Indium Corporation Blogs

When helping customers with the optimization of their soldering process, the question often comes up;

“What will my solder bond line thickness be when utilizing this material?” 

The amount of volume lost to flux content while utilizing a solder paste, in comparison to a flux-coated preform, is much greater.  Whereas a flux-coated preform only contains about 1-2% flux by weight, a stencil printing solder paste is approximately 10% flux by weight.   This may not sound like much, but when you consider the density of the powdered alloy in the solder paste (7.40 g/cm³ for SAC305) versus the density of the flux (~1 g/cm³), you end up with a material that is almost 50% flux by volume! 

Therefore, if you were to print a 0.5” x 0.25” deposit utilizing a 0.005” thick stencil (0.001in³ of printed solder paste volume), you would only end up with approximately 0.0005in³ of actual metal solder.  In short, your final bond line thickness will be half of the thickness of the solder paste printed.

For help determining your bond line thickness, or for help determining the appropriate solder material for your application, please contact AskUs@indium.com.

Here is a picture of an Indium Corporation solder flux pen, sectioned to show you the internals.  Who DOESN'T want to see THAT, right?!?

Flux pens are commonly used to accurately supply small amounts of flux to parts before soldering. In the case of hand soldering solar cells, this is the perfect packaging. As you press the flux pen tip (the yellow part in the picture) against your solar cell, the spring-loaded tip assembly moves back into the body of the flux pen, opening the valve and releasing a small amount of flux into the upper chamber. The pen tip, made of a felt material, carries the flux to the outer surface via capillary action. As you move the flux pen tip across the cell metallization, a thin, even trail of flux is deposited on the surface.

Although flux pens are designed for all types of hand soldering/rework applications, the felt tips generally measure 1.5mm x 4.25mm. This size is great for various sizes of tabbing ribbon!

If you’d like to try using flux pens filled with the best tabbing fluxes available, contact us at solar@indium.com

The Indium Corporation has developed a new solder research kit designed specifically to meet the needs of medical manufacturers who are soldering to Nitinol®.

The kit contains the two best fluxes for soldering to Nitinol:

• Indalloy Flux #2
• Indalloy Flux #3

It also contains Indalloy #121 (96.5Sn 3.5Ag) in a 0.030" diameter wire and some Nitinol wire from Fort Wayne Metals.  This kit gives you the tools you need to decide which flux works best for your application by allowing you to try them out with the supplied Nitinol.

You can buy the kit directly from our e-commerce site or contact me at cgowans@indium.com if you have more questions.

Carol Gowans

Folks,

Let's see how Patty and Pete are making out on their latest adventure....

“Here is the ProfitPro™ output," Dave Ferris said as he pointed to a PowerPoint slide on the screen.

Just then, the site general manager, Sally Wilson, and the head of purchasing, Blaine Ellis, arrived. 

“Long time no see,” Pete said to Ellis.

Ellis acknowledged Pete, but appeared to be in a foul mood.  Everyone settled down and the meeting came to order. Patty was again surprised, Pete always seemed to know everybody.

After introductions, Sally kicked off the meeting.

“As you know, we have a new corporate award program for saving money.  Dave is a candidate to win the first award.  But Blaine won’t sign off on it, because his solder paste expenses have, in his word, ‘skyrocketed' ”, Sally started.

Ellis exclaimed, “My solder paste costs are through the roof.  Last year we used 3,000 kilograms and this year we are using 3,100 kilograms and each kilogram costs $10.00 more.  That’s more than $40,000 dollars more.  How is this saving money?”

“How has the overall site profitability changed?” Patty asked.

“It’s pretty consistent with what Dave’s PowerPoint® slide shows", Sally answered.  "His result is for one of our six lines.  We are using the new solder paste on all of the lines now and profitability is up about 8%, or more than $6 million for a year.”

“A lot of the added profit is from cost savings that purchasing has implemented,” Blaine shot in.

“You don’t realize the pressure I am under to reduce the cost of purchased goods.  Components, PWBs, connectors, solder paste, flux, packaging, etc, is over 80% of all of our total cost. Corporate has been all over me because of the increase in solder paste cost,” Ellis went on in frustration.

“Part of the increased cost of solder paste is because we ship more product, we actually use less paste per board with the new paste,” Dave responded.

