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Background Statement for SEMI Draft Document 5427
New Standard: SPECIFICATION FOR SILVER PASTE, USED TO CONTACT WITH N+ DIFFUSION LAYER 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 5427
New Standard: SPECIFICATION FOR SILVER PASTE, USED TO CONTACT WITH N+ DIFFUSION LAYER OF CRYSTALLINE SILICON SOLAR CELLS
1 Purpose
1.1 This specification covers the requirements for silver paste (hereafter referred to as Ag paste), used to contact with N+ diffusion layerof crystalline silicon solar cells.
1.2 This specification provides common characteristics of Ag paste based on currently widely used for photovoltaic applications. And this specification also includes requirements for Ag pasteafter firing.
2 Scope
2.1 This specification covers the requirements of Ag paste, including but not limited to appearance, granularity, solids percentage and viscosity, silver layer adhesionand solder ability after firing.
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 Ag 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 ASTM Standard[1]
4.1.1 ASTM B678– 86(Reapproved 2011) Standard Test Method for Solderability of Metallic-Coated Products
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.
5.3 Definitions
5.3.1 Solids percentage —Weight of sample after firing divided by weight of sample.
5.3.2 Adhesion—Silver layer adhesion with silicon bulk after firing
6 Test Methods
6.1 Appearance
6.1.1 This test method is visual inspection of Ag paste. Ag paste to be checked is stirredproperly in as received container by using a spatula for 2 minutes. Then do the visual inspection.
6.2 Solids Percentage
6.2.1 This test method is measurement of the weight percentage of solid in Ag paste by determine of mass difference between before and after firing at suitable temperature and time, which is selected based on the Ag paste firing condition.
6.2.2 Test Procedure
6.2.2.1 After mixing the paste properly, place 0.5~2 g Ag paste uniformly on a tared Al2O3 substrate or in a tared crucible. Measure the Ag paste weight using analytical weighing scale, and record Ag paste weight W0 rounded to 0.001g.
6.2.2.2 Firing Condition:
6.2.2.2.1 Condition 1: Place Ag paste sample and the substrate to first box oven at temperature of 150℃±5℃for 10 minutes, and then move this sample to second box oven, which has been preheated to temperature of 850℃±5℃, for another 10 minutes.
6.2.2.2.2 Condition 2: Introduce Ag paste sample and the crucible into the box oven at temperature of 750℃±5℃gradually to allow the removal of low boiling components without spattering, and then leave the crucible in the hottest zone of the box oven for 20 minutes with the door closed.
NOTE:Condition 1 or 2 is carried out according to agreement between users and suppliers.
6.2.2.3 Remove sample out of box oven and cool the sample temperature down to room temperature in a desiccator.
6.2.2.4 Measure the Ag paste weight using analytical weighing scale again, and record Ag paste weight Wtaccurate to 0.001g.
6.2.3 Calculation
6.2.3.1 Solidspercentage X%is calculated using equation below:
X%= Wt／W0×100% (1)
Wt – Ag paste weight after firing
W0– Ag paste weight before firing
6.2.3.2 Determine the Ag paste solids percentage according to above equation, round to 0.01%. Report the solid content using average of two parallel sample results. The absolute difference value between solids percentage of two parallel samples shall be less than 0.3%.
6.3 FOG Test
6.3.1 This test method covers measurement of the FOG of Ag paste. Ag paste to be checked is spread uniformlyby drawing a straight-edged scraper from thedeep end to the shallow end of the gage. Particlesor agglomerates too large to pass between themoving scraper and the gage path are revealed as “scratches” or “points”, where these occuris read directly on the calibrated gage shoulder. This test method is applicable to any dispersion that is fine enough to fall within the 0–25um range of the specified grind gauge.
6.3.2 Test Procedures
6.3.2.1 Place the material to be tested in the deep end of the path, 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 (see Figure1). Make a reading as suggested in 6.3.4
6.3.3 Readings
6.3.3.1 Streaks will be seen in the reading if particles are present. Count the 4th continuous scratch and observe point at which the material starts to “break” or fade. Where scratches stop and clean area starts, about half and half is called the 50% point.
