Jim Hisert

Last week I spent some time in the simulation lab with Eric Bastow, verifying the printing characteristics of our newest low temp metallization paste LT-918. Due to its current success with a variety of customers, we needed to take production capacity to the next level. New equipment was purchased to keep up with the demand, but there is always the chance that material may not perform the same when it is made in substantially larger batches. Our testing confirmed the printing characteristics of the material made on the new equipment surpassed that of previous batches. That’s good news for everybody.

As you can see from the picture, we used a standard printer designed for stencil printing solder paste onto electronic circuit boards. The printer was not the only similarity to solder paste printing though. An interesting characteristic of LT-918 is that it has a higher viscosity than most metallization pastes, which helps with print definition. The high viscosity of LT-918 helps it print like a solder paste, this is great for solder paste printers (like Eric and I, and many of you for that matter) from the SMT and semiconductor assembly industries.

In my opinion, LT-918 is the best metallization paste currently available for interconnecting thin-film cells. It has not only excelled in printing, it also has industry-leading resistivity scores, and has passed customer reliability testing including thermal cycling, damp heat stability, and accelerated UV tests. Much of the data that we can share will be available soon as a product brochure that we hope to have ready for you at EU-PVSEC in September.

I recently had a discussion with Frank Zimone (VP of Business Development at Angstrom Sciences) about sputtering target utilization. He stressed the point: although "material by weight sputtered off the target" is how most folks define the ‘target utilization’, when judging the efficiency of a process, it is only the material that makes it to the product that counts. Frank said:

“What is happening now, is that we are seeing that many companies, after the rush to set up a process to create a good product and “get to market”, are now working on dialing in the process to save money by lowering production costs. This can be achieved by putting more of the target material onto thin-film cells, and wasting less by depositing less of the material elsewhere in the production tool.

“We have recently completed a study with a major photovoltaics company which evaluated enhanced magnetics from multiple competitors.  In a back-to-back comparison with identical process conditions (power density, line speed, etc.) both targets were utilized ~85%  as measured by weight loss.” (Remember folks – this is application specific.) “The main difference between the seemingly similar depositions was that one set of magnetics yielded 20% more material on the substrate.”

I asked the obvious question at this point: “How was that possible?”

Frank replied:

“One set on magnetics was able to get the 2 erosion racetracks more closely aligned, and more perpendicular to the target surface. This translated into higher dynamic deposition rate and less wasted material on the chamber shields.”

It’s a simple concept if you understand the physics of sputtering, and Frank agreed that most customers know this from an academic point but do not have the time/resources to properly test. He said, “More established customers are now looking into these particular issues.”

To learn more about moving magnetics, contact Frank Zimone at FZimone@angstromsciences.com or stop by and see him at InterSolar this week!

I'll be there, as well. Look for me in the Indium Corporation exhibit #5325.

~Jim

Today I received an interesting email that could be useful for my readers. Here goes:

“Dear Jim,

I saw your recent blog. I am in the process of prototyping a photovoltaic application. I am aware that Indium Corporation has a lead-free alternative for tabbing and bus wire. Can you comment on why the photovoltaic industry, specifically in the US, has not adopted this standard as a better non-toxic solution and what Indium Corporation has done to promote this alternative? I look forward to hearing your point of view!

Best Regards,”

That’s definitely an important question, what an ice breaker! This was my response:

“First of all, thank you for reading the blog and thank you for the thoughtful question.

What many people do not realize, is that there are actually a few different types of lead-free alternatives for cell tabbing. The 3 most common alloys for tabbing ribbon are :

• 96.5Sn/3.5Ag
• 57Bi/42Sn/1Ag
• 58Bi/42Sn

Here are the main reasons that people stick with Sn/Pb based tabbing ribbon coatings:

• Sn/Pb and Sn/Pb/Ag have been extensively proven with many different module designs  
  
• Indium (the metal) based alloys are quite expensive compared to Sn/Pb based alloys
• Sn/Ag melts at a higher temperature range, causing greater expansion of the base copper (and therefore greater coefficient of thermal expansion mismatches).
• Some people fear the melting point of Bi/Sn and Bi/Sn/Ag may be too low for their subsequent processes (such as lamination)

The key point I’d like to note is that there are companies currently using each one of these alternative, and finding them feasible in regards to cost and reliability. We promote the use of these alloys - I would personally like to see the 57Bi/42Sn/1Ag alloy take over the market. I like to see my customers making good modules and feeling good about the materials they use too!