“How so?” asked Sally.

“The old paste had poor response to pause.  If we stopped the line for a few minutes, the first one or two prints afterward would be poor because the paste stiffened up.  We would have to wipe the paste off those boards and reprint them.  This would happen a couple of times per day.  The ProfitPro™ output shows the increased productivity and profitability for the line for which I am responsible. Note that the profits are up $841K!” Dave Ferris went on.

“But my purchasing expenses have gone through the roof!” Blaine Ellis blurted as he stormed out of the room.

Patty, Pete, Dave, and Sally, sat there dumbfounded, looking at each other.

Pete finally spoke up, “Let me go talk to Blaine,” he said as he left the room.

“One of the issues is that Mr. Ellis should not be criticized if a consumable costs more money if it increases profitability. That doesn’t make sense,” Patty said.

“I agree” said Sally, “But much of the pressure comes from ‘Corporate.’”

As Sally was speaking, it occurred to Patty, that, in her new role, she may be able to impact this ineffective corporate policy.  As she was mulling over this thought, Pete and Blaine Ellis returned to the room.

Ellis spoke first.

“After discussing the situation with Pete, it occurs to me that young Ferris’s profitability argument may have merit,” Ellis started.

“But Dr. Coleman, I need your help,” Ellis implored.

At this Patty’s ears perked up.  First, she is not used to being called by her last name and second, she was unaware that she had a PhD!

“I think I know what you need,” Patty responded.  “We need to change the corporate criteria for evaluating the effectiveness of purchasing, to include situations like this.  I’m quite sure I can do it,” Patty finished cheerfully.

The meeting concluded with all agreeing that Dave Ferris should be given the corporate award and Patty reaffirming her commitment to change the corporate policy.

In several hours, Patty and Pete were on an airplane heading home.

"OK, out with it," Patty teased Pete.

"What?" was Pete's sheepish reply.

"How did you know Blaine?" Patty asked.

"Remember, when I told you that I tried out for Olympic volleyball years ago?" Pete responded.

"Yes, " Patty replied.

"So did Blaine. I'm not sure which one of us was more humbled by the experience," Pete chuckled.

Cheers,

Dr. Ron

Calculating the exact amount of solder paste needed for a given circuit board or for a full production run can be difficult for several reasons, including:

• print deposit variations
• paste left on the stencil and squeegees after the build is complete
• bead size needed for the build (which depends on the squeegee size)

The theoretical volume of solder paste can be calculated for each board using the Greely Formula and a simple volume calculation.

The Greely Formula:

Specific Gravity of the flux vehicle is generalized to 1. 

Example:

• Solder Paste: SAC305, Indium8.9HFA, Type 4.5, 87.75%
• Aperture Size: 0.012” Square
• Stencil Thickness: 0.004”

Solder Paste Specific Gravity = 4.14

Volume for this aperture can be calculated using the following formula:

Length x Width x Height

0.012” x 0.012” x 0.004” = 0.000000576 inches³

To get the theoretical weight of the solder paste for the 0.012” square aperture you must multiply the solder paste theoretical volume by the solder paste density. 

 0.000000576 inches³ * 4.14gm/cm³ = 0.000009439cm³ * 4.14gm/cm³ = 0.0000391gm

To calculate the theoretical amount of solder paste that will be used for each board, the weight of solder paste for each aperture on the board will need to be calculated.  Once all of the weights have been calculated they can be added together which will result in the amount of solder paste per board. 

Of course this is the theoretical value and not an actual value.  The easiest way to determine the actual paste weight per board is to weigh a board before the paste has been printed and then again after the paste has been printed.  The difference is the actual solder paste weight or consumption of solder paste per board. Of course, there will be some margin of error even in this calculation due to the weight tolerances of the board and the variations in solder paste deposits from print to print.

Let me know if I can help you calculate or estimate the amount of solder paste your project will consume.
Chris

It won't be long until we in the northern hemisphere are complaining about the snow and the cold, but right now, it is all about the heat! 

In particular about the heat that is needed to reflow high melting point (HMP) alloys.  These are generally high-Pb alloys that see very high operational temperatures. They are used for applications such as automotive under-hood or down-hole drilling equipment .

