Materials expert Dr. Ron Lasky is a professor of engineering and senior lecturer at Dartmouth, and senior technologist at Indium Corp. He has a Ph.D. in materials science from Cornell University, and is a prolific author and lecturer, having published more than 40 papers. He received the SMTA Founders Award in 2003.
I have enjoyed writing the Patty
and the Professor blog for about 10 years now. I’ve written about numerous
real-life electronics assembly examples that I have encountered in my career,
all disguised, of course.
To continue keeping things real, and to keep my readers
involved, I am inviting you to submit an authentic story from your career.
That’s right! You’re being invited to submit an idea, story, or experience that
can be built into the Patty & The Professor series.
Your experience will help many other electronics assembly
practitioners resolve their issues and avoid problems.
So, get your thoughts together, then shoot me an email at firstname.lastname@example.org. Share the details of your experience or observation. I may
ask a few questions to help me comprehend the full story. Then, I will write up
the segment and let you read it before posting. You will be credited, of
Bonus: You will also receive either a Dartmouth hat or coffee mug (similar to, not exactly like, those pictured below)!
Contact me if you are interested in submitting a story. I
look forward to hearing from you!
It’s been way too long, let’s look in on Patty and the boys…..
It was 5:30AM and Patty’s alarm went off. She was unusually tired
today because of a PTA meeting last night. She had become much more interested
in the school her twin sons went to when she found out that the school was no
longer teaching cursive writing. She was too late for that battle, but had
heard that the school was not going to teach long division. Another mother told
her that the reason was that long division was too hard and it could be done
with a calculator. When Patty heard this she “went through the roof.”
Fortunately, when Patty attended the PTA meeting, she and the other
parents were assured that long division was still being taught.
Patty’s sons would learn cursive, however, as both her mother
and her husband’s mother would teach the boys during baby-sitting sessions –
and once a week the boys would read one of the 100+ letters to home that their
great grandfather wrote to their great grandmother during World War II. All
written in cursive of course!
After her morning jog and workout Patty was in her office at Ivy
U by 7:30AM. She turned on her laptop and saw an email from Mike Madigan, her
former employer’s CEO. It read:
Dear Professor Coleman,
One of my golfing buddies owns a small jewelry firm, Galahad Jewelry in Providence, RI. One of the units in the company produces silver charms for charm bracelets. This unit is not performing well financially. After chatting with him I sensed that productivity is low, inventory is out of control, and the processes are not lean.
Could you visit his factory and perform an audit? Maybe Pete can go with you – just make sure he behaves.
The note finished with contact information for the company.
Not only was Pete willing to go, but Rob also had a colleague in
nearby Brown University that he wanted to visit. A few days later our trio
was heading south to Providence in Rob’s Buick.
“You guys don’t know squat about making charms for charm
bracelets. Do you really think you can help them?” Rob teased.
“Hey, we’ve got the great Professor Coleman here. She can solve
any problem! — Seriously, we’ve discuss this before, most manufacturing
processes are similar. I won’t be surprised if we can help them a lot,” Pete
They stayed in a hotel near the Galahad facility the night
before the audit. They arrived at the facility the next morning and met
with the site superintendent, Don Smithson. After exchanging pleasantries,
Patty and Rob toured the manufacturing, inventory storage, shipping, and
administrative areas. By then it was lunchtime. Pete had stayed behind to watch
the manufacturing line and collect productivity data. During a late lunch, they
requested some additional production and cost data from Smithson. They then
requested that Smithson give them two hours to develop a summary of their
After preforming all of the necessary calculations, Patty and
her team prepared a Powerpoint presentation. Smithson had gathered a few of the
process engineers and the manager of production Ervin “Bud” Clark. Clark was an
intimidating man with sharp features and, it appeared, a quick temper.
Patty started the meeting by reviewing the strengths of the
operation. The facility was so clean it could only be described as spotless.