6.3.3.2 Observe the tapered gage from size at an angle of 20 to 30 degree. Record the depth a of the 4th continuous scratch on the tapered gage, and the depth b where 50% of the area is clean. Report the results as a/b. 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 2um. If the difference is large than 2um, the third sample shall be tested, and the two bigger readings shall be averaged and recorded as the measurement results.
Figure 1FOG Testing
6.4 Viscosity Test
6.4.1 This test method covers the determination of the apparent viscosity of Ag paste by rotational viscometer (Brookfield HBDV viscometer or equivalent). The Ag 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 BrookfieldHBDV III Cone and Plate Viscometer withCPA-51 cone and plate setfollowing 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 plateat temperature within 25℃±0.5℃. Place about 1 gram 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 2 minutes, and then rotate at 1rpm. Record the reading of viscosity after rotating of 1 minute.
6.4.2.3 Repeat viscosity measurement using two parallel samples, and then average these three measurement results. The averaged result shall be rounded to 3 digits.
6.4.3 Test Procedures 2
6.4.3.1 Calibrate the rotational viscometer such as Brookfield HBDV with small sample adapter SC4-14/6 (utility cup & 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 0.5 rpm. Start the viscometer and observe the reading after 3 minutes.Without turning the viscometer off, then turn the control knob to the next shear rate specified and observes the reading after 3 minutes.Repeat this test stepuntil higher shear rates at 10 rpm.Calculate the viscosity by multiplying the scale reading by the appropriate factor.
6.4.3.4 Repeat viscosity measurement using two parallel samples, and average these three measurement results. The averaged result shall be rounded to 3 digits.
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 ofAg paste by determining the force needed to peel the tinned covered copper ribbon away from solar cell substrate. After soldering the fitted ribbonto the front side Ag busbaror continus parts of busbar by assist with the fitted flux, bend the ribbon to 180°±0.5° (parallel to the surface), place the sample onto the test device and fix it with the slotted jig, then pull the ribbon away from the substrate at a fixed speed. The averaged force applied on the ribbon is recorded as the peel strength of the Ag paste.
6.5.2 Test Procedures
6.5.2.1 After soldering the ribbon to the front side Ag busbar, bend the ribbon 180°±0.5°to parallel to the surface, fix the sample on to the test device, and pull the ribbon away from the substrate at speed of 100~300mm/min. Record the average force applied on the ribbon and the ribbon-busbar break mode. The peel strength tester shall record continuously readings of force applied on the ribbon during its peeling away from at least 10mm length busbar. Average the peel force collected on at least four busbarsas the peel strength. The test result unit is N/mm by the peel force divides by ribbon width.
Figure 2
Figure 2 Peel Strength Test
6.6 Solderability Test
6.6.1.1 Test Ag paste solderability according to ASTM B678 – 86 (Reapproved 2011). The specimen to be tested is coated with rosin flux, dipped briefly into molten tin-lead solder, and examined for complete and uniform coverage by the solder. Then record the result as Pass. Otherwise, record the result as Fail. The specimen preparation and the number of specimens, the type of rosin flux and tin-lead solder,shall be decided upon agreement between user and supplier.
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
- Supplier Part number
- Customer part number
- 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 Front side Ag paste property requirements.
Table 1Requirements
No. / Test Items / Requirements1 / Appearance / Uniform silver-grey , no visible inclusions
2 / Solids percentage / Depend on paste recipe, absolute tolerance is±0.5%
3 / FOG (4th scratch / 50%) / <16/8
4 / Viscosity, Pa.s
@25℃ / Depend on paste recipe and test procedure, tolerance is ±15%
5 / Peel Strength / 1.5N/mm
6 / Solderability / Pass
8.2 The specified requirements may change upon agreement between supplier and user.
8.3 Ag paste shelf life requirement
8.3.1 Paste property stated in CoA provided upon every delivery shall be still within specification after retesting within 6months of manufacturing date or shipping date.
9 Sampling
9.1 One bottle of Ag 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 Ag paste shall be added for testing for every increment of 100 bottles of samples. Or samplings as fitted quantity depend on Ag paste manufacture batch.
10 Certification
10.1 Producermay 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/ Shipping Date
(4)Expiry Date
(5)Test Result
- Brookfield Viscosity
- FOG 4th
- FOG 50%
- Solid Content
(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/ Shipping 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
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
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. 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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