SOLAR

I had a call with a few engineers today who wanted me to answer a question, “Which solder paste do I pick for my application.” Sure there were a few application-specific details that I feel were too specific to discuss with a general audience, but I think I can answer the question for any of you that are out there wondering the same question while reading this.

It’s an easy answer really; start with SR-8 unless:

1)     You are using laser reflow equipment.

2)     You have noticed solder spatter issues related to your design.

3)     Your company or end customers require you to use only halogen-free materials

4)     The residue must be clear and almost non-existent (ultra-low residue levels)

If you said “yes” to any of the above, you’ll want to try SR-7 (as long as you have nitrogen reflow capability). If you said yes to answer 3 (halogen-free) but you do not have nitrogen reflow capability, try SR-089.  

Jim’s note: This post was written in August 2010 – but it will be available to anyone searching for the info for quite some time. For updated information on newer solder pastes, send an email to Solar@Indium.com. Thanks! ~Jim

Some people collect stamps, or coins, or baseball cards – my father collects hardware. Almost every time I go to my parent’s house I notice a few jars or boxes of bolts, nuts, screws, washers, and clamps. They are bought in bulk and sorted by size. I used to think it was ridiculous to do this, but my Dad actually uses enough of the hardware to save money, and I have never needed to run to the store during a project to get a special size piece of hardware. An old bolt may not look as pretty as a new bolt, but in applications that are simply for utility, an old bolt works just as well.

Solar panels that do not live up to visual specifications also share a utility, much like old bolts. They are certainly cheaper - and for a solar farm, small imperfections may not matter to the customer.

So now it’s my time to collect something. I’m not looking to collect old hardware or utility grade solar panels, I’m searching for the different criteria that module assemblers use to determine if modules are fit for residential or commercial use. This information can be used to help set the (IPC) standards for the industry. If you have information that could help, please send it to jhisert@indium.com. Thanks! 

As many of you know, I’m focused on applications for the solar industry and the semiconductor industry. In fact, many of the readers of this blog have spent a good amount of time working in both fields as well. Dr. Ernest Levine is just like us, except he makes these topics way more interesting to learn about than I have figured out how to do yet…

Whether you’re learning about semiconductors or solar cells for the first time, you’re planning on learning more, or maybe you just want a refresher course – check out one of these courses in October. The IC Fabrication Class is offered Oct. 12-13 and the Photovoltaic Class is offered Oct. 26-27.

Back in 2008 I attended the IC Fab class and interviewed Ernest to learn more: http://blogs.indium.com/blog/jim-hisert/0/0/ic-fab-course.

I’ve been pulling some products together for the InterSolar tradeshow in July, and a thought occurred to me: “these tabbing ribbon kits for solar panel assembly are so interesting, I know someone at the show is going to want one”. If you’ve been in a booth at a tradeshow before it’s probably happened to you too – someone may have asked you for one of your display items, last pieces of literature, or maybe some ancillary equipment that you had at your booth. For argument sake, let’s say it’s the only sample of a hot new product at your booth, and the customer wants to purchase it with cash and walk away with it on the spot. (Equipment guys have been known to frequently sell the equipment they had brought to the show, but they send the machine after the show is over.) So what do you do if someone wants to purchase the item you have on display?   

A second question from a different perspective: as a customer, how would you feel if the vendor wouldn’t sell that one display item that you’d like to leave the show with?

I’m really excited about a new option for those of us who are prototyping solar assemblies or evaluating new tabbing ribbon materials. I’ve been waiting for something like this – everything you need to solder solar cells together in one package. The turn around time is key too – you may recall an older post where I learned how quickly these materials shipped.

