A flexible solar array strip is formed by providing printed circuitry between flexible layers of a nonconductive material, depositing solder pads on the printed circuitry, and storing the resulting substrate on a drum from which it is then withdrawn and advanced along a linear path. Solderless solar cells are serially transported into engagement with the pads and are infrared radiation to melt the solder and attach the cells to the circuitry. Excess flux is cleaned from the solar cells which are then encapsulated in a protective coating. The resulting array is then wound on a drum

Mueller, R. L.

Yasui, R. K.

English

NASA Technical Reports Server

United States Patent [191 
Mueller et al. 
[111 4,133,697 
PSI Jan. 9,1979 
[54] SOLAR ARRAY STRIP AND A METHOD 
FOR FORMING THE SAME 
[76] Inventors: 
[21] Appl. NO.: 
[22] Filed: 
Robert A. Frosch, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Robert L. Mueller, 
Azusa; Robert I(. Yasui, Monterey 
Park, both of Calif. 
Jrm. 24,1977 
[51] Int. CI.2 ............................................. HOlL 31/06 
[52] U.S. CI. ............................. 136/89 P; 136/89 CC; 
29/572 
[58] Field of Search .......................... 136/89 P, 89 CC 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,502,507 3/1970 Mann .................................. 136/89P 
3,509,431 4/1970 Iles et al. ............................ 136/89 P 
3,973,996 8/1976 Kennedy ............................ 136/89 P 
4,019,924 4/1977 Kurth ................................. 136/89 P 
Primary Examiner-John H. Mack 
Assistant Examiner-William Leader 
Attorney, Agent, or Firm-Monte F. Mott; John R. 
Manning; Wilfred Griilca 
Providing printed circuitry in a sandwiched relation 
with a pair of flexible layers of non-conductive material, 
depositing solder pads on the printed circuitry and stor- 
ing the resulting substrate on a drum, withdrawing the 
substrate from the drum and incrementally advancing it 
along a linear path, serially transporting solderless solar 
cells into engagement with the pads and thereafter heat- 
ing the pads for thus attaching the cells to the circuitry, 
cleaning excess flux from the solar cells, encapsulating 
the cells in a protective coating and thereafter spirally 
winding the resulting array on a drum. 
E571 ABSTRACT 
1 Claim, 9 Drawing Figures 
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U.S. Patent ~ m .  9, 1979 Sheet 2 of 3 4,1133,697 
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BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a diagrammatic view illustrating a method 
FIG. 2 is a diagrammatic view further depicting the 
SOLAR ARRAY STRIP AND A METHOD FOR 
FORMING THE SAME 
ORIGIN OF THE INVENTION 
embodying the principles of the instant invention. 
5 
The invention herein was made in the per- 
formane of work under a NASA contract and is sub- 
method of the instant invention. 
FIG. 3 iS a top-plan V k W  Of a machine for perforlhg 
ject to the provisions of Section 305 of the National 
 ti^ and space Act of 1958, public hw 85-568 
(72 Stat. 435; 42 USC 2457). 
the method Of the instant invention- 
FIG. 4 is a side elevational view of the machine 
10 shown in FIG. 3. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention generally relates to solar arrays and 15 
more particularly to a flexible solar array strip adapted 
to be stored in a helically wound roll, and a method for 
forming the same. 
2. Description of the Prior Art 
The prior art is, of course, replete with solar arrays 20 
and methods for forming such arrays. Moreover, it is 
well known that arrays of solar cells may be provided 
on flexible substrates for the use of such arrays aboard 
satellites and the like. Unfortunately, however, as can 
be appreciated by those familiar with the fabrication of 25 
solar arrays, the general utility of previously available 
arrays is impaired due to the inherent complexity of 
fabrication techuiques which result in arrays, expensive 
in terms of both time and materials. 
ing of emphasis on developmental efforts calculated to 
reduce costs in the production of electrical energy from 
solar flux, it became apparent that there exists a need for 
an economic solar cell army having a broader range of 35 
Utility. 
It is therefore the general purpose of the instant in- 
vention to provide a flexiile solar array strip formed by 
a method which readily lends itself to automated pro- 
duction techniques, whereby a continuous solar array 40 
strip may be economically provided for general usage in 
converting solar flux to electrical energy. 
OBJECTS AND SUMMARY OFTHE 
INVENTION 
It is an object of the instant invention to provide an 
improved flexible solar array strip. 
It is another object to provide an improved flexible 
solar array strip capable of being formed through meth- 
ods which lend themselves to automation. 
These and other objects and advantages are achieved 
through a the use of a flexible solar array strip fabri- 
cated employing a method in which printed circuitry is 
deposited in a sandwiched relationship betweem a pair 
of layers of a polyimide material, at least one layer 
having formed therein an ordered array of apertures, 
depositing solder pads in the apertures, orienting solder- 
less solar cells characterized by wraparound contacts in 
predetermined relation with the apertures, applying 6o 
infrared radiation to the pads for causing the solder to 
flow, cleaning flux from the solar cells, encapsulating 
the solar cells, and finally storing the resulting array 
strip on a take-up drum while simultaneously interwind- 
ing between layers of the strip a layer of protective 65 
material, as will become more readily apparent by refer- 