If you try and use a flux that is not formulated to withstand higher (greater than 220C) temperatures, your flux will burn off and char and never get a chance to really do its job.

So, the key is to use a flux that is specially formulated to activate at higher temperatures, like our 807HMP used in our flux cored wire.  It is ROL1 but has only 650 PPM of halogens.    (AUTHOR'S NOTE: After further testing via oxygen bomb, the flux classification for the CW-807 has been found to be ROL0. Added 11 June 2013).

You may also want to consider an alloy with a small amount of indium in it (such as Indalloy #164 which is 92.5Pb 5.0In 2.5Ag) since indium is well known for its thermal fatigue resistance.  This alloy works very well with the 807HMP.

Choosing the right alloy and the right flux are key to keeping your cool!

Carol

最近有一个客户向我们展示了他们公司新采用的“自动售卖机”库存管理系统（industrial vending machine）,真是大开眼界。在此和大家分享一下。 请看下面的图片。

这个自动售卖机和我们平时看见卖零食的机器表面上没什么大区别，最多是可以在机器旁边衍生多些大格子储存更多的货品。客户的采购员自豪的向我们介绍了采用这套系统后带来的好处（当然，所有好处都是围绕降低成本和容易系统管理）

• 免费机器，一年6%的rebate
• 拿到物品开始算钱: 员工凭自己的门卡在机器上取到需要的货品后，供应商才开始计算物品单价。月结。换言之，在机器上的所有物品，只要客户没有从机器中取出，供应商都不收客户钱。
• 网络监控管理：
  • 采购人员可以在机器上设置好，对所有物品的取出，谁取出，每次、每天取出多少，都可以通过机器变好程序，设置好。这样管理，知道谁拿了什么，减少浪费。一个很简单的例子：几种擦拭机器的不同牌子的纸，表面上看都一模一样，其实有一种是5分钱一张，有一种是1.5元一张。 1.5元一张的确实特别好用，某些特殊机器就是要用这种贵纸才能擦干净。采购员买了两种都放在车间。但是车间人员不知道差别，大家都随便取用，有时候用贵的纸什么都擦，甚至擦鼻子：-） 现在有了vending machine, 就可以控制只有擦贵机器的人才可以限量取到贵的纸。
  • 采购人员可以在网上实时监控，知道每种货品每个时间段的用量，谁用了、用了多少，机器中还剩下多少等。以前，很多公司的采购人员只能通过预算购买下一次的货品，但是他们对现存货品剩下量的多少，没有实时资讯，所以造成了很多取货现象。
  • 通过网络在线订货购买

看到介绍后我们都很感慨，觉得做这个vending machine的公司十分有创新性。而且那么优惠的条件（免费机器，“0”库存，年底的rebate）, 这些都是等于把现金都压在了客户那里。这个公司一定要有雄厚的实力和足够多和大的客户，才能利用规模相应(economic scales),不然毛利这么低，怎么赚钱……

我们还谈到了焊接产品(soldering materials)。目前，客户准备把焊锡棒（solder bars）和锡线 (solder wires)放在vending machine中管理，但是焊锡膏、焊锡球、助焊剂等（solder paste, solder spheres, wave fluxs）不能放, 因为solder paste 要特别的冷冻储存条件；spheres不易过多的人工操作，让小球们在瓶子里碰撞；wave flux的容器比较大，难放入vending machine……

Cheers！

Image Source

Folks,

It is hard to believe that I have been blogging for over 7 years now.  In all this time it has surprised me how much interest there has been in the solder density calculator that I developed.  At the suggestion of Tim Jensen, I have added a feature that can calculate the volume of solder paste and flux if given their masses or vice versus.  The densities of the solder paste alloy and flux are also needed.  Most fluxes have a density of about 1 g/cm³.   If you are interested in this updated software tool, download it here.

Knowing the volume of the solder and flux in a solder paste is critical if you are using the Pin-in-Paste process, with or without solder preforms.  I have also developed a software package called StencilCoach™ that can calculate stencil parameters and the special parameters needed for the Pin-in-Paste process.  I will also send this free software tool to those that are interested.

The image shows the schematic for the solder volume calculations for the Pin-in-Paste Process.  The equations were developed by Creyr Innovation’s Jim McLenaghan.

Cheers,

Dr. Ron

Folks,

There is a lot of interest in cleaning PCBs that have been assembled with no-clean solder pastes. 

