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The principles and process of electronic
component selection(part 5):
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Component Selection; "an art" for SMART and
cost-effective designs
Electronics components are the major part of the electronics
system design and are rapidly undergoing technology advancements
both, in performances and sizes. Obviously, the successful
companies and products have utilized 'smarter' components
in their designs. The method of choosing such "smart"
components thus becomes "an art" to be acquired
by the engineers today.
It appears as if the process of component selection for
the hardware design requirements is very simple and straightforward
but indeed there are many considerations and "techniques"
involved behind. An error made in the component selection
can cause serious damages up to an extent of thrashing and
disqualifying the entire design and the product. So, utmost
care and precautions are advisable while performing this
activity. Hence in most of the organisations, a dedicated
team of component engineers are formed to help the design
teams. The component engineers need to have the breadth
of knowledge and experience in the fundamental understanding
of components, their specifications, constructions, and
functionalities.
The component engineer is the one who is approached for
the selection of components and suppliers since he acts
as the liaison between sourcing/supply chain, design and,
manufacturing teams as well as strengthens the supplier
relationship. Choosing the right component is the most important
task involved in the product development cycle because a
wrong selection here creates heavy and unpredictable losses
(money, machine, men, time, etc.,) throughout the development
activities causing failures and delays in the product releases.
Even though the technology advancements, e-commerce and
globalisation have made the engineer's life easier, the
human interference and intelligence are still very much
essential in one or the other form. Utilizing the web-based
parametric tables and other user-friendly methods to select
a component is easy but one should know how, when and where
to use them appropriately. There are reference component
databases available in the market, both free and subscription-based.
However, these databases may take the engineer to the nearest
set-of-components but choosing the best one that suits the
design is still the selector's task. There are various parameters
such as electrical, mechanical, environmental, cost, reliability
factor, availability (life cycle), etc., which should, at
a minimum, be considered while selecting a component.
Component selection is a process of selecting a suitable
component or a set of similar components from different
suppliers for the designed circuit to perform its intended
operation. The component engineer may have to first understand
the circuit functionality or has to get the exact parametric
values with the permissible tolerance levels for each parameter
from the design engineer. The component engineer has to
volunteer in gathering as many details as possible from
the design engineer in order to speed up the component selection.
Most of the times, the design engineer invariably provides
the list of critical parameters alone, but for the component
engineer, the other non-listed parameters are also critical.
Hence it's important for the component engineer to query
the design team even for a small doubt and not to guess
or consider the attribute values for granted.
The component engineer should also consider the "underlying
factors" or the "competitive edge" of the
component when compared with the nearest competitors. Due
consideration should be given to the affordability - a factor
that guides the company to prefer an expensive component
to avail the additional features, become more competitive
and reap the most out of the investment made. Here a line
of compromise is drawn and compared between the investment
made and the return on the investment while choosing the
technology-based competitively-edged components.
Mere choosing the right component is just not sufficient
for product development but to track and control every component's
specifications throughout the supply chain and the product's
life cycle is also significant. Many companies implement
part-specific and product-specific specification control
documents which are updated as and when a change is made
with respect to the part or the product. These changes can
be due to external factors such as the component manufacturer
releases a product or process change notifications that
affect the component's form, fit or function; manufacturer
mergers and acquisitions; plant or factory relocations;
alternate fabrication sites; etc., and internal factors
such as preferring alternate part or supplier or distributor;
changes made in the design boards; inclusion/exclusion of
circuitry or components; changes in the test parameters;
etc., Even the component's end-of-life (EOL) period is tracked
in this specification control document. Hence, the traceability
factor can help the organisation to mitigate component risks
easily and proactively.
The life cycle of the component is yet another attribute
that should be focused while selecting a component, its
more relevent in case of semiconductor IC chips. The predicted
life of all the components inside the product constitutes
to the life of the product itself in addition to the other
variables. The present 'availability' factor of the component
