contamination control and electrostatics primer injection molding
TRANSCRIPT
A Primer on Contamination Control
and Electrostaticsand Electrostatics
Scott Mackler, Principal Consultant
Tom Albano, Certified Electrostatics Engineer
Cleanroom Consulting, LLC
www.cleanroom‐consulting.com
How Small Is Small?
Human Hair One Micron Equals
0 00003937 I h1/10,000
of an inch
• 0.00003937 Inches
• 1/1,000,000 Meter
1/1,000of an inch
of an inch
• 1/25,400 Inch
25 i 1 MilOne Micron • 25 microns = 1 Mil
3
Particle Settling Rates
Size µm Time to fall one meterSize, µm Time to fall one meter0.1 36 days0.5 1.4 days0.5 1.4 days1 8.6 hours5 21 mins10 5.2 mins15 2.3 mins20 1.3 mins25 50 secs
Particles Generated (0.3 micrometers / minute / activity)
Motionless, sitting or standing 100,000
Head, arm, neck, leg motion 500,000
All above w / foot motion 1,000,000
Standing to siting & vice versa 2,500,000
Walking at 2 mph 5,000,000
Walking at 3.5 mph 7,500,000
Walking at 5 mph 10,000,000
Room Cleanliness after a contamination excursion
E ffect o f A C P H o n R eco very R ate
6 7 5 A C P H 3 0 A C P H T im e (sec)
P artic les T im e (sec)
P artic les
0 1 00 0 0 00 0 1 0 0 0 0 000 1 ,0 0 0 ,0 00 0 1 ,0 0 0 ,0 005 .3 3 1 0 ,0 0 0 1 2 0 1 0 ,0 0 0
1 0 6 6 1 0 0 2 4 0 1 0 01 0 .6 6 1 0 0 2 4 0 1 0 01 5 .9 9 1 3 6 0 1
Typical Electrostatic Charges Found In Work Areas
• Components ‐ Ceramic 5 kV• Components – Plastic 2.5kVComponents Plastic 2.5kV• Plastic Film 20 kV• Polyethylene Parts 5 kV• Glass Plates 5 kV• Teflon® Subassemblies 25 kV• Fiberglass 2.5 kV• Silicon Wafers 5 kV
DischargeofanIsolatedPlate
Cleanrooms Generate Static Charge and Hold it Efficiently
Discharge of an Isolated Plate
50005500
• Low Humidity• Low Surface Contamination
Ai C diti i R
al V
olta
ge
25003000350040004500 • Air Conditioning Removes
Natural Air Ions• Use of Insulators
– Teflon®
Res
idu
5001000150020002500
500 V
Teflon– Quartz– Glass– Plastic
Time (hours)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 340 Plastic
– Oxide‐Coated silicon
What Happens When a Surface is Charged?
Gravitational
Aerodynamic
q q For electric fields
Aerodynamic
Fq q
r 1 2
4 02
For electric fields of 1000 V/inch, the greatest force is electrostatic!
Electrostaticis electrostatic!
Effect of Static Charge on Wafer Contamination
200 mm Wafer in a Class 1 Mini-Environment200 mm Wafer in a Class 1 Mini Environment
Wafer at 0 VClass 1 mini-environment for 6 weeks
Wafer at 2000 VClass 1 mini-environment for 6 weeks
Water
Why do Cleanrooms Develop Such High Levels of Charge?
Charge Generation:The Materials Used
Latex
Human Hands
Quartz
Positive+
Encourage Transfer:Nylon
Aluminum
Steel
P l hPolyurethane
Polyethylene
Polypropylene
PVC (Vinyl)
Triboelectric Charging
PVC (Vinyl)
Silicon
Mylar®
Teflon®
Negative-
17
Teflon
Processing of Plastic Film over Rollers Contact of Dissimilar Materials Pressure of ContactPressure of Contact
Separation after Contact Vibration Friction between Objects
IV Bags, Photographic Film, and Cleanroom Packaging Materialsand Cleanroom Packaging Materials
++++++++++++++++++++++++++++++++++++
Electrostatic Problems in Polymer Processing
Conveyance and blending issues withpolymer pellets/extrusions, both in compounding and in injection moldingHigh electric fields: particle attraction and Electrostatic Bonding to molded parts, some ofcritical surfaces, applications.
Conventional cleaning methods ineffective