Epoxy resin-coated polyimide plastic is used for bonding materials with different thermal coefficients in applications requiring precision mounting, especially where vibrations, temperature extremes, and low pressures are encountered. Low vapor pressure of the bonding material precludes outgassing problems

Mueller, T. F.

English

NASA Technical Reports Server

August 1969
	 Brcl9-101O 
NASA TECH BRIEF	 G .	 % f, 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Precision Mounting for Instrument Optical Elements Provided

by Polyimide Bonding 
Quartz Mirror	 Titanium Spring 
(Flexure)
Polyimide
Block 
Tl,	 Mounting
Bck
Mirror Mounting Detail 
Epoxy resin-coated polyimide plastic may be the 
material chosen for bonding materials with different 
thermal coefficients in applications requiring precision 
mounting, for example, of instrument optical elements, 
especially where vibrations, temperature extremes, 
and low pressures are encountered. 
Use of springs, set screws, or cushioned frames for 
mounting precision optical glass elements allows a
minimum of 10 arc seconds of alignment shift during 
vibration and further alignment shift and surface dis-
tortion upon exposure to high temperatures. Bonded 
structures may hold alignment but transmit stress to 
the glass, thereby breaking it or the bond under these 
conditions. 
For test purposes, a fused quartz mirror (6 in. X 
3.35 in. X 1.25 in.) weighing 2.5 pounds was used 
(coiitinucd ncrICif) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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as the optical element. The mirror mounting detail 
is shown in the drawing. 
A thin layer of potting compound was applied to 
both sides of a small 2-square-inch block of polyimide 
plastic, 1/16 inch thick. This block was then affixed 
between the mirror and the thin titanium springs. 
Subsequently, these springs were attached with screws 
to a magnesium mounting block and the potting was 
cured. 
The titanium springs serve as a bridge between the 
mirror and the magnesium mount, limit thermal con-
duction, and accurately maintain the mirror position. 
The magnesium frame serves for structural rigidity 
and allows heat radiated from the mirror to pass 
through the openings in the mount to prevent thermal 
expansion. 
After vibrational tests, alignipent of the mirror 
was within ±5 arc seconds. A more precise, deter-
mination was precluded by limitations of the refer-
ence system used for checking the accuracy of align-
ment. 
Following exposure to high vibration levels, the 
front of the mirror was heated with a sun gun and 
the temperature of the back of the mirror reached 
160°F. As determined by an autocollimator refer-
ence system, the alignment retention was within -1 
arc second. The temperature of the magnesium 
mount, to which the mirror was attached by bonding 
material and titanium brackets, increased less than
3°F from the initial 75°F temperature of the mirror 
and mount. 
It is predicted that this bonding technique will, allow 
alignment to be maintained within ± 1 arc second 
from —50 to 180°F, if the frame temperature re-
mains within 75 ± 5°F. 
Epoxy resin coated polyimide plastic bonding ma-
terial has extremely low vapor pressures, precluding 
outgassing problems and subsequent contamination 
in high vacuum. Polyimide is resistant to most or-
ganic solvents and dilute or weak acids; however, 
it is attacked by bases and by nitrogen tetroxide. 
Note: 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-10310 
Patent status: 
Inquiries about obtaining rights for the commer-
cial use of this invention may be made to NASA, 
Code GP, Washington, D.C. 20546. 
Source: T. F. Mueller of
Ball Brothers Research Corporation 
under contract to
Marshall Space Flight Center
(M FS-20293)
Brief 69-10310	 Category 05


Precision mounting for instrument optical elements provided by polyimide bonding

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