The production workers appeared to have very good attitudes and the quality of
the resulting charms they produced was excellent. Bud Clark beamed as Patty was
sharing this information. Then she reviewed the “Opportunities for Improvement”
‘The greatest OFI is the line uptime. From the data you gave us,
and from what we gathered today, we calculated that your uptime is 30%,” Patty
At this, Clark turned red in the face and demanded,” What do you
mean by uptime Dr. Coleman?”
“Simply the amount of time the line is running during an 8-hour
shift,” Patty responded.
Clark was now shaking with fury, “This is the greatest insult I
have ever experienced, my lines are running almost 100% of the time. Smithson,
let’s kick these Ivy Tower intellects out of here, they’re wasting our time!”
Smithson calmed Clark down and then said to Patty, “Thirty
percent seems very low, how did you calculate it?” he asked.
“We did it two ways. Rob and I took the production metrics you
gave us and calculated uptime, Pete also monitored the line and took readings,
both methods yielded about 30%,” Patty responded.
At this Bud Clark exploded, “My lines run nearly 100% of
the time. I can’t be convinced otherwise,” he fumed.
“Dr. Coleman, can you share some of the details relating to how
you calculated 30%?” Smithson asked reasonably.
“Of course. Pete monitored the lines from the start of the shift
through lunch. The time was from 8AM to 1PM.” Patty stated.
“Well, it shows right off the bat that you don’t know our
schedule,” Clark fumed, “lunch is over at 12:30.” He was so riled that his face
was red and he was shaking.
“That’s true Patty” said, “I’ll let Pete explain.”
“Technically the lunch period starts at 12 noon, but the workers
shut their machines down at 11:48AM today. The lunch period is supposed to end
at 12:30PM, but the workers did not get back to their stations until almost
12:45PM. It then took them until 12:55PM to get the machines running. So the 30
minute lunch period was actually 1 hour and 5 minutes,” Pete explained.
“Boy, what an eye opener,” Smithson said.
Bud Clark seemed numb, but then he chimed in, “There’s no
way that extra lunch time gives us only 30% uptime,” he snarled.
“True,” said Pete, “but the 15 minute break at 10:00AM was
really 35 minutes.”
Now Smithson was getting agitated at Clark.
“Bud, what is going on?” Smithson said.
Patty felt it was time to interject some calming comments.
“To be honest, this type of situation is what we see in most
audits,” Patty said sympathetically.
“Let’s let Pete finish,” Clark said glumly.
“Works starts at 8AM, but the team really didn’t begin making
parts until almost 8:30AM,” Pete went on. In addition, set-ups for new jobs are
performed on most machines two to four times per day. In theory they take 15
minutes, in practice more like 45 minutes,” Pete went on.
“So with all of this downtime our uptime is only about 30%?”
“Yes,” Pete responded.
Patty then showed how the production data for the last 3 months
support the 30% uptime number.
“The good news is that if you can increase productivity
by only 10%, your profits will more than double,” Patty added cheerfully.
“I find that hard to believe,” Clark said with an agitated voice
and a red face.
“Me too”, said Smithson, “ if I increase productivity by 10%, I
only have 10% more parts to sell, so profits will go up only 10%.”
“That would be true if you had no fixed costs, your fixed costs
are high. Every additional part you sell brings in more revenue, but costs less
to make because your fixed cost per part is lower,” Patty explained.
“I developed an equation the shows this,” she went on.
“In this equation nimproved is
the number of charms produced in a day after process improvement – let’s say
that is 10% more than the current amount. We’ll use nold as the current
amount per day. Pu is
the price you sell the charm for and Cu is
the material cost. CostFixed represent
the fixed costs,” she explained.
“I plotted a graph of profit versus productivity increase from the cost and production metrics you gave us. Note that current profits are at about $160,000/yr. With just a 10% increase in productivity the profits go to about $360,000/yr,” Patty continued.
Figure. Patty’s Graph of Profit Increase
vs Productivity Increase.
Both Smithson and Clark sat in their chairs dumbfounded. “If we
can’t improve productivity by 10% we should be fired,” Clark humbly replied.
