The following is an example of how a simple procedure like cleaning a soldering iron tip can make a world of difference in the quality of a solder joint. Eric Bastow responded to a customer after doing some testing in the lab – and confirming that a clean iron tip contributes to a clean solder joint:
“As I mentioned in our conversation, I did not think that a flux coated preform would fare any worse than a cored wire in a hand soldering application where charring is concerned. Rosin is rosin is rosin, regardless of whether it is within a cored wire or coating a solder preform. I did a quick experiment to see what would happen.
Using a Weller WS80 soldering station, set to an abusively high temperature of 850F/455C, I soldered some .250” square x .005” thick Sn63 preforms (folded-up as small as I could do by hand), flux coated with 1% NC9, to a nickel metallized FR4 test coupon. The contact time of the iron to the solder was ~5 seconds. The results look pretty good. The charred 
flux that you do see is flux that burnt to the iron and was transferred to the solder from the previous preform. I would anticipate this sort of appearance with a flux cored wire, as well, used under these conditions. I believe that with frequent cleaning of the tip, the amount of unsightly flux residue with be minimal, especially if a more appropriate iron temperature were used.” -Eric
The bottom image is what happens when you don't clean a soldering iron tip.
Soldering Basics
I had a call with a few engineers today who wanted me to answer a question, “Which solder paste do I pick for my application.” Sure there were a few application-specific details that I feel were too specific to discuss with a general audience, but I think I can answer the question for any of you that are out there wondering the same question while reading this.
It’s an easy answer really; start with SR-8 unless:
1) You are using laser reflow equipment.
2) You have noticed solder spatter issues related to your design.
3) Your company or end customers require you to use only halogen-free materials
4) The residue must be clear and almost non-existent (ultra-low residue levels)
If you said “yes” to any of the above, you’ll want to try SR-7 (as long as you have nitrogen reflow capability). If you said yes to answer 3 (halogen-free) but you do not have nitrogen reflow capability, try SR-089.
Jim’s note: This post was written in August 2010 – but it will be available to anyone searching for the info for quite some time. For updated information on newer solder pastes, send an email to Solar@Indium.com. Thanks! ~Jim
Some people collect stamps, or coins, or baseball cards – my father collects hardware. Almost every time I go to my parent’s house I notice a few jars or boxes of bolts, nuts, screws, washers, and clamps. They are bought in bulk and sorted by size. I used to think it was ridiculous to do this, but my Dad actually uses enough of the hardware to save money, and I have never needed to run to the store during a project to get a special size piece of hardware. An old bolt may not look as pretty as a new bolt, but in applications that are simply for utility, an old bolt works just as well.
Solar panels that do not live up to visual specifications also share a utility, much like old bolts. They are certainly cheaper - and for a solar farm, small imperfections may not matter to the customer.
So now it’s my time to collect something. I’m not looking to collect old hardware or utility grade solar panels, I’m searching for the different criteria that module assemblers use to determine if modules are fit for residential or commercial use. This information can be used to help set the (IPC) standards for the industry. If you have information that could help, please send it to jhisert@indium.com. Thanks!
As many of you know, I’m focused on applications for the solar industry and the semiconductor industry. In fact, many of the readers of this blog have spent a good amount of time working in both fields as well. Dr. Ernest Levine is just like us, except he makes these topics way more interesting to learn about than I have figured out how to do yet…
Whether you’re learning about semiconductors or solar cells for the first time, you’re planning on learning more, or maybe you just want a refresher course – check out one of these courses in October. The IC Fabrication Class is offered Oct. 12-13 and the Photovoltaic Class is offered Oct. 26-27.
Back in 2008 I attended the IC Fab class and interviewed Ernest to learn more: http://blogs.indium.com/blog/jim-hisert/0/0/ic-fab-course.
When he let me know about the upcoming classes he mentioned: “It really is a fun class for learning and I am happy to offer it.” That’s true, everyone I know who has taken this class enjoyed it, and was described as “a good way to fill in the gaps”. For more detailed information send Ernest an email at elevine@uamail.albany.edu or call him at (518) 437-8623.
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?
By the way: if you're at Intersolar this year, stop by and say 'hi' - and let me know your opinion about the tabbing / bus ribbon kit.
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:
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
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.
~Jim
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.
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 
Grid Ink, Silver Ink, Conductive Ink
Conference and Exhibition
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