All the best,

          ~Jim”

Later on in the day we discussed the technical aspects of using lead-free alloys and settled on Bi/Sn/Ag and GS-5454 as the go-to materials. It was great to have this conversation with someone focused on conscious material selection and eager to learn more about lead-free options.

What are your thoughts?

On behalf of our solar PV team here at Indium Corporation, I’d like to mention how excited we are to see you at Intersolar in July. I look forward to going to this event every year; what’s not to love? A beautiful city, 2 simultaneous premier tradeshows, and many of the customers, partners, and vendors I’ve been planning on meeting or just catching up with.

I hope that you do stop by and say ‘hello’. If you’ve already mapped out your stops at the show I’d like to note that we will be located in a different aisle than originally planned. According to the event organizers:

“Currently Indium is located in booth 5228, we will be relocating you to booth 5328.  Please reference the attached floorplan for your new location as well as access the online floorplans for an overview of North Hall. The new location has been updated in the print directory now in development as well as with our vendor partners for all orders submitted to date.”

Here’s the important message: come visit us at booth #5328!

Send me an email if you want to set up an appointment to chat.

~Jim

As a tech guy, I couldn’t be more excited about testing these 8 different c-Si solar cell / metallization designs!

In my last Secret Life of Engineers post I mentioned that you will need to travel to become a true expert in your field of engineering. The reason stated was, “You can’t expect to become an expert in a particular field from behind a computer – for that you will need to go to conferences and tradeshows, as well as visit customers and industry partners”. Travel is essential to building contacts with industry partners, it also improves networking and strengthens relationships. So how do you know where to travel and who to see? Become so popular in the industry that experts invite YOU!

Seen here: Indium Corporation's Amanda Hartnett learned how to combine travel and social media to become an industry leader.

Some companies will give you all the tools you need to become the go-to industry leader. When you work with your Marketing/Communications department, they can help you write and publish papers, start a professional blog, and use other forms of social media to get your message out to thousands of potential industry partners. The goal is to provide the right content and show other engineers that you are interested in working to discover more about the topic they too are interested in. I’ve found this works out very well, and opens the door to all types of invitations – from presenting at prestigious conferences to being interviewed for publications and even videos. Once you’ve gotten to this point, the networking multiplies as you are referenced in various ways as ‘the thought leader’. You need to be good at what you do first, but social media can take you much further than you had imagined if you do it right.

Q1) What the heck are we looking at in this picture?

A1) It’s a CuGa (copper gallium) target being sputtered at Angstrom Sciences, Inc. test lab. Since CuGa rotary sputtering targets are becoming more popular in the CIGS deposition industry, we wanted to see how they work with AS cathodes. The result: a winning combination!

Angstrom Sciences Lab








Q2) Why haven’t Cu-Ga rotary targets been more popular for production of CIGS solar cells (a thin film technology)?

A2) The big problem has historically been segregation of the copper and gallium in traditionally cast targets. This was a hot topic for those who stopped by the booth at the Society of Vacuum Coaters TechCon and checked out our full size CuGa display target. It is only natural to question if a display piece actually works well in a production sputtering process. In order to make this product work, we had to manufacture it using our proprietary hybrid consolidation technique.

Without giving away all the juicy details, I can tell you that it was a learning experience and that there were some setup issues that led to improved applied power settings. Our customers have been pleased with the results of our CuGa targets, although the fine tuning is proprietary to them and we cannot share their learnings. Now we have a much better understanding of the maximum power we can use for this type of target. That's why it was so important to work with an equipment supplier.

One thing that is obvious from looking at the spent target is the lack of an erosion groove from magnet dwell - a nice feature of the magnetron that was used. The spent target is on display in my boss’ office. It serves as a reminder of the time we spent with the Angstrom Science guys sputtering the target, gathering data, and learning from the team.

This year’s Society of Vacuum Coaters Technical Conference was certainly as focused on vacuum deposition as it has been over the years, but we were delighted by the new emphasis placed on solar cell fabrication. As I mentioned before , one of our key topics was thermal evaporation material - although we also presented on the topics of nano-bonding sputtering targets and the availability of indium and gallium. Along with these topics, the audience was treated to themes of cell fabrication, increasing solar cell efficiency, and roll-to-roll processing.

At the show, we had a chance to discuss new ideas with many of our existing and potential customers. Improved throughput and eliminating alloy segregation were hot topics at the Indium booth. Many customers wanted to learn more about CIGS materials like indium forms for evaporation, or full-size Cu-Ga, CIG, & In rotary targets for magnetron sputtering.

