Jim Hisert

I have been asked to explain why someone would want to use rotary sputtering targets instead of planar sputtering targets.

Certainly there is some expense involved with larger targets and new equipment (assuming you are currently using a planar system), but in a high volume process (such as roll-to-roll thin film deposition) the advantages lead to a lower cost of ownership:

• Compared to planar targets, rotary targets generally have more surface area per given length.

• Rotary targets have much more surface area, so the magnetron power can be spread out over a larger area in a given amount of time. This helps keep the target running cooler, decreases nodule formation, and reduces the occurrence of arcing.

1. Since rotary sputtering decreases nodule formation, targets can have longer continuous runtimes.
2. There is generally more material available to sputter on a rotary target, which increases runtimes.
3. Rotary target utilization is usually ~80%, as opposed to ~30% for planar targets – which decreases scrap and increases runtimes.

• Rotary targets are well suited for continuous sputtering processes. Continuous processing increases throughput since there is less time wasted preparing the sputtering chamber.

• Rotary targets are more cost effective for high volume processes. They provide a good platform for long runtime processes, with less chance of defects and downtime.

• Planar targets are still best suited for prototype work or elemental experimentation, especially when large amounts of material are not needed at once.

If you are interested in discussing sputtering targets, contact our team at: Solar@Indium.com

~Jim

I was recently asked to gather some data comparing Indium Corporation’s tabbing fluxes and our largest competitor’s leading tabbing fluxes. Using a new method of solder spread testing found in an upcoming issue of Global Solar Technology, two Indium Corporation tabbing fluxes were directly compared to three of the leading competitor’s fluxes.

The test consists of these simple steps:

• Apply flux to cell
• Dry flux on cell
• Apply solder preforms on cell metallization
• Reflow on a hotplate
• Measure solder length

Finally, the measurements are plugged into the equation:

S = (L_f/L_i)100-100

                   Where:         S = Increase in preform length

                                      L_f= Final solder length

L_i= Initial length of preform

In the end, the Indium Corporation tabbing fluxes (GS-3434 and GS-5454) both caused the solder to spread ~44% further on a given cell – compared to only 13%, 15%, and 16% for the competitors' fluxes.

If you’d like to learn more about the test method or the results, or want help conducting your own evaluation, send me an email at solar@indium.com.

Are you plating indium metal? If so, here’s a tidbit of information you might find useful [From a customer inquiry on the Indium Corporation website]:

Question: “Can the indium be deposited in specific areas of the target piece, i.e. a target with several metallic regions, where we would like to isolate just one? Or can it be easily masked?”

Answer: “Areas of metallizations not requiring plating can easily be masked off either by the use of plater’s tape, or, more commonly, with a screenable resist, either thermal cure or UV cure.”

For more information, always feel free to contact us at AskUs@Indium.com.

It is common to hear people that are skeptical about CIGS technology ask questions like:

• "Aren't indium and indium tin oxide (ITO) thin film deposition processes wasteful and inefficient?"
• “Aren’t we going to run out of indium soon? Doesn't the world use more than we produce!”

What are the truths?

Here they are:

WASTEFUL: A well-run process is NOT wasteful. Why? Recycling!

At first glance, a process like indium planar target sputtering seems ridiculous – generally only 30% of the indium actually makes it onto the substrate it is destined for (and that’s in a well-tuned process). As it turns out, the material that doesn’t land on the substrate is too valuable to just scrap. This translates into recycling, a lot of recycling…

According to presentations given at Minor Metals 2012: “indium production will total 1,500-1,700 tonnes in 2012, with virgin supply accounting for around a third of total output”.  It’s incredible that recycling accounts for such a large percentage of the indium used in the world today.

INDIUM AVAILABILITY AND SUPPLY: Another important conclusion made at the conference was (as reported in Metal Bulletin):

“proven indium reserves from existing mines at 50,000 tonnes, a volume that will be sufficient to satisfy demand for the next 75 years”.

While it’s not news at Indium Corporation, it is definitely assuring news for those looking to get involved with CIGS technology.

~Jim

Somewhat related: I found this picture in a reference text at a bookstore. It reminded me of the picture that Carol Gowans shared in her latest blog post about indium availability.

