved monitoring,
including continuous circuit monitoring, and active as well as passive testing approaches.
1. The EPRI reports developed by EdF (EPRI 2002 and EPRI 2004) show the impact of
component failures involving capacitance and inductance that are sensitive to frequency
variation tests.
2. Simple voltage tests could easily identify circuits that are drifting toward shorts or open
circuits.
Replacement of an aging component with a spare board may not always be possible, because of
obsolescence. If this is the case, then the ability to locate the failed component supports the
process of replacing individual components on a board when replacement circuit boards are not
available. This circuit board reconditioning can be enhanced by early identification of precursor
failures.
Potentially useful techniques for monitoring the aging of I&C boards are presented in Section 4.
The techniques have been grouped into six methods of periodic testing, reliability modeling,
resistance measures, signal comparison, external (passive) measures, and internal (active)
measures, representing unique theoretical approaches for detection and evaluation. The technical
tools that can be applied to monitoring within the methods have clearly improved within the last
few years as computers and networks have been enhanced to rapidly process large amounts of
data. Each technique has significant advantages and disadvantages. Human inspections can
detect a surprisingly large group of aging issues, but unfortunately, most likely after the failure
occurs. As the methods become more precise in their ability to measure aging factors, the design                                                                       of the hardware and software monitoring system increases in complexity.

Introduction

An important metric commonly used to measure and specify the lifetime of electronic
components and circuit boards is the mean time between failures (MTBF). This is the mean time
until the group of devices will fail. The MTBF is a function of the failure rate of the circuit
board and the components on it.

Bathtub Curve
The failure rate for most modem electronic components has a distinctive “bathtub” curve that
represents their failure characteristics (Kumamoto and Henley 1996, Wowk 1991, and Ireson and
Coombs 1988). The bathtub curve in Figure 1-1 provides a means for discussion of the
characteristics of the statistical failure rate during three phases of the component life burn in,
useful life, and aging dominated

Servo Drive failure rates

Bathtub Failure Rate Curve

As shown in the above curve, during the early life of the component (referred to as the bum-in phase),
it’s more likely to fail due to the initial manufacturing defects and introduction of damage during
assembly and testing. The initial testing of electronic components uses high temperatures to act
as a time accelerator to verify limits of failure conditions and eliminate obvious defects in the
subsequent manufactured devices.
Once this initial bum in phase is over, through factory tests and initial testing at the site, a
device’s overall failure rate typically remains quite low for a number of years. This MTBF or
useful life is expected to last more than ten years for electronic devices built in the 1980s, and
operated within specified limits for the entire time period.
The useful life ends when the failure rate increases due to age related failures. Examples of age
related failures include insulation breakdown, increases in current leakage, loss of resistance and
loss of capacitance. Aging is impacted by long term stress from voltage differential, voltage
cycles on specific components, and other factors.

Foundations for Addressing Aging
Utilities operating power plants are well aware of the aging issues and have adopted a variety of
rationales for protecting the plant from unexpected circuit failures that go beyond the simple
procedure of running the circuits until failure occurs. In general the proactive rationales can be
characterized in four groups. The groups are (1) application of technical specifications to
perform periodic testing, (2) replacement of a circuit board based on an estimated MTBF using
statistical component reliability methods1, (3) use of condition monitoring and operational
assessment models2 to predict the need for replacement, and (4) continuous monitoring to warn
of precursors of failure.

Framework for Improved Aging Monitoring
A framework for integrating the issues related to upgrading circuit board functional testing to
include aging monitoring is needed. Figure 1-2 provides a framework for considering how new
techniques can be considered for application in existing plants and what type of monitoring
might be associated with the technique. It also includes deciding if it is necessary to upgrade the
aging detection process.

Framework for ConsideringImproved Circuit Board Monitoring for Aging

Framework for Considering Improved Circuit Board Monitoring for Aging

Aging Failure Modes
A failure mode is the effect by which a failure is observed; whereas, a failure mechanism is the
chemical, physical, or material process that led to the component failure (EPRI 2003). For
electronic components, there are basically two general aging progressive failure modes and two
end state aging failure modes:
Progressive failures
• Degraded performance
• Functional failures
End states
• Short circuit
• Open circuit
Transistors, diodes, and certain types of capacitors typically fail short circuit, although resistors
and optoelectronic devices fail in a functional mode by having an output signal that is different
from what is expected. Failure mechanism can typically be corrosion, wire-bond fatigue, oxide
breakdown, electromigration, bond liftoff, and many others. The area of failure mechanism is
truly a fertile frontier for understanding the contributors to equipment failure and then being able
to first design the mechanisms out of components or at least understand the onset of failures and
be able to detect them and take preventive measures to combat them

METHODS FOR DETECTING l&C BOARD FAILURES

This section provides an overview of the framework element for selecting methods for
monitoring the aging of components on circuit boards. The first step is to define methods, which
uniquely capture different categories of theoretical under pinning for aging detection, using the
four rationales from Section 1. As shown in Table 4-1 six broad method categories are defined
and presented in order of increasing technical complexity.

