Cryogenic treatment of laminated copper-clad microwave circuit boards eliminates stresses that cause warpage when a circuit is etched on one side of the board. After etching, the stresses may be eliminated to reduce warpage

Boone, W. L., Jr.

English

NASA Technical Reports Server

Copper Foil 
(Typical)
Copper-Etched Circuit 
November 1967	 Brief 67-10454 
NASA TECH BRIEF 
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. 
Warpage Eliminated in Copper-Clad Microwave Circuit Laminates 
Unetched Warped Board
	 Warpage Toward 
Etched Side 
The problem: 
To prevent stresses, inherent in copper-clad micro-
wave circuit laminates, that cause warpage when a 
circuit is etched on one side of the board. This warp-
age causes various problems in manufacturing proc-
esses and decreases reliability of microwave compo-
nents. 
The solution: 
Treat the laminated circuit boards cryogenically. 
Prior to etching, the stresses may be eliminated to 
prevent warpage; after etching, they may be eliminated 
to reduce warpage. 
How it's done: 
The temperature required to stress-relieve a board 
depends upon the composition of the plastic which 
makes up the board. A copper-clad, fiberglass/ styrene
copolymer board (Rexolite 2200) employed for study, 
required —80°C to prevent warpage during etching 
and to eliminate warpage resulting from etching. The 
process used for the board tested follows: 
(I) Prior to etching, the flat boards are slowly 
cooled to —80°C, maintained at that tempera-
ture for one to two hours, and slowly returned 
to room temperature. 
(2) Boards that have not been treated, as described 
above, and have warped during manufacture, 
are first heated to +100 1 C. This is to allow 
clamping between two sheets of aluminum with 
minimum stress. After the boards are clamped 
flat, they are cooled to —80°C, maintained at 
that temperature for one to two hours, and 
returned to room temperature. 
(3) Etched boards, if warped, may also be treated 
as described in step (2) above. 
(4) The boards that were treated in this manner 
remained flat and were processed and assem-
bled without difficulty.
continued overleaf) 
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.
https://ntrs.nasa.gov/search.jsp?R=19670000454 2020-03-11T21:12:30+00:00Z
Notes: 
1. Further details of the method are contained in: 
Stress Relief of Copper-Clad Microwave Circuit 
Laminates to Reduce and Prevent Warpage, IBM 
Report No. 67-U60-0021, 25 May 1967. 
2. This report is available from: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10454
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: W. L. Boone, Jr. 
of IBM
under contract to 
Marshall Space Flight Center 
(M FS-1 3892) 
Brief 67-10454	 Category 03


Warpage eliminated in copper-clad microwave circuit laminates

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