20100531 TE Basic Knowledge Rev.1 from TW Lam

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Prepared by: TW Lam
Date: 2010/05/31
Cartoon from: Agilent
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 Test Engineering is a Profession
 Roles & Objectives of Test Engineering
 Quality Cost
 TE at VT Stage
 TE at MP Stage
 Consideration of Test System
 DFT (Design For Testability)
 Sharpen Your Saw
Content

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 By 1970’s, Test Engineering was already a separate function in
factories with high technology products such as computer.
 The more advance the products, there’s more need for a separate TE
function to ensure cost effective guarantee of functional quality.
 As the demand on quality becoming higher and higher, the demand on
professional test engineer and the adoption of automatic testing have
increased drastically.
Test Engineering is a Profession

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 TE needs to have the ability to learn related technology in addition to
electronics engineering. Examples: network system, electrical
engineering, acoustics, light, temperature, magnetism, pattern
recognition, air pressure, mechanical etc..
Test Engineering is a Profession
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 Base on the Quality Cost concept, define the test flow and test plan.
Identifying any quality and reliability problems as early as possible so
as to reduce testing and failure cost later on.
 Proactively involve in the New Product Introduction process, prepare
reliable testing system in adequate quantity.
 Always work in timely and cost effective manner to support the
production lines.
 Support RFQ of new business.
 5S control and implementation.
Roles & Objectives of Test Engineering
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 Work with the team to build up customer’s confidence in our
professionalism.
 Participate in continual improvement of test yield, quality level, cost
and delivery and customer satisfaction.
 Participate in the Evaluation, Failure Analysis and Corrective
Action/Improvement as required on functional problems.
 Support the other department in tester setup.
 Preventive maintenance of fixtures,
equipment and test systems. Timely support
and planning to minimize the downtime.

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 Maintain and enhance Quality and Management Systems related to
TE.
 Testing, as one of the Quality Assurance method, the final goal is to
guarantee a high quality product to be delivered to customer with
reasonable testing cost.
 Continual improvement in throughput rate, throughput yield, test
automation and test cost reduction.
 Continual learning and research to breakthrough in testing and trouble-
shooting technology and product knowledge.
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 Total Quality Cost $
= Prevention Cost $ + Appraisal Cost $ + Internal Failure Cost $ +
External Failure Cost $
 A design problem find at early design stage may be solved by the
design engineer with a minor change in the design. Same problem find
at VT stages may involve customer, regulator bodies, waste of
component….. If the problem was found at MP stage, it may incur high
failure cost such as rework of WIP, delay of shipment. If same problem
was found at the field, it may incur much higher effort and cost in recall
of products, rework, penalty….
Quality Cost
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 So, we must be very sensitive to the failure and the potential problem
that may or may not be detected in production tests. We also must be
careful and promptly in doing failure analysis, identifying the root
causes and apply corrective action.
 Keep in mind that the earlier we detect, eliminate and effectively
prevent a quality problem, the lower our failure cost.
Quality Cost

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 Early Stage:
 Participate in the Design review and contribute in DFT. Bear in mind that once
the design has fixed, it is hard to convince R&D or customer to change the
design and we have to suffer permanently from the quality and productivity
problems.
 Review the general design critically and seriously. Timely provide our
professional comment, idea and suggestion.
 If the product is new or comes with new technology, try to explore and learn
the general test requirement from various channels, like equipment vendor,
fixture house, internet, magazines and other colleagues.
TE at VT Stage

