Indium Alloy

Do you ever have a need for a "low temperature" solder (meaning an alloy that melts at less than 175C)?

You may have delicate components that cannot withstand standard reflow temperatures, or maybe you are looking to reduce costs by lowering the reflow temperature, or you may be step soldering.  Whatever your reason, there are two unique metals that are used extensively in low temperature solder alloys.

The first one I am sure you can guess: Indium.  The other one is Bismuth. While these two elements are used extensively in the over 100 alloys available in the 50C to 175C range, they couldn't be more different from each other.

Indium is a very soft, malleable metal and remains so even at cryogenic temperatures. It melts at 156C.  Bismuth, on the other hand, is very brittle, even at room temperature, and melts at 271C.  But both lend themselves very nicely to solder alloys that melt below 175C.

Let's look at the two most common alloys in these families.

The two alloys:

• 52In 48Sn (Indalloy #1E) Melts at 118C
• 58Bi 42Sn (Indalloy #281) Melts at 138C

What they have in common are:

• Both are lead-free
• Both are tin-based
• Both are eutectic (liquidus and solidus temperatures are the same, with no plastic range)
• Both can be made into a wide variety of solder forms and can be used in low temperature applications

But the indium-based alloy will give you better compensation of coefficient of thermal expansion (CTE) mismatch than the bismuth alloy.  The bismuth alloy has greater tensile strength but has a lower shear strength than the indium alloy and is generally not recommended in applications where the product has potential to be dropped (like cell phones).  The indium alloy will give you greater thermal conductivity than the bismuth, as well.  The bismuth will give you a cost advantage.

So, which alloy do you use?  Well, that depends on the metallizations you are working with and the environment in which your final product will be operating. For example, if you are soldering to two different surfaces that expand at different rates, then you will want to go with the indium alloy - to keep your solder joints from cracking.  But, there are a lot more considerations when choosing a low temperature solder, and we can help you sort through them.  Check out our Low Temperature Solder page on the web or contact us at AskUs@indium.com or contact me directly at cgowans@indium.com and we can answer your questions or put you in touch with one of our local experts to review your entire process for the best solution.

Let us help!

Carol Gowans

Maria Durham, Indium’s new Technical Specialist in Semiconductor and Advanced Assembly Materials, has been doing some research on indium lead (In/Pb) solder alloys. We chatted about her findings this week. 

 [Andy C. Mackie: ACM] Which indium/lead solder alloys are most common, and what are their properties?

[Maria Durham: MD] Firstly, the use of lead-(Pb-)containing solders in some soldering applications is restricted due to local environmental and RoHS compliance, but there are still many applications where they are  allowed. Many military, aerospace, and industrial equipment uses, as well as many applications related to vehicles, are exempt. The table below shows the most common indium/lead (In/Pb) alloys (pink) and their properties, sorted by liquidus temperature; the higher of the two melting points (solidus and liquidus) seen for non-eutectic alloys. In blue are three comparison materials.

Indalloy 205 is the most commonly used, probably because it has the closest liquidus temperature to the tin/lead eutectic (183°C), 63Sn/37Pb (Indalloy 106). This means it can be reflowed using a standard Sn/Pb eutectic profile. The next most common alloys that are used are Indalloy7, 204, and 206.  Besides the melting range, indium has comparable thermal and electrical conductivity to standard materials.

[ACM] What makes indium-lead (In/Pb) solders so attractive, and why have we seen a recent resurgence in their usage?

 [MD] One main attraction to using indium/lead (In/Pb) solder alloys in soldering to precious metal surfaces is that, unlike tin-containing solders, they do not leach gold. That is, gold does not dissolve in them to any appreciable extent. During discussions at Semicon West in 2011, one of our California customers reported going through 8 simulated reflows with Indalloy 205 in contact with a gold surface with no loss of joint strength and no joint embrittlement. That is pretty impressive. Note that embrittlement is often caused by gold-intermetallic formation. It has been noted that even at 250°C, 50In/50Pb dissolves Au at a rate 13 times slower than it does into 63Sn/37Pb, although this, of course, is a kinetic, not a solubility limit, study.

