Jim Hisert

Here is a fairly common question as answered by our Tech Team:

Question: “What equipment is needed to use the indium sulfamate plating bath, e.g. electrodes, power supplies, cleaning equipment, etc?”

Answer: “You will need plating tanks, a D.C. rectifier, anode bars, and indium anodes. In general one tank is used for each of the following operations: alkaline clean, [second] rinse, chemical activate, rinse, indium plate, [and final] rinse. There are several textbooks that describe the electroplating process in detail.”

If you have a question like this, send it to us @ askus@indium.com.

After the report by Isofoton regarding reliability testing of Bi-based alloys for tabbing ribbon, the world learned that Bi-based alloys could survive the lamination process and function in use. If you haven’t seen it yet, I consider this mandatory reading! Here is the info: B. Lalaguna, P.Sanchez-Friera, I.J. Bennett, L.J. Caballero, J. Alonso, “Evaluation of Bismuth-Based Solder Alloys for Low-Stress Interconnection of Industrial Crystalline Silicon PV Cells", 22^nd EU PVSEC, Milan, 2007Milan, 2007.

We all know the Bi based alloys like 57Bi/42Sn/1Ag and 58Bi/42Sn can be used in a standard module assembly process, but is there an advantage to using Bi/Sn or Bi/Sn/Ag when Sn/Pb and Sn/Pb/Ag alloys are so well known and trusted in the industry?

I’ll give you 3 benefits:

1)    1) Bi/Sn/Ag and Bi/Sn are Pb-Free

2)    2) Bi/Sn/Ag and Bi/Sn are low-temperature alloys, they allow you to lower your tabbing process temperatures

3)    3) When paired with the correct flux and metallization, these Bi alloys form a powerful bond without microcracks (due to the lower process temperature)

Below are results with SunTab^TM ribbon assembled on a Komax X series stringer and tested on a XYZTEC Condor 150-3 bond tester (provided by the respective companies).

You’ll probably notice the lack of y-axis scale – I’m not going to give away all the cool information that easily! Contact me at jhisert@indium.com to learn more.

Here is a question that was posted and answered on our website back in 2006, I think it is still quite relevant:

Question: “Why does your Application Note for cleaning of indium ribbon for thermal interface recommend a mild (5-10%) HCl acid solution, yet [the] MSDS for Indalloy #4 (100%) says to avoid contact with acid? My past indirect experience with indium usage indicated some cleaning procedure of the oxides was necessary to achieve good thermal contact resistance.”

Answer: “Thanks for contacting the Indium Corporation with your request. If the indium ribbon is stored and handled (stored unopened in an argon or nitrogen pack – placed in a dry box) properly and it solders well in your process, this procedure should not be necessary. When following this procedure, the HCl solution should be applied to the indium metal to clean it thoroughly, and then dried with nitrogen.”

If you want to know more about metal thermal interface materials (TIMs) (handling, preparation, or process parameters), send an email to our global technical team at: askus@indium.com. They are ready to answer your question!

~Jim

Recently I was testing the resistance of a new low temperature metallization paste* (for solar photovoltaic assembly) in the lab. The samples were initially tested with a 4-point probe, just before entering a chamber set at 85°C and 85% relative humidity. To my surprise, the resistance dropped noticeably (as seen in the chart).

I brought the results to the material’s creator in our R&D department, ready to wow him with my discovery. I exclaimed, “I just finished testing the samples we put into the 85/85 chamber and can’t believe the values I’m getting!” Without a flinch he replied: “The resistance went down, didn’t it? That’s a unique feature of this material.”

While I didn’t gain any cool points in R&D for discovering an awesome new feature of an upcoming product, I hope the trait of this material can be useful for our customers (some of whom have since noted the improved characteristics after reliability testing).

The thing I learned from this experience is how important end of life testing is for metallization paste – all too often samples are only compared based on time-zero testing. This will change the way I compare metallization pastes from now on.

~Jim

*For my followers who aren't familiar with low-temperature metallization paste,it is also referred to as "grid ink", "silver ink", and "conductive ink". Low-temperature metallization paste is a silver-filled contact material used in the assembly of photovoltaic solar cells. It gets its low-temperature label because it is processed at lower-than-traditional glass frit temperatures of ~1,000°C. In addition to its role as a contact for thin-film connections, low-temperature metallization paste is also useful as a low-temperature alternative metallization on Si-based cells.

Learn more here.

Indium metal has the unique ability to cold weld (bond) to itself at room temperature. Though this is, technically, not soldering, this property makes it especially useful for low-temperature bonding applications. Back in 2008 I mentioned indium cold welding on the semiconductor packaging blog. Here are some other resources for learning more about the process:

• The official Cold Welding Application Note
• Using indium in a cryogenic seal application.
• Using indium in Flip-chip applications

Cold welding is a great solution to some really tricky bonding applications. Some nice features of using indium cold welding as a bonding method are:

1) It offers an instant attachment. Because indium will stick together upon physical contact (with a slight amount of pressure) the bonding process takes a fraction of a second as opposed to reflow soldering processes for solders or curing processes for epoxies – which can take seconds to many minutes.

2) It requires no heat. Temperature-sensitive components can be assembled without heating. The stresses that occur due to CTE (coefficient of thermal expansion) are also not an issue, which makes this a great process for attaching large dissimilar CTE materials like brittle ceramics and high expansion rate metals.

3) The bond will have exceptional thermal and electrical conductivity due to the nature of the indium that is used for this process.

You can use the indium cold welding process on any material you can successfully sputter, evaporate, reflow, or plate indium onto.

