Tin: The Foundation Metal of Soldering


The vast majority of solders used in electronic assembly have, as their base metal, tin. There are some specialty gold solders, like gold-copper or gold-indium, indium based solders, and a few others that do not contain tin. Although these solders have important applications, the sheer volume of tin-based solders is overwhelming in comparison.

Tin was a metal known to the ancients, and it led them out of the Copper Age into the Bronze Age. Ten to twelve percent tin in copper yields bronze, which is much stronger than copper (see Figure 1) and has the added benefit of melting at about 950°C vs. copper’s 1085°C.

Figure 1. The addition of alloying elements, such as tin and zinc solid solution, strengthen copper. Note that about 8% tin in copper increases the copper yield strength by two and one half times. The solid solution effect also lowers the melting temperature. Find the image source here.

This difference in temperature is significant in that with primitive heating technology, 1085°C is hard to achieve. In addition, since bronze freezes at a lower temperature, it fills molds much better. This property enabled the casting of much more complex shaped objects. See Figure 2. All of these benefits resulted in a dramatically increasing demand for tin. This demand established much more sophisticated trade routes for tin and its most common ore, cassiterite; this enhanced overall trade and accelerated the spread of civilization and learning.

Figure 2. The addition of tin to copper created bronze, which is much harder and also easier to cast than copper. This castability enabled complex designs like this dirk. Image: Wikipedia

Back to solder. Soldering is a technology that has existed almost as long as the copper age. It is thought to have originated in Mesopotamia as long ago as 4000BC. Soldering was used for joining and making jewelry, cooking tools, and stained glass. Today, in addition to these applications, plumbing, musical instrument repair, and plated metal are common uses. However, electronics assembly is the largest user of tin-based solder by far. See Figure 3.

Figure 3. More than 50% of tin is used in solder. Source: Wikipedia 

One of the greatest benefits of solder is its reworkability. This property enables rework of electronics assemblies, plumbing, jewelry, and musical instruments. Without the ability to rework electronics, the industry would struggle to be profitable. Another benefit, of course, is the miracle of soldering I discussed in another post.

So, the next time you stare at your smartphone, tablet, TV, etc., remember tin-based solder and soldering are fundamental to its existence.  


Dr. Ron

The Labor Honeypot

Plexus, annually among the highest-ranking performers in the CIRCUITS ASSEMBLY Top 50 EMS Companies list, yesterday announced a new plant to be built in Thailand.

In its press release, the company touted the the facility as an example of “Plexus’ commitment to Environment, Social & Governance (ESG) best practices.” And on the surface, much of this sounds great: green building initiatives, an exterior green zone for employees, and other features.

But the Plexus Code of Conduct goes further than just green initiatives. There’s talk — lots of talk — about corporate and individual ethics, core values and leadership behaviors. And ESG criteria are more than green initiatives: the “social” component is tied to standards for managing relationships with employees, suppliers, customers, and the communities where a company operates.

From the Plexus website: plexus.com/en-us/corporate-social-responsibility

Plexus specifically cites its adherence to the Universal Declaration of Human Rights, a proclamation by the United Nations General Assembly in 1948, which in its preamble notes history’s uncomfortable past with free speech:

Whereas disregard and contempt for human rights have resulted in barbarous acts which have outraged the conscience of mankind, and the advent of a world in which human beings shall enjoy freedom of speech and belief and freedom from fear and want has been proclaimed as the highest aspiration of the common people

And commits its signers to the following:

Everyone has the right to freedom of thought, conscience and religion; this right includes freedom to change his religion or belief, and freedom, either alone or in community with others and in public or private, to manifest his religion or belief in teaching, practice, worship and observance.

– Universal Declaration of human rights, Article 18

And Thailand is complex. It routinely jails citizens, including minors, for speaking out. Defame the monarchy is punishable by up to 15 years in prison per incident. God save the king, but don’t badmouth him.

This is going to sound like I’m picking on Plexus. In fact, this is a problem facing numerous multinationals. One thing they have in common is membership in an official sounding organization called the Responsible Business Alliance (RBA). Formerly the Electronics Industry Citizenship Coalition (EICC), RBA is a group of companies that “share a commitment to ensure working conditions in the electronics supply chain are safe, that workers are treated with respect and dignity, and that business operations are environmentally responsible.”

Fancy words aside, the RBA is, in a word, a crock. The companies that make up its membership include Apple, Amazon, Foxconn, Pegatron, Wistron and other OEMs and ODMs that are routinely singled out by NGOs, in social media and in the mainstream media for disregarding worker health and local labor laws. In my view, the RBA is used as a shield: listen to what we say, don’t look at what we do.

