Any material, substance, particle, chemical, or other undesirable substance that is unwanted that can taint, pollute, defile, make impure or unclean, or adversely effect the process or product. Contamination can take many forms such as: particulate, chemicals (including gases), electro-static discharge, viables ( bacteria, molds, etc..), and other forms.
Particles are measured in microns. If you were to slice a 1-inch cube into 25,400 equal pieces, each slice would be 1 micron thick. (So thin that you could not see it.)
Since cleanroom facilities contain invisible particles that can cause defects, we need to have a way to determine their sizes and possible sources. These particles cannot be seen with the naked eye and yet may cause serious loss to our client and to their ability to manufacture devices without defects. We measure the amount of particles in the air with a device known as a particle counter. This helps us to determine when to perform or restrict certain activities.
Typical Pollutant Sizes That Cause Down Time
|Bacteria||.01 to 1.0 Microns|
|Dust||1.0 to 10 Microns|
|Mold||1.0 to 10 Microns|
|Hair||10 to 100 Microns|
|Pollen||10 to 100 Microns|
Following are some common sources of contamination. This list in by no means exhaustive, but it gives you and idea of the types of things to be aware of when you are looking for the source of contamination.
Coughing / Sneezing
|Gum, Cough Drops
Caulks and Paints
Food and Drink
To combat the tremendous amount of particulate released by the human body, cleanroom personnel are asked to wear special garments that are restrictive and may be uncomfortable if the working conditions (temperature, humidity) are not carefully controlled.
People are dressed in booties, gloves, helmets, hoods and special facemasks that are not part of a normal experience. You are also asked to move slowly, to clean up dirt you cannot see, and to follow practices and procedures that may not immediately make sense.
The approach to cleanrooms is designed in steps so as to ensure that every effort has been made not to introduce contaminants into the cleanroom.
The Human Factor
“Humans are walking, breathing, waste pits from a microbiological perspective and there is no indication we are going to evolve into anything cleaner.”
Human dust combined with sebum will tenaciously adhere to and contaminate surfaces, creating contamination problems that are simultaneously bacterial, chemical and particulate.
There is an additional complicating factor – normal human activity. Humans breathe, sneeze, cough, talk and move around. Body and breath temperatures cause heat turbulence in addition to air turbulence.
People slough off huge numbers of particles a half micron and larger and these are propelled around by air and body movement. Some examples of how many 0.5 micron and larger particles can be released by simple movement are shown below. Vast amounts of contamination need to be controlled in a cleanroom environment.
|Seated||100,000 particles per minute|
|Moving 2 miles per hour||5 million particles per minute|
|Moving 3.5 miles per hour||7.5 million particles per minute|
|Moving 5 miles per hour||10 million particles per minute|
Chart I. Contaminants, Sources and Potential Damage
|Metallics||Vacuum cleaner motor brushes, wear of A/C units, printer wear, raised floor and grid||Electrically conductive, magnetically attracted to micro-circuits|
|Carbonaceous||Automobile exhaust, tobacco smoke, printer toner, oxidized organic material, paper dust||Moisture absorbent, electrically conductive, combustible.|
|Synthetic Fibrous Particulate||Operator clothing, carpeted floor tiles||Low melting point, moisture absorbent, some type combustible , electrically conductive.|
|Cement Dust/Crystalline||Improper sealing or erosion of subfloor, ionization and crystallization of cleaning fluids, nicron wire heating elements, ion air purifiers.||May be propelled at high velocity into floor cooled components, clogged filters lead to overheating of disk media|
Contact SET3 for a free walkthrough evaluation of your facility.