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 Preparation:
 TE should join the project meetings to understand the project schedule and
status.
 TE must grasp the requirement essential for launching of the project.
Such requirement are listed as below:
 Overall project schedule from design stage, VT to MP.
 Estimated Annual Quantity (EAU) and the expected maximum production
output rate in order to estimate the testing capacity.
 Schematic, BOM, gerber files and product specification. Test requirement
as specified by R&D or customer and as judged professionally by TE.
 Clarify with R&D / Customer whether any equipment, software, Golden
Samples will be consigned and what we have to prepare.
TE at VT Stage
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 TE has to prepare in timely manner for the following items:
 Understand the product function and requirement, prepare the test plan,
equipment list and apply the budget if necessary.
 TI and training to operator, work with MFE to prepare the overall
manufacturing flow.
 Get ready the test fixture and equipment, also the test program if
necessary.
 We must have concrete idea and planning on what has to be prepared or
received and the schedule to be ready.
TE at VT Stage

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 During the VT, TE should:
 Actively involve into the process and team works.
 Monitor the workers to correctly perform the testing.
 Record down the test time and improvement that will need to follow up in
testing.
 Assist R&D / customer, APE in failure analysis.
 Timely review the test progress and result, perform preliminary analysis and
take corrective action.
TE at VT Stage
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 After the VT, TE should:
 Collect the test data and analysis the result. If there’s parametric data, try to
plot out the distribution of data (max., min., average and Cpk). Inform customer
if there’s any marginal case or potential trend to cause a large amount of
failures in mass production.
 Review the test flow and test process, plan for the action and improvement to
be taken before the next VT or MP.
 Join the VT wrap up meeting and provide necessary information for the team to
complete the VT report.
TE at VT Stage

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 Follow up the corrective action items in MVT.
 Periodically review the test log and study carefully on the failure
symptom and condition which may be indirectly related to the loophole
of test system or test process.
 Participant in the failure analysis to understand more on the failures
which may be related to the mechanical design of tester, test program,
test logic etc.. Close the loophole as early as possible.
 Strictly follow up the ECN changes.
TE at MP Stage

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 Closely monitor the stability of test systems, how the operator works
and take the improvement as early as possible.
 Continual Improvement of test yield rate and throughput rate.
 Pay high attention to the false reject which may be caused by
mishandling of operator, tester issues or design margin issue.
 Maintain the equipment, fixtures and test systems in their best working
condition.
TE at MP Stage
 Follow the pre-defined PM schedule and
procedure, keep the PM records properly.
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TE at MP Stage
 Properly keep the latest and updated list of equipment and fixture with
clear location and their condition.
 Pay high attention to those valuable
equipment, PC and spare parts. Keep them in
a safe place.
 Calibrate the equipment periodically. They
are the major reference unit in testing. Any
drift or inaccuracy in the measurement or
malfunction of an equipment will cause a
serious result.

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 Safety to Personnel
 Compliance to general safety requirement and regulation.
 When compressed air, water, oil or other fluid/liquid is used in the test system,
prevent any leakage, overflow, spilling etc. that would cause electrical hazard
or danger to the operator, work place and surrounding equipment and product.
 Check product and test specification, review the construction of the product for
more insight. For example, heat sink for high power component, isolation for
high power, high voltage circuitry and capacitor, battery etc..
Consideration of Test System

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 Pay attention to and control the harmful factors such as high temperature,
excessive sound level, too bright, presence of UV Light, Laser beam, strong
electro-magnetic field, harmful EMI, strong air flow etc..
 Avoid the operator to plug and unplug the high power to UUT, the connector
should be designed to full proof and polarity to avoid plugging in wrong polarity.
Also, the power should not be active during plug and unplug the connector.
 Isolation should be in place when using Hi-pot
tester and Ground continuity tester.
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 Pneumatic test system must use “double hands activation” method. The
moveable part should be stopped if either one hand is off from the activation
button.
 Under normal condition, operator should not be able to touch the test pins or
electrical conductive part with voltage existing.
 Operator should not be wound by the sharp tips of test pin, corner or edge of
the fixture.
 If UUT has large capacitor or high temperature
section, add a shield or cover to isolate the UUT
from the operator during test.