2011 raised the bar for the Society of Vacuum Coaters Tech Convention, I can’t wait for the 2012 event to top it!

I always imagined being an engineer would require me to sit in front of the same computer, in the same chair, in the same room, day after day after… (you get the point). Not only was this a wrong assumption, it couldn’t have ended up further from the truth.

Only a few weeks ago I visited Germany, a place I’ve always respected and had an interest for. The purpose of this trip was to meet customers and industry partners.

Life as an engineer has also sent me to other parts of Europe, as well as to Asia, and North America. Travel is something that college didn’t prepare me for, or even explain to me – but it is a very interesting part of being an engineer.

I’d say most engineers I meet travel in frequencies of once a year to multiple times each month.

Here are a few other examples of what to expect traveling:

• Engineering Travel
• Down-to-Earth advice on an auto forum

Ask anyone who travels for work – it’s both good and bad. Some people absolutely love traveling, and some get burnt out quickly. I do believe that, for an engineer to be awesome at what he/she does, some travel is necessary. You can’t expect to become an expert in a particular field from behind a computer – for that you will need to go to conferences and tradeshows, as well as visit customers and industry partners. You need to exchange ideas and information, From One Engineer To Another™.

Travel can seem glorious to those who don't travel much, but the next post in this series will discuss being an engineer AND a rock star...

A few weeks ago Brandon Judd and I had an opportunity to show 4 middle/high school students what it is like to be an engineer. In preparation, we decided the curriculum should be ‘what everyone else might forget to teach you about engineering’. As it turned out, the aspects of our jobs that were overlooked by our guidance counselors seem to be key career decision points. With that in mind, I plan to share a series of these lessons for anyone looking into becoming an engineer: From One Engineer To Another.

The first observation that we made, was that engineering does not stand by itself. Any field of engineering can shift slightly or completely towards one or more of 6 different departments. From our own experience, we noted many people within Indium Corporation that have started in engineering and went on to work in very different capacities within the company – such as president, VP, director, sales manager, and even corporate pilot! Being an engineer gives you experience with other departments, and you might end up in any one of those other departments someday.

30 years is a long time to spend doing a job that isn't right for you. My point is, if you think you will like being an engineer, don't be scared that you are locked into it. This occupation will allow you corporate mobility - and other job aspects (like travel) that I will discuss in later posts.

I have been further examining material optimization for thermal evaporation to prepare an upcoming poster session at the Society of Vacuum Coaters (SVC) Technical Conference next week. (Session 5 on Tuesday if you’re interested.) The data that was collected proved 3 important things:

1)    Most customers are not properly optimizing their evaporation material forms.

2)    Mixing round shot and other material forms decreases cost, provides less surface area for oxidation, and improves packing density. It’s a win-win-win!

3)    Crucible filling is a perfect (although somewhat obscure) option for most of our customers.

Since crucible filling is a new option for most users, I’ll explain it a bit: we can simply fill/cast your crucibles with an evaporation source (like indium) and send them back to you, or we can make custom inserts to drop into your crucible. When the data was assembled, no other option could compare to crucible filling as the lowest cost, highest density, lowest surface area option. I’m available to help you explore this option, or other evaporation source options: jhisert@indium.com

I’ve been told that sometimes a good headline will include two things that seem to disagree. Using that logic, I’d say “cell interconnection” and “standardization” make a good headline, since there is no unified standardization in the tabbing and stringing process.

My new friends (pictured at right) hope to help change that. Dirk Schade and Cynthia Blank from XYZTEC have agreed to help Indium Corporation and the IPC Solar committee work toward building a standard for tabbing ribbon-to-cell bond strength testing.

XYZTEC is known for their high precision test equipment, which was developed for the semiconductor industry. They have since modified their equipment to handle c-Si cells, and to test the interconnection as well as the mechanical strength of the cells. Check it out here. 

Is there a cell/flux/ribbon/equipment combination that you would like to understand better? Maybe we could test your application!

It was a pleasure interviewing Pat Gallagher, who developed the first automated photovoltaic solar cell tabbing and stringing machine back in 1979. (Before I was even born!) Pat has seen the tabbing industry mature, and he was kind enough to help answer some questions about the process that I’ve grown to love. 

Jim: What were the initial design goals? How have they evolved over the years with customer’s needs?