Discussion then ensued on how to improve productivity, much of
it focused on how to minimize or eliminate turning the machines off. Both
Smithson and Clark became energized by this discussion and also expressed their
gratitude to Patty, Rob, and Pete.
“Did you notice anything else beyond production that could help
us reduce costs?” Smithson
“You could save quite a bit by better inventory control,” Rob
“I’m off the hook on this one Smithson,” Clark teased.
“I own inventory control,” Smithson agreed, “what did
“Well you have way more inventory than you need. We especially
noted a block of silver as big as a microwave oven in your store room. We
calculated its value at about $500K. I asked some people who have been with the
company for over 15 years and they say it was there when they started,” Rob
“The block is so big and heavy, we could never figure out how to
work with it so we just put off dealing with it. Weeks became months and months
stretched into years,” Smithson sadly replied.
“In addition, the shipping department, although neat, had
multiple shipping cartons of the same box size that were partially used. People
also commented that they sometimes had to hunt for items for production or
shipping,” Rob went on.
Smithson sat in his chair looking glum.
“Dell estimated that the cost of one week’s inventory is about
1% of the value of the inventory, you have about 30 weeks of inventory. We
estimate that your inventory carrying charges are greater than your profits,”
“I always wanted to assure we never ran out of material,”
Smithson added a bit defensively.
“A worthy goal, but you can almost certainly accomplish that with five, or at most 10 weeks of inventory,” Rob replied.
The group then began discussing to how to reduce inventory and outlined a plan. Our trio agreed to come back in six weeks and access progress in both productivity and inventory control.
On the car ride back to Ivy University, Rob sensed that Patty
and Pete were a little pensive.
“Hey you two, what’s up?” Rob asked.
“It seems like déjà vu all over again,” Pete chuckled.
Patty agreed, “The first productivity problem the Professor
helped us with at ACME was so similar to this it’s so surprising.”
“That was the first of our many adventures together with the
Professor, too many years ago now,” Pete added.
Patty agreed and Rob noted a little catch in her voice ….
articles have added to the confusion regarding when fully autonomous vehicles
will become common. One
suggests that they around the corner with this quote:
“Alphabet plans to launch a self-driving service later this year,
while GM Cruise has targeted the introduction of a similar service in 2019.
Ford has that it expects to put self-driving vehicles into commercial service
it sounds like autonomous vehicles will be here this year or next. But wait,
here is a counter
article. This article points out the many issues to be resolved before
fully self-driving cars are launched. Consider this one quote from the article:
“There’s still a lot to be worked out. There are scenarios where
the car will have to break the law in order to proceed. One common scenario is,
you’re driving down a two-lane highway—one lane each way—and there’s a Fed Ex
truck in front of you, parked on the curb. You can’t go around it without
crossing the double-yellow line. Are you going to allow the car to break the
law? Now, you’re getting into a whole different set of rules, regulations, and
even morality decisions.”
two perspectives were brought home to me recently when I was on a review board
for a student projects course, Technology
Assessment, taught by friend and colleague, Eric Bish.
One of the projects was to assess the viability of bringing fully autonomous
vehicles to market by 2021. Reviewing this project helped to clarify the
dichotomy between the two perspectives discussed above.
ends up that the efforts of Alphabet, Ford, and GM are to be launched in very
controlled environments. They will only be used in well mapped out routes, with
good lane markers, no construction, on days with good weather etc. Note also
that the first quote refers to a self driving service, not private autos.
an autonomous vehicle that can completely replace a human is still (many?)
decades away. There are just too many issues such as the FedEx scenario
envisioned above that need to be resolved. I believe that over time, more and
more such issues will be discovered and push the date of such vehicles even
farther in the future.
if, on the whole, early autonomous vehicles are safer, accidents like the one
earlier this year, will put a spotlight on autonomous vehicles that will
further delay their full advent.
does all of this portend for the electronics industry? I think these issues
will require more electronics and sensors than many believe, so in a sense it
is good news for the electronics industry.
