Process Input Environment -Summary

The  four environmental factors, temperature, humidity, ESD and air particles which was published in the past 2 articles are summarized in below table.  Most of these environmental factors has an impact in electronic parts manufacturing,  and some factors such as temperature and particle could also impact industry with strict hygiene requirement such as food and medical industry. 

Environmental elements
Influence by
Example Implication
Common Control methods
Measure equipment

Chemical material
Viscosity of mixture
Food industry

Air conditioner
Any process which use hygroscopic material,
Battery cell manufacturing
Semi conductor process
Most of electronic products
Spray painting
Plastic molding
Air conditioner
Air movement
Relative humidity
All Electronic related industry
ESD Smock,
Wrist strap,
Conductive rod,
Grounding, Ionizer
Disscipative material
Digital high resistance meter, Charged-Plate Monitor, Electrostatic field-meter, Electrostatic Discharge Tester, Surface & Volume Resistance Meter, Electrostatic Voltmeter, Electrostatic Voltmeter,
Air particle

Surface finishing paint process
Most of electronic parts hard disk, semiconductor,
Medical device
Clean room
Particle counter
Recommended guideline to control and monitor environment :-

Products that are sensitive to changes in the environment must be manufactured in a stable control environment confine by a define space such as cleanroom.  Special infrastructure or equipment must be used to modify and control the environment to suit the needs of manufacturing process for the product.  Some control mechanisms are restricted to single process operation such as winding process of jelly roll in battery cell.  There are localized control with vacuum suction and magnet to remove air particle and conductive particles within the winding equipment to minimize conductive particle in battery cell.  This is because conductive could short both anode and cathode surface of battery cell which could lead to safety hazards
Slight change in environmental are not easily detected and could have major impact on part quality.  Surveillance monitoring should be used all the time to check for any abnormality event so that immediate action could be taken. 
A good control and monitoring system and procedure setup to control and monitor environment should consist of  :-

  1. Understand the raw materials to finished goods reaction to the 4 major environmental factors
  2. Develop a control of the environmental factor to an optimum range suitable to manufacture parts.  This range is the optimum range which has minimal impact on product quality characteristics.
  3. Invest in good infrastructure especially ESD and air particle control system.
  4. Install real time monitoring/surveillance system with gage capability to measure the environmental factors with auto trigger system to warn production floor if there is any noncompliance. 
  5. Measurement equipment use for monitoring must be calibrated and maintained regularly
  6. If there is trigger there must be proper reaction plan documented which include

  • Immediate production stop
  • Investigate the cause of triggering
  • Generate action plan which address root cause of triggering.
  • Establish an appropriate disposition on raw materials and parts which could be affected by the abnormal event.

Real time monitoring of environment


Environment is silent and invisible force which does not have immediate impact on the product and therefore sometimes it is difficult to test or screen out the affected parts.  This makes it difficult to control, however it is very 
critical to to ensure environment is controlled to reduce variation of this process input.  Most of the environmental variations could lead to outliers event where it could bring serious disaster in the field if it is not controlled properly.   

Some examples are latent damage of electronic component by ESD, conductive particle in battery cell anode and cathode surface where the failure usually happens after consumer had used the product for some time.  There had been many cases serious damages in the field which could link poor environmental control during manufacturing of the parts. 

Process Input Environment - The invisible force of Nature, ESD and Air particle

Electric static discharge

Nature is all about balancing and the same goes for electric static discharge. When there is imbalance of electron from one body to another body, the excess electron will move to balance the charge between the two body.  Movement of electron will create a small current which is known as electric static discharge (ESD).  In the world of miniaturization,  semiconductor integrated circuit (IC) transistor are in size range nanometer,  it would be hazardous for an IC to receive even a small ESD current. 

ESD has a direct relationship with relative humidity and dust particle.  Therefore the scope of ESD problem is not limited to electronic component as it also had an indirect impact on dust particle problem.  We will discuss about the impact of dust particle later in this article.

According  to EOS/ESD Association, Inc. ESD could cause up to billions dollar losses in electronic industry every year.  Therefore high precautions are taken by manufacturers who work with ESD sensitive parts (component IC, PCBA and final assembly)  to minimize potential ESD damage.  The common methods used to control ESD are :-

  • Conduct all electron from ESD from work station/human to main grounding rod.  This method is to divert all electron to discharge to earth through an easier path, the grounding rod.  Factory facility must build in main conductive rod and all workstation, human body are eventually connected to main grounding rod. 
  • Dissipate  surface ESD using ESD dissipative material
  • Neutralize electron discharge through ionizer in the work station
  • Relative humidity – Relative humidity over 30% RH, water vapour as a conductive material will minimize charge build up through dissipation of charge build up

ESD protection ranges building infrastructure, equipment use,  trolley, containers, storage rack, work station, tools and clothing. There are a lot of very detail and good write up in the website on topic related ESD impact and control of ESD.  A good reference would be EOS/ESD Association, Inc. website and reputable commercial company such as 3M Company.

