Modeling van Initiele Product Kwaliteit

+ .

Modeling of Product Initial Quality (MoViP)

Movip was an initiative to develop a methodology of predicting the product quality during the design phase. For this project a number of OEM's (ASML, Philips Healthcare, Fei, Assembleon), Knowledge Institutes (IMEC, TNO) and a number of common suppliers (Prodrive, TBP/Technolution, Neways, Variass, KMWE, NTS, CCM, Sioux, MI-Partners, Fibreworks and Bicore) deliverd the backbone of the product Quality prediction model (MoViP).

Measure of Product Quality (ZHDR)

When manufacturing products its evident that the risk of a failure increases with increasing the number of parts. This number of failures is the Zero Hour Defect Rate (ZHDR) of a product. Zero Hour Defect Rate (ZHDR) reflects the number of products which failed at the customer, with respect to the number of products delivered to the customer during an agreed period of time. A “failure” is the unplanned occurrence that prevents the product from meeting its functional requirements under the specified operating conditions.
The time period in which a product fails can be as short as on receipt of the product (consumer) or as long as the build and test time when this product (industrial) is used in a larger system.
After this agreed period the failure mechanism is life time related (reliability).

Practical Measure of Product Quality (ZHDR)

Product Design Failure Modes

When designing a product its evident that the risk of a failure increases with increasing the number of parts and/or design complexity.


Risk increases with #Parts

To determine the quality of the product the traditional methods such as design or process FMEA's, early design involvement of manufacturing, building prototypes, ... works well for products manufactured in large quantities and not having the pressure of fast market introduction. When manufacturing low quantities these methods helps but are costly and time consuming and doesn't help in cost price or market introduction. For industries in this category a methodology is developed to identify the manufacturing, part and the design risks during the design phase.

When designing a product there are only three failure modes (Parts, Processes and the Design) which contributes to the "Non" Quality of a product.
Parts are either vendor parts which are bought or manufactured parts which started with a material and ends up as a part manufactured according a drawing.
Processes are either the manufacturing processes (material -> part) or the assembly processes where vendor and manufactured parts put together lead to sub assembly(s) with in the end a product.
A design is the combination of parts when put together correctly deliver the required functionality.
The three failure modes are:

Possibly as fourth failure mode handling and transport is mentioned. This can be easely seen as a part which is packed and handled, stored or transported (process).

Failure Modes

Processes are always coupled to either a material or a part (vendor, manufactured or (sub)assembly). Based on this the Bill of Materials (BoM) contains everything to identify the part or material risks and based on the coupling of processes to either a material or a part also all processes. Each part or material and the coupled processes based on the BoM result in an Zero Hour Defect Rate (ZHDR) when added statistical correct.


Vendor parts - Material & Processes

The risks of a failure per part or process is based on the history of that part or process. To identify the risk of failure for the part of processes a number of defect opportunities are used.

Part Failure Modes/Defect Opportunities

When a part has a risk on failure a number of Defect Opportunities are possible. A part can be defect (not functioning at all), physical out of spec (sctatched, dented, dirty, no threaded holes,...) or functional out of spec (funtioning not according specification).

Part Defect

Part Defect

Part Related Risks

Part Related Risks

Part related risk described for vendor parts.
What's the risk on not working at all (defect) or not physical accpording specification (physical out of spec) or not functioning accpording specification (functional out of spec).

Part Defect

A part is defect when the part is not functioning at all.

Example: Hard disk is not functioning at all

Part is Defect

Part Defect

Part Physical out of Spec

Part is not conform the physical specifications. This can be a large number of physical defects.

  • Hole is missing
  • Hole is not threaded
  • Surface is scratched
  • Surface is dented
  • Part is not clean
  • Part has bend legs (Integrated Circuit)
  • ...

Example: Hard disk is either dented, scratched, has no threaded holes for mounting, connect broken,...

Part is Physical out of Spec

Part Physical out of Spec

Part Functional out of Spec

Part functions not conform specification but is still working.