On the website where these kits are offered, the description reads:

“Tabbing ribbon kits come with everything you need to evaluate how Indium Corporation materials will work with your solar cells and assembly process. The kits can be used to:
- Evaluate which tabbing ribbon size is best for your design
- Determine which flux is best for your operation
- Experiment with new solder coating alloys
- Assemble a few solar panels”

The tabbing ribbon kits come in 3 flavors:

- Standard Sn/Pb/Ag (62Sn/36Pb/2Ag)

- Pb-Free (96Sn/4Ag)

- Low Temp Pb-Free (58Bi/42Sn)

I have a feeling the Low Temp Pb-Free kits are really going to be the most popular of the 3 that are offered though. Application temperature ranges will determine which kit to use, but all three versions of the kits are said to offer similar base copper sizes and tolerances:
“The ribbon itself is industry standard CDA 110 (99.9% Cu) core flat wire, coated with a precisely controlled layer of solder. Each ribbon is manufactured using our proprietary softening process so you can increase the yield of your stringing process.” Basically, this means that the softer tabbing ribbon will help eliminate the breakage of thinned cells during the heating/cooling cycle.

It also includes some matching bus ribbon to complete your panel build. If you’re trying to find the right flux, this kit serves dually as a flux evaluation kit as well. The kit is loaded with VOC-Free flux, rosin-based flux, and resin-based tabbing fluxes. I prefer GS-5454 as a flux for most tabbing operations, but you can see how the others stack up as well.

Let me know how you like the kit after you try it out!

~Jim

(jhisert@indium.com)

在中國，現在還是厚膜太陽能光伏技術佔主導(Thick Film Solar PV)。所以，Indium公司相對成熟的太陽能產品中，也就是鍍錫銅帶（Tabbing Ribbon or Bus Ribbon）的生意機會比較多了。 

镀锡铜带是韌銅，單面或是雙面再鍍上一層含錫的合金薄層，用於焊接。常用的鍍錫層有：

• Sn63 Pb37
• Sn96.5 Ag3.5
• Bi46 Sn34 Pb20
• Bi58 Sn42
• Bi57 Sn42 Ag1

含有鉍(Bismuth Bi)鍍層的銅帶，適用于對高溫比較敏感的光伏太陽能板子的硬化，特別是薄膜技術的板子。



Video: Youtube

最近Indium 公司第一次成功參展了SNEC 第四屆(2010)國際太陽能光伏大會（上海）。 同事回來分享他的大概感受：

1．  展會的規模比Nepcon還要大好幾倍！(Nepcon是中國SMT行業的盛會)

2．  整個中國太陽能生産組裝產業鏈各個環節都相對成熟並具有規模。

3．  太陽能產業中的核心技術（光電轉換率什麽的）做得強的，目前還不在中國。

Indium公司在展會中，主要推出了三款成熟的產品：

1．  前端的太陽能板子製造：CIGS Target 铜铟硒化镓濺射靶， 和Metallization Paste含銀導電漿料。這兩款產品都主要是針對薄膜太陽能光伏技術的板子的。(Thin-Film Solar Panel)  

2．  后端的太陽能板子組裝：Tabbing Ribbon 鍍錫銅帶。這是太陽能板組裝所用到的材料。

Cheers!  



Pic: Indium Corporation

Wandering through the references to indium metal on the internet, I sometimes see it referred to as, "that 'rare' metal."  But is it really so rare?  I recently talked to my colleague, Claire Miko, Director, Metals and Chemicals for Indium Corporation and asked if the reports of the rarity of the metal (like the death of Mark Twain) were greatly exaggerated.

Question:  The element indium is widely used today in many electronic (glass coating, low temperature solder, hermetic sealing and thermal interface material) and solar applications (CIG solar panels), but very little is known about it.  Can you tell us where indium metal comes from?

Claire:  Indium is a by-product of several base metals such as zinc, lead, copper, tin and other poly metallic ores. It is very abundant on the crust of the earth (much more than silver for example and the annual silver production is at least 40 times bigger than the annual indium production). Geographically indium is abundant in South America, Canada, Australia, China and the CIS, i.e. the reserves are widely spread.

 
Question:     Does indium have to be refined after it is mined?

