A flexible solar array strip is formed by a method which lends itself to automatic production techniques. Solder pads are deposited on printed circuitry deposited on a flexible structure. The resultant substrate is stored on a drum from which it is withdrawn and incrementally advanced along a linear path. Solderless solar cells are serially transported into engagement with the pads which are then heated in order to attach the cells to the circuitry. Excess flux is cleaned from the cells which are encapsulated in a protective coating. The resultant array is then spirally wound on a drum

Mueller, R. I.

Yasui, R. K.

English

NASA Technical Reports Server

United States Patent 1193 
Mneller et d. 
[54] METHOD IFOW FORMING A SOLAR ARRAY 
[76] Inventors: Robert A. FPOSC~, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of, Robert I. Mueller, 
Azusa; Robert K. Yasui, Torrance, 
both of Calif. 
[21] Appl. No.: 891,358 
[22] Filed: Mm. 29,1978 
Related U.S. Application Data 
[62] 
[51] 
Division of Ser. No. 809,890, Jun. 24, 1977, Pat. NO. 
4,133,697. 
Hnt. (3.2 ............................................... HOW 3/34 
29/627: 136/89 P 
[52] U.S. (3. ........................................ 29/572; 29/588; 
[58] Field of Search ................. 29/627, 626, 572, 605; 
136/89 P 
~561 References Cited 
U.S. PATENT DOCUMENTS 
2,962,539 11/1960 Daniel ................................ 136/89 P 
3,151,379 10/1964 Escoffery ........................... 29/589 X 
3,255,047 6/1966 Escoffery ........................... 29/572 X 
3,724,068 4/1973 Galli ....................................... 29/626 
3,849,880 11/1974 Haynos .................................. 29/626 
3,914,856 10/1975 Fang .................................. 29/589 X 
3,991,462 11/1976 Engel ..................................... 29/605 
4,083,097 4/1978 Anagnostou et al. ............. 29/628 X 
Primary Examiner-Francis S. Husar 
Assistant Examiner-C. J. Arbes 
Attorney, Agent, or Firm-Monte F. Mott; John R. 
Manning; Wilfred Grifka 
A method for forming a solar array strip including the 
steps of depositing solder pads on printed circuitry 
deposited on flexible substrate storing 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 heating the 
pads for thus attaching the cells to the printed 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. 
1571 
7 C l ~ ,  8 Drawing Rgwes; 
KOVAR / KAPTON 
ON A REMOVABLE 
CONTACTS I N  
SOLAR CELL 
STA. E 
https://ntrs.nasa.gov/search.jsp?R=19800006217 2020-03-21T02:00:29+00:00Z
U.S. Patent ~ o v .  13, 1979 Sheet 1 of 3 4,173,820 
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U.S. Patent NOV. 13, 1979 Sheet 2 of 3 4,173,820 
U.S. Patent NOV. 13, 1979 Sheet 3 of 3 
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METHOD FOR FORMING A SOLAR ARRAY 
STRIP 
ORIGIN OF THE INVENTION 5 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
CROSSREFERENCETORELATED 
APPLICATION 
(72 Stat. 435; 42 USC 2457). 10 
This application is a Divisional Application of Appli- 
cation Ser. No. 809,890, filed June 24, 1977, now U.S. l5 
Pat. No. 4,133,697. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention generally relates to solar arrays and 2o 
more particularly to a method for forming a flexible 
solar array strip adapted to be stored in a helically 
wound roll. 
2. Description of the Prior Art 
The prior art is, of course, replete with solar arrays 25 
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 30 
solar arrays, the general utility of previously available 
arrays is impaired due to the inherent complexity of 
fabrication techniques 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 becomes apparent that there exists a need 
for an economic solar cell array having a broader range 
of utility. 40 
It is therefore the general purpose of the instant in- 
vention to provide a flexible solar array strip formed by 
a method which readily lends itself to automated pro- 
duction techniques whereby a continuous solar array 
strip may be economically provided for general usage in 45 
With the advent of renewed interest in and the plac- 35 
converting solar flux to electrical energy. 
OBJECTS AND SUMMARY O F  THE 
INVENTION 
It is an object to provide an improved method for 
forming a flexible solar array strip. 
It is another object to provide an improved method 
for forming a flexible solar array strip which lends itself 
to automation. 
It is another object to provide a method for forming 
a flexible solar array strip including the steps of feeding 
along a linear path a flexible printed circuit substrate 
and serially affixing thereto solar cells and thereafter 
spirally winding the substrate on a take-up drum. 
These and other objects and advantages are achieved 
through a method in which printed circuitry is depos- 
ited in a sandwiched-relationship between a pair of 
layers of a polyamide material, at least one layer having 