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 Provide appropriate fuse/circuit breaker and emergency “STOP” button to cut
the main power.
 When there’s large value capacitor mounted on UUT, thoroughly discharge the
capacitor before anyone touch the PCBA.
 Prevent the operator to touch the UUT during testing, especially with the
existing of high voltage source, high temperature.
 Ground the test system properly. All the
grounding points to PC, fixture and equipment
should be as close as possible.
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 Protection to Test Equipment
 All 110Vac main should use 13A (rectangular pins) AC plug and socket. All
220Vac should use 5A/15A (round pins) AC plug and socket. Clear
identification should be made. Avoid to use the other type of plug and socket
so as to minimize the confusion and mistake made.
 Pay attention to the current consumption of the test system, adequate power
source and connection should be used.
 Use fuse/circuit breaker to cut the main power if there’s abnormal situation.
 Include a self-protection to the test system. For example, cut the power when
there’s any abnormal high current draw from the test system.
 If possible, use UPS to supply the AC power to the test system and
programming stations.

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 Protection to Test Equipment
 When computer is used, it should be protected from illegal access and virus.
 Backup the data files on regular basis to avoid data loss.
 Test system should be placed an area where has enough space for people to
work around and doing maintenance.
 Test equipment is sensitive to temperature, keep the environment at a steady
temperature can eliminate the measurement variation.
 Keep the test system in a clean environment, periodically clean the dust.
 Equipment is fragile, so handle it carefully and it should be placed or mounted
properly to avoid falling down or damaged.
 Never leave an equipment or fixture on the floor.
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 Protection to Unit Under Test
 The design of the fixture should assure easy and safe loading and unloading of
the UUT to the fixture.
 No power should be applied to UUT during loading/unloading to the fixture or
connecting the cables.
 Avoid mechanical damage to the unit at testing due to bending, improper
positioning, excessive pressing by test jig, excessive force applied to tact
switch.
 Avoid ESD damage to the UUT, fixture should build with using antistatic
materials as much as possible.
 Avoid Electrical Overstress Damage due to poor grounding.
 To avoid micro-crack to SMT chip cap and resistor, bending to PCBA
(exceeding 1% length in any direction) must be precluded by using flat support
plane, even distribution of test pins and even pressure from the press down
fixture etc..

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 Protection to Unit Under Test
 All the supporting rods or blocks from the fixture should be placed with a clear
distance apart from the component of UUT.
 Observe the whole loading, press down, release and unloading process
carefully to make sure no excessive force and bending applied to the UUT and
component will not collide with guide pins, test pins for edges of fixture thus
causing component damage.
 Avoid damage to UUT due to improper power up and power down sequence,
excessive surge and the uncontrolled discharge of capacitor or inductor after
test.
 Avoid excessive loading to UUT.
 Limit the current of power supply to UUT.
 Burn-in Oven must be double temperature protection type with sufficient
ventilation.
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 Convenience and Full Proofing
 Apply basic principles in Ergonomics: push down to turn on, rotate clockwise to
increase, use decimal instead of binary for input and reading, locate indicator in
operators field of view, use “Red” to indicate fail and “Green” for pass while
“Flashing” for alert etc..
 Observe the details test steps and see if there is any way for operator to
wrongly operate or misunderstand a message.
 Message to be interfaced with operator should be
in Simplified Chinese (use in China) as much as
possible.
 Never has a chance for the operator to guess
during the test operation.

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 Bear in mind, some operators may not be able to handle testing steps of more
than 60 seconds cycle time.
 Consider the principle of ” 以人为本“ when designing or setup of a test
system.
 Label the cables and plugs with clear indication of their usage. Tie up the
cables and fix them in a position with reasonable length. A tidy working bench
can help to minimize the mistake made.
 Auto testing can help to full proof and this is the
trend toward using more ATE.
 Test system should be designed so as to eliminate
the human error and mistake.
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 Think about the “ease of test” concept. For example:
 There’s no chance for operator to make the mistake due to
misunderstanding, mishandling or absent mind.
 Indication or button is easy to access.
 Cables/plugs will not be able to connect to UUT incorrectly.
 Design the test sequence in such a way that the idle time of operator is in
continuously mode.
 Use automatic detection as much as
possible instead of relying on the judgment
of operator.
 Provide a “full sight” of working environment
such that operator can focus on the job.