Table4-1
Summary of Methods for Detecting and Monitoring Aging in Circuit Boards

Servo drive circuit board failure

Servo Drive circuit board failure

Summary of Methods for Detecting and Monitoring Aging in Circuit Boards

Circuit Board Failure Detection and Prediction Methods
The basis for listing a technique is the expectation that within the theoretical method there can be
various means for monitoring circuit behavior that can provide a better way for deciding when to
repair or replace the circuit board. The six basic theoretical methods listed in Table 4- 1 are
discussed below. Within each method, where appropriate, techniques are identified that provide
alternative technical approaches for monitoring aging.
Method 1: Periodic Inspections
There are two techniques for periodic inspections within this theoretical method, functional
testing and visual inspections. The theory for detecting aging in circuit board components with
periodic inspections is that the aging condition produces an observable measure during the test
such as an increase in the time for circuit actuation, or in the case of visual inspection a color
change somewhere on the printed circuit board (PCB). Most PCBs are operated under the runto-
failure philosophy. With this philosophy, PCBs may be monitored for proper operation, but no
attempt is made to enhance the PCB life until the PCB fails to function. Since many PCBs
operate beyond their design life, critical or essential boards may need to be refurbished at least
once in a plant’s operating life. Detailed methods of trouble-shooting and refurbishment are
discussed in EPRI 2003.

Functional Testing
Functional surveillance tests are generally specified as operability checks and calibrations in the
plant technical specifications and are considered to be an aging management technique (IAEA
2000). Such tests include circuit checks and evaluation of the results is used to verify that the
entire circuit is capable of operating as it should. For example, some tests measure time of the
signal to device actuation as a measure of the overall circuit and mechanical actuation. If the
time interval exceeds a specified value the system is examined to identify the problem
component. Successful functional tests of a circuit assume that the circuit can be returned to
service even though degradation might exist. This is the most common method used in power
plants. To reduce the potential for returning a degraded circuit board to service, visual
inspections can also be employed.

Visual Inspections
The interval for visual inspections is typically included as part of the technical specification to
coincide with the refueling outage cycle. Visual inspections of circuit boards may involve the
use of aids for detecting anomalies; for example, magnifying glass, microscope, X-Rays, ultra
violet light, etc. Inspections performed with an unaided eye or a low power optical microscope
on I&C boards during manufacturing can detect surface imperfections such as burrs, voids,
nicks, scratches, and gouges (EPRI 2002). They can be quickly identified and compared to a
standard. Inspection of the solder mask material involves investigating blisters, delamination,
bubbles, and thickness. Some subsurface imperfections such as foreign inclusions, voids and
delamination can often be detected from the external visual inspection. The same type of results
can be expected in examination of aging boards.

The types of aging anomalies that can be detected by visual inspection include:
1. Solder connection aging anomalies on printed circuit boards which include: Solder residues,
solder lifted from the circuit board, insufficient solder in joint, cracks or separations of
solder, brown spots around solder joint, holes, loose or broken wires, and solder bridges.
2. Cracked coatings on components such as capacitors, transformers, resistors, memory chips
and processors.
3. Excessive dust or pollution on the board and components.
4. Traces of localized heating by color changes.
5. Traces of corrosion from moisture, chemicals, smoke, or atmospheric exposures.
6. Cleaning process negative results.
7. Laminar separation or bowed circuit boards.
8. Mechanically damaged parts (leads or body).
9. Damaged or missing connectors.
10. Repeated repairs on the same component as an indication of other problems

Advantages
Aging anomalies can be observed on specific circuit boards without special tools or other costs
for new development.
Considerable experience from inspections during manufacturing provides an inspection standard
and has qualified the circuit board prior to aging impacts.
Lists of observable anomalies are available from manufacturers, EPRI 2002, and others.
Functional testing verifies signal to actuation reliability.

Disadvantages:
The frequency of inspections is generally no more frequent than once per refueling cycle, which
can range from 18 to 24 months.
Boards must be removed for inspection, which could damage connectors or cause other handling
induced problems.
Detection by visual inspection is limited to grossly visible characteristics (i.e., the assumption is
that circuit aging conditions will leave an outer trace of damage such as changing the color of the
board in an overheated area).
Many precursor aging failure modes are not observable (e.g., an open circuit in part of the board
might not be detectable by visual inspection alone).

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