Precision Replication of Micro-Optics Through Injection Molding

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Precision Replication of Micro-Optics Through
Injection Molding
David Gill -- Dr. Thomas Dow -- Alex Sohn
Precision Engineering Center -North Carolina
State University
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Project Goals

• Accurately Replicate Micro-Optics Using the
  Injection Molding Process
• Find The Injection Molding Factors That Have the
  Greatest Effect on the Replication of Micro-Optics

Blaze Grating Dimensions in nm
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Presentation Outline

• Injection Molding Process Factors
• Design of Experiment Process Factors gt
  Replication Fidelity
• Micro-Optics Features
• Research Results

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Nissei HM-7

• Machine Characteristics
• 6.2 cm3 Shot Size
• 102 mm Tie Bar Spacing
• 7 Ton Clamping Force
• Hydraulic Actuation
• Water Based Mold Temperature Control

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Injection Molding Process Factors
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Design of Experiment
(More Than 3000 Parts)

• Selected a High and Low Value for Each Factor
• Both Values Must Create a Measurable Part

Assumptions - Linear Response Between Factor
Values - No Interaction Between Factors
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Micro-Optic Features
Depth
Aspect Ratio
Width
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Feature Measurements

• Astigmatism
• Coma
• Spherical Aberration
• Residual RMS
• Residual PV
• Grating Step Height
• Wedding Cake Step Height

Phase Interferometer White Light
Interferometer Stylus Profilometer
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Replication Fidelity Achieved

• Blaze Grating Step Height Error

Fresnel Residual RMS Error
76 nm
Sphere Residual RMS Error
Wedding Cake Step Height Error
1.8µm (0.9)
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Fresnel Replication
1mm
Mold
PMMA Lens
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Blaze Grating
50µm
20µm
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1/p
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Optimization of DOE Results
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Summary

• Injection Molding Process and Factors in Molding
• Design of Experiment
• Micro-Optical Features and Measurement Methods
• Results of the DOE
• Confirmation of the Results

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Conclusions

• Repeatable Replication of Micro-Optics is
  Possible Using Injection Molding
• Molding Factors Influence the Replicated Shape of
  Micro-Optics
• Mold Temperature and Screw Rotation Speed Have
  the Greatest Impact on Replication Fidelity

The authors wish to acknowledge the support of
this research by the National Science Foundation
(grant 9908223, Dr. K. P. Rajurkar, Program
Director)
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