Recently I discussed the topic with my good friend Mike Bixenman of Kyzen.

Dr. Ron (DR)

Mike, many of the best performing lead-free and lead containing solder pastes today are no-cleans.  They have been designed to solve assembly problems like graping and the head-in-pillow defect.  For the vast majority of applications, the small amount of residue left by a no-clean is not a problem.  However, some assemblers want the performance of no-cleans, but need to clean the no-clean residue as they have extreme reliability or cosmetic requirements.  Are there cleaning solutions for these situations?

Mike Bixenman (MB)

Absolutely!

DR

Can you tell use a little bit about these cleaning solutions?

MB

Several factors come into consideration when engineering electronics assembly cleaning agents. Design factors include the soil make-up, heat exposure, Z-axis clearance under bottom termination components, material compatibility, and cleaning equipment. Typical process goals require that all flux be removed in one cleaning cycle, shiny solder joints (no chemical attack to the alloy), fast production speed, no material effect to labels and other materials of construction, long chemistry bath life, and low operating concentrations.  

Cleaning solutions vary depending on the cleaning equipment. For solvent systems, a solvent cleaning agent is needed - with properties that allow for non-flammability, constant boiling mixture, and being environmentally-friendly to workers and the environment. For solvent cleaning agents that are rinsed with water, the cleaning agent requires a solvent mixture that can be rinsed with water while matching up to the soil and cleaning equipment. For aqueous cleaning agents, the cleaning agent is engineered with properties that provide solvency for the soil, polarity for inducing a dipole and/ or to oxidize and reduce the soil, low surface tension to reduce the wetting angle, buffers to stabilize pH, defoaming to reduce the tendency to foam at high pressures, and inhibitors to widen the passivation range on metallic alloys.

The property most critical is the nature of the soil. As soldering temperatures rise and the time exposed to higher temperatures increase, solder paste material supplies must improve the oxygen barrier and prevent flux burn out. This requires higher molecular weight compositions that may change the nature of the soil and the cleaning solution needed to remove the soil. Other factors such as processing conditions and how these conditions can change the soil’s cleaning properties must be considered. For example, excessive exposure to heat may polymerize the flux residue rending the soil uncleanable. To better understand and plan for these factors, solubility testing and matching the cleaning agent to the soil assist formulators in designing cleaning agents that are effective on a wide range of soldering material residues.

DR

What type of equipment is typically needed?

MB

Two key factors must be matched to clean:

1: Potential energy of the cleaning agent for the soil and

2: Kinetic energy of cleaning machine for delivering the cleaning agent to the soil necessary to create a flow channel needed to rapidly displace the soil.  

The cleaning machine requires energy to deliver the cleaning fluid across a distance and create enough force to deflect fluids under the Z-Axis. The capillary attraction for moving the cleaning fluid into an out of tight gaps is created by fluid flow, spray impingement pressure and surface tension effects. When cleaning under tight standoffs, cleaning agents that wet (form small droplets) improves capillary action, penetration and wetting of the residue. The solubility rate is dependent on the soil, temperature effects and concentration of the cleaning agent needed to dissolve the soil. Hard soils clean at a slower rate and remove the soil in a concentric (tunneling effect) manner. Soft soils clean at a fast rate and remove the soil in a channeling (multiple tunnels) effect.

The Z-Axis gap height has a direct correlation to the energy required to penetrate and remove the soil under components, time required to clean the soil and wash temperature. The irony is that lower Z-axis gaps increase capillary action of the flux for underfilling the bottom side of the component. When this occurs, flux residue dams up and closes any flow channels under the component. Research findings indicate that high pressure coherent spray jets are needed since energy drop is less and defective energy is higher. The wash time needed to clean under a 1-2 mil gap as compared to a 4-6 mil gap can range from 4-8 times longer. Higher wash temperatures increase the softening effect and aid in penetrating and removing the soil. The net effect is that, as components decrease in size, the Z-Axis gap height reduces and the cleaning factors needed to clean the soil increase. These effects favor spray-in-air cleaning equipment over immersion cleaning equipment.

DR

How are the results of cleaning assessed, so that we know that the boards are truly clean?