ence to the following description and claims in light of 
the accompanying drawings. 
With the advent of renewed interest in and the plac- 30 
45 
50 
55 
FIG. 5 is a fragmented, partially exploded perspec- 
tive view of a portion of a solar array strip which em- 
bodies the principles of the instant invention. 
FIG. 6 is a plan view, not to scale, of printed circuitry 
deposited on a flexible substrate employed in forming 
the flexible solar array strip which embodies the princi- 
ples of the instant invention. 
FIG. 7 is a fragmented, top-plan view of the strip. 
FIG. 8 is a perspective view depicting one manner in 
which the solar array strip is stored. 
FIG. 9 is a fragmentary top plan view of a portion of 
the strip illustrating electrical connections for the cells 
attached thereto. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring now to the drawings with more particular- 
ity wherein like reference characters designate like or 
corresponding parts throughout the several views, 
there is depicted in FIGS. 1 and 2 a method embodying 
the principles of the instant invention. 
Briefly, the method currently is performed using a 
strip of flexible substrate, generally designated 10, inter- 
mittently withdrawn from a supply drum 12, and there- 
after delivered to a take-up or storage drum 14 as a 
completed solar array strip 10. The strip 1 0  is charac- 
terized by an average thickness of 0.0067 inch. In prac- 
tice, the completed strip 1 0  is helically wound about 
the drum 14 as a strip of protective resilient material 15 
is withdrawn from a supply reel 16 and interwound 
therewith. 
As best illustrated in FIG. 5, the completed strip 1 0  
includes a pair of laminated layers, designated 18 and 
20, having interposed therebetween printed circuitry, 
designated 22. In practice, the layers 18 and 20 are 
approximately 0.001 inch in thickness and are formed of 
Kapton polyimide film (type H). The layers 18 and 20 
are suitably bonded together employing proven tech- 
niques. Between the layers 18 and 20, the circuitry 22 is 
approximately 0.0012 inch thick and is repeated twelve 
times in a 9 inch length of the strip on 0.82 inch center 
lines. As a practical matter, the printed circuitry 22 also 
is deposited and etched employing known techniques 
and comprises conductors formed of copper or other 
suitable conductive material. 
The substrate 10 is fabricated with strips of metalh-  
tion 24, FIG. 6, running along both sides of the printed 
circuitry 22 and connected to the circuitry through 
index tabs 26. Solar cells 28 ultimately are deposited on 
the substrate in edge-to-edge engagement along imagi- 
nary transverse lines bisecting oppositely oriented tabs 
26 and are connected with the circuitry through solder 
pads 30 which are completely covered by base layer 20. 
These pads are affied to the cells 28 at points including 
contacts 32 provided for the cells, each contact being 
bonded through a separate aperture. Hence, as shown in 
FIG. 9, the strip of metallization must be carefully 
trimmed from the index tabs at the line of junction of 
4,133,697 
3 4 
the tabs and the circuitry in order to maintain proper in preparation to receive another solar cell fed thereto 
substrate width and cell alignment. from the cassette 48. It will, of course, be appreciated 
It is important here to note that in order to facilitate that the receiver 52 simultaneously accepts as many 
connecting the circuitry 22 with the solar cells 28, and solar cells 28 as are required to span the width of the 
to provide access to test points for the circuitry, the 5 strip 10’. 
layer 18 is suitably perforated to form perforations 34. The drums 12 and 14 are now indexed and the flexible 
within the perforations 34, solder is deposited to thus substrate 10 is advanced for advancing the solar cells 28 
form the solder Pads 30, ~fO~~mentkmed- preferably, attached to the substrate 10 to station B at which a spray 
the substrate is cleaned with acetone, using cotton applicator 56 is employed for spraying under pressure a 
swabs, before the solder is deposited in the perforations. 10 suitable flux solvent for performing a cleaning function 
In practice, a eutectic solder which meets Federal spec- for the cells. Upon again being advanced, the substrate 
ification QQ-S-S-571E is employed in forming the Pads 10 advances through a distance sufficient for position- 
30. Such solder comprises 62 percent tin, 36 percent ing the in close proximity with a plurality of elec- 
lead, and 2 percent silver composition which is plastic trical probes 58, located at station C. 
Over a temperature range Of 177” to lg9’ c* The flux l5 extend through apertures registered with the index tabs 
now used is Alpha 320-33, a liquid. 26 and serve to engage the tabs for determining the 
The cells as are the so-called electrical performance for the solar cells. The cells are 
28 is joined to the circuitry 22 by four solder Pads 30 so Z0 cells. An epoxy resin, if desired, can be employed for 
that the cell does not require a layer of solder. Thus a this purpose. The cells are now ad- 
soldered contact cells is realized. This results in a light- again testing the electrical performance of the cells, in 
economically less expensive than an array in which a 25 defective cell is detected, it is appropriately identified 
substrate. array strip 10 is advanced from station E, it is caused to 
The supply reel 16 of course, feeds a protective layer of 
wound relation between the helical layers of the strip 
‘0 as the 
Thus the method which embodies the principles Of 
the instant invention provides an improved flexible 
While the invention which embodies the principles of 
