Commercially available sonic welding system and a specially-designed tip bonds aluminum foil interconnects to titanium-silver solar cell contacts

Keller, L. B.

Schwartz, S.

English

NASA Technical Reports Server

1972	 B72-10058 
NASA TECH BRIEF 
Ames Research Center 	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Aluminum Foil Interconnects for Solar Cell Panels 
Solar cell panels which must operate in a tempera-
ture range of 173° to 483°K require solar cell inter-
connects which can withstand elevated temperatures. 
Examination of state-of-the-art techniques indicates 
that solder-plated copper wire mesh is a suitable 
interconnect when bonded by a high-melting solder 
to the titanium-silver contacts of high-temperature 
resistant solar cells. However, difficulties were en-
countered in fabrication, and the results of shear and 
peel tests indicated that a preponderance of failures 
in the interconnect bonds was due to the high heat 
fluxes used to form the solder bond. 
Thermal diffusion bonding of nickel-titanium sur-
faces using silver mesh interconnects was investigated. 
Satisfactory results were obtained in tests for bond 
strength and temperature shock; however, there are 
several disadvantages to the use of thermal diffusion 
bonding as a production technique: 
(1) Bonding must be accomplished in a vacuum; (2) 
Approximately 2i hours are required to bond the 
interconnects; (3) Available tooling space limits the 
number of cells that can be interconnected at one 
time. 
Prior experience suggested that ultrasonic diffusion 
bonding might alleviate many problems, since it 
could provide a true metallurgical bond (even with 
dissimilar metals). This technique required no special 
tooling to maintain cell alignment; moreover, strong 
bonds (40 to 60 percent of parent material) can be 
achieved within a few seconds, removal of oxide or 
organic films is not required, and post cleaning of the 
bond is not necessary.
Excellent results were obtained by bonding alumi-
num foil interconnects to the titanium-silver contacts 
of solar cells with a commercially available sonic 
welding system and a specially-designed tip. A solar 
cell group of nine cells was easily fabricated. The 
performance curve for the group shows a sharp knee 
in the maximum power region, indicating that the 
process did not cause any significant degradation of 
solar cell performance. 
The technique has also been successfully employed 
for bonding aluminum foil interconnects to deposited-
aluminum cell contacts. However, in order to prevent 
shorting of solar-cell junctions during the contact-
deposition process, it is necessary to use the masks 
and etching processes normally employed by solar-
cell manufacturers. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10058 
Patent status: 
No patent action is contemplated by NASA. 
Source: S. Schwartz and L. B. Keller of 
Hughes Aircraft Company
under contract to

Ames Research Center 
(ARC-10374) 
Category 08 
Thisdocumentwas 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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Aluminum foil interconnects for solar cell panels

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