Claire:    Indium is present in the base metal ores at ppm levels. It first needs to be separated from the base ore and concentrated. This is done at the base metal smelter (for example during the refining of zinc, lead, copper, tin etc). It is then further refined and purified at indium refineries.

Question:  Indium Tin Oxide (ITO) is the one of largest indium-containing products today.  How much of the indium mined goes to making ITO?

Claire:   About 50% of the indium refined is used for making ITO. A larger percentage is needed to start the ITO target productions but the sputtering process used (when putting the ITO layer onto the glass) is inefficient and generates a large quantity of indium which is reclaimed and is then recycled and put back into circulation.

Question:     Is there enough indium available to meet the current and future needs of the marketplace?

Claire:   The indium production has always expanded to meet growing demand. Indium production grew from 70MT (metric tonnes/year to over 500MT/year over the last 20 years. At the moment only one-third of the indium mined yearly is being refined in indium metal, another third accumulates in residues that are more expensive to treat but they remain available for future processing, and the last third is currently lost because it does not reach a base metal smelter which has the equipment to separate it from the base metal ore. Investments at these smelters would enable the extraction and refining of these quantities if the need arose.

Question:    Are there recycling programs in place to recover unused ITO from the targets used to deposit it onto the glass surfaces where it is used?  What is the rate of recovery?

Claire:   There is ample capacity to treat spent ITO targets (as per point 3) and the recovery process is now mature and very efficient. The cycle time of this process has also now become very short enabling a very quick return of the refined indium for new consumption.

Question:    Are there any viable alternatives to ITO?

Claire:   A far as we know ITO remains the best material for LCD and other flat panel displays applications. It offers the best performances in terms of optical transparency, electrical resistivity, uniformity of both transparency and resistivity, chemical and mechanical stability, resistance to corrosion, and, finally, uniformity of etching.

The cost of the ITO on 42” TV represents less than $2 and less than 1% of the display cost. It is a small cost to pay to ensure that the quality of the display is maintained. Alternative materials have shown significant process problems with resistivity, uniformity and chemical and mechanical stability.

I should take a minute a publicly thank our solar tabbing ribbon engineers for doing an excellent job today. We needed 6 different tabbing ribbon and bus ribbon spools for a project - so I contacted production mid-morning. By the afternoon, I had all the material I needed re-spooled and delivered to my desk.  Wow! I know these guys are fast, but I didn’t expect it to be that instant.

Thanks guys!

~Jim

In the surface mount technology (SMT) electronics and semiconductor packaging industries, Indium Corporation has a reputation for offering custom solutions.  In the world of solar cell manufacturing, I hope that same status is obvious.  I feel custom solutions are even MORE important in emerging technology fields like CIGS cell manufacturing.  Being the leading global supplier of indium (the metal), and a supplier of unique solder alloy shape/size/tolerance forms, we are well equipped to offer you evaporation sources that are tailored to your application.  Sure, we can supply round shot, teardrop shot, wire, ingot, preforms, and various other bulk forms of solder to keep your evaporation chamber filled.  Did you know we can also make custom solder castings to fit your particular crucible?  The process is easy, let us know if you are interested!

(Just click here to get started)

The SNEC 4th International Photovoltaic Power Generation Conference & Exhibit in Shanghai is known as one of the BIG solar shows of the year. Indium Corporation’s Bill Jackson (Director of Solar Products) commented that the 2010 SNEC was: "A busy, well attended show exuding with confidence about the beginning of a worldwide economic recovery and good solar-related growth for the foreseeable future".  That’s good to hear! Luckily, we had a strong team there to handle technical inquiries. Attendees from Indium Corporation included:

• Bill Jackson
• Thomas Tong
• William Aw
• Tommy Fan
• Michael Qiu
• David Hu

Even Indium Corporation President Greg Evans stopped by to visit the booth, to network, and to take the pulse of the industry.

