An automated solar panel production line which reduces the module assembly costs was designed. The module design, solar cell assembly phototype, and solar panel lamination prototype are discussed

Somberg, H.

English

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AUTOMATED SOLAR PANEL ASSEMBLY LINE
LSA TASK; PRODUCTION PROCESSES & EQUIPMENT
Quarterly Report No. 1
JPL Contract No. 955278
Prepared For:
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91103
(NASA-CR-158671)	 RUTCFATFD SCLA6 PANEL_	 X179 -24455
ASSEMBLY LINE. LSA TASK; FBCLUCTICN
PROCESSES AND EQUIPMENT (ABCO Solar, Inc.,
Chatsworth, Calif.)	 18 F BC A02/MF A01	 Unclas
CSCI 10A G3/44 22163
April 8, 1979
	
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Submitted By:
ARCO SOLAR INC.
20554 Plummer Street
Chatsworth, California 91311
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AUTOMATED SOLAR PANEL ASSEMBLY LIVE
QUARTERLY REPORT NO. 1
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JPL Contract No. 955278
PREPARED BY: H. Somberg
REPORT DATE: April 8, 1979
The JPL Low-Cost Silicon Solar Array Project is sponsored
by the U.S. Department of Energy and forms part of the Solar
Photovoltaic Conversion Program to initiate a major effort
toward the development of low-cost solar arrays. This work
was performed for the Jet Propulsion Laboratory, California
Institute of Technology by agreement het:•reen NASA and DOE.
Submitted By:
ARCO SOLAR, INC.
20554 Plummer Street, Chatsworth, Ca l ifornia 91311
fir,-_
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This report was prepared as an account of work sponsored by
the United States Covernment. Neit'_.er the United States
Government nor the United States Department of Energy, nor
any of their employees, nor any of their contractors, sub-
contractors, or t'A r employees, makes any warranty, express
or implied, or assumes any legal liability or responsibility
for the accuracy, completeness or usefullnes of any infor-
mation, apparatus, product or process disclosed, or represents
that its use would not infringe privately owned rights.
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ABSTRACT
The objective of this program is to design,
fabricate and demonstrate an automated solar cell module
production line with the ulCimate goal of reducing module
assembly costs.
During this reporting period the automated
module design was completed. The design of the solar cell
assembly prototype (SCAP) was about 75% completed and the
solar panel lamination prototype (SPLP) was built and tested.
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TABLE OF CONTENTS
i Section Title Page
1.0 SUMMARY 1
1.1 Introduction 1
1.2 Module Design 1
1.3 Solar Cell Assembly Phototype (SCAP) 4
1.4 Solar Panel Lamination Prototype (SPLP) 9
2.0 RESULTS AND DISCUSSION 11
3.0 FUTURE PLAN - 12
APPENDIX A 13
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1.0 SUMMARY
	
1.1	 Introduction
The objective of this program is to design,
fabricate and demonstrate an automated solar panel production
line with the ultimate goal of reducing module assembly costs.
The pra.ncipal tasks in this program are 1) the
generation of a module design compatible with automated assembly
methods, 2) the design and fabrication of automatic soldering
equipment capable of interconnecting 12 solar cells/minute,
3) the design and construction of automatic laminating
equipment capable of producing 12 modules/hour and 4) operation
of an automated pilot line.
The approach used in the design of the solar cell
module was to adapt a field-proven encapsulation_ system to a
circuit design compatible with automated assembly.
The major differences between the conventional
and automated module are larger cells (100mm vs. 75mm), module
size increase to .3m xl.2m (1 x 4 feet), halving of the encap-
sulant thickness to 2-.38mm (.015 inch) thick layers of PITB and
extruded aluminum side and end channels instead of an enclosed
box. The peak power of the module is 33 watts and its NOCT
is 47oC.
The approach to solar cell interconnection was
to design equipment capable of making series strings from
individual cells. The design includes automatic cassett
unloading and wafer alignment, ribbon feed and deployment,
simultaneous soldering of top and bottom interconnects, in-line
removal of soldering flux and attachment of a Mylar* strip to
each string for dimensional stability and handling.
ARCO Solar uses a superstrate module design to
which the circuit is laminated using PVB. Lamination of PVB
is accomplished using a "vacuum bag" approach which is intgrated
with infrared heating into a single system. Multiple lamination
stations are part of a rotating carousel so that all work can
be directed from one area.
	