Air Particle (Dust)

Air particle, mainly dusts exist, everywhere together with the air we breathe in.  Dust consist of soil particles, fungi  spores, pollution, plant pollen, fibers, human skin cell etc. and the content may varies in different geographical location, outdoor and indoor.  Dust content from manufacturing environment would depend very much on what type of raw material and finish product the factory use and produce.  Normally in electronic factory where it involve trimming or cutting of circuit material would have conductive material such as cooper dust.

Dust particle is the biggest enemy in the electronic component manufacturing world. Sometimes presence of even a single particle could lead to fatal failure such in integrated circuit.  Current detection technology using magnification such as electron microscope or electrical testing are only able to increase the opportunity of particle detection.  Most of the failure due to particle only manifests itself after consumer use the product.

Particle in semiconductor between transistor gate line could short between two lines

Some examples of the industry  which is impacted by particle and product have to manufactured in control cleanroom environment are :-

  1. Semiconductor industry  has the most stringent particle control.  With miniaturization of component in semiconductor where the size of transistor could be in nanometers when the most particle in micrometer, it would be hazardous to have even one particles in integrated circuit (IC).  Therefore semiconductor fabrication process  clean room is control at sub zero particle level.
  2. Electronic component such hard disk drive, LCD assembly where clean room environment requirement is not as stringent as semiconductor
  3. Spray painting process where before spray painting,  surface of the product must be very clean to ensure good paint finishing.

The only way to control particle is to manufacture products in an enclosed entity where airborne particles, temperature, humidity and ESD (it could repel particle) is under control. This is known as clean room. Cleanroom are classify using the number (from 1 to 100K)  particle count per cubic feet. Typical environment particle count per cubic feet would be around 1 million. There are several very detail international standards on clean room -  ISO 14644-1,  BS 5295,  GMP EU and NEBB testing procedures which serve as good reference on air particle control.  
Typical clean room with people in protective clothing,  there should as little human activities as possible as human is one of the main source to generate particles

Process Input Environment - The invisible force of Nature, Temperature & Humidity

Among the 6 process input identified in manufacturing process, environment is the most powerful and the most difficult to control.  It is nearly impossible to fully control the force of nature.  The elements of environment which have major impacts to process output are temperature, humidity, air particle and electro static discharge (ESD). Sometimes all these elements could have relationship with each other.

Environment control is apply to 2 areas,
  • Ambient condition in production floor
  • Localized environment control confine to only one process in specialize manufacturing equipment.  Confine environmental control to one unit operation is more stringent than ambient condition.


According to Wikipedia definition temperature it is a measurement of how hot or cold the object is and can be measured using thermometer.  In manufacturing, control of temperature is important due to

  1. Use of heat sensitive material such electrical component, chemical will experience accelerated deterioration under high temperature
  2. Impact on worker productivity - temperature must in comfortable zone for worker
  3. Temperature affect relative humidity and relative humidity affect ESD.  Refer to below for more detail explanation.

Temperature can be controlled to certain extend by using air conditioning or heater depending on the requirement of the process.


Humidity is the amount moisture in the air.  One of the universal methods to measure humidity is using relative humidity.  Relative humidity (RH) compare the actual amount of water in the air to the maximum amount of water the air can hold and it is express in percentage (%).  RH give an indication of water saturation in the air,  100% means that water vapor in the air had reach its maximum capacity.  RH is inversely related to air temperature, the same amount of water vapor in the air will have different RH reading at different temperature.  The lower the temperature, the higher the RH and vice versa.

Different amount of water vapor in same amount of space,  the higher the amount of water vapor the higher the RH

Presence of water vapor in the air has an influence on manufacturing process and product quality.  Below are some common examples of the humidity impact which I have personally experience in different manufacturing process and product.  I would welcome addition from my readers. 
  1. Soldering process in PCBA assembly.
  2. PCBA moisture sensitive device (MSD) component.
  3. Photolithography process in wafer and LCD fabrication due to some photo resists used is very sensitive to moisture and cause high variation in critical dimension on the output.
  4. Battery cell making process such as electrode coating and jelly roll forming, electrolyte filling.  Moisture could cause failure and in worst case it could cause safety hazard.
  5. Plastic molding process.
  6. Paint curing process as moisture would prolong paint curing time in turn if paint is not properly,  the surface will become more scratch.
  7. Low RH will generate greater electric static discharge (ESD) which would injure ESD sensitive components. 
  8. Humidity will accelerate the oxidation of metal parts such as component leads thru water vapor condensation.

