Elementary, Mr. Watson: The Anatomy of Your PCB Component, Part 2

At the start of my series on the anatomy of a component, I noted that the component has two major divisions. The first is information that consists of name, description, parametric information, sourcing (part choices), and the datasheet (Figure 1). Next, the component comprises a symbol, PCB footprint, 3D model, and simulation models.

I then gave the example of the dissection of the frog, with the analogy that every part has a purpose. In the same way, each part of our component has a distinct purpose in our PCB design, including our models.

Watson_July_Fig1.jpg

Schematic Symbol
The first model is the schematic symbol. As we all know, a schematic symbol is a pictogram representing various electrical and electronic devices or functions. A glance at some of the symbol's standards, such as IPC-2612-1, IEC 60617, or ANSI standard Y32, shows that it is a vast study area—fortunately, with industry-wide standards.

Simple vs. Complex Component Symbols
Most libraries I've seen consist of discrete and straightforward components. The schematic symbols used are only a few pins, simple representations, such as resistors, capacitors, inductors, transistors, and diodes. These types of simple symbols are created once and used multiple times. There are also complex symbols. These are the reverse: often single-use symbols tied to a specific component with hundreds or even thousands of connections. With such complexity comes the need for organization and best practices.

Schematic Symbol Best Practices
When constructing your schematic symbols, it's essential to have accuracy, consistency, and quality. But more importantly, remember that the symbols are the building blocks for everything else in your design. It is often said that if your schematic design were a novel, the symbols would be the words. This could not be more accurate. The quality and clarity of your schematic are based on the precision and structure of your symbols. Got a messed-up schematic? Most likely, you've got messed-up symbols. So, start with your end-objective in mind to have good schematic design practices and place those same principles in your symbols. Our goal is to have a clean schematic that is clear, understandable, and easy to follow. There is a certain quality to an exemplary schematic that always amazes me. When you can quickly identify the power, ground connections, and the flow of the circuit from left to right, top to bottom, there is uniqueness and beauty to reading a schematic like that of a fine novel.

Keep in mind how you want your final schematic to look. The same thoughtful steps should be put into your symbols. Many times, symbols are arbitrarily thrown together. One of the worst things I've seen is when someone copies the position of the pins on the component precisely as they are on the footprint. I know this may come as a shock to some, but the IC designers were not thinking of you as a PCB designer, the flow of the circuit, or the routing of the PCB when they laid out the silicon chip inside that IC. They were making the fastest route to get connections to the outside world.

Watson_July_Fig2.jpgDivide and Conquer
The first best practice is to divide and conquer your symbols. Learn in detail the breakdown of every component you use; for example, ATMEGA2560-16AU Atmel microcontroller with 256 KB in-system programmable flash, 8-bit. The datasheet classifies and shows the purpose of each pin. You see the organization of the 11 ports of 8-bits (except Port PG). Then have the reset circuit. You then have the connections to the crystal and the power and ground. When building this symbol, do not organize the pins of the component numerically. That may be the physical layout of the IC silicon die but not the electronic operations. Instead, order the pins based on their grouping and purpose. Doing so can easily make the required connections to the same ports, control lines, power, ground, etc. That allows more flexibility when creating your schematic.

Most EDA design software allows you to create various parts connected to a single component. It allows you to take components and break them into smaller, manageable pieces. Of course, we would do that on a large pin count component. Still, it should also happen with even small and low pin count components; when a component has the same functionality, you can easily separate and break it into manageable parts. This practice will open much more flexibility and help create a clear and readable schematic.

One of the most critical parts of your schematic symbol is the "pins." These will be where the connections are made for your circuits and ultimately into your PCB design. Pay attention to several details. Have a set standard and follow that standard. All components should have the same pin length and characteristics. It was drilled into me as a young PCB designer: grid, grid, grid, and that the layout of your schematic begins with the symbol. All pins should be on a 100-mil (25 mm) grid. One of the biggest mistakes new designers make is ignoring their grid settings. By keeping the symbol pins on a large grid, you then place those components on the grid and finish it by making the connections on the grid. That process assures that you make all connections. Many times, it is easy to miss an off-grid pin and connection. To the naked eye it looks fine, but you miss it, and don't realize it until your circuit doesn't work.