Pat: Our primary goal was to replace variable hand labor in soldering with a machine and a process. That still holds today. Back then, solar cells were very expensive, thick, brittle, and not very efficient. So the biggest issue was to avoid breaking cells. Our first advice to the cell people was to turn the crystal 45 degrees to the bus bars so that the sides of the cell wouldn't break off along the solder joints. That little trick remains in place today.


Jim: Were the first machines designed to tab and string separately, or in a combined process?

Pat: Our first design was to make strings of cells in one shot. The two-step process, fronts then backs, was a holdover from hand soldering and there was no reason to do that anymore. Surprisingly, however, we ended up accidentally inventing the mechanized tabber on the way to creating a fully automated one-step stringer.

Jim: So that’s where the stand-alone tabber came from! I would have guessed it was the other way around. Have there been any changes to the heating method?

Pat: Oddly, the first thing we tried was induction heating. It was wonderful except that it took 5,000 watts to bring a small solar cell to temperature. It seemed rather wasteful, but that was the smallest industrial RF system available. Then we tried IR light, which also worked well. That's what we used in the first automated system.

Jim: Early tabbing ribbon must have been pretty crude. Have you noted anything that has changed with the copper or solder coating used over the years?

Pat: Basically, it's the same flat conductor that we started with in the 70's. The coating chemistry has changed dramatically. Taking cues from the electronics people, we started with lightly tinned copper and that was it. Solder was introduced on the cell so the ribbon did not need a heavy solder coating as is common now.

No-Lead (Pb-free) has been challenging mostly because the process window is smaller and simply hotter. The cells can be hurt if heat exposure is too long or too fast.

If you’d like to meet Pat (the President of Solar Automation) and learn more, you can email him by clicking here or visit the Solar Automation website.

Jon major recently joined the Indium Corporation as a Product Manager for Solar back-end assembly products. I greeted him with this impromptu interview.

Jim: First of all Jon, welcome. It’s great to have you as a new addition to the team!

Jon: Thank you Jim – it’s an exciting time to be at Indium Corporation and a fantastic time to be a part of the growing solar industry. I am extremely enthusiastic about my new position and am looking forward to making a positive contribution to the solar industry.

Jim: I noticed it didn’t take you long to get up to speed. Your time in Silicon Valley must have helped.

Jon: Coming from the electronics industry with a focus on product development, new product introduction, manufacturing, and external partner management, I am excited that my past experiences can contribute both to the industry and to Indium Corporation. After joining Indium only a few weeks ago, not only am I getting used to Upstate NY weather, but I have been immersing myself in solar with the goal of gaining a comprehensive understanding of:

•       Both rigid and thin-film technologies

•       Technology trends

•       Global and regional markets (EU, China, US, North America)

•       Solar supply chain (Silicon, wafers, cells, module, equipment, inverters, integrators)

•       Equipment manufacturers, contract manufacturers, and how we can collaborate with them to move the industry forward

•       Our products and pricing

•       Our current and future customers

•       Our short and long term opportunities

•       Our competition

•       Our roadmap

•       Our strengths, weaknesses, and threats

•       Our manufacturing capabilities and our QA process

•       Our sales channels, value proposition, key differentiators

•       All Indium processes

Jim: I know you've got solar products on your mind. Let our readers know a little bit more about your role here at Indium?

Jon: As a Solar Backend Product Manager I will focus (officially) on the business development and growth of Indium’s Solar Back End product offerings.  Now that sounds great but what does it actually mean? I could cut and paste my official job description but I prefer to explain it in my own words. As I think about the first part of that statement, “business development and growth…”, I see my role as:

–      Know the market, the customers, the product, and the competition

–      Develop relationships with the Indium team, reps, partners, equipment manufacturers, and, of course, customers

–      Write valuable data sheets, publications, and sales literature

–      Listen to our customers' needs and provide solutions

–      Manage schedules and orders with minimal surprises

–      Build cross-functional collaboration (sales, distribution, marketing, engineering, R&D, QA, production, management)

–      Never let down partners or customers

–      Support all functions of the organization, both internal and external

–      Deliver above & beyond commitments

–      Make great bets – on technology, customers, and opportunities

–      Understand the product life-cycle

–      Ship high quality, consistent product

The second part of that statement “..of Indium’s Solar Back End product offerings” is fairly straightforward. Of course this means I will focus on Indium’s current back end products (tabbing ribbon, bus ribbon, metallization paste (or as I prefer to call it – “grid ink”), flux and flux cored wire). With a product development background, this also means I have an opportunity to work with customers, partners, and R&D to develop and bring new products to market that will advance the module assembly industry – very exciting for me personally.