I can’t argue with Plexus’ decision to locate factories where the labor is skilled and generally cheap. But I can’t rationalize how Plexus’ lofty goals of good corporate citizenship fit with Thailand’s pattern of state-sponsored oppression.

Just as we thought the bloom was off the rose in China. Will the EMS industry trade one labor honeypot for another?

SMT Assembly is an Optimization Process


SMT assembly is an optimization process. There is no single stencil printing process for all PWB designs. The stencil printing parameters of stencil design, squeegee speed, snap off speed, stencil wipe frequency, and solder paste for assembling all PWBs will not be the same; just as there is no single reflow oven profile for all PWBs. Fortunately, most solder paste specifications give good boundaries for all of these parameters, but typically some trial and error experiments will be needed when assembling a new PWB design that is not similar to past assemblies.

The need for optimization is most obvious when trying to minimize defects. As an example, minimizing graping is often facilitated by using a ramp to peak reflow profile. However, the ramp to peak profile may acerbate voiding. See Figure 1.

Figure 1. The ramp to peak reflow profile may minimize graping, but acerbate voiding.

Figure 1. The ramp to peak reflow profile may minimize graping, but acerbate voiding.

Thankfully your SMT soldering materials and equipment suppliers deal with these optimization issues on a daily basis. So if you are ever stuck with some challenging SMT assembly process, contact these solder materials and equipment experts first.


Dr. Ron

Is Quantum Computing Emerging to Solve Practical Problems?


I read with interest Zohair Mehkri’s SMTAI 2020 paper titled “How Quantum Computing (QC) will Revolutionize Electronics Manufacturing.” I will start by saying that he gives a very good Quantum Computing 101 overview. This is no easy feat, as QC is a difficult technology to understand. I will humbly state that I still struggle to understand the basics, and I’m sure I don’t understand QCs as well as he does.

Figure 1. IBM is a leader in QC. Image source: https://www.ibm.com/quantum-computing/

However, I have two main concerns with Zohair’s paper. One is that it may give the impression that QC is becoming a practical technology and will soon be widely available — to the point that we can use it to solve electronics manufacturing problems.

QCs are rare; there are about 30 worldwide, 15 of which are owned by IBM. Although to be fair, Shenzhen SpinQ Technology gave this recent announcement: “On 29 January 2021 Shenzhen SpinQ Technology announced that they will release the first-ever desktop quantum computer. This will be a miniaturized version of their previous quantum computer based on the same technology (nuclear magnetic resonance) and will be 2 qubit device. Applications will mostly be educational for high school and college students. The company claims SpinQ will be released to the public by the fourth quarter of 2021.”

Since the device has only two qubits, it will more than likely be for educational purposes not intended to solve real problems. It will be interesting to see how it emerges later in the year. 

Almost all QCs are superconducting, meaning that they require very low temperatures to operate as cold as -460°F, which is colder than liquid helium. They are also extremely delicate; even slight vibrations causes them to fail.

So, we might be able to rent time on a useful QC sometime in the future, but QCs won’t be common any time soon.

The other concern I have is what is the need for QCs? Most of the practical problems that face us can be solved by conventional computers. In addition, only certain types of problems can be solved by QCs. As stated in Wikipedia: “However, the capacity of quantum computers to accelerate classical algorithms has rigid upper bounds, and the overwhelming majority of classical calculations cannot be accelerated by the use of quantum computers.”

QC is an exciting technology and many wonderful discoveries will no doubt come from it. However, I am skeptical that it will solve practical problems anytime soon.


Dr. Ron

The Rule of 72

Four years ago, the big boss, 6′ 6″ tall, 350 pound Mac Savage, said that the goal for the sales of a new product was at least 20% growth rate per year. The team is in a room prepping for a review with Savage (sometimes called Big Mac or, in jest, “The Whopper”) when the person responsible for analyzing the data, Charlie, comments:

“Well in 2016, sales were 100K units and four years later in 2020 they are 200K. So, in four years, sales increased 100%. Therefore, the yearly increase was 100/4 or 25%. So, we beat the goal by 5. So, Big Mac should be happy,” Charlie says.

There is a murmur of agreement among the 10 or so people in the room. And a few comments like, “It’s always good when The Whopper is happy,” were quietly said.

Helen chimed in, “That’s not true; using the ‘Rule of 72,’ the growth rate is 72/4 = 18%. So, we are a bit short.”  