The caption states: “A lapel pin from a company obviously proud of its work with indium.”

It's true, we ARE very proud of our history and our company. If you have questions about indium metal, why not talk to people who share live your interest?

Send your questions to AskUs@indium.com.

~Jim

I recently had a chance to catch up with a friend and colleague, Jasbir Bath. If you’ve spent time in the electronics assembly industry you have most likely met him, heard of him, or used an industry standard that he has helped create. Jasbir is a founding member of The Solar Engineering & Manufacturing Association,  SEMA. Who better to talk to about a new association than a founding member?

Jim: The Solar Engineering and Manufacturing Association (SEMA) is a relatively new association for engineers in the solar industry. Can you tell me a little about why it was created?

Jasbir: It was created about 2 years ago based on a need by the solar engineering/manufacturing base to address issues in the industry. There are many organizations in the solar industry but none are wholly dedicated to the engineering/manufacturing profession. SEMA was formed to address this need. We are working to address a number of gaps in the industry highlighted by the SEMA membership which include Education, Training, Standards, Reliability, Cost Reduction and Technology Gaps.

SEMA is a group of engineers, manufacturers and related professionals in the solar manufacturing and related disciplines who volunteer to conduct activities in the organization. The projects/programs we work on are driven by the active involvement of the membership.

Further details on SEMA and what we do can be found on the SEMA website at www.solar-ema.org

Our membership costs are low as we are not an organization looking to make a profit but to encourage participation and work to advance the solar industry as well as advancing education, training and collaboration within the solar manufacturing industries.

Jim: I heard there’s a new solar conference coming up? Can you tell me what makes this one different than all the other solar conferences we go to throughout the year?

Jasbir:  SEMA is collaborating with SMTA (Surface Mount Technology Association) to develop a conference meant for engineers and managers in the field to look at the areas of concern in the industry and develop ways to address them. We don’t see a similar conference to this which covers such a broad range of subjects which is specifically focused to address the needs of the industry. The program will consist of presentations and discussion covering the reliability testing of PV Modules covering gaps and where future work needs to be done. It will highlight various reliability programs being done in the industry with an assessment of current and evolving standards in manufacturing and reliability.

We are pleased to have a great line up of speakers and presentations. SEMA will present its reliability report assessing the reliability of PV modules at the conference. We will also have speakers from UL, IPC and NREL to discuss international solar standards together with a discussion of the work of the PV QA Task Force forum from leaders in that Task Force group. Areas covered will include temperature, humidity, voltage, mechanical and UV testing of PV modules and diode testing.

We will also have presentations on the reliability of microinverters/inverters and future trends from organizations including Sandia. PV Manufacturing Issues will be discussed by companies including Flextronics. The Global Solar Outlook will be reviewed by companies including Navigant, Custer Consulting and Prismark. Finally we will review general PV Module hazardous issues such as Electrical and Fire Concerns and well as Module Warranty/ Traceability Issues.

In addition we have industry leading training courses at the event on PV Module Manufacturing and Troubleshooting and PV Standards in addition to exhibitions.

The SEMA/SMTA Conference, Training Courses and Exhibition are from March 21^st to 23^rd at the Fairmont Hotel in San Jose. Further details on the program and sign up can be found at http://www.smta.org/solar/

Jim: One more question for you Jasbir. I know from working with you in different associations, that you are personally invested and involved in the future of module assembly. What attracted you to this field, and what keeps you interested in it?

Jasbir: I have been involved previously in the electronics manufacturing industry during the transition from tin-lead to lead-free soldering due to environmental legislation requirements. This was a challenge being involved in both from a technical and logistics perspective, but it was also fun as you saw the rewards of your efforts when the transition occurred successfully.

The solar/PV industry has challenges in addressing how to produce good quality and reliable products at lower cost, and it gives me the opportunity to try to make a positive contribution in an evolving expanding industry.

Jasbir and I look forward to seeing you in San Jose!

~Jim

No one likes being controlled by the cost of silver. We deal with fluctuating Ag costs here at Indium Corporation on a very large scale – so I understand the issues with using Ag-filled low temperature metallization paste for thin-film solar cell interconnection.