This year, the SNEC was especially important for us. We had a chance to show off some of our new technology and sputtering target capability. The visitor interest seemed to mirror this thought with “…high interest in rotary CIG (Copper Indium Gallium) and Cu-Ga targets, also high interest in target bonding with NanoFoil®".

I also wanted to take a second to thank the people behind the scenes that help to make shows like this possible. Special thanks to Bill Wilson for helping to make sure our display targets looked their best, Gene Loparco and his team for dealing with the logistics of transporting our materials to/from the show, and Anita Brown for helping out with the details of coordinating the show.  These Indium Corporation employees help us all shine at solar trade shows!

~Jim

The Society of Vacuum Coaters 2010 technical conference took place last week, so this week I’ve been rounding up the display sputtering targets and evaporation sources to display at our next event in China. If you’re not familiar with it, the SVC (Society of Vacuum Coaters) conference focuses on deposition materials, equipment, and processes. The Indium Corporation has a specific interest in both sputtering and thermal evaporation since we provide materials for these processes. There are too many applications to list, but some specific sputtering/evaporation apps that are close to my heart are:

• Absorber layer (ex. Copper Indium Gallium) for thin film solar cells
• TCO layer (ex. Indium Tin Oxide) deposition – also for the solar industry
• Sputtering target bonding with NanoFoil®

Last week we set up a very impressive array of sputtering targets (shown in the picture), so I hope they all make it safe and sound to SNEC next week!

~Jim

This blog has been in existence for a little over two years now, and we would like to thank our readers for the feedback and inquiries you have provided. I welcome your comments on what you would like from us. Leave a comment below, or email me at jhisert@indium.com.

And now a look back on past topics of interest:
 

Grid Ink, Silver Ink, Conductive Ink

Bismuth/Tin Tabbing Ribbon, A Low Temperature Pb-Free Alternative

Plated Metallization for C-Si Solar Cells

Increase Packing Density for Evaporation Crucibles

Photon’s 5th PV Tech Show 2010 USA

IPC Solar Standards Update

Solder Shelf Life as Explained by Eric Bastow

Tips to Speed Your Solder and Flux Selection

What's Happening in the Technical Service Department 

A Day in the Life of a Tech Guy

A Clean Laboratory

CIGS for Beginners

3rd Renewable Energy Expo 2009 in New Delhi, India

Solar Products and Representatives

Kleenex®, Google™, FedX®, CIGs?

Indium Solar Products Reunited

Trade Show Visitors Love the Ground Floor

Solar Product Data Sheets

Intersolar 2009 – What Barrier to CIGS Technology?

Concentrator Photovoltaic Systems - Will they reach 50% Efficiency?

Standards for Solar Panel Manufacturing

Solar Panel Certification: “Barrier and Benefit” Reviewed by Eric Bastow

Low Temperature Metallization Paste

What Will Your Interest Be At InterSolar? Meet the Bloggers And Let Us Know.

Share Your Solar Images

SAC vs. Sn/Ag for Solar Soldering

Solder Thickness for PV Interconnect

What is Bus Ribbon?

Standard PV Interconnect Ribbon Sizes

No-Clean Flux

Photovoltaics in EMS Sector

PV Interconnect Products

Eric Bastow - East Coast Technical Support

Mario Scalzo - West Coast Technical Support

Au/Sn Sputtering Targets

SMT Goes Solar

A Trip Down Memory Lane 

More Information About Metallization Paste

A year in the Life of a Solar Blog

CIG Target

23rd European Photovoltaic Solar Energy Conference and Exhibition

TCO choices for CIGS manufacturing 

CIGS Absorber Layer Electroplating

No Slump Metallization Paste

Meet the Bloggers

CIGS - Can sputtering make a breakthrough?