The higher melting Indalloy 164 (92.5Pb/5In/2.5Ag) has the lowest coefficient of thermal expansion (CTE) of all of the In/Pb solders and is able to withstand the higher temperature excursions that can be seen in step-soldering type applications (where a very high melting solder is used to form the first joint, followed by a next lowest melting alloy, and so on). This is seen in applications such as power electronics assembly, where the first step solder is often used for die-attach either as a solder paste, wire, or preform. The high melting point helps the solder withstand the operational temperatures associated with under-the-hood electronics, in applications such as engine control modules, where Indalloy 151 (92.5Pb/5Sn/2.5Ag) or Indalloy 163 (95.5Pb/2Sn/2.5Ag) are most commonly used. In/Pb solder is excellent on very rigid structures such as ceramic-to-metal or ceramic-to-ceramic. The desired solidus / liquidus temperature range can be adjusted by changing the indium:lead ratio, making it very easy to “dial in” the alloy to a specific reflow process.

Another attraction to using In/Pb solders is that they exhibit good fatigue resistance in thermal cycling from -55°C to 125°C.  In testing, the 50In50Pb solder joint fatigue life is about 100 times greater than that for 63Sn/37Pb.

 [ACM] What fluxes are used in these applications, and how are they formulated differently?

 [MD] The fluxes most compatible with the lower melting point (<200°C) indium-containing solders are NC-SMQ-80 (solder paste) or the lower-tack TacFlux® 012 (suitable for use with wire, preforms, and spheres). These are no-clean fluxes, specifically formulated for lower temperature reflow.  Under appropriate low temperature reflow these fluxes leave behind benign residues that do not need to be cleaned off (“no-clean” flux), although they are often cleaned off in most practical applications, usually to ensure reliable wirebonds absent of flux spatter.

 To learn more, please contact us.

 Cheers!  Andy

Solders, as a class, are "interesting" metals.  And the properties of indium-containing solders are exceptionally interesting.  Indium’s (and indium's alloys') physical and mechanical properties are unique when compared to the metallic elements and alloys typically examined.

To put this into context, a metallurgist from a customer company called me because, after looking over our table of solder alloy properties, he claimed our data couldn’t possibly be correct!  After a detailed conversation, I understood the nature of his concern.  His background was not in solder materials, and the shear strength data for indium (890PSI) is exceeded by its tensile strength (273PSI). This "interesting" situation prompted further questioning.  These numbers are, however, accurate.

The graph on right numerically depicts the shear nature of this material.  Over a test area of approximately 0.5 square inches, a soldered interface that was sheared at a rate of 1mm/minute to fracture extended 1.6mm before yielding. This extension is indicative of the putty-like nature of pure indium.  As expected, The load at yield roughly matched the shear strength cited above for the bulk material  because the yield location in this assembly was through the bulk material, rather than along the intermetallic edge.    

More extensive information on the physical constants of indium can be found in this application note.

Finally, click here to link to more information on indium metal properties and its uses.

As a sneak peak:

• Indium has a low vapor pressure when molten, rising quickly as the boiling point approaches (2080°C)
• Indium cold welds to itself
• Molten indium will wet glass and glazed ceramics
• Although the softest metal, indium will impart hardness, when added as an alloying agent to other metals such as gold. In fact, the gold indium alloys are used in dental crowns.

上周是一年一度的行业盛会APEX, 这次的地点在风景优美的海滨城市San Diego. 

我代表公司参加了展会。这次的客户流还是很多的，许多客户都是带着特定的问题来和我们交流。同事们都热情招待了客户，提供了解决方案和介绍了产品。 我们也很高兴看到许多现有的“老客户”特意来我们的展台和我们打招呼！

在众多的技术论文和演讲中，Low Ag Alloy, Parkage-on-Package (PoP), Finer Solder Powder, QFN Voiding等是热门的话题。许多客户和同行们都十分欣赏Indium公司常常能发表如此有科技含量的技术文章。其实这些文章都能够在Indium公司的主页上免费下载：http://www.indium.com/techlibrary/whitepapers/

最好笑的是我们的一位同事听到一个竞争对手在公众场合大声讲电话，那个人说公司所有经理都几乎被老板骂了，因为老板看见Indium公司有8篇技术文章在展会上被演讲，而这个公司一篇文章都没有……

Cheers!