Humidity is control thru adjustment of temperature and ventilation.

In the next article we will study about  another 2 environmental impact, electric static discharge and air particles. 

Process Input Method - Managing change in process

Process method documents are always subjected to changes due to process improvement which strive for variation reduction that lead to quality improvement.  Improvement could be from other process input mainly material and machine (tooling design, jig and fixture, equipment setting, software changes). Once improvements are made, the new ways of transforming product need to be captured in new document or revised the existing documents.

It is imperative that we need to follow rigorous document control process which is major element in quality management system.   One of the key aspects in document control is managing manufacturing process document changes.  No matter how successful is the process improvement, if there is no proper documentation of the improved methods, and then it is equal to nothing? 
Normally in manufacturing entity, most organization follow proper process change notification (PCN) or engineering change notification process (ECN).
Recommended engineering change process would be:-

  1. Identify the potential change which could improve the current method of transformation in manufacturing process.
  2. Propose the change in engineering change notification (ECN) system.
  3. List down which process input  are impacted from the change such as man – operator training required and machine - special tooling required or new setting
  4. Ensure improve action plan which lead to changes in the process are reviewed and authorized by all stake holders
  5. Trial run the change (process improvement) in pilot scale. The parts for pilot must represent the population of the process. 
  6. Generate a report of the pilot batch which includes the key metrics of quality and productivity.
  7. Evaluate the results feedback loop to check the effectiveness of the change through production parts. 
  8. Once the change full fill its intention, document all changes in formal document such as work instruction according to company document control procedure.
  9. Develop a system to ensure all change notifications being implemented in the applicable area
  10. After the change is implemented in mass production, there must continuous monitoring to ensure it is successful in mass production.

Proper documentation of the changes is also called for in six sigma methodology under standardization.  In standardization we are required to capture all changes which can improve the process in official documentation followed by proliferation throughout the manufacturing entity.

The outcome of method, work instruction which capture 3 process inputs (Material, machine and method).  Therefore method is the most dynamic process input as other process inputs changes could impact work instruction.  
Since change management is very tedious process, it is best that we could follow advance quality planning approach to invest more time in developing proper design and process FMEA to minimize change. Changes could also bring unnecessary variation to the process and product. 

The most essential process input method is the documentation of how a product is being transformed in the form of work instruction (WI) or standard operating procedure (SOP).   WI/SOP had to be simple and easy to follow and there must governing process to ensure all operators follow the same work method to reduce variations.

Summary of process input method:-

  1. The best method which documented clearly for each unit operation in manufacturing (work instruction, SOP).
  2. Overview of end to end process deploying process management plan (PMP).
  3. Transportation, kitting and packaging must be included in method of product manufacturing.
  4. Manage changeover ,  human and product with structural approach to reduce variation during changeover in production
  5. Manage change to ensure the latest improved method are document and operator follow the latest revision in production floor.
Change for the better 

Process Input Method – the connector transportation process

No matter how good is the method that is used to transform a product, it would be pointless if we do NOT have a method to govern the movement of the product in the production floor from one process to another process.  Although transportation does not transform the product however it could potentially induce defect to the product mainly dent, broken, component or part being knock off for PCBA etc.   Moving parts from one work station to another station is also a process.   Like any other process, transportation of parts have input and output.  Most of the manufacturers had neglected this point.  Having conducted audit in more than 100 suppliers from Asia to North and South America,  almost all manufacturing sites had audit findings related to transportation and handling of the parts in the production floor.  We shall put our focus on manual process as parts transfer for manual process has more variation  compare to automated process.

We will focus on 2 important elements in transportation, a place to hold the part and vehicle use to move the parts.