The answer to the age-old question: “What is the expected lifetime and associated strengths of an indium cold weld?” is:

The cold weld bond will last indefinitely and the bond strengths approach that of a solid piece of indium, 273 PSI.

If you have questions, please email them to askus@indium.com.

Here is a question that was received and answered on our website almost a decade ago – but it is still quite relevant:

Question:
“I have an application where I need to solder to 0.5µm thick gold. What alternatives do I have? What alloys are likely to work?”

Answer:
“Being that your gold is relatively thin, you really do not have any limitations as far as [indium-based solder] materials go. You should consider the temperature that the solder will see and try to choose an alloy that melts at least 40°-50°C higher. You should also consider the sort of mechanical strength that you will need.”

Here is a list of solder alloys we offer, including indium based alloys: Indalloy Chart

Here is a list of tricks to help you overcome the issues that can arise while hand soldering silicon-based solar cells (and other applications as well). Some of these ideas are obvious for most, but all the suggestions can help you form a better solder joint - and build a better final product:

1)    Use the correct soldering tip. I’ve made the mistake of using an inappropriate solder tip before, and so have many of my customers. It’s a frustrating problem you will only let happen to you once: everything is set up perfectly but nothing will melt, until you notice the solder tip is not the correct size or shape. This has happened to many of my customers who were initially using cone point soldering tips when they were working with 2mm wide solder coated tabbing ribbon. Simply changing the tip to a 2mm wide chisel point made all the difference, and promoted soldering readily. Why such a big difference in performance? The chisel tip allows heat to flow across the ribbon, instead of only heating a single point. More heat flow = more heat in your solder joint.

2)    Pre-tin the soldering iron. Just as an appropriately sized soldering tip will distribute heat across the soldering surface, a bit of molten alloy can help create a thermal interface to maximize heat transfer. Remember to melt a small amount of solder onto the tip of your iron before soldering, and be sure it’s the same alloy you are soldering with. (Leave the custom alloying to us ;)

3)    Consider the alloy you are soldering. All the heat your typical soldering iron can produce will not be enough to melt some of the highest temperature alloys. Be sure to have a good understanding of the alloy you have selected. In some cases with low-temperature alloys (like bismuth or indium alloys), excessive soldering temperature can de-wet the alloy and char low temperature fluxes.

4)    Use the correct flux. Fluxes are quite different, I’ve spent my entire soldering career trying to get that point across. There are fluxes for high temperatures or low temperatures, cleaning with water or not cleaning at all. There are specialty fluxes for specialty alloys and there are fluxes for different soldering surfaces. Use the correct flux. If you don’t know what the best flux for the application is - just ask; that’s what I am here for.

5)    Use a bottom side heater. Silicon is known to pull heat away – that c-Si solar cell that needs to be soldered is a heatsink! Some solder equipment vendors also provide underside heating pads to help prevent excessive heat loss.

6)    Keep your soldering iron clean. That black crud that builds up on your soldering iron tip, it’s not helping you form a good solder joint. Those oxides and charred flux residues can easily be removed by wiping the hot iron across the wet sponge (that should be at your soldering station). A clean tip will lead to better heat transfer, and it will make the fluxes you use more effective.

This is the soldering station I use, it’s a PS-900 supplied by OK International. Just about any soldering iron will work, but they won’t all work as well – or come with as good support.

I’m still learning all the tricks to hand soldering, so feel free to share any you have learned over the years!

~Jim

As unlikely as it sounds, your reaction to this picture is probably similar to my reaction to Solar Power International 2011. Allow me to explain…

Aside from the fact that both the picture and the conference took place in Dallas Texas, there was another similarity: The show seemed to lack a clear audience. Just as you might ask, “Why am I looking at this picture?”, or “Why did you take that picture?”, I could not answer my own question of “Who is the audience for SPI 2011?”.

At SPI there were vendors who were selling retail solar water heaters, there were big name module assemblers, and there were materials manufacturers like us. There was no clear group of people on which the tradeshow seemed to focus. The result was a slow stream of traffic throughout the show compared to events like InterSolar, PVSEC, and SNEC.

In the end, it was still a good chance to meet with some industry partners, and with customers I haven’t seen in a few months. It was also a great chance to work with the IPC team on the upcoming module assembly documents. That, in itself, was a good enough reason to visit Texas!

~Jim

A friend recently mentioned to me that I don’t look like I’m really happy in my pictures online, this one is for you…



I found this picture that someone took from across the way at the PVSEC (European Photovoltaic Solar Energy Conference and Exhibit) in Germany a few weeks ago. (It has been zoomed in and cropped.) I don’t always love to travel, but I must admit that this was a very good trip. Our team had a great time in Germany – and met with many of the key people we talk with throughout the year. I felt that the show this year was a little slow, although our conference room was almost always full and our leads have been rather successful so far.

So here’s what I thought about the 2011 PVSEC:

• The conference hall (as usual) was a long walk from the exhibition. Tech guys are sometimes spread thin between working at an exhibit and catching a presentation. It would be great if it was easier to juggle these activities.
• Germany IS the location for the premier solar show of the year, good job!
• There is so much to see. Four-day tradeshows are long, but this one stayed interesting with so many things going on.
• It’s good to see so many equipment vendors still showing off their products. Other shows this year have been (in my opinion) light on equipment, but the PVSEC is the place to be to get demos – especially for tabbing/stringing lines.

If you made it out to the show, feel free to leave a message - I’d be interested in knowing what you thought of the PVSEC this year!

Your PV Application Engineer,
~Jim

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.