20100531 te basic knowledge rev.1 from tw lam

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Prepared by: TW LamDate: 2010/05/31Cartoon 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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Safety to Personnel 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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Safety to Personnel 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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Safety to Personnel 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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Convenience and Full Proofing 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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Convenience and Full Proofing 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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Convenience and Full Proofing 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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Convenience and Full Proofing 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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Convenience and Full Proofing 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 errorWorkmanship 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

ProductSpecification

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

D1V-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 TP2Coverage Report:Total net: 4Accessible net: 2Pin Coverage: 50%Untested Component:R1 No test pointR2 No test pointR3 No test pointD1 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 methodacceptable?

Functional test coverage

enough?

Problem in Fixture

fabrication?Feedback toDesign 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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