is important, but how long the component is going to be
available in the future is much more important. The designs
and products end up costly because of their improper selection
of components. Selecting a component which is near to end-of-life
is an added risk or an overhead to the company and choosing
a component which was just invented (just born) is risking
with the component's survivability itself. So, wise judgement
that promotes the usage of the low-risk, long-life components
in the BoMs (bill of materials) should be taken. To mitigate
the component's unpredicted risks, one should always maintain
a list of alternate components and sources. More details
about the component's life cycle management are presented
in a separate module. Many organisations invest lot of efforts
and money due to component's unavailability and obsolescence
issues. "Better be prepared with alternate components'
list than to struggle with odd and costly situations".
The next important aspect to consider is the "reliability"
of the component which is termed as the chance of the component
to perform its planned function for the specified time interval
under the defined conditions with a given confidence level.
To put it simpler, the reliability of a component is the
quality of the component's performance over a period of
time. The amount of time period where the failure rate is
constant is the useful life period of the component and
usually the component's reliability is provided in reliability
% or MTBF score or failure rates. The popular three methods
of predicting component's reliability are PRISM (217+ method),
Telcordia (Bellcore method) and MIL-HDBK-217. The component's
reliability helps the design team to verify the design's
ability to meet its objectives early in the development
stage. Also, the reliability factors helps to calculate
the warranty and safety durations as well as perform decisions
on design substitutions.
Having understood the generic factors such as component's
availability or the life cycle, affordability or the feature-rich
expensive selection, traceability or the component's history
log and the reliability or the quality of the component's
performance over a period of time, let's go through few
important technical parameters. Technical parameters, for
our understanding, can be classified into electrical, mechanical
and environmental.
1. Electrical parameters are the ones which directly dictate
the functionality of the component. Each component category
has its own primary specifications rated and designed for.
There are few specifications which are category-specific
and few others are generic in nature. For example, operating
temperatures, voltages, etc., are almost applicable for
all the component categories and hence are generic in nature.
Whereas examples like capacitance value, memory width, cut-off
frequency, etc., are applicable to few specific categories
only and hence these attributes are category-specific attributes.
The table below is a reference of few categories and their
key electrical attributes' list which helps in searching
a component in its respective category.
Component Category |
Attribute 1 |
Attribute 2 |
Attribute 3 |
Attribute 4 |
Attribute 5 |
Aluminum Electrolytic Capacitor |
Capacitance value |
Tolerance |
Polarity |
DC Voltage |
ESR |
Analog to Digital Converter |
ADC type |
Input voltage limit range |
Conversion time |
No. of bits and functions |
Output format and bit code |
Audio Control IC |
Harmonic distortion |
Supply voltage |
No. of channels |
Negative supply voltage |
Channel separation |
BNC Connector |
Contact gender |
Terminating to |
Body/shell type |
Dielectric & contact material |
DIN & IEC conformances |
Bridge Rectifier Diode |
Breakdown voltage |
Repetitive peak voltage |
Power dissipation |
Configuration |
No. of phases |
Fixed Inductor |
Inductance value & tolerance |
No. of functions |
Rated current |
Core material & shield |
Quality factor |
LED Display |
Display height |
Forward current |
Configuration |
Color |
No. of functions |
RF/Microwave Coupler |
Insertion loss |
Operating frequency |
Input power |
Characteristic impedance |
VSWR |
SMPS Transformer |
Power rating |
Input voltage |
Output voltage |
No. of pri./sec. windings |
Operating frequency |
Static RAM |
Memory size |
Organization |
Negative supply voltage |
Access time |
No. of ports & Port type |
Certain parameters should be given due consideration and
these parameters depend upon the end application of the
product. The end-application can vary between military,
commercial and industrial purposes. Weather withstanding
capabilities of commercial grade devcies are not so good
as industrial grade and the military grade devices withstand
extreme and extended conditions that the military products
operate with. The extended temperature ranges, thermal shocks
and vibrations, humidity and moisture tests, dampening tests,
etc., are few parameters to be considered carefully. Also,
there are many manufacturers who qualify their components
to military standards and exclusively trade those components
as MIL-qualified components. Be-aware of the difference
between MIL-qualified and tested as per MIL-standards.
2. Mechanical parameters are the ones which indicate the
physical form, mounting styles, size and weight of the component.
These parameters can be felt or physical in nature. These
features decide how the component connects with other components
in the circuit board. See the below list of mechanical attributes
list which can be suitably considered while choosing the
component.