A good transportation method should have the following criteria at the minimum:-

Place to hold the parts

  1. A well design storage medium such as tray which minimize part handling, easy to maintain. And clean to store the part during transportation. Best practice would be point of use storage system which do not need any repackaging or sorting.
  2. Convenient for operator to transform the parts, does not have complicated bag or seal bag where operator need to spend time to get the part out.
  3. Able to protect parts from transportation damage and accidents
  4. Regular checking and cleaning of the storage medium.
  5. All storage medium should be having an individual ID for tracking purpose.
  6. Made from durable material and must strong enough to hold the parts and suitable to use for the type of part such as ESD compliance for ESD sensitive device. Prefer recyclable material.
  7. Clear identification on storage tray on the process steps of the parts eg. before and after testing 
Point of use storage tray for PCBA where the boards are place in ESD safe storage tray with individual compartment.  Operator able to either take part out easily for next process and can do simple transformation on the tray

Vehicle to transport part

  1. Vehicle size such as weight height that is suitable and ergonomic friendly to operator.  Ensure part is not stack too high to prevent falling.
  2. Vehicle has design to protect part such as ESD compliance for ESD sensitive device and protective shock absorb pads
  3. Vehicle must have ID and have preventive maintenance system to ensure vehicle is in good condition
  4. If conveyor belt is used, it must also be cleaned and maintained to ensure smooth running.

Various trolley which can used to transport part in production floor

It is not encourage using bulky wrapper which is difficult to clean, wrapper can only protect part during transportation and most handling could be induced during the actual manufacturing.  This does not make good return on investment sense.  Most the bulky wrapper which I have come across is difficult to clean and operator had to waste time to put part into the wrapper.  No matter how good the part is protected in a bulky wrapper, we still need to bring the part out for further processing. 

Example of bulky wrapper

In lean manufacturing, it is prefered all transformation process close to each other in U shape configuration continuous manufacturing line with one piece flow. This type of manufacturing line would prevent unnecessary transportation and fit very well in assembly process.  In this way we would minimize/prevent variation created by long distance transportation within manufacturing entity.  This type of process will reduce variation and serve the purpose of design a process input to produce consistent good quality products.

Process Input Method - the beginning and the end

The beginning - Preparation method before start production

Before product can be transformed, a consistent method is required to ensure the necessary material is available for production.  A kitting process is deploy to ensure all parts are kitted properly In assembly process before start of production.   In this article, we shall focus on 2 types of material kitting, mechanical parts and chemical material.

The proposed guideline for kitting of mechanical parts :-

  1. A proper kitting method must be developed to ensure uniformity in kitting activities.
  2. It would be best if parts comes in packaging material point of use design which alleviate the kitting process
  3. For some mechanical parts which are sensitive to cosmetic defect such as external case must be pack individually.  Similarly ESD sensitive parts must be packed in ESD compliance material.
  4. Take into consideration of good handling techniques in kitting to minimize any potential part handling defect such as scratch, dent, broken .
  5. Use easy to clean and durable material storage bin
  6. Part storage bin must label with legible part #, photo and or bar code.
  7. It would be a good practice to have different identification storage bin such as different color bin for different part category.
  8. Specify the correct handling methods suitable for the product such as in battery pack assembly; operator must NOT use the dropped battery cells.
Kit Part Bin with label of the part #

If the production process is quite complicated and involve many parts in high volume environment, it is good to invest in kitting system such as pick to light system. 

Pick to Light kitting system 

The count of parts to kit must follow production volume and do not kit parts in big quantity. This will cause inventory in production and inventory hides quality issue.  A good system to use is Kanban system which has its prominent presence in lean manufacturing to control inventory level in production.

Chemical materials kitting/preparation recommendation:-

Expiry date control - Almost all chemical material will change or lost some of its effectiveness over time, therefore expiry date must be checked during kitting and before start of production. Beware some chemical material has 2 expiry date,   without break seal expiry date and used by date after break seal.  All expiry date must be recorded and controlled.

Break bulk for consumption - For bulk packed chemical material such as lubricant, the transfer method for smaller production batches must not contaminate the bulk material.  All transfer tools,  eg.hand pump, must be dedicated to one type of chemical material only.  It is advisable to buy single use packed material or smaller quantity suitable for low production volume.

Thawing process - If there is a requirement to store chemical material in cold storage, thawing for the material to return to ambient temperature is necessary.  Time must be calculated and tracked  which include time out from storage, time material ready to use, time break seal, and expiry time in room temperature if not break seal and time material must finished consumed.  An example would be solder paste material where time tracking should be very stringent.

Besides material, we must also ensure that other process input such as machine and method which directly use in the process is also ready before any transformation work can begin.

The end of the manufacturing process

In most manufacturing process, packaging is the last gate in production floor or the manufacturing entity. Although packaging process seems simple and does not transform product, it could become a process which create the most mistakes that will find its way to consumer. Mistakes such as missing, wrong and mix part are often associated to packaging process.  Sometimes damage parts are also associated to poor packaging handling method or poor packaging design.  These defects can cause high customer dissatisfaction as customer would immediately notice those defects even before they start using the parts!

Attention must be given when developing packaging process to prevent customer frustration of not is able to use the product. 