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 Ease of testing should include the consideration of ergonomics. For example:
 Operator can operate the test without any trouble, difficulty or
inconvenience.
 Placement of fixture, keyboard, mouse, display is suitable for operator to
work and view without feeling tire quickly.
 Indication is not too bright, sound level is not loud.
 Indication should be placed in the view of
sight, operator does not need to turn around
her/his head.
 Placement of UUT, cables or label etc.
should be in line such that the operator can
pick up the item in sequence and easily.
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 TI should be written in simply way, easy for operator (note it is operator, not
technician or engineer) to understand. Each check item should be clearly
specified in one individual line. The pass and fail criteria should be clearly
specified.
 It is expected anyone without technical know-how can follow the TI step by
step and complete the test without hesitate and problem.
 Avoid putting too much information in the TI
which is not a concern of operator.
 Use appropriate picture or photo to illustrate
the test procedure, check item and test result.

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 Test record and useful information should be traceable. Backup the data log
files and test program periodically. Include this job this into the PM.
 All the old test program, firmware should be removed from the test system.
 Incorporate the test process in INMS. Use the flow control to prevent any skip
of testing or programming station.
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 Why do we need IQC?
 Why do we need QC?
 Why do we need ICT?
 Why do we need FCT?
 Why do we need QA?
 Why ……..?????
DFT - Design For Testability
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 General Flow
DFT
Material SMT/MI Assembly Shipment
Wrong
material
Machine error
Workmanship
Workmanship
Design Margin

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 Actual condition
DFT
Material SMT/MI Assembly Shipment
Check Point
(IQC)
Check Point
(QC, X-Ray, ICT
FCT …)
Check Point
(FAT, FQC…)
Purpose of check point: Ensure the manufacturing quality of the product.
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 Time to Market & Time to Volume
 The faster of the product moves from design to mass production, the higher of
the market share and profit.
 Simpler & Minimum Test
 Lower the COT (cost of testing): investment of test equipment, fixture, man-
power, testing time.
 High Quality of Product in design and manufacturing
 Eliminate any design problem
 High pass yield
 Zero manufacturing defect
 No RMA unit
DFT - NPI Expectation

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 Think Testing AFTER design.
DFT - NPI in the old days
Define Product
Specification
Circuit Design
PCB Layout
Test Development
For Production
Mass Production
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 What will happen?
 Lack of test pad for testing.
 Low test coverage.
 Test need to be done manually.
 Frequently maintenance of tester.
 Long test time.
 More test steps/stations.
 Longer development time for testing.
 Higher testing cost.
 ……..
DFT- NPI in the old days

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 Think testing DURING design.
DFT - NPI with DFT
Define Product
Specification
Circuit Design PCB Layout
Test Development
For Production
Mass Production
DFT Review
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 Cost of testing
 Test development L/T
 Test Time
 Coverage
 Time to market of product
 Test Yield
 ……
DFT – Expected Result
 Lower
 Shorten
 Minimize
 Maximum
 Faster
 Better

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 1st
: Set the Goal
 Screen out manufacturing defect
 100% fault coverage
 High pass yield
 Lower the testing time and testing cost
 Design the test for mass production
 Reduce unnecessary test
DFT - Review Process
What’s the
goal?
Can we test
it?
How?
Which
section is
important?
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 2nd
: Know what to test and what should do
 Get familiar to the product: study the product specification, schematic. Different
product has different test requirement.
 Study the test specification and requirement.
 Define the manufacturing test flow for the best test coverage with the
consideration of test time, equipment utilization and line balance.
 Define the best approach for any IC programming, off-line or on-board program.
In-line program verification process should be considered.