Watson_July_Fig3.jpgYou should distinguish each pin with both a pin identifier and name. The name should include the full name according to the datasheet. Don't take shortcuts on the naming of your pins. With many complex components, pin identification gets rather elaborate. But identifying the pin by its "full name" helps the development, debugging, and troubleshooting process down the road. Of course, that does take more time to create your symbol, but the return on your investment is enormous.Watson_July_Fig4.jpg

Figure 4: Similar components can lead to problems unless they're identified by their full names.

A moment ago, I purposely said to use a pin identifier rather than a pin number. I have left the best for last, and it’s probably the most controversial. When we look at the footprint model, it is vital to have the symbol pin identifiers match the pins of the footprint. A common practice, especially with some components, is not to use numbers at all but rather pin identifiers, especially for components such as diodes, transistors, MOSFETs, etc.

fig5_watson_0722.jpg
Figure 5: In a footprint model, be sure your symbol pin identifiers match the pins of the footprint.

For example, with an ordinary diode, you identify the pins as anode (A) and cathode (K) or MOSFETs as gate (G), drain (D), and source (S). The transistor with base (B), collector (C) and emitter (E). Of course, having an alpha or numeric pin identifier has pros and cons. But I have used both systems and have seen that using alpha allows for more standardization of the footprints. We will take a deeper look into this with the footprint models.

John Watson, CID, is a customer success manager at Altium.

Download The Printed Circuit Designer’s Guide to… Design for Manufacturing. You can also view other titles in our full I-007eBooks library.

Back

2022

Elementary, Mr. Watson: The Anatomy of Your PCB Component, Part 2

07-13-2022

In the start of my series of the anatomy of a component, I discussed that the component has two major divisions. The first is information that consists of name, description, parametric information, sourcing (part choices), and the datasheet (Figure 1). Next, the component comprises symbol, PCB footprint, 3D model, and simulation models. I gave the example of the dissection of the frog, with an analogy that every part has a purpose. In the same way, each part of our component has a distinct purpose in our PCB design, including our models.

View Story

Elementary, Mr. Watson: The Anatomy of Your PCB Component, Part 1

06-16-2022

One of the classes I dreaded the most in school each year was biology. This was because I knew it was only a matter of time before I would face the rite of passage for most high school students: dissecting a frog. It wasn’t something I ever looked forward to. We had to go through the same educational exercise and maybe with the same apprehension for most of us. But my point in bringing up the painful experiences of our high school years is, although it was difficult, I did learn a powerful lesson: Every part has a purpose.

View Story

Elementary, Mr. Watson: The Five Pillars of Your Library, Part 5—Traceability

05-12-2022

We have reached the end of this series regarding the five pillars of the component library. We now have a robust library that provides the required resources for the ever-changing industry. Above that is having a flexible library to grow with the company. The final pillar is traceability. Why is traceability so essential and considered a pillar of our library? Read on for details.

View Story

Elementary, Mr. Watson: The Five Pillars of your Library, Part 4—Review

04-14-2022

I trust that you have been enjoying this series on the five pillars of your library. Now that we have a single library managed using our revisioning, and we have lifecycle schemes organized so that we can easily find something in the component category, family, and subfamilies, we are now ready to look at one of our library's most vital principles and pillars: reviewable.

View Story

Elementary, Mr. Watson: The Five Pillars of Your Library, Part 3—Architecture

03-10-2022

Before I continue with the series of the five pillars of your library, I want to do a little review. Although every library is different, the five pillars are consistent with any sound library. You place these pillars to support a specific building section in building construction. To pull one out requires the remaining ones to hold the total weight above. So, each of these supports is needed for your library to succeed. You cannot choose which of them you intend to follow; to pull just one out results in the toppling of the others.