So far the meeting with The Professor had proven very valuable, John thought. He was anxious to hear the other suggestions that The Professor had. The Professor began to speak.
“Changeovers are what really hurts ACME’s uptime and, hence, productivity,” The Professor commented.
Pete was surprised. “Even you were impressed with our system of having a white board to document the logistics’ status for each future job,” said Pete.
“You are correct,” responded The Professor. “However, a changeover takes you about 2-3 hours and you have one or two changeovers per line per day,” The Professor added.
“We have a high product mix business. It’s what we do,” said John.
“The good news is that you can cut your changeover time to 30 minutes,” shared The Professor.
“How?” asked John increduously.
“By using feeder racks,” explained The Professor. “These racks allow you to set up the component reels for the next job while the current job is running. Admittedly they cost about $30,000, but they will pay for themselves in weeks. Right now you lose more than two hours per changeover loading the feeders onto the component placement machines. With the feeder racks, you just roll them and lock them in place,” said The Professor.
Pete moaned, “We already have feeder racks. We only used
them once, because they stick on the carpet when we move them.”
This comment caused The Professor to groan internally, but he hid
it well. He had noticed the frayed carpet near the component placement
John was beside himself. “It’s a good thing we are not
The Professor’s students……I don’t think we would be heading for an A,” he
thought. John responded to Pete’s comment, “Pete, let’s get
facilities to remove that rug and start using the feeder racks
Patty listened to all of this with comical fascination. She had harassed Pete about using the feeder racks several times. While the meeting was going on she drew a sketch of The Professor, who is notoriously camera shy. Oh, and she decided on the restaurant, Aujourd’hui in nearby Boston. Maybe they can pick up a Red Sox game while they’re there.
Epilogue: Six months later ACME’s uptime was a respectable 30.4%. John never had to buy another line. The improved productivity enabled ACME to increase their market share. Patty’s dinner and ball game were a complete success. She handled her victory modestly and she and Pete became best friends. Pete also joined the ranks of The Professor’s many admirers.
Dr. Ron’s note: I know that a story like this must seems too comical to be true. Every point and the associated uptime numbers, lost time etc, are all based on a real situation with no exaggeration. The Epilogue, however, is ficticious, as is the Patty/Pete friendly (?) conflict. The names have been changed to protect the innocent (guilty?).
“Well what should we do Professor?”
John said weakly.
not shut the line down over the lunch break,” The Professor responded
can’t!” said John, “The operators are all friends and they
count on having lunch together.”
much are they paid per hour?” asked The Professor.
dollars,” replied John.
can pay them $15 per hour and still make more profit if they keep the line
running over the lunch break,” The Professor opined.
dollars per hour for the lunch time or the entire 40 hour week?” John
the whole week,” was The Professor’s reply.
find that hard to believe,” John shot back.
this,” said The Professor. “Your line is up only 9.7% of an 8 hour
shift, that’s only 47 minutes. Today you lost 95 minutes over the lunch hour.
You may be able to increase your uptime to greater than 15% by keeping the line
running over lunch. I modeled your business with ProfitPro3.0 cost estimating software. Your
company will make millions more per year if you keep the lines running over
lunch. I have worked with other companies to make this change; it is really
easy with a 30 minute lunch period. If 5 people normally run the line, you
have just one stay back during lunch. That way each person only misses the
regular lunch break once a week.”
thought optimistically, “There is such a thing as a free lunch.”
let’s talk about what we can do to double the uptime from the 15% we will get
by running the lines over lunch,” said the Professor.
listened to all of this in amazement. The Professor was helping ACME more than
she thought possible.
steps? Yes, John will keep his job. But, what is The Professor’s plan to get
uptime to 30% or more? And, we still haven’t learned where Patty will go to
dinner. Stay tuned for the latest.
Ron note: As surprising as this may seem, this story is based on real
events. The uptime numbers and improvements are from real examples. Any company
that can achieve 35% or more uptime can compete with anyone in the world, even
in low labor rate countries. Sadly, few companies know their uptime or have an urgency
to improve it.