Fred, who was always a bit annoyed at smarty-pants Helen chimed in, “I think Charlie is right, 100% growth in four years is 25% per year.”

Helen responded, “With your logic, if the growth rate was 25% after the first year, sales would be at 125%, right?”

Everyone in the room murmured in agreement.

Figure 1. The Team: Helen is to the far left. Charlie is the bald guy with the beard holding a sheet of paper. John is the chap wit his laptop open. Fred has the red shirt on and June is to the right with the long blond hair. 

“But would second year sales be 150%?” Helen went on.

There was some mumbling, then John, a young new hire said, “You would add 25% of 125%. My calculator says the total would be 125% plus 31.25% equals 156.25%, not 150%.”

John, then got excited and did some more calculations, “The third year is not 175% with 25% growth per year, but 195.3%, and then the fourth year is 244.14%… much higher than 200%. The growth compounds.”

Everyone groans anticipating the disapproval of “Big Mac.”

Charlie finally asks, “is Helen’s 18% growth rate right?”

John makes a few trial and error calculations and says, “18% seems a little low; it’s more like 18.9%, but it’s not 25% or even 20%. But 18% was a pretty good first estimate.”

“The rule of 72 is an estimate, it gets more accurate around 8 years,” Helen chimed in.

“Jeepers, look at the clock, we only have 45 minutes before Mr. Savage comes to the meeting and wants our report,” June warned.

After a brief chuckle that June was the only one to call the big boss Mr. Savage, instead of Big Mac or The Whopper, the team got to work putting together Power Point slides for Charlie’s presentation. They finished with 5 minutes to spare, enough time to freshen their coffee cups or hit the restroom.

At 11AM sharp, Savage came into the room and Charlie started his presentation. Everyone was nervous about Savage’s response.

Charlie summarized that by using the Rule of 72, the growth rate was short of the 20% per year target, but was more like 72/4 or 18%. He pointed out that a more precise calculation showed that the growth rate was 18.9%.

The entire group expected that Savage was going to blow his top that the 20% target was missed. But, he calmly said, “Well, the 1.1% shortage is unfortunate, but I’m impressed that you didn’t say the growth rate was 25%. I am more impressed that that you knew to use the Rule of 72 and more so that you were able to fine-tune your work to get the more precise. Great work Charlie!”

Everyone in the room rolled their eyes, especially Helen and John. Someone from the group was about to speak up, when Charlie, red faced said, “Sir, I should point out that Helen suggested using the Rule of 72, and John did the more precise calculations.”

“Charlie, you are a good leader, giving credit where it is due. Let’s have this team develop an action plan to improve the growth rate. We should meet in a week to review your plan,” Savage said.

There was a palpable sigh of relief among the team.

Savage, ended with, “Who is this new guy John?”

John was introduced by Charlie as a recent grad of Tech.

“John, I got my MBA from Tech,” Savage said.

“John, I want you to derive The Rule of 72; it will be a good experience for you. See if you can do it without looking anything up,” Savage went on.

John was a bit shaken, but he was able to derive The Rule of 72. See his derivation below.

The derivation of The Rule of 72


Dr. Ron

The Miracle of Soldering


Imagine you are Guglielmo Marconi, and you opened the first radio factory in Chelmsford England in 1912. Using Lee De Forest’s 1906 invention, the triode vacuum tube, your early radios needed a way to connect the various electronic components together. Enter soldering. Soldering is the most cost effective and reliable, some might say only, way to connect electronic components together. It has been since the birth of electronics with the radio.

It is interesting to ponder some of the effects that the radio had on civilization and society. Before the radio, most of the United States was disconnected. People in California didn’t know what was happening in New York in anything like real time. There was also no national entertainment. Following early broadcasts in the 1920s, radio was a staple of most American homes by the 1930s. Families would gather around the radio after dinner to listen to the news and comedy, drama, music, etc. This golden age of radio lasted from the 1920s through the 1950s until radio was supplanted by television. See Figure 1.

Figure 1. A young girl listens to the radio in the 1930s. It would be difficult to overstate the impact of radio…all enabled by soldering.

Electronic soldering, in a sense, is a miracle of technology. It enables connecting copper to copper at a temperature of less than 230°C. The connection is reversible, conducts electricity well, and is mechanically strong. This soldering temperature is crucial for electronics, as the printed wiring boards and component packages contain polymer materials that cannot withstand temperatures much higher than 230°C. This low soldering temperature is especially impressive when considering that to bond copper to copper without solder would require temperatures near that of the melting point of copper or 1085°C.