  • Motor turns slower than specified
  • Transmission lens is lower than specified
  • Bandwidth/noise is not within specification
  • ...

Example: Hard disk turn slower than specified rpm, access time slower,...

Assembly Defect Opportunities

Assembling is building together one or more vendor parts with one or more manufactured parts to create a new part ((sub)assembly or even product). The assembly process consist three steps (placement, connection and common processes). When creating a (sub)assembly or product each vendor or manufactured part must be placed. Connection takes only place when the part connects one to another part (screw, glue, bond,...). Common processes takes only place when they are required on (sub)assembly level (cleaning, testing,...).

Assembly Defect

Assembly Defect Opportunities

First step in the assembly process is placement of the parts.

Part Placement Risks

Part Placement Risks

Risks of placing the part in the (sub)assembly in the wrong way, forget or damage the part.

Missing Part

The risk that a part is not placed in the assembly.

  • Washer is missing
  • O-Ring is missing
  • Electronic parts missing on a Printed Circuit Board (PCB)
  • Cover missing
  • ...

Part is missing

Missing Part

Wrong Part

Another part is placed in the assembly than specified in the Bill of material (BoM)

  • Wrong electronic component (value) in a Printed Circuit Board Assembly (PCBA)
  • Magnetic fasteners where non magnetic fasteners are required
  • Bolt length
  • ...

Part is wrong

Wrong Part

Misoriented part

Part is placed with the wrong orientation in the assembly.

  • Inside out
  • 90° rotated
  • ...

Part is misoriented

Misoriented Part

Misplaced Part

The part is not mounted on the specified position.

Part is misplaced

Misplaced Part

Part is damaged during placement

Part is damaged during placement. How bigger the part how easier the damage occurs. This is also true if a part is fragile.

  • Sheet metal
  • Enclosures
  • ...

Part Connection Risks

Second step in the assembly process is connecting the parts together.

Part Connection Risks

Risks of connecting the part in the (sub)assembly not according specification. (screw not tigtening according torque, glue step not resulting in required strenght,...

Missing Connection

Risk of not connecting at all.

  • No glue dispenced
  • cable or hose not connected at all (hanging loose)
  • ...

Misplaced Connection

Risk of connecting at the wrong place.

  • glue dispenced on wrong position
  • cable or hose not connected at the wrong place
  • ...

Misoriented Connection

Risk of connecting in the wrong orientation.

  • Cable connected in the wrong orientation (3W3 sub D connector)
  • ...

Connection process

Risk of not correct connecting.

  • Screw not tightened according specified/requirred torque
  • cable not connected correctly
  • Glue not according specified/required strenght
  • Solder not according IPC
  • ...


Part is Misconnected

Common Process Risk

Last step in the assembly process before it is a (sub)assembly or product are the common processes which take place on the (sub)assembly or product level.

  • Cleaning
  • Testing
  • Adjusting
  • .....

Theses processes even if they influences the (sub)assembly can be treated as the part processes with as difference they occur on (sub)assembly or product level only once.

Manufacturing Defect Opportunities

Manufacturing parts starts with a material and follows a sequence of process steps where each process contributes to the risk of the manuactured part.

Assembly Defect

Manufacturing Defect Opportunities

Material Physical out of Spec

Material is not conform the physical specifications. This can be a large number of physical defects.

  • Surface is scratched
  • Surface is dented
  • Material is of wrong size
  • Material is of the wrong material
  • ...

Example: material is of wrong material, is bended, scratched, to short,..

Manufacturing Process Defect Opportunities

Manufacturing is a flow (workflow) of processes. Each manufacturing process contributes to the risk of not meeting the required manafuctured part. Where in assembly DPMO's are used as measure of the risk in manufacturing the Cpk, Ppk, sigma's are more used. When for each manufacturing step the Cpk, Ppk or sigma's are known these can be easely translated to DPMO's. Processes are:

  • Mill
  • Drill
  • Threading
  • Surface Threatments
  • ...

The manufactred part risk is noting more than the material riks and the 'added' process risks.