For the next few weeks I plan to repost some of the first Patty and the Professor episodes. As I visited several facilities, some of them in other industries, I found that uptime is as vital a topic as ever. Although these facilities were tracking a few metrics, uptime was not one of them. I estimated they were little better than ACME in the following vignette. Let’s all be committed to measuring and improving our processes uptimes. Now on to Patty and the Professor.
Two weeks passed quickly and The Professor returned to ACME. Patty met him at the door. “Professor, it’s great to see you,” Patty said with enthusiasm. “We collected the uptime data in real time on a laptop, no one has seen that results yet. We wanted it to be a surprise,” said Patty. The Professor suggested that he go out on the shop floor to observe the manufacturing activities until shortly after lunch. He pointed out that his observations may help to understand the uptime results.
The morning seemed to drag for Patty, she was very anxious to see the resets of the uptime data. She bet Pete a dinner for two that the uptime would not be more than 50%. If she wins, Pete and his wife will treat her and her boyfriend Jason to dinner at the restaurant of her choice.
Around 1:30 p.m. The Professor suggested that he was ready for the meeting. Patty had written a simple Excel macro to perform the calculations for the uptime. She only had to push a button and he whole room would see the result in a moment, as Patty connected her laptop to a projector. There was tension in the air, friendly wagers had been made, but the entire process team realized that their reputation was on the line.
When the number emerged on the screen, John, the manager’s face became ashen. Pete’s visage was redder than two weeks ago. John thought, “I should be fired. How could I manage this team for five years and not know that our uptime was only 9.7%.” Patty was thinking about her choice of restaurants.
“How can we be so bad?” John asked The Professor. The Professor responded, “The good news is that there are tremendous opportunities for improvement. After observing the operations out on the floor this morning, I think we can get the uptime to greater than 40%.” Pete shot back, “You’re kidding, only 40%?”
“I’ve only seen two operations that have greater than 45% uptime, and I’ve been to over 150 facilities worldwide,” answered The Professor.
“Where do we start?,” asked John.
“How about lunch?” beamed The Professor.
“We just had lunch!” Pete groaned.
“No, no Pete,” The Professor chuckled, “I mean how lunch is handled out on the line. Lunch costs the company more than 1½ hours of production in an eight hour shift. That’s nearly 20% of the entire shift.”
Now John was a little agitated. “Professor, lunch is only 30 minutes. We purposely have a short lunch period to avoid the line being down for a long time,” John said with a note of annoyance.
“John, this is true, but I watched what the operators did. Lunch is supposed to start at 12 noon, but the operators turn the line off at 11:40 a.m. They don’t get back to the line until 12:40 p.m. and it takes them more than 30 minutes to get the line running again. Today, the line was not running until 1:15 p.m. It was down for 1 hour and 35 minutes,” stated The Professor.
John thought again, “Yes, I should really be fired.”
Will John keep his job? What restaurant will Patty choose for dinner? What should be done about lunch? Where are all of the other hours lost? Stay tuned for the answers to these and other questions.
I teach a course at Dartmouth on manufacturing processes: ENGM 185. In this course, I use many of the chapters from “The Adventures of Patty and the Professor.” This book started as a series of posts on this blog and the posts ended up being gathered into the book. It’s hard to believe that the first post was nearly 10 years ago.
I think most students that have read “The Adventures of Patty and the Professor” have a sense that the vignettes in the book are exaggerated, even though I point out that I have attempted to make them as close to real events as possible. Recently, one of my grad students, Amritansh (Amro) Varshney, had a chance to see some of the real world of manufacturing. After Amro returned to Dartmouth, we chatted and he shared that not only do the stories convey the sense of how poor some manufacturing operations are run, but, in some cases, the realities are worse!
In light of this epiphany, I decided to repost some of the original episodes from the book for a new generation of readers. As you share Patty and the Professor’s experiences, remember they are strongly based on real events. I hope you enjoy the “Adventures!”