View Story

Elementary, Mr. Watson: The Five Pillars of Your Library, Part 2—Managed

02-17-2022

The 1972 classic movie “The Candidate” tells the story of Bill McKay (played by Robert Redford), who was running for the state senate. Although he was a long shot and an underdog, McKay ends up surprising everyone with an incredibly close win. After the concession speech of his opponent, a vast mob surrounds McKay. He fights through the crowd, trying to reach his campaign manager Marvin (played by Peter Boyle). Finally reaching him, McKay pulls Marvin aside into a hotel room, sits on the bed, and after several seconds of silence, finally asks a very intense question “So, what do we do now?” The campaign manager looks bewildered, so McKay asks the question again, “What do we do now?”

View Story

Elementary, Mr. Watson: The Five Pillars of Your Library, Part 1

01-13-2022

I have recently had some great conversations with many of you, and the same question keeps coming up: What does it takes to have an excellent component library? So, I have decided to kick off the new year by taking a deep dive into your PCB component libraries and looking in detail at the five pillars of your library. So along with taking the tree and the decorations down and making your New Year resolutions, let's resolve to take an honest look at our component libraries and get them in order.

View Story
Back

2021

Elementary, Mr. Watson: PCB Data Management and Security

12-12-2021

As a grandfather of six grandchildren, one of my great joys is spending time with them. There is nothing better than spending an afternoon at the park and especially playing on the teeter-totter. It's all fun and games until grandpa gets on one side, and they try to lift me. Then the harsh reality and a teachable moment in leverage, balance, and just how heavy grandpa really is hits pretty hard.

View Story

Elementary, Mr. Watson: We’ve Never Done It That Way Before

11-11-2021

The September edition of Design007 Magazine discussed the theme of collaborating and working with a team. In that issue, I wrote a feature article called “PCB Design Is a Team Sport.” After that edition was published, I had several follow-up questions and conversations with individuals; they agreed on the importance of teamwork but felt that it's easier said than done. It's challenging because of the inherent problem of team members accepting or handling change very well. Change it's a word that sends shivers down the spine of some. You know those sort of individuals. They're easy to identify. The ones that constantly remind everyone, "We never did it that way before." As if how we did things in the past was so much better.

View Story

Elementary, Mr. Watson: First, Component Shortages, and Now Hot Dogs?

10-14-2021

When I considered the title for this month’s article, I seriously considered calling it "From the Frying Pan Into the Fire" because I’m sure you’ve noticed recently that the component shortage problem has only worsened—we’re now seeing other supply lines breaking down.

View Story

Elementary Mr. Watson: PCB Design—It's a Team Sport

09-29-2021

One of the hard lessons of this past year was about the value of the team and collaboration. I have repeatedly heard how many of us have a newfound respect and appreciation for the teams we work with inside our companies. Out of necessity, we had to find new ways to collaborate.

View Story

Elementary, Mr. Watson: The Danger of Rogue Libraries

09-16-2021

For PCB designers, the most common part of the library is the collection of components used in the PCB design process. But, I have seen some libraries have other information, including a resource area, a group of documents, standards, and articles. So basically it can have anything you want.

View Story

Elementary, Mr. Watson: Epic Fails with Design Rules

08-12-2021

Various sciences, including physics, mathematics, chemistry, are significantly involved throughout the PCB design process, rules that can sometimes be bent but not broken. However, the rules that designers break and ignore altogether and very often are the design rules.

View Story

Elementary, Mr. Watson: Managing Risk in PCB Design

08-05-2021

PCB design is like bungee jumping. With the complexity of a PCB design, the intricate details, and various steps, it's rather easy to make mistakes. Those mistakes, many times, do not show up until it's too late and the board has gone off to fabrication and assembly. By the way, a good rule is not to use your assembly house as your quality control team for PCB designs.

View Story

Elementary, Mr. Watson: Time to Market, from Ludicrous Speed to Plaid

07-18-2021

Mel Brooks may have something to teach us about going "ludicrous speed" in getting our designs to the finish line. John Watson explains.