MB

The first level that we judge cleaning performance by is the visual presence of the residue post cleaning. Most cleaning processes have no problem with removing surface residue from the assembly. The issue is the residue under the bottom side of the component. This complicates the issue since the residue under a specific component is where most failures occur. These site-specific failures may reduce the confidence in existing IPC standards that correlate anion and cation ionic residues over the entire board surface area. So, when designing the cleaning process, we use test cards with bottom termination components and judge cleaning performance by the level of flux residue remaining under those components. To achieve this value, all components are removed and the surface area of the residue under components is graded and statistically analyzed.

Let me finish by adding that highly dense interconnects assembled onto circuit boards is advancing at a rapid pace. Traditional SMT component spacing between conductors was larger. No-clean post soldering residues posed minimal risks to reliability. The information age has spoiled us in expecting higher functionality in smaller spaces. As assembles reduce in size and increase the levels of functionality, cleaning becomes more important.  I hope that the cleaning factors discussed in this interview provide insight into cleaning process design considerations that may be of help.

DR

Mike, thanks.  Who should folks contact if they would like more information on cleaning boards assembled with no-clean solder pastes.

MB

Thanks for letting me share with your readers.   I would be glad to help anyone with the cleaning challenges they face.  Contact me at mikeb@kyzen.com.

Cheers,

Dr. Ron 

While it is important to have at least 10µm of solder on each side of a tabbing ribbon to form a proper solder joint during cell interconnection, more is not always better. What we have found is that thicker solder coatings may provide adequate and consistent solder joints, but at a reduced bond strength.

The test was performed on c-Si cells, with an industry leading flux, and 3 sets of tabbing ribbon with different solder coating thicknesses. The tabbing ribbon was made from the same ribbon stock to minimize any variation between test subjects. The samples were prepared on a Komax X-series tabber/stringer, and the tabbed cells were allowed to rest at ambient conditions for >48 hours after soldering to relieve stresses. Next, the tabbing bonds on each cell were peel tested at 90°F using a XYZTEC Condor 150-3. Average (not peak) bond force values across the cell were recorded. 

We are happy to apply custom solder coating thickness to tabbing ribbon for you.

I hope this helps you make a good decision when you are specifying material.

Shoot me an email!

~Jim

It is not often that we get a request for SIR (Surface Insulation Resistance) and/or ECM (Electro-Chemical Migration) results for a water washable/soluble flux or solder paste, but often enough to "inspire" me to blog about it. Generally, it is a contract manufacturer that is being asked to provide the data by their customer. So, it is difficult to get my following "argument" to flow upstream to the original requester. Often times the CM does not care. The CM has been pushed into a CYA scenario and just wants to please their customer. That is not a criticism....it is just the reality of it....and we've all been there at one time or another.

The IPC J-STD-004, for example, does provide instructions for performing SIR on water washable materials. It is definitely a valid and meaningful test. However, asking for such results from the flux or paste supplier is a little bit like asking an on-line dating participant for a photograph. Why do I say that? The SIR/ECM results of a water washable/soluble material are heavily dependent on how well the test coupons are cleaned after reflow. So, you can bet that the supplier is going to do a complete and thorough job of cleaning the test coupons for the sake of producing the best SIR and/or ECM results possible. It is only to be expected that the supplier is going to want to show the best performance of their product. (BIG) But!!!! It does not represent how well assemblies are going to be cleaned on the factory floor; and, hence, the suppliers' SIR/ECM results probably will differ from the sort of performance that will be had from an assembly cleaned on the factory floor. Depending on how well the factory cleans, it could be better or it could be worse.

So, the message is, YOUR MILEAGE MAY VARY.....if the factory is using water washable/soluble solder pastes or fluxes, and there is true concern about the SIR/ECM performance of their products, it is best to perform the test on coupons that have been processed on the factory floor with standard operating procedures, equipment, and equipment settings.  

Many thanks to Covington for making shirts that have pockets handily sized to accommodate IPC-B-24 SIR test boards ; )

A few months back, while discussing tricks for hand soldering c-Si solar cells, I mentioned flux . One tip I didn’t mention is how to APPLY flux before soldering.

Tabbing fluxes are commonly sprayed and dipped in automated processes, but flux pen application is best for hand soldering. Flux pens are small plastic containers with a spring loaded felt tip at one end. With a slight amount of pressure, the tip allows flux to wick through the felt and onto the cell.