Business was good at ACME. Even in these challenging times, the company’s three assembly lines could not keep up with demand. John, the manager of the assembly lines, decided to request the funds for an additional assembly line. A member of his team, Patty, suggested he might want to consult “The Professor,*” before getting a new line. The Professor taught a course on line balancing that Patty took at the SMTAI conference last summer. Line balancing is an important part of optimizing productivity in electronics assembly. A balanced line ensures that the component placement process, usually the “constraint,” is the fastest possible by assuring that each placement machine spends the same amount of time placing components. If any machine is waiting for the others, assembly time is being wasted. In a sense, line balancing is an application of Goldratt’sTheory of Constraints. John remembered that when Patty applied what she learned from The Professor, throughput increased 25%. Unfortunately, Patty did not attend The Professor’s other class on “Increasing Line Uptime.”
John decided to have a chat with Patty about The Professor. “Patty, why do you think I should consult with The Professor, about getting a new line?”
“Well John, perhaps with some effort to improve our uptime, we wouldn’t have to buy another line,” said Patty.
“Patty, that’s a good point,” said John.
Patty contacted The Professor and he agreed to fit ACME into his busy schedule. Upon his arrival, The Professor was given a tour. As part of the tour he was shown the process that ACME used to minimize changeover time between jobs. The Professor appeared to be impressed. After the tour, The Professor asked if a brief meeting could be held with the engineers and managers to discuss the situation.
“What is the average line uptime?” The Professor asked the assemblage. There was some hemming and hawing, finally Pete, the senior process engineer replied, “I’d say at least 95%, we work our fannies off out there.” There was a murmur of agreement from the 9 or 10 people in the room. Finally John spoke up, “Professor, what is your definition of uptime?” The Professor responded, “Simply the percent of time an assembly line is running.” Pete again responded that 95% was the right number.
The Professor asked for some production metrics and performed some calculations on his laptop. In a few moments he commented, “From the data you gave me, I estimate that your average line uptime is about 10%.” Upon hearing this, Pete became red in the face, especially after Patty whispered in his ear, “I told you so.” The noise in the room became so loud that John was concerned he might have a riot on his hands. The Professor asked to speak and John, in a booming voice, asked for calm.
“Let’s not become angry, perhaps my calculations are off. Why don’t we measure the uptime for a few weeks to be certain.”
“How do we do that?” asked Pete, his face still crimson.
“Each day one process engineer will go out to the lines every 30 minutes. If the line is running, he will put a 1 in an Excel® spreadsheet cell, if the line is not running a 0 will be entered,” responded the professor.” It was agreed that this will be done and The Professor will be back in two weeks.
Will Pete’s red face return to normal? Will the line uptime be 95%? Will Patty and Pete ever be on speaking terms again? Stay tuned on May 27 for the next episode.
* The Professor, as he is affectionately called by his many students, is a kindly older man who works at a famous university. Few know his real name. The Professor is an expert in process optimization.
Soldering copper to copper with a tin-based solder, such as tin-lead eutectic solder or a common lead-free solder like SAC 305, requires only the liquid solder and copper to form the tin-copper intermetallic bond. This simplicity, with one small catch, was brought home to me by some colleagues at Speedline Technologies. They took a PWB with through-hole components mounted and ran it through a wave-soldering machine without using any flux. The result was comical. The PWB weighed about 10 pounds as it had huge solder ice cycles hanging off of it. Oxides that form on the copper created this mess. Running the board though again with a nitrogen blanket produced a beautifully wave-soldered board that could be ready to ship. So in reality, either a flux or nitrogen, preferably both are needed for successful wave soldering in addition to the solder and copper; however, it is still relatively simple.
Have sympathy for the solder scientists of the late 1970s and early 1980s. SMT was an emerging technology and the world wanted to buy solder paste; however, the only experience many solder scientists had was with wave soldering. In wave soldering, the flux’s main job is to remove the oxides from the PWB pads and components. The solder is in a molten state and its oxidation is not a main concern. In the soldering process, the solder only touches the board for a few seconds and the board only experiences the high temperatures during this brief period.