Fluxes for Soldering Tabbing Ribbon

Computer Brain vs. Solar Photovoltaic

Beam it down from space

Selection of the Optimum Lead-Free Solder for Solar Tabbing Ribbon

Record Makes Thin-Film Solar Cell Competitive with Silicon Efficiency

Why Thin-Film Solar Cells are Here to Stay

Hot Rooftops to Flashy Digital Cameras

Synchronize Your Solar Cell

Solar Conversion Efficiencies  

Government Support is the Key

It's Just a Beginning ...

Whatever you call it, low temperature metallization paste is the silver- (Ag) filled material used to electrically connect thin film solar cells. So why does it go by so many names? Perhaps because it is a relatively new product with no industry standards referencing it. (Feel free to leave a comment if a standard is added…) For a very short period of time, silver ink was planned to be included in the upcoming IPC solar standards: ‘IPC PV Module Technical Standards Committee’.  It was recently decided that the standards would initially focus on C-Si module assembly – thin film assembly may be included in later revisions.

So who is right? Honestly, we are quite accustomed to calling it ‘metallization paste’, but we know what you are talking about if you use the other terms or describe what you are looking for. I think that in future blog posts you will notice Indium Corporation using the terms ‘grid ink’, ‘silver ink’, and ‘conductive ink’ much more to describe the material, since all those terms are correct. What term do you think best describes this material?

Okay, I have a confession to make: I’ve always had a grudge against bismuth, ever since I started recommending thermal interface materials. It is the polar opposite of my favorite element (indium) – well, as much as a metal can be. These 2 elements (indium or bismuth) are added to almost every solder with a lower solidus temperature than Sn/Pb. The choice for most thermal interface applications that I have dealt with was indium or an indium alloy, but now I am starting to become very fond of my new friend bismuth for solar applications.

Bi/Sn and Bi/Sn/Ag are now available as a solderable coating for our Tabbing and Bus Ribbon. After getting a feel for this material, I must say I find it pretty nice to work with. Both alloys melt at 138-139degC, with the Bi/Sn/Ag having a greater tensile strength (which is not necessarily a good thing for tabbing ribbon). With a little bit of lab time I have isolated an existing flux that works very well with these alloys. So far GS-5454 has formed good solder bonds down to 160degC. This is great news, because it allows you to minimize the reflow temperature (and stresses) of your C-Si/tabbing ribbon interface. 

~Jim

The latest issue of Circuitree Magazine came to me the other day and it was clear that this issue had a solar assembly focus. The cover story “Photovoltaics, The Great Illumination” was admittedly a very generic title, I didn’t expect much more than some ‘bright future of solar’ marketing outlook – I’m so glad I kept reading.

The article (written by Don Cullen of MacDermid) was a well-written introduction to Nickel, Copper, Silver plated conductors as a replacement for the traditional Ag/glass frit material and process. This metallization offers various benefits as outlined in the article, but why am I so excited? The same reason you should be, this should be an easier and more reliable surface for soldering tabbing ribbon. Instead of the partial Ag surface, the plated conductors offer a 100% solderable surface.  

This is an image of a nickel seed layer on monocrystalline silicon 'pyramids'.  The first step in building this metallization.
 

Don had this to say about plated metallizations: "The standard method for conductor formation on silicon solar cells is too wasteful, too expensive, and too restrictive for really widespread deployment of solar cells on the world's rooftops.  We need to make the same leaps in technology that the circuit board and semiconductor industry have made time and time again.  We need the elegant design of plated metal conductors.  The superior contact, improved adhesion, predictable soldering, and excellent conductivity of a nickel, copper, silver conductor will allow the strong, consistent, cost-effective cells that will change our planet's thinking about energy."

In an evaporative deposition process, source material is evaporated and then condensed onto a substrate which is being coated. One of the common uses that our solar team encounters is the deposition of indium (provided as shot) for CIG thin film technology.

It’s an easy concept: if you can fit more indium shot in a given crucible, the evaporation process can run for a longer period of time before material needs to be added. The traditional form of solder shot is a teardrop shape, which is easy to produce as a bulk form of solder. 