1.2	 Module Design
The basis for the ASI module design is a glass
superstrate to which the solar cell circuit is laminated using
PVB and Tedlar* as a back cover. Circuit terminations are
installed through the back cover and fitted with an ABS
junction box. Extruded aluminum side and end channels complete
the module and provide for structural support. Figures 1 and 2
are laminate and module assembly drawings respectively.
*Dupont trademark
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In this automated assembly design the solar
cells have been increased from 75mm to 100mm in diameter. Fully
redundant interconnects consisting of two parallel solder
plated copper ribbons are attached to small discretetcontacts
on both sides of the solar cell. Since the module ec:asists
of 3 series connected strings, automated interconnection
of cells is simplified by the parallel ribbon approach. A
second feature of this module design is a reduction in the
number of layers of PVB (.38mm-.015 inch) f 6om four to two
which in turn lowers both cost and NOCT (47 C).
1.3	 Solar Cell Assembly Prototype (SCAP)
The solar cell, assembly prototype (SCAP)
mach'ne is designed to receive finished solar cells applied with
solder paste and produce series interconnected strings. These
strings can then be made into completed module circuits.
The SCAP consists of five elements exclusive
of instrumentation and safes (e.g., overtemperature protection):
1) cassette unloading and wafer alignment
2) ribbon feed and deployment
3) soldering mechanism
4) solder flux removal
5) handling strip attachment station
A schematic of the SCAP is depicted in Figure 3.
Cassette indexing and cycling will. be
accomplished by conventional handling equipment familiar to the
semiconductor industry. 	 Cassettes are stacked 5 - 7
high in a transport tube and attached to the in-feed track
of the SCAP. A chain carrier/alignment mechanism revolves
between the cassette and soldering leads. As the cassette
keys the wafer for removal, the carrier accepts and aligns
the wafer. The carrier, being part of the revolving chain,
transports the cell into the soldering mechanism. The wafer
alignment and carrier mechanism is in the detail design phase.
The function of the ribbon feed and
deployment mechanism is to feed, shear and deploy two parallel
ribbons to the top of the cell for soldering. This rather
complex operation is schematically depicted in Figure 4. The
ribbon mechanism is in the conceptural design phas-
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FIG.4
RIBBON FEED & DEPLOYMENT
STEP 1	 SOLDERINGJ HEADS
MOVE CELL INTO POSITION
STEP Z
SHEAR RIBBON ^ DEPLOY
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ST r P 3
SOLDER RIBBONS
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STEP  4
CELL ADVANCE
6
7`See appendix h
The soldering mechanism consists of two precisely
machined and opposing heads that match the solar cell metal-
lization pattern. The heads move vertically to and away from
the cell during each machine cycle and heat input is through
conduction. Between. the relieved pads on each soldering head
are holes that provide for adiabatic cooling of the solder
connections.
The soldering heads are each attached to a
sequencer whose role is to act as a c:.;1 in coordinating the
vertu^al head movement, and to provide both heating and cooling
during each soldering cycle. The soldering head/sequencer
arrangement have compliance to the solar cell by means of the
spring load in a wave washer.
As the sequencer rotates through its cy^le, heat
input is provided by contact with copper heat sources that are
resistively heated.
The soldering mechanism has been designed,
fabricated and mechanically operated at room temperature. The
copper heat sources have been fabricated, and the control and
instrumentation package is near completion.
The defluxing station is an in-line ultrasonic
cleaning tank which is replenished with clean distilled
solvent by an off-line solvent reclamation unit. The sizing
of the ultrasonic tank was based on the machine cycle of 12
