Transcript US19746 Element 1 - cashmerescience12and13

Element 1
Factors affecting quality and
reliability of electronic products
1.1 Factors affecting quality are
identified, their causes described, and
methods of improvement outlined.
1.2 Sources that adversely affect
reliability are described.
1.1 Factors affecting quality are identified,
their causes described, and methods of
improvement outlined.
Typical factors affecting the quality of
electronic products are:
Interference
Noise pickup
Feedback
Distortion
User-unfriendly design
Appearance
User-unfriendly design
Definition
Design of a product which is difficult to use
for intended users
Typical Cause
Lack of research / Incomplete analysis of
product requirements / Inadequate testing /
Failure to evaluate user response
Method of Improvement
Appearance
Definition
The appearance of an object is the result of a
complex interaction of the light incident on
the object, the optical characteristics of the
object, and human perception.
Typical Cause
In appropriate size / colour / shape /
texture / weight; Unpleasant feel
Method of Improvement
Interference
Definition
Extraneous energy, from natural or man-made
sources, that impedes the reception of
desired signals
Typical Cause
Another transmitter at the same frequency /
mains frequency (50Hz) interference
Method of Improvement
Feedback
Definition
The return of a portion of the output of an
active device or system to the input
Typical Cause
Speaker sound re-entering a microphone /
coupling between the input/output circuits
Method of Improvement
Distortion
Definition
Any departure of the output signal waveform
from the input signal
Typical Cause
Non-linearities in the devices such as a
transistors and op-amps
Method of Improvement
Noise pickup
Definition
An incoherent emission from a natural or manmade source
Typical Cause
Lightning / Commutator noise / Ignition
system noise from petrol engines
Method of Improvement
1.2 Sources that adversely affect reliability
are described.
There are a number of sources which directly
contribute to adverse reliability such as:
Intermittent connections
Humidity
Temperature
Dust and dirt
Radiation
Electronic component failure
Mechanical component failure
Electrostatic discharge
Vibration
Shock
Corrosion
Intermittent Connections
Connections which spasmodically become a
high resistance current path can affect the
reliability significantly.
Humidity
High humidity can lead to a build up of
moisture within equipment leading to shortcircuit paths developing and causing equipment
to fail.
Temperature
High ambient temperatures can lead to
insufficient cooling of electronic components
and junction temperatures exceeding their
specification, leading to component failure.
Dust and Dirt
Often contain carbon or other conducting
material, leading to short circuits and
equipment failure.
Radiation
Causes electrical interference, leading to
distortion of analogue signals or incorrect
operation of digital equipment.
Electronic component failure
If there is no parallel redundancy in the
equipment design, component failure produces
system failure.
Mechanical component failure
Often leads to electrical failure if:
a failed mechanical joint is also an electrical
connection
OR
the failed joint results in an open circuit.
Mechanical failure can result in a broken
product which works electrically but cannot
be used.
Vibration
Vibration can lead to mechanical failure of
components which leads to electrical failure
and system failure.
Shock
Can produce sudden mechanical and electrical
failure of components or connections.
Corrosion
Corrosion of components or connections leads
to their mechanical and electrical failure.
Electrostatic Discharge
Produces electrical damage of semiconductor
components and subsequent system
degradation or malfunction.
Sometimes the damage is initially undetected
but produces premature failure in the
component.