Background Statement for SEMI Draft Document 5426
New Standard: SPECIFICATION FOR ALUMINUM PASTE, USED IN
BACK SURFACE FIELD OF CRYSTALLINE SILICON SOLAR CELLS
Notice: This background statement is not part of the balloted item. It is provided solely to assist
the recipient in reaching an informed decision based on the rationale of the activity that preceded
the creation of this Document.
Notice: Recipients of this Document are invited to submit, with their comments, notification of
any relevant patented technology or copyrighted items of which they are aware and to provide
supporting documentation. In this context, “patented technology” is defined as technology for
which a patent has issued or has been applied for. In the latter case, only publicly available
information on the contents of the patent application is to be provided.
Review and Adjudication Information
Group:
Task Force Review
Committee Adjudication
Metal Paste for Crystalline Silicon Solar
Cells Task Force
China PV Committee
TBD
TBD
Time & Timezone:
TBD
Location:
March 20th, 2014
City,
State/Country:
TBD
Shanghai, China
Leader(s):
Rulong Chen
Standards Staff:
Kris Shen
Guangchun Zhang(CanadianSolar)
Jun Liu(CESI)
Kris Shen(SEMI China)
kshen@semi.org
Date:
9:00--18:00
Kerry Hotel
Meeting date and time are subject to change, and additional TF review sessions may be scheduled if
necessary. Contact the task force leaders or Standards staff for confirmation.
Check www.semi.org/standards for the latest schedule.
If you have any questions, please contact the ballot author at:
Arthur Liang/ Suntech
Tel: +86 510 8531 7080
E-mail: zhe.liang@suntech-power.com
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA 95134-2127
Phone: 408.943.6900, Fax: 408.943.7943
DRAFT
SEMI Draft Document 5426
New Standard: SPECIFICATION FOR ALUMINUM PASTE, USED IN
BACK SURFACE FIELD OF CRYSTALLINE SILICON SOLAR CELLS
1 Purpose
1.1 This specification covers the requirements for aluminum paste (hereafter referred to as Al paste) used in back
surface field of crystalline silicon solar cells.
1.2 This specification provides common characteristics of Al paste based on currently widely used for photovoltaic
applications. And this specification also include requires for Al paste after firing.
2 Scope
2.1 This specification covers the common characteristics of Al paste, including but not limited to appearance,
granularity, solids percentage, viscosity; and the requirements of Al paste after firing, including but not limited to
adhesion test, bowing test and hot water test.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their
use. It is the responsibility of the users of the documents to establish appropriate safety and health practices, and
determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 Upon agreement between user and supplier, other additional Al paste property tests than those stated in this
standard can be added into incoming quality test.
3.2 In case of non-conformant of the requirement stated in this SEMI standard or supply agreement, user shall
feedback to supplier within 30 days after receiving paste.
4 Referenced Standards and Documents
4.1 IEC Standard1
4.1.1 IEC 61215 Crystalline silicon terrestrial photovoltaic (PV) modules –Design qualification and type approval
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Refer to the SEMI Standards Compilation of Terms (COTs) for a list of the current Abbreviations, Acronyms,
Definitions, and Symbols.
5.2 Abbreviations and Acronyms
5.2.1 FOG — Fineness of Grind, same as granularity.
5.2.2 BSF — Back Surface Field.
5.2.3 EVA — Ethylene-Vinyl Acetate
5.2.4 TPT — Tedler- PET-Tedler thin film
5.3 Definitions
5.3.1 Solids percentage —Weight of sample after firing divided by weight of sample.
5.3.2 Adhesion — Aluminum layer adhesion with silicon bulk for Al paste after firing.
1
International Electrotechnical Commission, 3 rue de Varembé, Case Postale 131, CH-1211 Geneva 20, Switzerland. Telephone:
41.22.919.02.11; Fax: 41.22.919.03.00; http://www.iec.ch
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Doc. 5426  SEMI
LETTER (YELLOW) BALLOT
Document Number: 5426
Date: 2/9/2016
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Phone: 408.943.6900, Fax: 408.943.7943
DRAFT
6 Test Methods
6.1 Appearance
6.1.1 Al paste to be checked is stirred in as received container by using a spatula properly for 2 minutes. Then the
visual inspection is carried out.
6.2 Solids Percentage test
6.2.1 This test method covers measurement of the weight percentage of solid in Al paste by determine of mass
difference between the Al paste before and after firing.
6.2.2 Test Procedure
6.2.2.1 After mixing the paste properly, place 0.5~1.0g Al paste sample into the tared porcelain crucible. Measure
the Al paste weight using analytical weighing scale, and record as W0 rounded to 0.001 g.
6.2.2.2 Place the porcelain crucible with Al paste sample into first box oven at 150℃±5℃ for 30 minutes, and
