What is a Centroid File?

Call it what you may, but surface mount assembly robots need a magic file to determine where to place your components and how to orient them. We call it a centroid. What is a centroid file and why is it important to your PCB assembler?

Many assemblers use automated equipment to place surface mount components on PCBs. One of the tools we use to rapidly program these machines is the centroid file (aka insertion, pick-and-place or XY file).

Some CAD packages automatically generate this file, some will not. Sometimes you may simply need to modify the file, and some assemblers can make minor changes to the file or create it for you for a small fee.

Ultimately, the centroid file describes the position and orientation of all surface mount components on the PCB. A centroid file includes: the reference designator, X and Y position, rotation and the side of board (top or bottom). Only SMT parts should be listed in the centroid file the basic format for the centroid file is a comma delimited (.csv) file with data in the following order: RefDes, Layer, LocationX, LocationY, Rotation.

Here’s a breakdown of the data:

The reference designator that matches your BOM and PCB markation.

Either the word “top” or “bottom.” This is not necessarily the CAD layer designator. Just “top” for a part located on the top of the board and “bottom” for parts on the bottom side of the board. Top is often referred to as the component side and bottom the solder side by assemblers and fabricators.

The “LocationX” and “LocationY” values describe the part’s offset from the board origin. The location values require that the part origin be centered in the part. The board XY origin of 0,0 is in the lower left corner of the board. The 0,0 origin for the bottom of the board is in the lower left corner, looking at the top of the board, though the board. Preferred units are in inches (0.0000″).

Rotation goes counterclockwise for all parts on top and clockwise for parts on the bottom. In both cases, this is from the perspective of looking at the top of the board. For bottom side parts, it is looking through the board, still from the perspective of looking at the top of the board.

LED & Diode Markation Guidelines for PCBs

Have you ever had an LED or other diode placed backwards? PCB assemblers work hard to place every component from the largest, highest pin-count logic chip down to the smallest passive components and micro wafer-scale BGAs correctly every single time. A key element of that accuracy is our understanding of your board and the component markings.

If you use surface mount diodes or LEDs, you probably understand the challenges involved in correctly and consistently indicating diode polarity. LEDs are usually cathode negative, while zeners and uni-directional TVS diodes can be cathode positive. Barrier diodes can be either orientation. It all depends on whether the diode is a rectifier, an LED, a uni-directional TVS, part of a daisy-chain and a host of other considerations.

When you start looking at the CAD libraries, you not only have all the differences from that manufacturer, you may also have different markation schemes from each CAD package developer and from each library builder.

Guidelines for diode polarity mark silk-screening — the diode symbol, “K” for cathode or “A” for anode. To ensure the best accuracy, we recommend extra care in marking diodes to remove any ambiguity.

The preferred method is to place the diode schematic symbol in the silkscreen. You may also place a “K” for cathode adjacent to the cathode. “K” is used because “C” could imply that the spot wants a capacitor. An “A” adjacent to the anode on the board works too, though it’s less common. If you are producing a board without silkscreen, put the mark in the copper layer or submit a clear assembly drawing with the other board files.

Relying on +, – or _ are not definitive in what they indicate and are not recommended. For example, a “+” or “-“ sign isn’t good enough, because it’s not always true that current flows through a diode from the anode to the cathode. For the common barrier diode or rectifier, it’s a pretty safe bet. However, with a zener diode or TVS, it’s not necessarily true. That is why marking a diode on your PCB with the plus sign (+) is not good practice.

Has the Economic Tide Turned?

2018 experienced a year of pump priming unlike any other during an economic growth period in our lifetimes. The US tax bill made significant revisions to the tax code, slashing taxes for (higher-income) individuals and corporations. The corporate rate alone was cut 14 percentage points, to 21%.

Moreover, taxes on profits held by US companies abroad were cut by 20 percentage points or more. That facilitated the repatriation of those cash reserves — estimated by Bank of America at $3.5 trillion, or more than 1/5th the size of the annual US GDP.