Design Defect Opportunities

Design defect opportunities are divided in two risk types.

Design Functionality Risks

Functionality risks are normal determined after building the part. To be able to predict the design Risks only a few methodologies are available.

Traditional Design FMEA

The traditional design FMEA is a methodology to determine the risk based on a design review where experts give a score of 1 to 5 if a risk can occur. This mostly leads to an list of risks based on the expert level of the team. This is brought in the design review and must lead to a solution to prevent the risk.

Quantized Structured Design FMEA

An other approach to start with the Bill of Material (BoM) and for each part on the BoM determine the maximum load per part and based on the safety margin set a risk of failing in a scale between 0 and 100%.
Next step is the take the specification of the product and determine per specification the risk of not meeting the requirement. Again this risk is between the 0 and 100% of occurence not meeting the spec.

Worst Case Design

The other risk is a worst case design where based on the design even when it is assembled and manufactured perfect still can lead to a not functioning product. This can be derived from the design and is used to determine the product risk.

  • Timing (electronics)
  • Noise (electronics)
  • Offset
  • Dimensions
  • ...
Again the scale of occurence is between 0 and 100% and is easely translated to DPMO's.

Determine Defect Opportunity Risk

To be able to calculate the product Zero Hour Defect Rate (ZHDR) for each defect opportunity a risk on occuring must be known. For calculation purpose the Defect Parts per Milion Opportunities (DPMO) is used. DPMO's are widely used or could be calculed from the Cpk, Ppk or sigma's.
When all DPMO's which can occur are known a product risk calculation can be done.

Zero Hour Defect Rate (ZHDR) Calculation

ZHDR Calculations

This calculation result in a product ZHDR. Based on this also a list of Part Risk and process risks can be created.

Risk Mitigation

When having calculated the Zero Hour Defect Rate (ZHDR) and this is larger than the specified product ZHDR there are three options to lower the ZHDR.

Zero Hour Defect Rate (ZHDR) realized

ZHDR Specified/Calculated

Design change is the first step in mitigation. Based on the list of part or process risks a design change must be made which avoids those risks. When not possible the second best option is to improve the processes which contribute most to the high ZHDr of the product. Last resort is to test the remaining risks which could not be solved with a design change or process improvement. Realize that a test when its detected a Not Ok lead to scrap and as such increasing the cost price.

Design Change

Select out of the list of risks those parts and/or processes which contribute to the not meeting the product ZHDR. For parts a replacement or avoidance is the only way to improve. For processes is take an other design which avoids those processes.


Design Mitigation

As a result of the design change the BoM is also changed. The ZHDR has to calculated again.

Zero Hour Defect Rate (ZHDR) realized

ZHDR Specified/Calculated

Process Improvement

When a design change is not sufficient to meet the product ZHDR process improvemnt is the next option.

Zero Hour Defect Rate (ZHDR) realized

ZHDR Specified/Calculated

In an assembly process, even with skilled/trained operators, perfect workinstructions, sign off lists, ideal environment or ... incidents happen. To avoid these process incidents the process must be controlled in itself. The most easy way is automating the process, or put in other words avoid manual labour. Worldwide is manual labour a risk. To get a feeling for the contribution of manual labour an average incident rate is 1000ppm (1 of the 1000).
When manufactured part processes contributes to not meeting the product ZHDR those identiefied process must be improved. When manual labour with manufactured part is the contributor the process must be improved. When there is no manual labour which can be improved an other strategy can be another machine or again avoid a process risk by relaxing the requirement which causes the risk.


Process Improvement

Improving processes has no influence on the part or design risk.


Even when the design changes and process improvements are not sufficient to meet the product ZHDR the last resort is testing.

Zero Hour Defect Rate (ZHDR) realized

ZHDR Specified/Calculated

Each part or process which is tested and is Not Ok results in scrapping the product. When testing not on product level but on part or (sub)assembly level the consequences are the same but the cost involved is lower. For design risks this will always lead to scrap.