View Story

Elementary, Mr. Watson: Trust but Verify

06-10-2021

Over many years, I have seen some elaborate PCB library systems. However, the best ones were those not based on the size but rather the quality of the information. That old axiom is definitely “not quantity but rather quality.”

View Story

Elementary, Mr. Watson: Paying the Price To Be a PCB Designer

05-13-2021

Today, the electronics industry is flourishing with innovations and technologies. The result is that the “good” designers are left in the dust. Truthfully, our industry doesn't need more good designers; rather, we need great designers—those who can face any challenge and instead of cowering in the corner, looks at the task at hand and says, "Bring it on."

View Story
Back

2020

Elementary, Mr. Watson: Demystifying Bypass Capacitors

12-17-2020

As PCB designers, we work under the simple rule of cause and effect, and a PCB design can quickly become a petri dish for the butterfly effect to flourish. One of those areas that can quickly snowball into major problems is your PCB power distribution structure. When it goes wrong, it usually goes very wrong and has significant issues throughout your design.

View Story

Elementary, Mr. Watson: Density Feasibility Putting 10 Lbs in a 5-Lb Bag

11-18-2020

Whether on a customer, a system, or a PCB level, it’s essential to understand the final objective and how you intend to get there and meet the customer need at the forefront of any project. In this column, John Watson addresses density feasibility and more.

View Story

Elementary, Mr. Watson: Location, Location, Location

10-15-2020

When it comes to PCB design, one of the most overlooked principles is component placement. Similar to a home, the component location has a considerable impact on the quality and is the real value of a PCB design. John Watson examines five rules to follow when it comes to component placement.

View Story

Elementary, Mr. Watson: Overcoming PCB Designs Pitfalls

09-10-2020

When starting every PCB design, the hope is that we can navigate through any pitfalls that arrive. Unfortunately, many times, issues happen that you do not handle correctly; they fall through the cracks and end up in your PCB design. John Watson explains how that is when the real problems begin.

View Story

Elementary, Mr. Watson: How to Ruin Your PCB Design in 4 Easy Steps

08-06-2020

John Watson has seen firsthand how quickly PCB designs can “go off the rails” by not following a few simple principles. In this column, he looks at four practices that can easily ruin your PCB design.

View Story

Elementary, Mr. Watson: PCB Components Naming Conventions

07-09-2020

How you accurately analyze and identify certain information has a direct connection to the overall success of your PCB designs. In this column, John Watson focuses on the conventional naming scheme for the schematic symbol and footprint to prevent headaches and ulcers later.

View Story

Elementary, Mr. Watson: Collaboration in the PCB Design Process

06-11-2020

The past few months have been trying for everyone, with many of us working from home. However, there are still the underlining principles of collaboration to step into a role to finish the necessary tasks to keep a project moving forward. John Watson, CID, explains.

View Story

Elementary, Mr. Watson: Reinventing Yourself

05-28-2020

When COVID-19 first hit, many businesses were forced to close, and we immediately saw its impact on the service industry. Whatever challenge you’re facing, John Watson emphasizes that it’s time to hit the switch on reinventing.

View Story

Elementary, Mr. Watson: The Positive Side of COVID-19

04-16-2020

With the recent COVID-19 outbreak worldwide, most of us have been forced to reshuffle how we work, live, and play. Something like this has never happened before in our lifetimes, and it is scary and challenging, but difficult times develop resilient people. John Watson shares some of the positive things he has already noticed come out of this situation.

View Story

Elementary, Mr. Watson: Are We There Yet?

03-12-2020

Anyone who has taken a road trip with children knows the question, “Are we there yet?” very well. This question also applies to PCB design. If you are not careful, your PCB project could easily go off track and you could lose sight of what you are doing (objective), why (motivation), how (process), and when (schedule). John Watson emphasizes the importance of these fundamental questions.

View Story
Copyright © 2022 I-Connect007. All rights reserved.