Ultimately, I think of my role as both building awareness of Indium’s products and superior technical support available to our customers as well as helping to shape our growing industry.

Jim: Okay Jon, you’ve had a while to settle in and get familiar with our Solar Team’s past and present – what are you planning for the future of module assembly?

Jon: Regarding the future of module assembly it’s a bit early to know for sure but I am excited about our low-temperature bismuth-containing alloys. These low temperature, lead-free, bismuth-containing alloys reduce the soldering process temperatures, thus reducing thermal stresses. I’m also working with the Indium production team to further reduce our tabbing and bus ribbon yield strength. A lower yield strength will reduce mechanical stress on cells during the assembly process. This is crucial to minimizing the possibility of microcracks and cell breakage during the solar module assembly process.

In closing, having lived in California for the last 10 years, I am not 100% familiar with our Upstate New York climate, and especially not all the snow shoveling. I see in my future a solar powered driveway heater!

Jon can be reached at jmajor@indium.com

Since I couldn’t find a good beginners guide to c-Si metallization paste, (not even from Wikipedia) I thought I’d provide an explanation of this important module assembly material:

The silicon solar cell has a low-temperature glass-frit paste applied to the active surface. This combination of glass, Ag, and other binder materials is printed onto the solar cell and fired around 850-1000degC to form the solderable metallization on the cell. This glass-silver mixture recombines during the firing process to break through the passivation/antireflective coating layer on the cell and form a strong bond to the cell. During firing the glass and silver are suspended in a mixture with silver forming an electrically conductive path from the top to the bottom of the deposit – and ideally a silver-rich layer is formed on top. This silver is the surface that tabbing ribbon is soldered onto when interconnecting cells.

Because the structure of the glass-silver is formed in the firing process, the firing can impact the solderability of the final metallization. That is the reason it is so important to determine the bond strength and diffusion/intermetallic formation of the interface between the cell metallization and tabbing ribbon solder coating.

Now here’s my challenge to you:

If you know of another good description, post a link to the document in the comments field below!

Thanks,

          ~Jim H.

You’re reading this because you want to know more about LTTF-6363 low temperature metallization paste right? Perfect.

I wanted to get your attention, because I want to talk to you about using this material. We have released a tech paper and (more recently) presented a poster at EU-PVSEC in Valencia earlier this year. With all the buzz about the “Novel Flexible Silver Paste”, I’ve had a chance to print, cure, and solder to LTTF-6363. I’ve had a chance to get my hands (well, gloves…) dirty like a good applications engineer should.

As you may already know from studying the other documents surrounding this material, it was designed for thin-film solar cell interconnection, as a solderable polymer met paste. It went a long way towards teaching us what properties we still need to work on. The material is currently not a product we actively promote, because we know there are properties that need to be improved to give you a wide process window for high volume manufacturing.

Soldering to an epoxy-based material has many intricacies, as I’ve learned. Maximum temperature, Ag dissolution, and a short pot life make processing challenging – honestly, it’s not good for everyone. Of course there’s no way I could have tested the material in every application, but I’m starting to get a good feel for the type of applications that it could work in. 

If you want to evaluate if this material will work for your application, please save yourself some time searching for the answer and just call me: (315) 853-4900 x7592. I can help make your decision easier. 

~Jim Hisert

“Hi, this is Jim Hisert. I just read an interesting article and I wanted to share it with you. In the 2010, October edition of PV magazine, the cover story on page 70 was pretty interesting, so here it is…

It’s called Rotatable Rotatables, and it discusses rotatable targets. The really nice thing about the article is: it goes through the physics of sputtering and gives you the background of what magnetron sputtering is all about. Then it talks about different kinds of targets. It talks about the difference between rotatable targets and planar targets, the different compositions of targets. And then it also goes into talking about the supply of indium and gallium, different target materials, as well as the difference between thermal vapor deposition and sputtering – the advantages and the disadvantages. It even wraps up with refining and recycling of the material and talks about the process overall.

So I advise that you check this out. It’s in the latest (October) edition of PV magazine. Thank you.”  ~Jim

Keywords: Solar, sputtering targets, copper indium gallium, CIG, indium, thin film technology

Last week in L.A. I met up with Hoa Nguyen (VP of R&D, OKInternational) at Solar Power International. The full post and video are available here.