To work its magic, solder forms intermetallics with copper. See Figure 2. The intermetallic closest to the copper is rich in Cu3Sn, and that closest to the solder is rich in Cu6Sn5.

Figure 2. A schematic cross section of a component lead soldered to a PWB pad. 

It is important that the soldering bond is reworkable. The electronics industry would have difficulty being profitable without this important feature of soldering as most assembly processes have some yield loss that requires rework.

So, the next time you use your smartphone, PC, or TV, remember it wouldn’t be possible without the miracle of soldering.


Dr. Ron

Figure 1 source: By Franklin D. Roosevelt Library Public Domain Photographs – This media is available in the holdings of the National Archives and Records Administration, cataloged under the National Archives Identifier (NAID) 195876., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2151524

Passive Demand Anything But Passive

The component distributor TTI has released its first quarter market report and the outlook is ominous: 28 passive electronic component types have increasing lead times, while 24 saw price increases. Tantalum molded chip cap lead times are now up to 32 weeks.

Lead times for most connectors remain stable, although prices are climbing. The exception is TE, whose lead times are climbing.

Memory supplies are also generally getting tighter.

With some component manufacturers now requesting 18 month forecasts, the risk for double-bookings is on the rise. Beware! Someone always gets stuck holding the bag of chips.


‘We are Stronger by What Unites Us’: An Open Letter from PCEA and SMTA

My name is Stephen V. Chavez CID+ and I serve as the President of the newly formed Printed Circuit Engineering Association (PCEA). PCEA is a trade association for professionals in the electronics industry. There are several other trade associations, some large or small, some old or new that currently exist. We seek to affiliate in a cooperative manner with each one. I have observed that we all attempt to serve the greater good in the electronics industry. Each group has evolved, grown and hopefully we all seek to coexist.

I know at the PCEA many individuals are involved and have historically been involved with IPC, SMT, IEEE, and many other associations. We have served and continue to serve in each other’s ranks. In particular I have the distinguished privilege to serve as an IPC-CID+ Master Instructor. I also serve as a volunteer on some of the IPC standard committees. I am honored for the privilege to serve in their ranks.

A recent column [Ed. note: Because the column was not in PCD&F/CIRCUITS ASSEMBLY, we are not linking to it here.] I read takes issue with the efforts of IPC in our industry, and while well-intended, I do not recognize the picture it paints. Among other things, the author suggests a lack of contact between IPC and the American educational system. In fact, IPC has a robust college outreach program across the US, and dedicated staff to support it. Keep in mind, the effects of the COVID-19 pandemic has slowed many good efforts to engage with engineers and future engineers worldwide, and this is no exception.

Moreover, in my opinion the best path to take is to volunteer our time – as we in the PCEA are doing – to educate our colleagues, the newer members of our industry, and the future
ones. Note the emphasis on the word “our.” IPC is a reflection of ourselves. Its staff, like
that of PCEA’s and many other associations and professional societies, comes from industry. We are all evolving and attempting to serve the industry at large in so many ways. It is a tribute to IPC that it has successfully navigated the changing industry so well over 60 years, and we all owe them a debt of gratitude and allegiance for so many of their great achievements. I once communicated a perspective about the IPC that bears repeating, “IPC is not a Them, rather, it is an Us!”

SMTA – Tanya Martin, Global Executive Director
SMTA has been fortunate to be serving the global electronics manufacturing and design
industry since 1984. We support professionals by facilitating access to national and international communities of experts, as well as accumulated research and training materials from those dedicated to advancing the industry. Some of our most important work is done within our local chapters (national and international) in connecting professionals for education, training, and fellowship. We have invested great resources into the college and university programs and support many SMTA student chapters around the US to be a bridge between industry and academia.

SMTA and PCEA both agree that IPC along with other trade organizations such as SMTA, IEEE, EIPC, others including the newly formed PCEA can coexist and collectively make this industry better. Each of us has the potential to serve the participants. Many of those participants are involved with several trade associations. We have seen IPC successfully reach into the community, academia, professional development, government advocacy, standards development, engineering, manufacturing, OEM business, contract manufacturing and the list can go on… The same thing can be said about the other trade associations. We believe we are all better served by our common welfare and the things that unite us are bigger than the things that divide us. We at the newly formed PCEA are ardent supporters of the IPC and their mission within the industry. We seek to affiliate and be proponents of their mission to serve the electronics industry. We encourage everyone to respect them not for their perfection but for the general overall benefit that our industry receives on so many fronts.

If faced with the question of whether to be givers or takers to the industry, we choose “givers.” Like all the trade associations, IPC is organic and adaptable, addressing the needs of those they serve the best they can. We are grateful and support their mission!

