Transcript Optical Adhesives - University of Arizona

TUTORIAL ON ADHESIVES AND
HOW TO USE THEM FOR MOUNTING
Jared Talbot
12/9/2016
TYPICAL TYPES
• Optical Adhesives
 Transparent for specific wavelength ranges, and their optical
properties are known and controlled.
 Typically used to bond two optical surfaces to make things
like doublets, triplets, cube beamsplitters, etc.
• Structural Adhesives
 Generally used as a replacement for a mechanical fastener
 Tend to be lower weight, high strength & stiffness easy to
implement, and low cost by comparison
• Elastomers
 Tend to be more compliant than structural adhesives
 Can serve as a dampening agent in the system.
• Cyanoacrylates
 High strength, and fast curing (typically in 30s).
 Good adhesion to both glass and metal.
 High potential for outgassing which can ruin optical coatings.
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
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TYPICAL TYPES
Adhesive
RTV112
3M 2216
Milbond
Hysol 1C
RTV 142
E-30CL
NOA 61
Temperature Viscosity Tensile
Shear
Total Mass
Range
Strength Strength
Loss %
-55 to 200 C
325 psi
1.00
-55 to 90 C
High
2,500 psi
1.01
-60 to 100 C
High
2,100 psi
0.98
-55 to 100 C
High
2,000 psi
0.81
-55 to 200 C
Medium
550 psi
300 psi
0.24
-55 to 100 C
Low
8,000 psi
4,200 psi
-150 to 125 C Medium
3,000 psi
-
NOA 61 Spectral Transmission (From Norland Products)
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
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MECHANICAL MODELING
Everything is a Spring!
𝛿𝐹𝑎𝑥𝑖𝑎𝑙
𝛿𝐿
𝐸0 𝐴
𝐿
Axial Stiffness:
𝐾𝑎 =
Shear Stiffness:
𝛿𝐹𝑠ℎ𝑒𝑎𝑟 𝐺𝐴
𝐾𝑠 =
=
𝛿𝑦
𝑡
Axial Stiffness at
Reduced Thickness:
𝛿𝐹𝑎𝑥𝑖𝑎𝑙 𝐸𝐵 𝐴
𝐾𝑏 =
=
𝛿𝑡
𝑡
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
=
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MECHANICAL MODELING
Axial Stiffness Under Compression:
𝐾𝑐 =
𝑆=
𝛿𝐹𝑎𝑥𝑖𝑎𝑙 𝐸𝐶 𝐴
=
𝛿𝑡
𝑡
𝐸𝑐 = 𝐸0 1 + ∅𝑆 2
𝐿𝑜𝑎𝑑 𝐴𝑟𝑒𝑎
𝐴
𝑙 × 𝑤
=
=
𝐵𝑢𝑙𝑔𝑒 𝐴𝑟𝑒𝑎 𝑃𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟 × 𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 𝑡 × (2𝑤 + 2𝑙
Apparent stiffening in thin bonds (From Hatheway, A.E., Proc. SPIE, 1993)
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
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MOUNTING OPTICS BY ADHESIVE BONDING
• Advantages to mounting via bonding
 Can help reduce size and weight
 Tend to reduce complexity of the mechanics
 Still able to provide high strength and rigidity
 For components like prisms which can be a little heavier this
can be an ideal way to keep weight down.
• The key to successful implementation is choosing the correct
adhesive, and ensuring adequate control of the area and
thickness of the bond.
• Control of the thickness is key to maximizing the bond strength,
which can typically done one of two ways:
1) Using shims and spaces to control the gap between parts.
2) Mix small glass or plastic beads into the adhesive, where the
diameters of these beads should match the desired bond
thickness.
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
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MOUNTING OPTICS BY ADHESIVE BONDING
Many time epoxy is what is used to mount a prism to
its mount in an assembly. Typically what you will have
is an maximum acceleration which the bond need to
be able to withstand.
𝐴𝐵𝑜𝑛𝑑
Abond
W
J
amax
SF
𝑊 ∙ 𝑎𝑚𝑎𝑥 ∙ 𝑆𝐹
=
𝐽
is the ideal bond area
(From Yoder & Vukobratovich 2015)
is the weight of the optic
is shear or tensile strength of the adhesive
is the maximum relative acceleration (), and
is desired safety factor to ensure a buffer between the design
specification and expected failure.
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
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MOUNTING MIRRORS BY ADHESIVE BONDING
• Many adhesives upon curing will undergo some shrinkage.
• This can cause stress in the optical components and will partially
deform their surfaces of the optic.
• For designs which require a high bond area one way to compensate
for this is to divide up the bond area into multiple smaller bond areas
Ideal bond configurations
are triangular or a ring
shape at about 70% zone
(From Yoder & Vukobratovich 2015)
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
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THERMAL CONSIDERATIONS
9
• In the case of thermal mismatches where an adhesive bond is used for
mounting, the differences in the CTE of the two components is
generally accommodated by the adhesive.
• This is due to the fact that the adhesive tends to be the most compliant
of the three.
• To find the maximum shear stress:
𝑎
𝛾=
𝛼 − 𝛼2 ∙ ∆𝑇
2𝑡 1
𝐺𝑎
𝜏 = 𝐺𝛾 =
𝛼 − 𝛼2 ∙ ∆𝑇
2𝑡 1
NOTE: in multi-element assemblies adhesives can be used to help
passive athermalize a system as well.
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.
REFERENCES
1)
2)
3)
4)
5)
6)
7)
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J. Burge, “Intro to Opto-Mechanical Engineering” Notes, University of Arizona, 2016.
K. Schwertz, J. Burge, “Field Guide to Optomechanical Design and Analysis”, SPIE, 2012.
P. Yoder, D. Vukobratovich, “Opto-Mechanical Systems Design”, Volume 4, 2015.
A. E. Hatheway, “Analysis of adhesive bonds in optics”, Proc. SPIE, 1993.
E. Norland, “Techniques in using UV adhesives for optomechanical designs”, Proc. SPIE, 1995.
B. G. Yacobi, S. Martin, K. Davis, A. Hudson, and M. Hubert, “Adhesive bonding in microelectronics and
photonics”, Journal of Applied Physics, 2002.
https://www.norlandprod.com/adhesives/NOA%2061.html
PROPRIETARY - Property of Edmund Optics, Inc. | 2012 Copyright© Edmund Optics, Inc.