the instant invention is believed to be apparent from the 
Preceding description thereof, it is important to note 
that the invention is embodied in a method particularly 
adapted to be fully automated. The method utilizes a 
flexible substrate including minted circuitrv dewsited 
“solderless” N on P Silicon Solar cells characterized by next advanced to station D at a suitable coating 
is applied to the surfaces thereof for encapsulating the passivated Each Of the 
weight saving Of 30 percent Over vanced to station E at which pro& 62 are applied for 
weight which enjoys the advantage Of being their encapsulated condition. Of co-, in the event a 
layer Of ‘Older is provided for joining the to the for subsequent removal. As the thus completed solar 
Turning for a moment to FIG. 3, therein is illustrated 
a machine, generally designated 40, having a capability 
of performing the method embodying the instant inven- 30 
for supporting the supply drum 12 and a bracket 44 for 
prosess along a path located beneath a f i d e  roller 64 
drum 149 to be wound thereabout* the 
tion. The 40, as shown, includes a bracket 42 
supporting the take-up drum 14 and the supply reel 16. 
The brackets 42 and 44 are located at opposite ends of 
a Teflon track 46 over which the flexible substrate 10 is 35 
drawn as it is incremenay advanced through stations 
formed. cated in FIG. 8. 
illustrated in FIG. 1, the station A includes a 
spring-lo&ed cassette 48 adapted to feed solar cells 28 
to a solenoid operated elevator 50. In practice, a stack 
of solar cells 28 is deposited in an inverted disposition 
within the cassette 48 and ultimately fed therefrom, at 
timed intervals, to the elevator 50. The elevator 50 
resilient as polyethylene, in an inter- 
is On the drum 14* 
A through E, at which steps of the method are per- on a take-up drum 14, as 
includes a receiver 52 which accepts and advances each 
individual solar cell 28 upwardly through a slotted 
opening, not shown, provided in the Teflon track 46. 
Thus the receiver advances each of the cells into en- 
gagement with the lower layer 18 of the flexible sub- 
strate 10. The receiver 52 supports the solar cell in an 
oriented engagement with the flexible substrate 10 until 
the solder of the pads 30 engaged thereby is caused to 
first flow and then set. Also provided at the station 
designated STA. A is an infrared lamp, not designated, 
the purpose of which is to cause radiation to impinge 
upon the upper surface of the flexible substrate 10 for 
thus heating the solder. As a practical matter, the infra- 
red lamp is mounted for transverse adjustment above 
the Teflon track 46, at station A. Simply by positioning 
and then energizing the infrared lamp, the solder of the 
solder pads 30 liquified and is caused to flow into en- 
gagement with the adjacent surface of the solar cell 28 
supported thereagainst by the receiver 52. The lamp, of 
course, ultimately is de-energized, or, where desired, 
removed from station A to permit the solder to “set”. In 
any event, the solder is permitted to set for thus attach- 
ing the cell 28 to the printed circuitry 22 of the substrate 
10. The receiver 52 then is retracted by the elevator 50 
45 thereon which is connected through the &e oi solder 
pads to surfaces of solar cells characterized by wrap- 
around contacts. The solar cells thus attached to the 
flexible substrate ultimately are cleaned, tested, and 
encapsulated in a protective coating to provide an im- 
50 proved flexible solar array strip capable of being readily 
stored in a helically wound configuration upon a take- 
up drum for subsequent usage in the manufacture and 
fabrication of devices and systems having a capability of 
utilizing electrical energy developed in the strip in re- 
In view of the foregoing, it should readily be appar- 
ent that the flexible solar array strip and method for 
providing the same provides a practical solution to the 
perplexing problem of supplying relatively economic 
60 flexible solar array strips for use in industry at substan- 
tially reduced costs. 
Although the invention has been herein shown and 
described in what is conceived to be the most practical 
and preferred embodiment, it is recognized that depar- 
65 tures may be made therefrom within the scope of the 
invention, which is not to be limited to the illustrative 
details disclosed. 
55 sponse to incident solar flux. 
What is claimed is: 
5 
4,133,697 
6 
1. improved flexible solar may strip particularly C. means defining a segmented printed circuit ex- 
tended between the layers of film for electrically 
interconnecting said solar cells; suited for automated production comprising: 
A. at least one pair of wrap-around contact solar cells 
arranged in juxtaposition, a h  cell of said 
having its contacts arranged in coplanar relation; 
a flexible substrate for said Pair of Comprising 
an elongated strip consisting of a pair of layers of 
@yimide film bonded in superimwsod relation, 10 
one layer of said pair comprising a base layer and 
one layer of the pair comprising a cover layer; 
D. means defining in said cover layer a plurality of 
apertures disposed in registered relation with seg- 
ments of the printed circuits, said segments being 
completely covered by said base layer; and 
E. electrically conductive solder pads substantially 
filling said plurality of apertures for bonding the 
contacts of said solar cells to segments of said 
printed circuit, each contact being bonded through 
a separate aperture. 
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Solar array strip and a method for forming the same

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