Jim Hisert

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)

Indium Corporation has won the Innova Award for Best Technology for its Heat-Spring^® metallic thermal interface material (TIM).

Heat-Spring is a clean, high-performance thermal solution for the increasing demands of high brightness LEDs. It is a compressible metal foil with proven performance in such demanding environments as electronics, aerospace, and power devices.

The compressible TIM provides low thermal resistance as a result of its high thermal conductivity (86W/m-K) and its ability to conform intimately to interface surfaces.

Unlike other thermal interface materials, such as thermal grease that bakes out, dries out, or pumps out during use, the thermal resistance of the Heat-Spring continues to improve with time and power cycling.

According to Jordan Ross, Market Manager for Thermal Materials, “Indium Corporation is honored to be recognized with the Innova Award for our patented Heat-Spring product. With its patented compressible interface design, Heat-Spring provides optimized surface contact, superior thermal conductivity, and enhanced heat flow.”

Sponsored by LED Journal, the Innova Awards feature leading companies within the LED market which have shown, through their products and services, the most innovative and advanced technology breakthroughs in LEDs. The award is designed to recognize companies each year for industry leadership, product development excellence, best new technology, and outstanding LED applications, which will eventually lead to the widespread adoption of LED technology in the marketplace.

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

Okay, I admit it, I was sneaky and grabbed a photo of Tommy Acchione during his presentation of “Measuring the Performance of Low Melting Point Alloy Sputtering Targets Bonded At Room Temperature” while at the SVC show in Orlando a few weeks back. Congrats to Tommy for presenting our paper after doing so much background testing and preparation work for it!

~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

Thermal News recently interviewed Amanda Hartnett regarding thermal management with metal TIM (thermal interface materials). You can read the full article here:

http://www.thermalnews.com/eprints/Indium_0310.html

I really like this interview, so I’m not going to give away the best parts – I want you to read it yourself. I do, however, want to provide a couple teasers to pique your interest. I’m leaving out the especially cool parts…

“Pure indium, used as a solder TIM, delivers a thermal resistance to…”

“Also, it is important to consider the reworkability of an interface material. TIMs such as … are very simple to rework. Others, such as conductive epoxies, can be quite difficult.”

“When I measure the performance of thermal interface materials, I characterize them based on ... This value is typically more valuable than bulk thermal conductivity. For a compressible TIM, the … assumes the actual contact which will be made between the interface material and it’s mating surfaces. This provides a measurement of thermal performance which is as close to real-world per Watt or per cm2 as I can provide without being application-specific.”

Are you still reading this blog? Go read the article!

~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 ...

I work for a company that manufactures solder, so I have a pretty keen eye for it. Even so, it’s still hard to tell a Sn/Pb ingot of bar solder from a Pb-free bar at a glance. The best way to keep these solder alloys separate at your facility is to have a good storage/tracking system and to have them made in different shapes. These pictures depict 2 lots of solder ingot, one is Sn/Pb and the other is Pb Free. Notice the physical difference of the two. This is a fail-safe, in case the ingots are misplaced or left untracked at your facility. Of course, this isn’t anything revolutionary – but perhaps an way to easily add an extra measure of safety into your wave solder process.

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

Shelf life of solder is a concern that is raised by customers on a somewhat regular basis.  Solder pastes typically have a well defined shelf life, however the useable life of a solid form of solder may be much longer and harder to define.  This was the topic of one of my first blog entries, although I think Eric Bastow has a better explaination than I did. Here is Eric's explanation:

“One of the issues surrounding solid forms of solder (no incorporated flux) is determining the usable (or “shelf”) life of the solder. Solder manufacturers have to draw a “line in the sand” somewhere to establish a time limit on the duration of their “warrantee” period. For better of for worse, in our document driven world, many electronics manufacturers live and die by the solder manufacturers stated shelf life, and will even petition the solder manufacturer to recertify the solder after the shelf life has expired so that it can continue to be used. Otherwise, it is excluded from further use and discarded.

There are many solder alloys in existence and each alloy “ages” in a unique way. However, the most common issue with aged solder is oxidation. Is there a level of oxidation at which a solder is no longer usable? With normal storage and handling and use of a flux, the author believes that the answer may be “no” based upon the results of an experiment.

60In/40Pb spheres, 300 microns in diameter, were reflowed in air or nitrogen onto ENIG coupons with two different activity level no-clean fluxes; reduced activity ROL0 (passes J-STD-004A SIR un-activated) and ROL1. The spheres were oxidized to four different levels; fresh, 4 days at room conditions, 5 hours at 85C & 85%RH and 3 minutes of violent shaking. The appearance of the “fresh” was shiny; the “4 days at room conditions” and “5 hours at 85C & 85%RH” were very similar in their slightly dull appearance, and the “3 minutes of violent shaking” were noticeably darkened.

The experiment was performed with a reflow profile that had a peak temperature of 231C. After reflow, the diameter of the wetted spot was measured.

Interestingly, the determining factors were the flux type and reflow environment (air or nitrogen). For a given flux and reflow environment, there was no statistical difference in the size of the wetted spot among the different levels of oxidation.“

-Eric

In an earlier post I listed some tips for tech guys to get the most out of their trade show experience. One of the readers mentioned that it would be good to list a similar set of tips for customers – so here is how you (the customer) can reap the rewards that most don’t realize a trade show has to offer. You might notice there are many similarities, that’s because suppliers and customers are there for the same basic reasons - to meet each other and learn.

1) Plan. Know what presentations you want to attend, what booths you want to visit, and which suppliers you want to meet up with. Set a time to meet in advance, so there isn’t a last minute scramble to match schedules.

2) Listen. Get to the tech sessions and learn. When you are interested, meet the speaker and ask questions after the session. This will be better for you than any published article you’d read throughout the year.

3) Write. Don’t forget paper and a pen! I admit, I’ve been in the situation many times where I’ve searched for scrap paper or a brochure to jot notes on. You should note all the things you want to follow-up on in one place so nothing gets lost. Along the same lines, don’t forget your business cards!

4) Speak. Present a paper at the trade show or chair a session. This puts you in front of all the suppliers eager to help you with your application. If they see a solution to your issues, they will find you. You’ll be amazed at Q&A time when the crowd collectively tries to find answers to the questions you pose.   

5) Invite. Ask a vendor to join you for lunch or dinner. Most suppliers would love the chance to understand you on a personal level. This will give you the chance to talk about broader supply, technical, and social issues that you may have never set up a meeting to talk about. This will help your supplier realize how they can best support you.

-Bonus-

5) Enjoy. If you have some vacation time and the trade show is in a location you’ve never been, take a few days to relax after the show. The travel plans are as simple as the initial work travel, but you have the advantage of enjoying the perks of travel - like seeing new places - without any extra flight.