I imagine some early solder pastes consisted of solder powder with fluxes similar to those used in wave soldering. If so, they probably didn’t work too well. Consider the dramatic differences that solder paste experiences as compared to solder in wave soldering. The “flux” in solder paste has to remove oxides from the PWB pads, component leads, and solder particles, but it also has to protect all of these surfaces from re-oxidation for several minutes while in the reflow oven. To achieve this protection, the “flux” has to contain materials that act as an oxygen barrier. The most common materials used in no-clean solder pastes are rosins/resins. Rosins, or resins which are modified or synthetic rosins, are generally medium to high molecular weight organic compounds of 80-90% abietic acid. They are typically found in coniferous trees. Rosins/resins are tacky in nature, and provide some fluxing activity and oxidation resistance during the reflow process.
The reason I wrote “flux” in the above paragraph is that what most people call the flux in solder paste is a complex combination of materials. These “fluxes” will consist of:
Rosins/resins: for oxygen barrier and some fluxing activity
Rheological additives: to give the best printing properties, e.g., good response-to-pause, good transfer efficiency, excellent slump resistance, good tack, etc
Solvents: to dissolve the other materials
Activators: to perform the main fluxing action (removing oxides)
Figure. Solder pastes are one of the most highly engineered materials.
Modern solder pastes must have good oxygen barrier capability. In most reflow profiles, the solder paste is at temperatures above 150ºC for more than several minutes. During this time, an oxygen barrier is needed to protect both the solder particles and the surfaces of the pads and leads.
A common example of an insufficient solder barrier is the graping defect or its relative, the head-in-pillow defect. If you are experiencing one of these defects, a solder paste with better oxygen barrier properties is bound to help.
Before reflow, the solder paste must print well, possess good response-to-pause, not shear thin, resist cold slump, and have good “tack” to support the components after placement. During reflow, in addition to the oxygen barrier challenge, the solder paste must not exhibit hot slump, should “Avoid the Void,” not create the “head-in-pillow” (HIP) defect, work with all common PWP pad finishes, and produce reliable solder joints in thermal cycling, drop shock, and vibration environments. Whew! What a complex challenge.
As a result I would argue that solder paste is a candidate to be the most highly engineered material in the world… and it certainly is NOT a commodity.
Pity Ötzi, The Iceman, circa 3500 BC. It is believed that he was involved in copper smelting as both copper particles and arsenic, a trace element in some copper ores, were found in his hair. Not only was he being slowly poisoned by the arsenic, but to smelt the copper he had to achieve a wood fire temperature of about 1085ºC (1985ºF), as discussed in my last post. The arsenic in the copper did have a benefit, as it gave the copper a little more strength than if it were pure.
Shortly after Otzi’s time, metal workers discovered that adding 10% tin to the copper produced bronze. Bronze is not only markedly harder than copper, but it melts at almost 100ºC lower than pure copper, making metal working much easier. The Bronze Age had begun. This period coincided with what scholars would recognize as the beginning of modern civilizations, such as those in Egypt and Greece.
Since it melts at a lower temperature, bronze also fills molds better. This improved mold filling is evident in Figure 1. This photo shows a copper and bronze hatchet that I had made. The copper hatchet on the left shows evidence of poor mold filling.
Figure 1. Copper, on the left, and bronze hatchets that were made for Dr. Ron’s Dartmouth College course ENGS 3: Materials: The Substance of Civilization. Note that the copper hatchet shows poor mold filling due to copper’s higher melting temperature..
In my opinion, it is almost certain that the Bronze Age is related to the development of soldering. The first evidence of soldering was about 3000º BC where, arguably the first civilization, the Sumerians assembled their swords with high temperature solders. Since the base metal for most copper-to-copper soldering is tin, the early metal workers almost certainly learned that tin could be used to join copper or bronze pieces together at much lower temperatures than smelting.