PS: 一个有意思的小插曲，展会的某天晚上和一个重要客户吃完饭后，我和同事在回酒店的路上碰见同行朋友，被抓去当地的钢琴酒吧（钢琴手现弹现唱，并和在场的所有人互动）。同行朋友和我开玩笑，“骗”钢琴手和在场所有人说那天是我的生日，结果我被拱上台，坐在钢琴上面，听现场所有男士起立唱了一首美国著名情歌“You’ve lost the loving feeling” ala Top Gun；第一排的男士还半跪做各种深情的动作……Hahaha，城市中劳累了一天的人们都以各种理由找些乐子，放松放松。

March 13th is the 78th anniversary of the founding of Indium Corporation.  Dr. William S. Murray, J. Robert Dyer JR, and Daniel Gray combined to create a company that was, in 1934, on the cutting edge of technology at the time - and that still is today.

Although some of the initial attempts to utilize indium were decidedly low-tech (plating of silverware and use in gold dental alloys), the first real breakthrough came when Mr. Dyer developed the process to indium-plate aircraft engine bearings to make them last longer.  Today our indium metal is in thermal interface materials, batteries, medical devices, aerospace devices, solar panels, flat panel displays. Of course, the full range of Indium Corporation products (including materials that contain no indium at all) can be found in a myriad of electronic devices.  We hold a wide variety of patents and have conducted endless tests and experiments including some aboard the space shuttle.

In between we have been featured in the Wall Street Journal, Business Week and many other technology journals and received awards for our technical expertise and our customer service.

Our original founders were very "hands on" in their approach to developing their company and we still follow that approach today.  Our sales and technical staff, locally located around the world, are as comfortable in a lab or on a production floor as they are presenting a technical paper.

Contact us at AskUs@indium.com to utilize our expertise and let us help you with your challenge.

Shown here is an original bottle of indium solder preforms with a hand written label.  Today we have a variety of packaging options with printed labels and bar codes to fit your product and application.

Carol Gowans cgowans@indium.com

Reducing the surface oxides of Nitinol is just the first step in getting a good solder joint with this versatile medical assembly material.

Next you have to choose the right solder alloy.  You will probably want to stay away from anything containing lead, cadmium, or antimony, particularly in medical applications.  And you will want something with a high tensile strength.

The best choice is Indalloy #121 (96.5Sn 3.5Ag).  It has a tensile strength of 5,620 PSI and a melting temperature of 221C and is obviously lead-free.  It wets well to the cleaned Nitinol.

If you need a higher melting temperature solder (one that can withstand autoclave temperatures for example) you should consider Indalloy #182 (80Au 20Sn) which melts at 280C, has a tensile strength of 40,000 PSI, and has long been considered a highly reliable solder.  Additionally, this alloy is available in very fine diameter solder wires to minimize waste.

Soldering temperatures should be 25C to 50C above the liquidus temperature of whichever solder you use and proper cleaning should be always be performed afterwards.

Contact us at medical@indium.com for more information about soldering for medical devices or visit our web site at www.indium.com/medical

Carol

在平时和客户们的会议交流中，因为Indium公司的产品线比较广，不同的客户群常常有针对自己独特的应用或是技术、销售服务等各种问题。

刚刚开始正式做一线销售，我有时候在会议前会有点紧张（特别是新的客户），怕自己回答不上客户的各种问题，帮不上忙。但是后来老练了一点，即使有些问题我自己真的不懂或是即时没有答案，但是总是可以“follow up”跟进的。会后积极主动利用各种资源找出答案，及时回复客户就好了。 现在的会议中， 我更会了“审时度势”的提问，从客户口中问出对项目、生意有用的信息。

最近我们在联系一个国际大客户做一些项目。 客户要求我们的科研副总裁李宁成博士(Dr.Ning-Cheng Lee)过来和他们交流，做一个roadmap meeting. 客户还提出相关的内容请李博士来讲。在我们和李博士内部交流后，决定先向客户提问，问清楚他们的需求后，我们才好“对症下药”。 比如说，客户想了解低银合金Low Ag Alloy, 低温合金在波峰焊中的使用Low Temp Alloy for Wave Soldering，微间距印刷0.3mm fine pitch printing等等。我们知道客户已经在使用别的供应商的SAC0307的低银合金了，并且客户的NPI工厂里没用波峰焊，但是为什么客户会叫我们来介绍呢？对现在的SAC0307合金不满意？哪些性能不满意需要改进呢？波峰焊又是怎么一回事呢？等等。 所以，我们也决定向客户提问，问清楚他们为什么有这些“需求”，真正的原因是什么……

有一个销售同事更有意思，当我告诉他我有一个做激光设备的客户（他们在使用我们含铟金属的材料），有一次我被客户的几个“资深工程师”追问关于铟金属的一些不太相关的问题，我根本不知道答案……我的销售同事建议说，以后出现这种情况，当你觉得他们问的东西有点过的时候，你可以反问他们一句“Why you asked this question? Why you want to know?”  这样就可以尝试挖掘出客户问问题的真正目的了。当然，要见机而行!