then move into second box oven, which is preheated to temperature of 500℃±5℃ for another 30 minutes. Finally
move out from second box oven and cooling down to room temperature in a desiccator.
6.2.2.3 Measure the total weight of porcelain crucible with Al paste sample using analytical weighing scale again,
and record the Al paste weight Wt accurate to 0.001 g.
6.2.2.4 Calculation
6.2.2.4.1 Solids percentage X% is calculated using equation below:
X% = Wt ／W0 ×100%
(1)
Wt – Al paste weight after firing
W0 – Al paste weight before firing
6.2.2.4.2 Determine the Al paste solids percentage according to above equation, round to 0.01%. Report the solid
content using average of three parallel sample results. The absolute difference value between solids percentage of
three parallel samples shall be less than 1%.
6.3 FOG Test
6.3.1 This test method covers measurement of the FOG of Al paste. Al paste to be checked is spread uniformly by
drawing a straight-edged scraper from the deep end to the shallow end of the fineness gauge. Particles or
agglomerates too large to pass between the moving scraper and the gage path are revealed as “scratches” or “points”,
where these occur is read directly on the calibrated gage shoulder. This test method is applicable to any dispersion
that is fine enough to fall within the 0–50 μm range of the specified grind gauge.
6.3.2 Test Procedures
6.3.2.1 Place the Al paste to be tested in the deep end of the path, or paths, so that it overflows the path slightly.
When using the double-path gage, place material in both paths.
6.3.2.2 Holding the scraper in both hands, nearly vertical but inclined slightly toward the operator, draw the
material down the length of the path toward the shallow end of the gage with a uniform, brisk motion in
approximately 1 to 3 s. Exert upon the scraper only sufficient pressure to clean excess material from the face of the
gage. Make a reading as suggested in 6.3.3.
6.3.3 Readings
6.3.3.1 Streaks will be seen in the reading if particles are present. Observe the scratch where it starts to appear.
6.3.3.2 Observe the tapered gage from size at an angle of 20 to 30 degree. Record the depth where two longitudinal
continuous scratches start to appear on the tapered gage. Report micrometer readings to the nearest multiple of 1μm.
6.3.3.3 The measurement shall be repeated on two parallel samples, and take average of these two samples, if the
difference between these two measurements is less than 2 μm. If the difference is large than 2 μm, the third sample
shall be tested, and the two bigger readings shall be averaged and recorded as the measurement results.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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LETTER (YELLOW) BALLOT
Document Number: 5426
Date: 2/9/2016
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Phone: 408.943.6900, Fax: 408.943.7943
DRAFT
6.4 Viscosity Test
6.4.1 This test method covers the determination of the apparent viscosity of Al paste by rotational viscometer
(Brookfield viscometer or equivalent). The Al paste viscosity is determined by measuring the torque on the cone or
spindle at a constant rotation speed in the material at controlled temperature. There are two test procedures as follow.
6.4.2 Test Procedures 1
6.4.2.1 Calibrate the rotational viscometer such as Brookfield CAP2000+ with CAP-8 or other suited cone and plate
following equipment calibration procedures, with measurement error of the rotational viscometer being less than ±
1% in the full scale range, and repeatability of torque being less than ±0.2%.
6.4.2.2 Maintain the cone and plate at temperature within 25℃±0.5℃. Place about 1g paste uniformly on the
center of the plate, and load the plate onto the equipment. Upon sample loading onto the viscometer, maintain the
sample motionless for 5 s, and then step by step rise the rotate rate to 9 rpm at the shear rate of 18 s−1. Record the
reading of viscosity after rotating of 30 s.
6.4.2.3 Repeat viscosity measurement using two parallel samples, and then average the two measurement results.
The absolute difference between viscosities of two parallel samples shall be less than 3%.
6.4.3 Test Procedures 2
6.4.3.1 Calibrate the rotational viscometer such as Brookfield HBT with CP-51 or other suited spindle following
equipment calibration procedures, with measurement error of the rotational viscometer being less than ±1% in the
full scale range, and repeatability of torque being less than ±0.2%.
6.4.3.2 Maintain the small sample adapter at temperature within 25℃±0.5℃. Load the cup with a well, but gently,
mixed sample so that when the spindle is inserted in the cup, the level will rise to the top of the cup but not above.
In no case should the level be below the small ridge, which is 1/8” above the top of the bob. Be sure there are no air
bubbles or voids in the sample as this will result in false readings. Assemble the cup and spindle to the viscometer.