People always ask for alternative fillers like copper – although the chemistry of metallization paste doesn’t allow the substitution of most filler materials. Our solution is a new material: silver-plated copper particles.

Silver-plated copper particles allow us to utilize a very low amount of silver precisely where it needs to be, on the surface of the particles. By tricking our metallization paste chemistry into thinking it is still working with silver flakes, we are able to maintain the same high levels of flexibility, fine line printing, and adhesion that we have become accustom to with materials such as LT-918 metallization paste.

Due to the inherent bulk conductivity difference between copper and silver, very lowest resistances will still be achieved with solid silver flake metallization pastes. The silver-plated copper material has performed unexpectedly well in electrical performance though, winning over some customers due to a substantial difference in price.

Our new silver-plated copper particle material is currently in beta testing, and has completed over 2,000 hours of dry and damp heat testing. Our data so far has confirmed superior print performance, and customers like the fact that the material can be shipped at room temperature. If you are interested in beta testing the material, please let me know.

~Jim

Back in 2005 a customer left a question on our website and it was answered by one of my solder heroes. Here is the Q&A:

Question: “With regard to Indium Corporation's indium sulfamate plating bath… …can it be deposited onto platinum-gold thick film inks? Namely DuPont solderable inks on 96% alumina?”

Answer: “Thick film inks often contain low melting glass frit particles which enhance bondability to the alumina substrate. Solderable thick film inks are designed so that the glass particles do not reside on the surface, thus allowing the solder to wet. As in solder wetting, having a glass frit-free particle surface will also allow electrodeposition of any metal. Therefore if the ink is solderable it should be plateable.”

I learned from this answer so I thought it would be good to share with you. Call me or email me to discuss your questions.

~Jim

Readers have asked how to visually assess a tabbing ribbon interconnection after a bond test.

This image is a cell that has been bond tested after soldering.

The first indication that you have a good bond is the physical resistance during the bond test. Even if you are peeling the ribbon off by hand, you will still notice if the ribbon jerks as it tears away from the cell. Fluctuation of bond strength may be caused by insufficient or inconsistent tabbing parameters, incomplete fluxing, or even contamination on the tabbing ribbon. If the resistance varies rapidly across the length of the bond, there could be an issue with microcracks. Microcracking of the underlying silicon is usually caused by built-up CTE (Coefficient of Thermal Expansion) stresses from tabbing. The ideal bond will peel apart where the tabbing ribbon meets the metallization, and it will be uniform. It should look like the image seen here.

There are some things you can do before, during, and after tabbing to get a better looking, and higher reliability, tabbing bond.

Before

Consider using alternative tabbing alloys and fluxes. Using Bi-based alloys at lower temperatures will lower the stresses caused by CTE mismatch and help eliminate microcracking. Softer tabbing ribbon can help keep stresses to a minimum as well.

During

Cell tabbing/stringing machines have many adjustable parameters. You owe it to your customers to explore the effects of parameter changes so you know you are building the best modules possible. (If I have time I’ll probably come to your facility to help – all you have to do is ask.)

After

Not everyone has time to wait, but if you have the luxury to let the tabbed cells sit for a day you should notice much better test results. Stresses built up in the silicon are partially relieved after 24-48 hours, which will result in less microcracking.

Let me know if I can help you make some beautiful cell interconnections!

~Jim (jhisert@indium.com)

A customer raised an interesting question regarding the use of our indium plating baths. I thought it was interesting enough to share. The question is:

“What are – if any – the health, safety, and environmental issues with this (indium plating) process?”

The answer: Indium metal has a toxicity similar to copper and a TLV of .1 mg/m³ in air as particulate air borne particles, which is not normally encountered using a plating bath. The plating bath would be toxic if ingested. Routine hygiene/safety practices include wearing safety glasses, wearing plastic gloves when handling, and washing hands after handling the metal or plating bath solution.

From time to time our Technical Service department conducts plating experiments, and it really is pretty simple when you know what to expect. (Especially compared to some of the other electronics manufacturing process they encounter.) If you have questions or concerns about the indium plating process, make sure you contact the experts: askus@indium.com

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