As those gains worked their way through the system, the effects included corporate buying sprees that topped anything we’d seen in at least a decade. Business capital investment budgets swelled, and suppliers’ bottom lines ballooned.

The bloom is off the rose, I’m afraid. While not a free fall, the economic reality today is that buyers are cooling off and budgets are returning to more conservative positions. Several EMS firms are guiding for slowing business conditions, and now fabricators are reporting the same. End-markets like automotive are leveling, which will have a ripple effect across the entire supply-chain.

No one likes a cynic, especially so close to the holiday season. But my advice is to go easy on the parties while aggressively going after market share. A large customer base is the best hedge against a slowing economy.



The Professor’s second visit to ACME … continued


“Well what should we do Professor?” John said weakly. 

“Clearly, not shut the line down over the lunch break,” The Professor responded quickly. 

“We can’t!” said John, “The operators are all friends and they count on having lunch together.” 

“How much are they paid per hour?” asked The Professor. 

“Ten dollars,” replied John. 

 “You can pay them $15 per hour and still make more profit if they keep the line running over the lunch break,” The Professor opined. 

“Fifteen dollars per hour for the lunch time or the entire 40 hour week?” John asked nervously. 

“For the whole week,” was The Professor’s reply. 

“I find that hard to believe,” John shot back.

“Consider 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.”

John thought optimistically, “There is such a thing as a free lunch.”

“Now, 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.

Patty listened to all of this in amazement. The Professor was helping ACME more than she thought possible.

Next 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.


Dr. Ron

Dr. 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.

Best Wishes,

The Return of Patty and the Professor: Uptime Part 2


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.


Dr. Ron

Guest Blog: The Future of Collaboration

Sawyer completes jobs quickly and accurately, works safely alongside co-workers and is an integral part of the workforce. However, Sawyer is not your average employee — he is a robot. Here, Jonathan Wilkins, marketing director at obsolete industrial parts supplier EU Automation, explains how advances in technology are changing the way that humans interact with robots.

Rethink Robotics’ robot Sawyer, is just one example of automated technology being introduced to factories. Increased automation in factories is optimizing productivity in manufacturing. While some people fear that the human workforce will ultimately be replaced by robots, manufacturers disagree as they are aware that both machine efficiency and human intuition are vital for optimum productivity.

So, how can manufacturers ensure that robots and humans can work efficiently and safely in the same workspace? Industrial robots are in the factory to complete either repetitive tasks or those that are too dangerous for human workers. Traditionally robots are heavy, simple and isolated to prevent humans getting too close.

There are now technologies that allow humans to work side by side in the factory with collaborative robots, otherwise known as cobots. But, what makes them collaborative?


Collaborative robots are specifically designed to work in direct cooperation with a human, in a defined workspace. There are also collaborative workplaces that are safeguarded spaces where the robot and human can perform tasks simultaneously. There are multiple reasons why robots like Sawyer are becoming more popular in factories.

Cobots are affordable, highly adaptable and easy to install. Small and medium sized enterprises (SMEs) are eager to adopt the technology and the manufacturing sector expects to see huge growth of cobots over the next few years.

Cobots also support the human workers themselves. Robots can complete the heavy lifting and repetitive jobs that can cause human strain. This gives human workers more time to complete more creative and intricate work.


The key consideration for manufacturers that want to benefit from human and machine interaction is how to keep workers safe. Cobots have features that prevent them from injuring any humans when in operation, because humans will be working in close proximity with the machine.

All cobots have rounded and soft surfaces to reduce the risk of injury if a human gets too close to the machine. They are also fitted with sensors that detect anything entering their proximity and have force-limited joints that will instantly stop if a human gets too close.

These safety features are vital in preventing injury, but there are other factors that manufacturers must consider when investing in collaborative robots.

There are regulations, such as ISO 10218-2:2011, that control how facilities integrate robotics into the assembly line to ensure all workers are kept safe. As part of this regulation, all manufacturers that use cobots will be required to implement safety protocols on site. However, the application will ultimately determine the safety requirements, rather than the robot itself. For example, if the robot has sharp knives attached to it then manufacturers should avoid human-machine interaction.