cells/minute and the residence time necessary in the U.S. tank
for thorough residual flux removal. Both 1-1-1 trichloroethane
and a freon-alcohol azeotrope (Blacotron TMS Plus, Baron-
Blakeslee) were assessed for cleaning efficiency. E8ch solvent
was he8ted tg its optimum cavitation temperature, 57 C (i.35 F)
and 30 C (86 F) respectively. The optimum cavitation temperature
is a threshold level at which solution degassing is complete and
maximum cavitation efficiency is achieved. Below this tempera-
ture dissolved gases absorb the generated ultrasonic energy
and cleaning efficiency is poor.
Both solvents were found to remove residual flux
(rosin) within 20 - 30 seconds. Absence of rosin was verified
using both microscopic and colorimetric rnethods. l The U.S.
tank was subsequently sized to permit residence time in the tank
of 40 second.3 minimum/cell. A refrigeration coil will be
incorporated at the top of the tank to minimize solvent
evaporation and a spray of hot clean solvent distillate ,gill
remove any rosin dragout from the tank as cells emerge from
the solution. The ultrasonic system has been sized and ordered.
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The handling strip attachment station will apply
a thin .080mm (.003 inch) strip of Mylar to the back of each
cell in orde •_ to provide a dimentiona'.'v stable and manageable
circuit string. This mechanism will also count and shear each
series string at the appropriate length. The Mylar has a thin
.025-.050mm (.001 - .002 in.) layer o': thermoplastic polyester
adhesive which is heat-applied to the back of each cell. This
machine element is 90% designed and is being assembled.
1.4	 Solar Panel Lamination Prototvpe (SPLP)
The encapsulation system utilizes a superstrate
design and extruded layers of polyvinyl butyral (PVB) as the
adhesive to form a thin profile laminate, 4.5mm (.180 inches)
thick.
In order to effectively remove the interfacial
air between the layers of PVB, the laminate stackup (glass,
PVB, solar cell circuit and Tedlar* back cover) must be evacuated
within a vacuum. The approach taken to accomplish both evacuation
and heating was to combine them in a s=ngle chamber. The chamber
design is shown in Figure 5. Each half of the chamber can be
evacuated independantiy of the other so that after the initial
pumpdown period, the top half can be backfilled to atmospheric
pressure.
The first approach to sealing the two chambers
from each other was to extend the flexible back cover (Tedlar) of
the laminate over the gasket seal in the flange area. In this
way a new diaphram (back cover) would be introduced for each
new laminate. The reliability of this approach both for main-
taining adequate sealing properties and providing a smooth uniform
back cover was inadequate.
The second approach simplified ectling and also
eliminated the need for a gasket or O-ring. In this approach
a large rubber diaphragm was placed over the laminate stackup
and the flange area. The weight of the top chamber initiated
a seal around this flange perimeter and repeatable evacuations
were achieved. The one prerequisite for using a rubber di.aphragm
is a breather-release material. The purpose of this material is
to prevent the rubber diaphragm from applying non-uniform pressure
to the Tedlar back cover when atmospheric pressure is applied. It
also serves to permit better evacuation or "breathing` of air
between the rubber and Tedlar. Presently two materials are used
for this application; a teflon-coated textile serves as a non-
stick or release material and thin felt is used as a breather.
In the prototype chamber inexpensive nichrome
infrared lamps were used for heating the laminate. Initial
temperature measurements indicated the presence of hot spots,
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*Dupont Trademark
8
FIGURE 5
LAMINATION SYSTEM
Rubber diaphragm
Upper vacuum chamber
Atmospheric
Eck Fill Valve
— Tcdlar Back Cover
— PVB
— Glass Superstrate
/— Solar Cell Circuit
To vacuum)
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/ I.R. Heater
Laminate Support Grille