Packaging process must governed by a work instruction which call for 

  • Part number of all packaging materials and labels
  • How to put parts in packaging material and placing orientation in the packaging box
  • Defined a standardized location to paste the label on the box. 
  • Correct handling of the parts to prevent handling issue.

There must a verification process during packaging to check the following items

  • All items are correctly packed without missing or wrong parts, labels, acessories at customer site.
  • All option parts, instruction manual, required accessory are packed per requirement. 
  • All parts count are correct and no missing parts
  • Ensure all parts complete and pass all the process and test steps in manufacturing process

Besides focusing on parts transformation process methods in manufacturing line, manufacturer must take into consideration the preparation process method and final packaging process.  If all operators were to follow the same method from start to end and anything in between we would get a more consistent good quality product.  Another aspect of process which will be covered in next article would be parts transportation in between process.

Process Input method - Product and human conversion in manufacturing line

There are 2 major types of change over in a manufacturing line which we need to consider in this article:  model change over  and human change over.

Model change over 

No manufacturing process will continue to produce a single part until the product life cycle ends.  In fact with consumer growing appetite for variety,  most of the organization is trying to compete using variety either in the product aesthetics or feature with different pricing to suit different market segment.  A good example would be in the early 21st century,   laptop computer were only offered in black colour (equivalent to Ford model T automobile in early 20th century).  Later on Apple started to sell laptop and desktop computer in different colour which had been a delighter to the PC consumer market at that time. 

Variety in consumer market would mean that manufacturing facility must be able to convert a manufacturing line to produce different part and still achieve consistent good product.  This is done through development of standard method for model conversion for manual to fully automated line.
Recommended procedure for seamless manual line conversion to manufacture other models would be  :-

  • Determine the common  parts use for production which do not need to purge and identify those common parts clearly
  • Ensure all materials, hardware items such as jigs and fixture for next model is kitted properly off line
  • Where possible,  prepare just enough to complete the quantity required by customer for that batch  to prevent purging of the extra parts in the production floor
  • During conversion ensure all materials which is not needed are purge from the line
  • Developed a line conversion checklist for operator to do verification to ensure standardization throughout the manufacturing.  This will help to reduce variation. 

It had always being challenge to convert a highly automated line with heavy machinery.  A  good equipment conversion method should follow the principle of a lean methodology,  single minute exchange of dies (SMED) developed by Toyota engineer Shigeo Shingo. In the early days the biggest pain point for Toyota was long conversion time (> 1 day) needed to change tooling die in heavy stamping equipment to produce different automobile body parts.  Equipment will be down for days just to prepare another model die for change and time was also wasted to fit die precisely to the stamping equipment.  Conversion method had to carry out with accuracy and precision to prevent defect from being produce.  If you follow my previous article,  we already know equipment or automated process could produce consistently bad part if not setup properly.

After a series of experiment,  Shingo and team manage to reduce the change over time from days to less than 10 minutes, thus SMED was originated.  The strategy in SMED is to divide changeover activities to 2 categories and then minimize machine shut down and have as many preparation done off line as possible. The 2 categories of conversion activity are :-

  • Internal -  activities which need to stop equipment operation and done in the equipment
  • External -  activities which can be done off line and equipment can run as normal. As we would like to minimize equipment downtime therefore  it is ideal to have as many external activities conversion process.

SMED is achieved through

  1. Determine which conversion activities are internal and external
  2. Where possible convert internal to external conversion
  3. Regulate external off line activities
  4. Standardize machine parts where possible
  5. Use auto alignment mechanism to fit conversion machine part
  6. Design easy to install and uninstall fasteners or clamps
  7. Do internal and external activities in parallel

Concept of SMED

Human change over

Besides model conversion,  we would also need to address human change over,  operator shift change.  Once again standardize method must be developed to manage the variation cause by operator shift change.  An acceptable practice for operator shift change method would be

  1. Communication -  create a communication channel for shift handover to communicate items which need attention eg. quality issue
  2. Establish beginning of the shift checklist which include 5S  check on the work station such as cleaning, Verify all tools needed for production are available and in good condition
  3. Confirm all the setting of tools and equipment are correct
  4. Production supervisor  must ensure operator perform all above and work other team to rectify item which is not in accordance to the documented procedure. 

Very often,  change over method is overlooked by manufacturers as it always form a weakest link in production.   Change over in the form of parts and human should follow  a structural approach with standardize methods to govern the whole process. 

If  there is no standardization a changeover method  in a manufacturing it could lead disastrous quality issue such as shipped mix/wrong  part to customer.  Change over process especially equipment should encompass 1st part verification process.

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