formed therein an ordered array of apertures, deposit- 
ing solder pads in the apertures, orienting solderless 
solar cells characterized by wraparound contacts in 
predetermined relation with the apertures, applying 
infrared radiation to the pads for causing the solder to 
50 
55 
60 
65 
flow, cleaning flux from the solar cells, encapsulating 
the solar cells, and finally storing the resulting solar 
array strip on a take-up drum while simultaneously 
interwinding between layers of the strip a layer of pro- 
tective material, as will become more readily apparent 
by reference to the following description and claims in 
light of the accompanying drawings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a diagrammatic view illustrating a method 
embodying the principles of the instant invention. 
FIG. 2 is a diagrammatic view further depicting the 
method of the instant invention. 
FIG. 3 is a top-plan view of a machine for performing 
the method of the instant invention. 
FIG. 4 is side elevational view of the machine shown 
in FIG. 3. 
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 of printed circuitry deposited on 
a flexible substrate employed in forming the flexible 
solar array strip which embodies the principles 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. 
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 10’ is charac- 
terized by an average thickness of 0.0067 inch. In prac- 
tice, the completed strip 10 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 10 
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 polyamide 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 3 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 metalliza- 
tion 24, FIG. 6, running along both sides of the printed 
circuitry 22 and is 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. These pads are affixed to the cells 28 at points 
a Teflon track 46 over which the flexible substrate 18 is 
drawn as it is incrementally advanced through stations 
A through E, at which steps of the method are per- 
formed. 
As illustrated in FIG. I, the station A includes a 
spring-loaded 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 
time intervals, to the elevator 50. The elevator 50 in- 
cludes 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 PO. The receiver 52 supports the solar cell in an 
oriented engagement with the flexible substrate 18 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 is liquified and 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 
4,173,820 
3 4 
including contacts 32 provided for the cells. Hence, the any event, the solder is permitted to set for thus attach- 
strip of metallization must be carefully trimmed from ing the cell 28 to the printed circuitry 22 of the substrate 
the index tabs at the line of junction of the tabs and the BO. The receiver 52 then is retracted by the elevator 50 
circuitry in order to maintain proper substrate width in preparation to receive another solar cell fed thereto 
and cell alignment. 5 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 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 10 substrate 10 is advanced for advancing the solar cells 28 
form the solder pads 30, aforementioned. 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. 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 15 BO advances through a distance sufficient for position- 
30. Such solder comprises 62 percent tin, 36 percent ing the cells in close proximity with a plurality of elec- 
lead, and 2 percent silver composition which is plastic trical probes 58, located at station C. These probes 
over a temperature range of 177” to 189” C. The flux 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 solar cells 28, as employed, are the so-called 20 electrical performance for the solar cells. The cells are 
“solderless” N on P silicon solar cells characterized by next advanced to station D at which a suitable coating 
wraparound passivated contacts. Each of the solar cells is applied to the surfaces thereof for encapsulating the 
28 is joined to the circuitry 22 by four solder pads 30 so 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 encapsulated cells 28 are now ad- 
weight saving of approximately 30 percent over 25 vanced to station E at which probes 62 are applied for 
soldered contact cells is realized. This results in a light- again testing the electrical performance of the cells, in 
weight array which also enjoys the advantage of being their encapsulated condition. Of course, in the event a 
economically less expensive than an array in which a defective cell is detected, it is appropriately identified 
layer of solder is provided for joining the cells to the for subsequent removal. As the thus completed solar 
substrate. 30 array strip 10 is advanced from station E, it is caused to 
