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