A newer version of shot is now available without the tail, we call this ‘round’ or ‘tailless’ shot. This material is similar to solder spheres, but not as precisely spherical. Compared to traditional shot, round shot offers a packing density increase of 15% - 20%. This means you can fit more source material in a given crucible, which can keep your evaporation process running longer, more efficiently, and more profitably.

After returning from San Francisco, I’ve had a chance to think about the Photon PV Technology show. This show was hosted at the Moscone Center, which also hosts the rapidly expanding Intersolar show each summer. Other than location and industry, these two shows have little in common.

With only 6 active aisles, the Photon show was easy for most visitors to cover in only half of a day. Since many exhibitors chose not to bring equipment, there wasn’t really a lot to see either. The silver lining to all of this to a visitor – you could spend a good amount of time at almost any booth you wanted without feeling rushed or distracted by a crowd of people. It was a good atmosphere to discuss technology.

I like to see other versions of the products I work with, so it was a let down to only see one booth with tabbing ribbon at the bottom of a display, and no solar sputtering targets (there was 1 target there, but it was aluminum – used to show equipment utilization.) 

The price to just attend the show was almost nothing ($29) although that doesn’t cover the exciting part the technical conference. It’s common to charge extra for admission to the tech sessions at shows, but over $600 per day for 3 days (if my memory serves me correctly) is a huge burden on an engineer that needs to justify that cost to his boss. In my opinion the conference attendance was crippled by this cost.

Will this show survive? After discussing this question with others at the show, the idea of combining the Photon USA and APEX shows began to sound very logical. The point was made during discussion, that APEX is starting to have a small solar focus and the Photon attendance seems to fill that need. Another good argument for the combination is that some of the OEM engineers and material suppliers go to APEX anyway, this is a good way to eliminate one costly trip.

Last week some familiar (and some new) faces from the electronics industry met in San Francisco to set standards for the assembly of solar modules. This group, the “IPC PV Module Technical Standards Committee”, is comprised of module assemblers/OEMs, consultants, equipment makers, and materials suppliers. We aim to remove non-value-added processes and provide a common set of terms and practices, including acceptance criteria for different aspects of both incoming materials and finished product.

Much of the work done in this meeting was identifying and specifying defects throughout the module assembly process. This is where a diverse group of engineers really makes a difference. The group, having seen the module assembly process from many angles, worked together to fill in the gaps that would have been otherwise gaping if any one of us had tried to tackle this task by ourselves.  One attendee may know almost everything there is to know about lamination materials, or tabbing ribbon, or cell specifications, or the assembly procedure, but there is sure to be someone that knows more about the other topics.  This group had all those areas of expertise covered.

Pivotry Consulting had this to say about the event:

”The IPC Technical Standards Committee Meeting for Solar PV Modules was held February 1, 2010 in San Francisco.  This new committee is focused on supporting the PV panel manufacturers by providing baseline standards for manufacturing process defects from solar cells, cell assembly/stringing, substrate glass, deposited films, lamination, framing and assembly, junction box, and final panel assembly.  Contributing panel manufacturers at this meeting included Q-Cells, SoloPower and Trina Solar.  Many companies in the value chain included Burkle, Celestica, Jabil, Flextronics, Indium Corporation, Christopher Associates, 2BG Solar, and Atlas Materials Testing Solutions.  An initial and partial defect dataset was also provided by CEP Solar.  This was just the third meeting of the Committee.  The meeting minutes will be provided on the IPC website.  With the recent explosion of panel manufacturers entering the market in the past couple of years (total over 400 worldwide), this manufacturing industry is racing to capture opportunities…and the adoption of Standards as developed from such committees as this one will undoubtedly help these manufacturers be even more successful by reducing costs.”

I feel that this meeting really warmed up quickly, and the new members had a great deal of input. There really aren’t that many events where a new member can step into a group of professionals and feel this comfortable and empowered. We all learned from our peers, and everyone had a lot to offer to the group.

~Jim