Lower Vacuum Chamber
SEQUENCE OF OPERATION
1. Evacuate lower chamber
2. Evacuate upper chamber
3. Backfill upper chamber to atmospheric pressure
4. Heat to 150 0C (302 0F)	 and hold for 15 minutes
5. Backfill lower chamber to atmosphere
5. Remove finished laminate
9
and narrow strips of aluminum foil were strategically placed
improve uniformity. Using 4-1kW lamps a temperature uniformity
of 50C (90F) was achieved over the 1.2 meter (48 inch) length of
the laminate. Tungsten filament lamps will be incorporated into
the production chamber design to eliminate the hotspot problem.
Temperature measurement was made using a very
small thermocouple located against the glass on the front of the
laminate. Correlation :)etween this thermocouple (in vaccuum)
and a thermocouple placed in between the two layers of PVB
indicated a difference of about 15 0C (270F). The proportional
temperature controller was thus increased by 150C to 1500C (3020F)
to compensate for this difference and insure proper lamination
temperature within the PVB.
Good quality laminations were produced typically
in the vacuum region of 1-5 Torr. Quantitative measurement of
the laminate quality was made by performing a 90 0 peel test of
a 2.54cm (1 inch) wide strip of PVB/Tedlar from the glass super--
strate. Peel strengths in the order of 1.1-1.4kg/cm (6-8 lb/in)
were obtained with 2-.38mm (.015 inch) thick layers of PVB. This
compared favorably with laminations made by a high pressure
(12.6kg/cm2 - 180 psi) autoclave process (.9-1.6kg/cm-5-9 lb/in).
Early laminations were allowed to cool under
vacuum to 650C (1500F) since it was thought that edge blow-in
of air would occur while the PVB was still soft. Investigation
of this problem revealed that removal of the laminate at elevated
temperature (1500C) did not result in air blow-in. It was further
determined that the grille on which the laminate is supported did
not require cooling for the next lamination cycle. Since the
glass in the laminate stackup is a relatively poor thermal con-
ductor a new layup could be placed in the chamber and evacuated
before the PVB softened. Premature heating of the PVB before
complete air evacuation can result in sealed-in air pockets.
The cycle time for the complete lamination process has thus been
reduced from 45 minutes to about 30 minutes.
To demonstrate a pilot line capable of producing
12 laminates/hour, a moving carousel with nine lamination chambers
is to be designed and constructed. The first phase design of a
production lamination chamber has been completed and is in
fabrication. The conceptual design of the carousel is complete.
10
i
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2.0 RESULTS AND DISCUSSION
f
During this quarter the prototype lamination
chamber was operated and a process was determined. The
 production laminator was designed. A module design was
selected that is compatible both with automated inter-
connection and lamin. --ion. A major effort in the design/
development of the soldering equipment resulted in signi-
ficant progress on three of the machine elements.
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3.0 FUTURE PLANS
During the next quarter physical and enviornmental
tests will be performed on the 100mm solar cell/i.nterconnect
design. The design and fabrication of the SCAP and SPLP will
be completed and performance testing will be initiated.
12
A^PENDIX A
COLORIMETRIC DETECTION OF ROSIN
TYPE OF TEST:	 Rosin isolation and qualitative
identification using sucrose/
sulfuric acid test.
DESCRIPTION OF TEST: Extract rosin from assembly using
methylene chloride (dichloromethane)
or toluene. Concen a-rate extract by
forced evaporation. Shake extract
with small amount of concentrated
sucrose solution. After addition
of 2-3 drops of concentrated sulfuric
acid, a scarlet red color will develop
if rosin is present.
INTERPRETATION:	 Detection limit of rosin is —.-1.Omg/
liter using this test.
13


Automated solar panel assembly line. LSA task; production processes and equipment

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