Cheers!

Pic: Google Image

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)

FLUX:
To solder directly to stainless steel, Indalloy #2 Flux (activation range 100-371°C) must be used to remove the surface oxides, allowing a clean surface for the solder to wet. This flux is recommended for mechanical assembly joining only. Due to the corrosiveness, it is not recommend for electrical applications because, if the post reflow flux residue is not thoroughly removed using warm water with mechanical scrubbing, the joint will be compromised due to the potential for corrosion during its life. An alternate solution would be to nickel plate the stainless steel, so a weaker flux (RA, ROL1) can be used that is less corrosive and can be easily removed with an appropriate solvent.   

Another alternate solution is to use a forming gas consisting of nitrogen and hydrogen. This method of oxide removal is generally used when the soldering temperature can be above 350°C which is ideal for activating the hydrogen to reduce the oxides. With this method, there is no post-reflow flux residue to clean up.

SOLDER:
The solders usually recommended for stainless steel joining applications contain a considerable amount of tin; however, the actual solder choice has to fit the temperature range of the application. Generally, a low-temperature application may require Indalloy #1E (52In,48Sn) - 118°C (eutectic), while Indalloy #182 (80Au,20Sn)- 280°C (also eutectic) is a great solder choice for high temperature. If you are looking for a solder in the moderate range of temperatures, Indalloy #121 (96.5Sn, 3.5Ag); 221°C (eutectic) is an excellent choice as well as any of the SAC alloys in the same temperature range. There are also many other solders to choose from that will work equally as well. Please see our solder alloy physical properties chart or consult our Applications Engineering staff at Indium Corporation.

We are frequently asked if it is possible to solder to aluminum. The answer is yes, if the following guidelines are followed: 

FLUXES:
Because it is difficult to solder to aluminum, Indium Corporation developed Indalloy Flux #3 (activation temperature is 96-343°C) to remove the tenacious oxides that prevent the solder from wetting to the surface. This flux is very corrosive and is not recommended for electronic applications because, if any of the post-reflow flux residue remains after a warm water rinse with mechanical scrubbing, the joint may be compromised. This flux is recommended for mechanical assembly joining applications only. 

Another alternate solution is to use a forming gas consisting of nitrogen and hydrogen. This method of oxide removal is generally used when the soldering temperature is greater than 350°C which is ideal for activating the hydrogen to reduce the oxides. With this method, there is no post-reflow flux residue to clean up.

METALLIZATIONS:
An alternate to corrosive fluxes is to nickel plate the aluminum so a weaker flux (RA, ROL1) can be used. These fluxes are less corrosive and can be easily removed with an appropriate solvent.   There are many solder alloys that will wet to nickel. Check out our solder alloy physical properties table.

SOLDER ALLOYS:
The solders that are normally recommended for joining aluminum are:

• Indalloy #201 (91Sn, 9Zn); 199°C E
• Indalloy #176 (95Zn, 5Al); 382°C E. 

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 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

Tombstoning

• the transition to Pb-Free (higher reflow temperatures, and related flux issues)
• miniaturization (0201s and 01005s)

• The reflow oven operator can slow down the ramp rate. A slower ramp rate allows for more uniform warming of the PCBA.
• Another technique is to employ a "soak" just below the melting temperature (solidus) of the alloy. For example, for a SAC305 profile (217°C solidus), one may implement a "soak" at 205 to 210°C for 30 to 120 seconds. This allows for the cooler parts of the PCBA to "catch up" to the warmer parts. After thermal equilibrium has been achieved, one can spike the temperature up to the appropriate peak temperature (i.e. 245°C). This technique (depicted in the reflow profile shown at the right) allows for all of the solder paste deposits to melt and wet the component terminations at roughly the same time; thereby, mitigating tombstoning.