• Since the tip valve closes between uses, evaporation is kept to a minimum.
• The unit is disposable; there are no needles or micro valves to keep clean.
• Application is uniform so there is less chance of flux inconsistencies.

I use flux pens for non-automated testing of fluxes.

If you are interested in trying one of our fluxes in pen form, send us an email at solar@indium.com.

~Jim

Indalloy Flux #2 is not the only option for soldering to Nitinol.  There is also Indalloy Flux #3.

Both fluxes are strong enough to clean the tenacious oxides off Nitinol, as well as aluminum and stainless steel.

So what are the differences?  To start with, it is the consistency of the material.  Flux #2 is a liquid flux; Flux #3 is much more viscous and is usually applied by brushing it onto the surface.  Flux #2 can also be brushed on, but it can also be sprayed or dispensed.

If you are using a higher temperature solder or have particularly tough oxides, Flux #3 is the right choice.

If your solder contains indium, you will want to choose the Flux #2 because the indium is sensitive to chloride-induced corrosion.  However, if you are using a tin-based solder, Flux #3 is an excellent alternative.

Where these two fluxes are the same is that they both require good cleaning and should not be used in electronics applications.  Both fluxes MUST be cleaned as soon as possible after reflow.  This can be done with warm (not greater than 50°C) water and mechanical scrubbing.  If the water is greater than 50°C, you risk additional reactions and possible pitting of the material.

Both of these fluxes are available online at http://buy.solder.com/Medical-Assembly-Materials/C1036_1/ .  If you have more questions, check out our medical products page or contact me and I will be glad to help!

Carol Gowans

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.

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

Folks,

Let’s look in on Patty and Pete and see how they are handling Rex “The Torrent.”

Patty wanted to give Pete a little more exposure so she nodded to him to chime in.

“It is true that Pinnacle’s line cost only 70% of Optoplace’s line and it does have a lower ‘cost of ownership’ in that it costs less to own, but we lose our shirt because of its 6 hours per week less uptime,” Pete began.

Torant stormed in, “There ain’t no way that 6 hours a week can make up for 30% savings in cost of ownership. We must be talking about over $600,000 dollars difference in capital cost.”

Patty heard this comment and wondered why people that make poor arguments need to add bad grammar, too.

“Torant makes a good point Pete,” Madigan quickly interjected.

“Actually it is $660K in additional initial capital investment per line, plus about $40K a year in service for the higher profit potential line,” Pete responded with a smile.

“I told you so,” Torant said excitedly.

At this comment Pete put up a PowerPoint® slide that showed the resulting comparison:

Pete explained, “The average of 6 hours/week of increased uptime in our typical 3 shift operation results in the additional production of more than 22,000 units per line per year for the higher profit potential line.  Each line producing on average more than $340,000 more profit.”

“But that’s not as much as the additional $660K cost of the line,” Torant countered.

“The extra capital cost is included in the calculation,” Pete calmly replied.

“Well, Torant, that’s one you lost,” Mike Madigan said in a way that indicated that discussion on this point was finished.

Torant looked temporarily defeated, but he recovered quickly. “What about the solder paste? Ultima costs $0.02/gram less than the ElectroMaterials paste,” Torant challenged.

“That’s true,” said Patty. “But we have to stir it out of the jar for it to print well, and it has poor response to pause.”

Torant wouldn’t let her finish, “But that can’t make up for two cents per gram,” he snarled.

“Not true,” Patty snapped back. “Every time the line is down for a short time we have to wipe the first print because the transfer efficiency is so poor.  We lose an hour a week of production time.  In addition, when we are printing a lot, the paste shear thins and we have to replace it with fresh paste.  We actually pay more for the Ultima paste because we scrap so much.  However, the lost time is what hurts the most financially.”

“Only one hour per week!" Torant screamed. “I spend more time than that on smoke breaks. One hour per week can’t possibly make a big difference.”

Patty rolled her eyes and then displayed another slide that showed the profit comparison.

“This slide shows that by using the Ultima paste we lose over 3,700 units of production and over $140K of profit per year per line in that 1 hour hour per week.  One hour per week is 52 hours per year, let's not forget” Patty responded.