The Future

In the future, advancements in machine learning and artificial intelligence could increase the capabilities of cobots. If cobots become more intelligent, they will be able to complete more difficult tasks and remember previous work to help them in the future. Machine learning may also mean that cobots will be able to diagnose themselves and fix any technical issues to complete work more efficiently.

Cobots have the potential to radically change the manufacturing sector. However, there are still some skills that a robot has not been able to perfect. A robot may be able to complete a repetitive task with complete accuracy, but it is not as agile as a human. Cobots lack dexterity and therefore cannot complete more intricate tasks that humans can.

Unlike older, industrial robots, cobots have design features needed to keep workers safe. Facilities managers must combine the machine strength and precision of robots like Sawyer, with human ability to see, think and adapt for the perfect factory. So, if you find out you’ll be working next to a robot like Sawyer, you can sleep well knowing that he will be a safe, supportive and efficient colleague.


Ever Use a TI X2SON Packaged Part?

The name stands for extra small outline no-lead. It’s a newish package from Texas Instruments. In my experience, TI is one of the better companies insofar as testing and documenting manufacturability is concerned. The datasheet for this device is no exception.

The TI part is the five-lead thing above the grain of Jasmine rice, surrounded by a few 01005 ceramic capacitors. I’m selling the capacitors for $500 each. (Just kidding.)

The part is 0.8 x 0.8mm, with the five leads. TI suggests either a 4 mil (0.102mm) trace coming out of the center pad, or a 4 mil via in the pad (the via must be filled and plated at the fabricator ) to escape the center pad. They also do a nice job of detailing out the solder paste stencil layer, as in the following image:

You’ll most likely need a custom CAD footprint for one of these. Either very carefully do it yourself, or go to a solid source like SnapEDA. If they don’t already have it in their library, they’ll make it for you.

These small packages aren’t going away. We’re only going to see more of them. They may seem intimidating, but with a good footprint and a competent manufacturer, they aren’t so bad.

Duane Benson
“A ruler of follows”? That makes no sense.
How about ” a rule of followers”?


Do Bolts Go On Your PCB Bill of Materials?

The short answer: Yes. If you want prototype assemblers like Screaming Circuits to install it, it must go in the bill of materials.

For the most part, we solder through-hole and surface mount components on PCBs. As most everyone knows, all those parts need to be put in the bill of materials (BoM). The BoM is a list of all of the components to be placed on the PCB. The file typically includes an index number, the number of times a specific component will be used on the board, the reference designator from the schematic, the component manufacturer, and the manufacturer’s part number.

If a specific component is used more than once — a common bypass capacitor, for example — it will take only one line in the BoM. One field in the BoM will list the number of times the component is used, and another field will list all of  the reference designators for that part number.

You may also want to include alternate parts for components likely to go out of stock. Passives, like capacitors and resistors, are notorious for going out of stock without notice. Invariably, though, there will be a half-dozen nearly identical parts that will fit the bill just as well. Create an alternates list so your purchasing folks or manufacturer won’t get stuck not knowing if a substitute is valid or not.

But what about things that aren’t soldered, like nuts and bolts, double-stick tape, or display panels and such? Where do they go? The quick answer is they go in the BoM like all the other parts. Manufacturers build from the BoM. That means that if it’s not in the BoM, they won’t know to install it.

Some of these parts are nonstandard and can’t easily be quoted online, but they still need to be in the BoM. If you have such things, give your manufacturer a call to see how much it will cost and they can assemble it. Then either put the reference designator in the silkscreen or offer an assembly drawing with a reference designator for whatever it is.

That means a set of bolts might be BT1, BT2, BT3 …. Washers could be W1, and nuts N1. A glue dot could be G1. It doesn’t matter that much. Just make sure the reference designator in the BoM matches that on the silkscreen or in an assembly drawing.

If it requires hand operations like double-stick tape under a display, again check with your customer service rep first, but then put the display and tape in the BoM and provide any non-obvious information in an assembly drawing or special instructions.

The Return of Patty and the Professor


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’s Theory 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.


Dr. Ron

* 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.