It's very important to have prior information about the
physical dimension and mechanical specifications requirements
from the design team because almost many suppliers have
the same functional component in more than one package styles.
The ordering information would definitely vary with the
package styles and hence choosing the right package code
is vital.
3. Environmental parameters are the ones which are related
to the component's behaviour and ratings with respect to
the different environmental conditions. Extreme environmental
conditions are simulated in the lab for test purposes and
that's how the component's ratings are measured. In addition,
there are regulatory authorities governing the ban or the
restricted use of certain hazardous substances in the components
thereby providing instructions to the manufacturers to comply
with these regulations in order to perform the business
in the specified countries or markets. The list of important
environmental attributes is given below.

Above all, one should not forget about the new requirements
posed by the environmental regulators worldwide. The new
regulations may require suitable evidences in the form of
IPC-1752 material composition declarations, test reports,
RoHS certificates, certificates of conformances (CoCs),
custom-declarations, etc., Without these evidences, it's
very risky and dangerous to consider or use the related
component in the designs and perform business in that particular
region or country. However, there are certain exemptions
permitted with respect to few substances, their permissible
usage and applications in which the selected components
get in.
The packaging preference is another parameter to consider
in selecting a component. The presence of different manufacturing
or board assembly methods and feasibilities necessitates
specific flow of components in the production line. The
flow of components depends on the type of packaging or shipping
method used. Packaging is the method of placing the components
in an order which is suitable to be picked up one by one
automatically by the computer-controlled machines in the
manufacturing or assembly plants. So, components usually
are delivered in tape and reel, bulk, ammo packs, tubes,
and boxes. Choosing the right packaging method simplifies
the assembling or soldering activity.
Of course, there may arise one or the other form of supply
chain constraints such as counterfeits, obsolescence, long
lead times, minimum order quantities, extra cost for preferred
packaging and quantities, logistics and warehouse issues,
free samples, lot rejections, damages, sustainability, vendor
compliance, etc., during the selection and qualification
process. With the help of cross-functions and previously
made agreements, these issues can be solved on a need basis
and more details are presented in the "Supplier selection"
module. Hence, the role of component engineers is so valuable
and productive in the supply chain
!
Few important points that should be considered:
1. Try to maintain the company-wide "preferred parts
list" (PPL) - a list that contains pre-qualified components
list where component and supplier evaluations are conducted
and passed. This list should be a controlled database (even
an MS-Excel can work as a controlled database) and only
designated authority should have editing permissions. Always,
give 1st preference to select the components from the PPL
for new or existing designs.
2. One should not come to a conclusion or select a component
by just glancing through the main description given at the
top of the datasheet. Go through the datasheet thoroughly
and evaluate for the electrical parameters given by the
design team.
3. Make a list of critical components in the designed circuitry
and possibly try to conduct piece part reliability predictions
and test the samples accordingly.
4. Ensure effective supply chain processes are in place
and practised in order to control the redundant and duplicate
components dwelling in the inventory.
5. Emphasize to re-use existing component as much as possible
- so that intangible benefits can be ripened.
6. Standardize the component descriptions in the component
database or the PPL (if maintained) - has the magical ability
to deliver so many options for a variety of purposes in
the supply chain
.!
7. Prefer to select a component from the approved list of
manufacturers or suppliers. Practically it's hard to find
all the components required for the design from the given
list of approved/preferred suppliers. In this case, it's
better to perform vendor or supplier qualification and to
have a process incorporated to monitor and evaluate the
deliveries made by the non-preferred suppliers.
8. Selection of parts should be mature enough to satisfy
a wide range of design applications - hard task right
?
That's the reason why this writer called it's an art to
acquire. And lastly, update your knowledge with the latest
trends, technology advancements, industry regulations and
dynamism in the market with respect to your field of operation.
Author:
S Jaya Kumar, Consultant, Component Supply Chain Management
Conatct
him at:

Part1:Smart
component sourcing is about green, clean, rugged, and the
$:The basics of
modern component buying methodologies are explained in these
series of articles.

Part2:
Counterfeit components: Methods to protect against fake
parts: Save reputation,
severe loss of time and money by not buying fake parts

Part3:
Green Component Sourcing through environment conscious part
selection:: Selecting
electronic components causing no/least harmful to environment

Part4:
Electronics component supplier and device selection guide:
Evaluation and selection of semiconductor IC chips and other
parts and their suppliers

Part
6: Electronic components Life Cycle management:
Methods to manage sourcing issues of obsolete components
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