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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
Task Force Review / Committee AdjudicationGroup: / Metal Paste for Crystalline Silicon Solar Cells Task Force / China PV Committee
Date: / TBD / March 20th, 2014
Time & Timezone: / TBD / 9:00--18:00
Location: / TBD / Kerry Hotel
City, State/Country: / TBD / Shanghai, China
Leader(s): / Rulong Chen / Guangchun Zhang(CanadianSolar)
Jun Liu(CESI)
Standards Staff: / Kris Shen / Kris Shen(SEMI China)
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 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:
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 toappearance, granularity, solids percentage, viscosity; and the requirements of Al pasteafter 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 Alpaste 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 Standard[1]
4.1.1 IEC61215Crystalline 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 pasteafter firing.
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 thevisual inspection is carried out.
6.2 SolidsPercentage 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 Alpaste 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 sampleintothetared porcelain crucible. Measure the Al paste weight using analytical weighing scale, and record asW0rounded to 0.001g.
6.2.2.2 Place the porcelain cruciblewithAlpaste 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 fromsecond box oven and cooling down to room temperature in a desiccator.
6.2.2.3 Measure the total weight of porcelain cruciblewithAlpaste sampleusing analytical weighing scale again, and record the Al paste weight Wtaccurate to 0.001g.
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 scratchesstart 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 2μm. If the difference is large than 2μm, the third sample shall be tested, and the two bigger readings shall be averaged and recorded as the measurement results.
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 to9 rpmat 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 HBTwith 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 adapterat 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 9.6s−1. Record the reading of viscosity after rotating of 1minute.
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 Figure2). 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.
Figure 1Step 1 of Peel Strength Test
Figure 2Step 2 of Peel Strength Test
6.6 Bowing Test
6.6.1 This test methodcovers 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 highestposition 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 bowingof 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.
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 powderdropped 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)
- 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 1Requirements
No. / Test Items / Requirements1 / 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
8.2.1 Paste property stated in CoA provided upon every delivery shall be still within specification after retesting within 6months 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 Alpaste 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
- 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
13.2 ASTM D1316 – 06Standard 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
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