Until the European Union’s restrictions on lead in solders in 2006, most electronics solders were tin-lead eutectic. Eutectic is a Greek word that roughly translates into “easy melting.” Figure 2 shows the tin-lead phase diagram. Note that the melting point of tin is 232ºC and that of lead is 327ºC, yet at the eutectic concentration of 63% tin/37% lead, the melting temperature drops to 183ºC. This concentration and temperature is known as the eutectic point.
Figure 2. The tin-lead phase diagram. Note the eutectic point at 183ºC.
After the EU’s lead restriction went into effect, most electronics solders are based on a tin-silver-copper alloy that melts in the 217-225ºC range. The most common of these alloys being SAC305 (Sn96.5Ag3.0Cu0.5, where the numbers are weight percentages.)
Although the eutectic point is an interesting and usually beneficial phenomenon due to its lower melting point, the true miracle of soldering is that two pieces of copper that melt at 1085ºC can be bonded together with a tin-based solder at less than 232ºC. The value of this benefit cannot be overstated. Nature has allowed us to mechanically and electrically bond two pieces of copper together at a low enough temperature that we can do this bonding in the presence of electrically insulating polymer materials. Without this feature of solder, we would not have the electronics industry! An added benefit is that the bonding is reworkable, so that if a component fails, it can be replaced without scrapping the entire electronics printed circuit board.
Soldering is an ancient technology. It is estimated that soldering was first discovered as long ago as 4000 BC. So soldering was much more ancient to Julius Caesar (100 BC – 44 BC) than Caesar is to us today. Before considering soldering, let’s discuss early copper smelting, as copper is usually the metal soldered to.
My Cornell colleague Steve Sass wrote a book, Materials: The Substanceof Civilization, on which I based my course of the same name on. In his book, Sass points out that the importance of the firing of clay can’t be overstated as it is the first time humankind changed the nature of a material. Once clay is fired it forms ceramic, a material much stronger than dried clay. Artisans first performed this feat about 26,000 years ago in what is now the Czech Republic.
While I agree with Sass’s assessment, it could also be argued that the beginning of modern technology can be traced back to the first smelting of copper. The firing of clay is too simple a process to encourage much further experimentation, which is needed for technology growth. The process of smelting of copper, the first metal liberated from its ore, is quite complex and this complexity led to further experimentation that gave us iron and steel. Continued working with metals likely developed the scientific method, hence led up to all of the breakthroughs to this day.
Consider the novelty of the first smelting of copper. To smelt copper, our ancestors had to grind copper ore, malachite (Figure 1), into a powder, mix it with carbon, and heat it to greater than 1085ºC (1985ºF). By the way, you can estimate the Fahrenheit temperature by multiplying the Celsius temperature by a factor of two and will only be off by <10% from 100º-1700ºC.
Figure 1. Malachite (copper ore) is quite attractive. Perhaps this attractiveness brought it to our ancient ancestors’ attention as a candidate for smelting. (Copyright 2018, Ronald C. Lasky, Indium Corp.)
After I cook on my outdoor grill, I clean the grates by turning the propane to maximum to cook off the grease. Typically the grill’s thermometer will read about 600ºF during this process. The grill gives off so much heat that it is oppressive to approach it to turn it off. Needless to say, noting what 600ºF feels like suggested to me that it is very hard to achieve 1985ºF with a wood or charcoal fire.
Anyway, I recruited some graduate students to try and smelt copper as described above. They purchased many bags of charcoal, used a leaf blower to supply air and worked for two hours on two different attempts and failed both times. The next year some students built a tower with vents and put charcoal on the bottom with the copper ore and carbon in a crucible on top. Their tower was similar to a roman smelting furnace for iron (Figure 2). They were successful and produced a piece if copper about the size of a penny.
Figure 2. A Roman style furnace. Dr. Ron’s students built a similar tower from cinderblocks.
These two attempts demonstrate how amazing our distant ancestors were. How did they think to do it? There were certainly many failed attempts. How did they persevere? One thing is certain, they started the trend of discovery, in about 5000 BC, that led us to today. We owe them much.