Stephen V. Chavez CID+
Chairman, PCEA
Collaborate, Inspire and Educate
Cell (602)369?3349

AI and Autonomous Vehicle Challenges: Common Sense, Flexibility, Dexterity, and Situational Awareness

I have been following advances in artificial intelligence (AI) and autonomous vehicles (AV) for some time now. At first, I was a cautious; then I became a skeptic; and now I am a doubter.

AI can do some amazing things. More than 20 years ago, Deep Blue beat World grandmaster Garry Kasparov. Today, AIs can routinely beat chess grandmasters and other world experts at games like Go.

Although impressive, these accomplishments play to AI’s strengths. Any activity that can be reduced to algorithms are natural for AIs. These AI victories have created a belief by many that AIs will soon take over most jobs and eventually become our masters. Witness such motion picture franchises as The Matrix and The Terminator. Some serious intellects buy into this concern as shown in the book Our Final Invention. This book posits that AIs pose a threat to human existence. The book extrapolates the successes of AIs discussed above and predicts that AIs will eventually be many times more intelligent than humans and will somehow develop something like consciousness. Ultimately, the AIs will seek to eliminate us.

I find these concerns almost comical. AIs connected to robots can do some very impressive things. In electronic assembly, they can hand solder very effectively. Perhaps better than humans, and they don’t get tired. But, they are not flexible. If the hand soldering operation changes to a different design, the AI must be reprogrammed. Whereas a human can quickly change from design to design. Lack of flexibility is a major AI drawback.

AIs also lack common sense. As Stephen Pinker has pointed out, no AI can empty a dishwasher. This is a profoundly common sense operation for humans. Yet this task is not only beyond AIs of today, but likely will be for a long time. Even something as simple as unloading boxes from a truck is a challenge to AIs as pointed out recently in Bloomberg BusinessWeek.[i]

This lack of flexibility and common sense makes it very hard for AIs to compete against humans when multiple tasks are required.

It is also difficult for AI robots to display dexterity. They may be able to pick up a chestnut, but crush a strawberry. This task is simple for an 18-month-old human.

The promise of autonomous vehicles is also greatly exaggerated. For a few years, some self-driving cars have been able to drive 95% of the route from my house in Woodstock, VT, to Boston’s Logan airport. However, they have made little progress in negotiating country roads, detours, and routes with complex signage. In addition, AVs lack situational awareness. As an example, AVs can’t look at a group of people near a street corner and sense if they are planning to cross or not.

Detours are hard for AVs. (Source: https://nj1015.com/is-the-detour-sign-a-thing-of-the-past-in-nj/)

So, I don’t see AIs taking all of our jobs or AVs putting truck drivers out of work any time soon. But the good news is that more electronics will be needed as these technologies make their slow advancements. So I see a busy future in the electronics assembly world.


Dr. Ron

The Pareto Chart: Crucial in a Continuous Improvement Plan

The Pareto Chart is a simple way to plot failure data that gives priority to the failure modes with the highest number of fails. This technique was developed by Vilfredo Pareto in the late 1800s to early 1900s. Pareto was studying social and economic data in Italy. He was one of the first to observe the 80/20 rule. In that, about 80% of property in Italy was owned by 20% of the people. Today many people use this rule. I have heard salespeople say that 80% of their business is from 20% of their customers as one of many applications of this rule.

In categorizing fails in electronics assembly, about 80% of fails are in 20% of the failure modes. Let’s look at an example (Figure 1). In this figure, we have plotted the number of fails versus the failure mode. Note that shorts is the most common failure at about 300, whereas opens is 75, missing components is about 50, and solder balls about 35.


Figure 1. A Pareto Chart of Electronic Assembly Failure Modes

These data should be used to develop a continuous improvement plan. Obviously, shorts should be focused upon first. Typically, one would use process data such as statistical process control (SPC) data to solve the shorts problem, most likely looking at a process metric like the volume of the stencil printed deposit.

I developed a graph similar to Figure 1 when I visited a client. The manager was convinced that solder balls were a big problem. When I asked the quality engineer for the supporting data, he said there was none. So, I asked if they collected failure data; he said they did. I then asked what they did with the data; he said they filed it away having never looked at it!

I asked to see the last several weeks of data and I plotted the data similar to that in Figure 1. It ended up that solder balls was the fourth biggest defect, not the first. As a result of using a Pareto Chart, the company focused on fixing their defect with the greatest number first, etc.

Pareto Charting is a simple yet crucial process in continuous improvement.


Dr. Ron