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 3rd
: Know our capability
 What kind of tools we can use? ICT or MDA? AOI? FCT?
 What is the fault spectrum in our production line for this kind of product?
 Material
 Process
 Workmanship
 Fixture
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 4th
: Input for DFT
Gerber Data
Schematic
BOM
Test
Specification
Product
Specification
DFT
Review
Sample Board

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 Pin Coverage for ICT & FCT
 The fastest figure for test coverage analysis.
 Pin coverage shows us a preliminary scene on the testability of the product.
100% pin coverage = more flexible for testing, doesn’t mean the best.
 Always study the schematic, BOM, specification and think all the possibility
of testing. The most important is the component coverage, functional
coverage.
DFT – Key Consideration
D1
V-apply (TP1,TP2): R1, R2 test as one resistor, D1
in correct direction.
V-apply (TP2,TP1): R3 // (R1 + R2), D1 is existing.
Pin Coverage: 50%
Component Coverage: 100%
R1 R2
R3
TP1 TP2
Coverage Report:
Total net: 4
Accessible net: 2
Pin Coverage: 50%
Untested Component:
R1 No test point
R2 No test point
R3 No test point
D1 No test point
Component Coverage: 0%
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 Test Pad
 Size of test pad is large enough for access.
 Distance between two test pads is far enough.
 Test pad is placed far from tall component.
 Test pads are evenly distributed on the PCBA.
 Put test pad on the bottom side of PCBA as much as possible.
 Fixture
 Size and number of tooling holes.
 Any difficulty in fixture fabrication due to the size, shape or thickness of PCB,
location of connector etc..
 Fixture needs to be single-sided access or double-sided access.
 Any milling is needed?
DFT – Key Consideration

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 Visual Inspection – Component placement, soldering
 Human Inspection: Simple but not effective
 AOI: Take time to setup and fine tune but the inspection process is fully
automatic. It is the most effective inspection method with the consideration of
cost, time and coverage.
 X-Ray: The only tool of solder joint inspection for BGA package device.
 Measurement – Open/short, passive component value, IC function,
soldering
 ICT: Cost effective, fast speed, high coverage but limited by probing target on
PCBA.
 MDA: Same as ICT but no power function. Good for product with lesser digital
component.
DFT – Test Strategy
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 What kind of tool we can use in our factory?

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 Test Strategy for the highest test coverage
 ICT + FCT? ICT + AOI + FCT? AOI + FCT? Only ICT or FCT?
 Potential Risk we may need to face
 Untested Component
 AOI or visual check?
 Need to add a specific function check?
 Need to enforce the in-line process control?
 Functional Test Coverage
 The minimum requirement: meet the test
specification.
 Any circuit does not cover in the FCT? What can
do?
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 5th
: Output of DFT
Pin Coverage?
Any “untested”
Component?
Test method
acceptable?
Functional
test coverage
enough?
Problem in
Fixture
fabrication?
Feedback to
Design team
Size/location of
Test pad?

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 Test Engineering can help to enhance the competitiveness of our
company through professional and world class image and provision of
value-adding service to our customers who may not have strong
experience in test engineering or suffering from high cost in
development of test software and hardware by doing that in their
countries.
 Continual learning to breakthrough the testing and trouble-shooting technology
and product knowledge.
Sharpen Your Saw
 Strategic planning and tactical planning to plan
and execute breakthrough in order to be more
competitive.
 Benchmark, know the outside world through
internet, visiting exhibition, reading magazine.

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 Monitor and learn the using condition of a tester from operator. You may find
some valuable comment or idea to improve the tester. Note the principle of
“ease of test”, one of the purpose is ” 以人为本“ .
 We have many customers with different kinds of product, the test strategy,
technique and test method of each kind of product is valuable knowledge. Try
to learn, understand and implement. Wider the scope of view and knowledge.
 On top of technical know how, enhance the quality of work, report format and
management skill.
Sharpen Your Saw
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Thank you.

20100531 TE Basic Knowledge Rev.1 from TW Lam

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