Test Scrap

Process & Test resulting in OK/FOK/NOK

Calculation of the Zero Hour Defect rate (ZHDR) includes now the test coupled to the defect opportunity.For the test the slip is defined as:

0 > No slip (no process failure slips through)
1 > No test (all process failures slips through to next stage)

Zero Hour Defect Rate (ZHDR) Calculation

ZHDR Calculations including test

When testing identifies a Not Ok this mabey can be reworked. When reworked this can solve the NoK but also can introduce new risks. Testing the reworked product is mostly done on another test fixture than the test used for production.

Test Scrap Rework

ZHDR Calculations including test & rework

Testing results in a lower risk at the customer.


Test Mitigation

Handling and Transport Failure Contributions

When a product is handled and transported, before its reaches the customer, the handling and transport risks must be taken into account. The methodoology to determine the risk is the same as an assembly where the parts are the product and packaging materials. The processes as handling and transport are treated the same way as assembly processes.

Handling Related Risks

Products are handled to go to a storage area or packaging area.

  • Electro Static Discharge (ESD)
  • Packaging Risks
  • Storage risks

Transport Related Risks

  • Transport damage risks

Calculate the New Zero Hour Defect Rate (ZHDR)

Based on the changes in the handling and transport process the Zero Hour Defect Rate (ZHDR) must be calculated.

Zero Hour Defect Rate (ZHDR) Calculation

Mitigated Zero Hour Defect Rate (ZHDR) Calculation

The Zero Hour Defect Rate (ZHDR) handling and transport risks are multiplied with the corresponding slip.

Zero Hour Defect Rate (ZHDR) Calculation

This results in a new Zero Hour Defect Rate (ZHDR) which must be checked if the Zero Hour Defect Rate (ZHDR) is within specification.

Life Time Failure Contributions


(1 First pass Yield (FPY)
(2 Yield
(3 Mcarthy, Thomas. The Six Sigma Black Belt Handbook, p. 307. 2004 McGraw Hill Education. ISBN10: 0071443290
(4 Througput Yield (TPY)
(5 Rolled Throughput Yield (RTY)
(6 Lunau, Stephan. Design for Six Sigma + Lean Toolset, p. 133. 2009 Springer-Verlag Berlin Heidelberg. ISBN 978-3-540-89513-8.
(7 Institute for Interconnecting and Packaging Electronic Circuits(IPC) IPC-7912A
(8 Yang, Kai, Design for Six Sigma, Chapter 11 2003 McGraw Hill, ISBN: 0-07-141208-5
(9 Mcarthy, Thomas. The Six Sigma Black Belt Handbook, p. 383. 2004 McGraw Hill Education. ISBN10: 0071443290.
(10 Yang, Kai, ''Design for Six Sigma'', Chapter 10 2003 McGraw Hill, ISBN: 0-07-141208-5
(11 Tien-Chien chang, Richard A. Wysk, and Hsu-Pin Wang. Computer-Aided Manufacturing, Second Edition, Pages 596 to 598. Prentice Hall 1998
(12 The bathtub Curve and Product Failure Behaviour (Part1)
(13 The bathtub Curve and Product Failure Behaviour (Part2)

Litirature on Quality

George, Michael l., ''What is Lean Six Sigma'', 2003, McGraw Hill, ISBN-10: 007142668X
George, Michael l., ''The Lean Six Sigma Pocket Toolbook'', 2004, McGraw Hill, ISBN-10: 0071441190
Morgan, John, ''Lean Six Sigma For Dummies'', 2012, Wiley Publishing, Inc., ISBN-10: 1119953707
Gygi, Craig, ''Six Sigma for Dummies'', 2005, Wiley Publishing, Inc., ISBN: 0-7645-6798-5
Webber, Larry, ''Quality Control for Dummies'', 2012, Wiley Publishing, Inc., ISBN-10: 0470069090
Kemp, Sid, ''Quality Management Dymistifeid'', 2006, McGraw Hill Education, ISBN: 0-07-144908-6