The sample has to reach the correct temperature. If no incubator can be used, wait 5-10 minutes in the water bath.
6.4.3.3 Set the speed control knob to the speed indicated at 5 rpm. Start the viscometer and observe the reading after
5 minutes. Then back down to 2.5 rpm at the shear rate of 9.6 s−1. Record the reading of viscosity after rotating of 1
minute.
6.4.3.4 Repeat viscosity measurement using two parallel samples, and then average the three measurement results.
The absolute difference between viscosities of two samples shall be less than 3%.
NOTE: Test Procedures 1 or 2 is carried out according to agreement between users and suppliers.
6.5 Peel Strength Test
6.5.1 This test method covers measurement of the peel strength of Al paste by determining the force needed to peel
the aluminum layer away from solar cell substrate.
6.5.2 Prepare a piece of glass, two pieces of EVA films and a piece of TPT backsheet (This encapsulation materials
combination should be certificated according to IEC61215 standard). Lay the above materials and the solar cells
from the bottom up in this order: glass, EVA, solar cell (BSF upward), EVA, TPT backsheet (see Figure 1).
6.5.3 Follow normal module manufacture process to laminate the solar cells to a module, cooling and stabilize the
module to room temperature for 12 h after lamination. Then, cut the TPT backsheet into 1 cm×30 cm strips.
6.5.4 Separate the TPT backsheet and solar cells by manual for a length of about 2 cm and bend the TPT backsheet
backward 180 degrees to parallel to the BSF (see Figure 2). Fix the sample on to the test device, and pull the TPT
away from the substrate at a speed of 120 mm/min. Record the average force applied on the TPT peeled away for a
10 cm length. Average the peel force collected on at least two sample strips (10 cm×2) as the peel strength.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Document Number: 5426
Date: 2/9/2016
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Phone: 408.943.6900, Fax: 408.943.7943
DRAFT
TPT
EVA
Solar Cell (BSF upward)
EVA
Glass
Figure 1 Step 1 of Peel Strength Test
Figure 2 Step 2 of Peel Strength Test
6.6 Bowing Test
6.6.1 This test method covers measurement of the bowing of the solar cell, which is mainly caused by the
difference of expansion coefficient of silicon and aluminum.
6.6.2 Test Procedures
6.6.2.1 Put the finished solar cell on the flat platform with the BSF downward.
6.6.2.2 The part of the solar cell to be checked is the highest position against the platform by feeler gauges. Choose
one of the smaller blades, and try to insert it in the gap between the chosen part and the platform. If it slips in and
out easily, choose the next size up. If the feeler gauge feels too tight, select a smaller size. Repeat this procedure
until the feeler gauge fits snugly in the gap. For each sample, the test should also be done on the opposite side of the
cell. The average of the two is the bowing value round to 0.1 mm.
6.6.2.3 One can stack a combination of feeler gauges to gauge intermediate values. While doing the measurement,
make sure that the solar cell won’t be moved. Record the markings on the blade or the total value of the combined
feelers.
6.6.2.4 The measurement shall also be repeated on three parallel samples. Report the bowing of the solar cell using
the average of three parallel measurement results.
6.7 Hot Water Test
6.7.1 This test method covers measurement of the anti-humidity ability of the solar cell, which is mainly caused by
the TPT backsheet water permeability.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
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Document Number: 5426
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Phone: 408.943.6900, Fax: 408.943.7943
DRAFT
6.7.2 Test Procedures
6.7.2.1 Put the finished solar cell into the hot DI water at 70℃and keep 10 minutes. Then observe whether bubbles
were generated and rise from the aluminum film layer because of chemical reaction between the aluminum film
layer with DI water. When bubbles were generated, the sample was marked X and when the bubbles were not
generated from the sample, the sample was marked O. In the hot water test, the generation of bubbles indicated that
the electrode was highly reactive with moisture in air or had low stability, thereby causing deterioration in reliability
of a solar cell module.
6.7.2.2 At the same time, the operator observes whether aluminum powder dropped from the aluminum film layer.
When the aluminum powder were dropped, the sample was marked X and when the aluminum powder were not
dropped from the sample, the sample was marked O.
6.7.2.3 The Al paste sample get two marked O from ¶¶ 6.7.2.1 and 6.7.2.2, then record the result as Pass. Otherwise,
record the result as Fail.
6.7.2.4 The measurement shall also be repeated on two parallel samples. Report the hot water test of the solar cell
using three measurement results.
7 Ordering Information
7.1 Purchase Order (PO)– user shall provide the following information on the PO:

Sold to address

Ship to address

Invoice to address

Order quantity

Delivery date

Quoted price

Customer PO number

Payment term

Incoterm ( DAP, Ex-work)
7.2 User and supplier may establish additional supply agreement other than this SEMI standard.
8 Requirements
8.1 The requirements for Al paste are listed in Table 1.
Table 1 Requirements
No.
Test Items
Requirements
1
Appearance
Uniform silver-grey , no visible inclusions
2
Solids percentage
Depend on paste recipe, absolute tolerance is ±3%
3
FOG
≤25 μm
4
Viscosity, Pa.s
@ 25℃
Depend on paste recipe and test procedure, tolerance is ±15%
5
EVA peel strength
≥ 15 N/cm
6
Bowing test
≤2.5 mm
7
Hot water test
All pass
The specified requirements may change upon agreement between supplier and user.
8.2 Al Paste Shelf Life Requirement
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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LETTER (YELLOW) BALLOT
Document Number: 5426
Date: 2/9/2016
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Phone: 408.943.6900, Fax: 408.943.7943
DRAFT
8.2.1 Paste property stated in CoA provided upon every delivery shall be still within specification after retesting
within 6 months of manufacturing date.
9 Sampling
9.1 One bottle of Al paste shall be randomly selected for testing by user when total sample number is less than 100.
In case total sample number is larger than 100, one bottle of Al paste shall be added for testing for every increment
of 100 bottles of samples.
10 Certification
10.1 Producer may declare the conformant of RoHS for the restriction of the use of certain hazardous substance.
10.2 Producer may provide certificate of analysis (CoA), which shall include information:
(1) Product name
(2) Lot ID
(3) Manufacturing Date
(4) Expiry Date
(5) Test Result

Viscosity

FOG

Solid Percentage
(6) Company Contact
(7) Suggested Storage Condition
11 Product Labeling
11.1 Product labeling – producer shall provide the following information on product label:

Product Name

Lot ID

Quantity

Manufacturing Date

Expiry Date

Warning/Precaution Note

Company Contact

Suggested Storage Condition
11.2 Additional information can be added on label upon agreement between user and producer.
12 Package and Package Labeling
12.1 Package method – Pack jars in regular slotted carton box made of corrugated material with polyethylene foam
insert, or equivalent or better package method, subject to user and supplier agreement on package requirement.
12.2 Package labeling – Follow the practice set in product labeling.
13 Related Documents
13.1 ASTM D1210 - 05(2010) Standard Test Method for Fineness of Dispersion of Pigment-Vehicle Systems by
Hegman-Type Gage
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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LETTER (YELLOW) BALLOT
Document Number: 5426
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DRAFT
13.2 ASTM D1316 – 06 Standard Test Method for Fineness of Grind of Printing Inks By the NPIRI Grindometer
13.3 ASTM D2196-1999 Standard Test Methods for Rheological Properties of Non-Newtonian Materials by
Rotational (Brookfield Type) Viscometer
13.4 DIN EN ISO 1524-2002 Paints, varnishes and printing inks - Determination of fineness of grind
NOTICE: Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as
to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The
determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. Users are
cautioned to refer to manufacturer’s instructions, product labels, product data sheets, and other relevant literature,
respecting any materials or equipment mentioned herein. Standards and Safety Guidelines are subject to change
without notice.
By publication of this Standard or Safety Guideline, SEMI takes no position respecting the validity of any patent
rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of
this Standard or Safety Guideline are expressly advised that determination of any such patent rights or copyrights,
and the risk of infringement of such rights are entirely their own responsibility.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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