Phone: +1.315.853.4900
E-mail: ebastow@indium.com

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

Anyone who has used wave soldering to assemble PCBs knows about that chunky layer of metal that collects on the smooth surface of the molten solder. This is solder dross; it is composed of oxidized metals and impurities that collect as the molten solder contacts the air and manufacturing environment. This happens regardless of alloy and is a normal part of the process, often consuming up to 50% of the bar solder added to the solder pot. In the past, this dross was collected as waste and disposed of, but solder dross is more than 90% valuable metal. This value should be recovered.

Nowadays, typically, this dross is collected and returned to a metals supplier for recycling. Indium Corporation now offers two programs for recycling solder dross. The first program involves simply sending back dross waste in return for a portion of the metal value as a credit. The second option involves sending back dross, which is converted to bar solder (within the original spec) and returned, with you paying only a fee for processing. When dross arrives, regardless of which program is chosen, it is electrolytically refined and the pure metals are recovered and converted back into usable bar solder. Often, this reclaimed/recycled metal has a better purity than virgin metal.

Dross is not the only form of solder that can be recycled. For instance, when changing to a different alloy in a wave soldering process, the entire solder pot will need to be emptied. The old alloy can be collected and recycled, lowering the amount of capital necessary to switch alloys. Bar solder and wire that have not been used within the shelf life can also be recycled to get back some of their value.

Contact me if you want to discuss this.

Hi there!

I am excited, this is my first blog post -ever. I am excited that it is a technical blog of Indium Corporation.

My story is very interesting; a common village boy has grown to become part of a BIG corporation in which everyone is obsessed with soldering! It was my passion to learn electronics assembly techniques 10 years ago. I strived and spent many sleepless nights on this – I would say on SMT.  When our Marcom Superstar Anita told me about the blogging opportunity I was really excited… how would I…? Anyway I am here!

So … soldering and solder paste is my passion. I have published two technical papers on solder paste and reflow. And you will see more thru this blog.

My two cents on soldering… although soldering process looks simple and any one can define with a single sentence; it is not a simple process. It is comprised of chemical, physical, and metallurgical process and deals with fluxing, melting of alloy, wetting, spreading, surface tension, coalescence, wicking, intermetallic growth/bonding, time above liquidus (TAL), cooling down for smooth grain structure etc.

We will have more discussions in upcoming post; stay hungry, stay foolish!

Best Regards
Liyakathali.K (Liya)
Sr.Technical Support Engineer - India
Based in Chennai, Tamil Nadu

Folks,

An obvious disadvantage of lead-free electronics soldering assembly is that the oven must be hotter and therefore will use more electricity (versus 63Sn37Pb soldering). But is the extra amount of electricity significant? Bill O’’Leary claims that a typical SMT oven uses $7K of electricity a year at $0.072/Kilowatt hour (Kwh) or about 100,000 Kwh. That number strikes me as about right, as a household uses about 5-20,000 Kwh per year.

In the late 1990s there were 35,000 SMT lines in the world, at a 3% growth rate that would be about 50,000 lines now. So worldwide SMT reflow oven use would be about 5E9 KWhr (50,000 ovens x 100,000 Kwh/per year) world wide.  

With most heat loss be due to convection, the increase in energy use will be approximately proportional to the difference between the oven temperature and the room temperature (25C). An oven processing tin-lead solder would run at about 210C versus lead-free’s 250C. So the added energy for a lead-free oven would be about (250-25)/(210-25) or about 22% more. So if all assembly lines in the world are SMT the added energy use would be about 0.22x 5E9 Kwh = 1E9 Kwh. The cost of this extra electricity would be about $100 million (US) at $0.10/ Kwh. The electronics industry generates about $1.5 trillion in sales. So this added cost would be about 0.0067% of sales. Since world electrical use is about 150,000 E9 Kwhr per year, this increase is about 1/150,000 of all of the electrical use or 0.00067%.

So although more electricity is used, the increase is not significant to the value of the electronics sold or the total world use of electricity.

Thinking about higher temperatures reminds me that my Indium Corporation colleague Dr. Ning-Cheng Lee is presenting a paper this week on a high melting temperature lead-free solder based on a BiAgX alloy system. Higher melting temperature solders are often needed in what is referred to as a solder hierarchy. Solder hierarchies have solders that melt at decreasing temperatures in multiple soldering steps, starting with the highest melting solder.

Cheers,

Dr. Ron