At this, Torant slammed his fist on the table, packed up his briefcase, and literally left the room in, well.... a torrent.

Patty, Pete, Madigan, and Sam just looked at each other.

“Well, maybe we won’t have to put up with him for awhile,” Pete said smiling.

“Nice work Patty and Pete", Madigan said. "Let’s develop an implementation plan phasing everything in you recommended as soon as is practical.”

Patty was always surprised when Madigan showed a little warmth by calling her and Pete by their first names.

“Sure thing, Mike,” she answered.  It was the first time she ever called him by his given name.

“Oh, and I guess it was a good thing we didn’t get around to discussing solder preforms,” Patty teased. "The ones Torant sells have too much flux and they gum up the pick & place nozzles.”

With that comment, they all chuckled and took it as a key that the meeting was over.

Cheers,

Dr. Ron

Eric Bastow recently wrote about using our Indalloy Flux #2 for soldering to Nitinol.  He did many tests and wrote an Application Note called Soldering to Nitinol.

Fort Wayne Metals, a leading supplier of medical wire (including Nitinol) also did a test on various fluxes as they relate to break load (maximum load before the joint breaks.

The fluxes tested included:

• Indalloy Flux #2 and Flux #3
• Indalloy Flux #5RMA; #5R; #5RA
• Indalloy Flux #4R
• Flux #400 (no longer commercially available)

The #5 series and the #4R were found to not be strong enough to clean off the tenacious oxides formed on Nitinol. Therefore, they didn't enable the solder to wet the surface properly.

Flux #2 and Flux#3 gave the best results (of the fluxes tested for break load) since they removed more of the oxides and allowed for a stronger solder bond.

Want to know more about soldering to this important medical material?  You can contact Eric Bastow directly at ebastow@indium.com or email us at medical@indium.com. 

Carol Gowans

cgowans@indium.com

Folks,

Let's look in on Patty and her colleagues......

Sam Watkins, ACME New Hampshire site GM, had just finished meeting with his boss, ACME CEO Mike Madigan. He was embarrassed that these meetings always stressed him; Mike was an intimidating character. Still, why should he be nervous? Things were going really well. Profits were up at all sites since NMAC/I/O was implemented as their new profitability metric. Patty Coleman, who suggested this metric, visited all of the ACME sites with weaker NMAC/I/O and profits, and, after performing process audits, helped these sites get their acts together. Oh, and we can’t forget Pete Ortiz, who works for Patty. They seemed to have a terrific synergistic relationship. He was an integral part of this success story.

Sam started writing an email to Patty. He and Mike concluded that, building on the recent NMAC/I/O success, they need to make ACME a “copy exactly” company. They agreed that if they were implementing a copy exactly strategy they should do it with the most cost effective assembly equipment and materials. It seemed to both of them that that the lowest “cost of ownership” should be the most important metric in this strategy. Sam finished his note to Patty asking (ordering) her to implement this strategy. She was to present a plan to achieve this goal to Sam and Mike in 6 weeks. Her presentation was to include the recommended equipment and materials, a phase-in plan, the budget needed to achieve the goal, and the projected ROI of the endeavor.

Patty was in her office having lunch while reading Golf Digest and USA Today. She looked up at her laptop screen and saw Sam's email. Reading it energized her. She was happiest when working on a significant project. After digesting the contents she thought she would call The Professor and ask his advice. Sam and Mike had insisted that she put The Professor on a retainer as he had added so much value to ACME. Patty had to chuckle, it was hard to get him to send in his bill; he seemed little motivated by money.

The Professor would never tell her how many languages he spoke, so she was going to try a little French on him.  She and Rob had been studying it at home.

“Bonjour Professeur, comment ca va?” Patty cheerfully said as The Professor answered the phone.

“Très bien Patty. Comment sont Rob et vos fils? Ma femme et moi avons été inquiets au sujet de Rob. Est-ce le dos guérit bien?” The Professor replied with a Parisian accent. (Very well Patty. How are Rob and your sons? My wife and I have been worried about Rob. Is his back healing well?)

Patty sighed and thought, “Well that makes about 10 languages I have verified so far.”

“Rob is doing quite well. Word got around and my Lean Six Sigma Green Belt instructor, Jim Hall called and shared his thoughts with me about over doing it in exercise programs. Jim is a fitness instructor and a big believer in moderate exercise. Rob has promised me to tone it down a lot,” Patty answered.