Turning for a moment to FIG. 3, therein is illustrated progress along a path located beneath a guide roller 64 
a machine, generally designated 40, having a capability toward the take-up drum 14, to be wound thereabout. 
of performing the method embodying the instant inven- The supply reel 16, of course, feeds a protective layer of 
tion. The machine 40, as shown, includes a bracket 42 resilient material, such as polyethylene, in an inter- 
for supporting the supply drum 12 and a bracket 44 for 35 wound relation between the helical layers of the strip 
supporting the take-up drum 14 and the supply reel 16. 10’ as the strip is wound on the drum 14. 
The brackets 42 and 44 are located at opposite ends of Thus the method which embodies the principles of 
the instant invention provides an improved flexible 
solar array strip wound on a take-up d & n  14, as indi- 
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 
45 adapted to be fully automated. The method utilizes a 
flexible substrate including printed circuitry deposited 
thereon which is connected through the use of solder 
pads to surfaces of solar cells characterized by wrap  
around contacts. The solar cells thus attached to the 
50 flexible substrate ultimately are cleaned, tested, and 
encapsulated in a protective coating to provide an im- 
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 
55 fabrication of devices and systems having a capability of 
utilizing electrical energy developed in the strip in re- 
sponse to incident solar flux. 
In view of the foregoing, it should readily be appar- 
ent that the method for providing a flexible solar array 
60 strip as herein described provides a practical solution to 
the perplexing problem of supplying relatively eco- 
nomic flexible solar array strips for use in industry at 
substantially reduced costs. 
We claim: 
1. In a method for forming a flexible solar array strip, 
A. feeding along a linear path a flexible substrate 
comprising a pair of laminated layers of polyamide 
40 cated in FIG. 8. 
65 
the steps comprising: 
4,173,820 
5 6 
having printed circuitry deposited therebetween, 
at least one layer of said pair of layers having de- 
fined therein apertures within which solder pads 
are deposited in engagement with the printed cir- 
cuitry; and 
B. individually transporting solar cells into engage- 
ment with the solder pads and subjecting the solder 
pads engaged by each solar cell to infrared radia- 
tion for a period sufficient for causing the solder to 
flow. 10 con solar cell. 
2. A method for forming a flexible solar array strip 
A. forming a flexible substrate comprising a pair of 
laminated layers of polyamide having printed cir- 
cuitry disposed therebetween, at least one layer of 15 
said pair having defined therein an ordered array of 
apertures disposed in registered relation with the 
printed circuitry and solder pads deposited in the 
apertures in engaged relation with the circuitry; 
B. feeding said substrate along a linear path; 
C. serially orienting silicon solar cells, characterized 
by wraparound contacts on said substrate in en- 
D. subjecting the solder pads to infrared radiation for 
attaching the solar cells to the printed circuitry. 
3. The method of claim P further comprising the steps 
of spirally winding on a storage drum the flexible sub- 
5 strate having the cells attached to the printed circuitry 
and interwinding between adjacent layers of the strip a 
protective strip of resilient material. 
4. The method of claim 1 wherein each of the, cells 
comprises a solderless wraparound contact N or P sili- 
5. The method of claim 1 further comprising the step 
of obtaining the electrical characteristic of the cells and 
thereafter encapsulating cells attached to the printed 
circuit. 
6. The method of claim 5 further comprising the step 
of cleaning flux from the cells prior to encapsulation 
thereof. 
7. The method of claim 1 wherein the substrate is 
advanced along a horizontal path extended beneath an 
20 infrared lamp located at a fixed station, and the solar 
cells are transported upwardly into engagement with 
the pads at said station. 
comprising the steps of: 
gaged relation with said solder pads; and e + * * +  
3 
25 
30 
35 
40 
45 
50 
55 
65 
UNITED STATES PATENT OFFICE 
CERTIFICATE OF CORRECTION 
PATENT NO. 4 , 173,820 
DATED November 13, 1979 
INVENTOR(S) Rober t  L. Mueller,  Robert  K. Yasui 
are hereby corrected as shown below. 
It i s  certified that error appears in the above-identified patent and that said Letters Patent 
Robert L. - Mueller i n s t e a d  of Robert  - I. Mueller as shown 
i n  the  p a t e n t .  
ISEALJ 
Attest: 
Attesting OBcer 
signed and Scaled th,s 
~ i k i n l  Day o f  June1980 
SIDNEY A. DIAMOND 
Commissioner 01 Patents ud TNdemrh 


Method for forming a solar array strip

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