“I’m relieved,” said The Professor, “Rob needs to be healthy to keep up with your sons.”

“But, I imagine you have some business to discuss,” the Professor went right to the point.

“Yes, Sam and Mike want me to head up implementing a copy exactly program with equipment and materials, and they are strongly suggesting that the equipment and materials have the lowest cost of ownership,” Patty summarized.

“Copy exactly can be very beneficial, if the materials and equipment are good choices,” The Professor answered thoughtfully.

“But I have real problems with ‘Lowest Cost of Ownership.’ It is a good metric to compare something like automobiles, but to compare equipment or materials that are used to generate a profit it can be misused.” he replied.

Patty felt she understood where he was going, but wanted to hear it from him.

“Can you give an example?” she asked.

The Professor answered, “Let’s say a man mow lawns for a living. He considers two lawn mowers for his business, one is a push mower that cuts a 20 inch path and costs $300. Assume he takes 3 years to pay off the loan to buy it. Maintenance is $150 per year and fuel is $1200 for a 30 week season. The other is a sit down lawn mower that costs $3000, with $500 maintenance per year and it uses $3,000 in fuel per year. It cuts a 50 inch path. Which has the lower ‘Cost of Ownership?’”

“That’s easy,” Patty said, “the 20 inch push mower.” “But clearly the lowest cost of ownership is meaningless,” she went on.

“Explain,” replied the professor.

Patty answered, “Well, the man is in business to optimize profit. Clearly he can mow more laws with the sit down mower. Let’s say with the push mower he can do 4 lawns a day and with the sit down mower he can do 10 lawns a day. We can also assume he gets $35 per lawn. So, for a New Hampshire 30-week lawn mowing year, he earns 4x7x30x$35 = $29,400 with the push mower and 10x7x30x$35 = $73,500 with the sit down mower. Let me make a spreadsheet to determine the profit in each case.”

Patty was one of those young people who could type so fast that it made The Professor’s head spin. In seconds she had a spreadsheet developed.

“Wow, with the push mower he only makes $27,950 and with the riding mower he makes $69,000!” Patty exclaimed.

“And the same is true in electronics assembly. The best equipment, solder paste, solder preforms, underfill, cored solder wire, and solder fluxes are the ones that help your company make the most profit. Not the ones that have the ‘lowest cost of ownership,’” The Professor summed up.

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)

With regard to soldering or wetting (coating) with indium, we are often asked to comment on the oxide formation of indium and how to remove it. We are also asked how long will it take for the oxide to reform on the surface. The procedure, below, will help you to better understand indium oxide, its removal, and how to handle it once it has been removed.

Indium is self-passivating. At room temperature, the oxide formation on the surface of the indium will be between 80-100 Angstroms thick.   Generally, this amount of oxide is not considered significant to hamper the wetting of the indium to a substrate, especially if a flux is used. Even if a flux is not used, the indium should not have any difficulty forming a joint or coating a surface.

If the application calls for an oxide-free joint and a flux cannot be used, the indium oxide can be easily removed following these steps:

·         Clean the indium in isopropyl alcohol or acetone to remove any surface organics. Allow to dry.

·         Etch the indium in 10% HCl for 1 minute to remove the surface oxides.

·         Rinse the indium in DI water to remove the acid.

·         Rinse the indium in isopropyl alcohol or acetone to remove the water.

·         Blow dry with dry nitrogen or allow to air dry.

While this etching procedure will remove the oxides, it has also opened up a whole new surface on the indium which will be prone to oxidation. Generally, the formation of oxide will begin on the surface of freshly etched indium as soon as it is exposed to air. At this time the thickness of the oxide layer is between 30-40 Angstroms. After 2-3 days of being exposed to air, the oxide has reached its passivating thickness of 80-100 Angstroms.

Note: 

Indium has the unique ability to cold weld to itself when the oxides have been removed. During the etching process, care must be taken to keep units of indium separated so they will not stick together. If they do stick, it is very difficult to separate them without distorting the indium.

If the etched indium is not going to be used immediately, storage in a nitrogen dry box is recommended . Alternatively, the etched indium can be submerged in clean acetone to prevent exposure to air.