Estimated reading time: 6 minutes

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

One of the classes I dreaded the most each year in school 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.

Figure 1: A mandatory high school experience: frog dissection.

Imagine doing the same thing to your PCB components. What would we find if we took a simple component, placed it on the table, sliced it open, and dug deep down? More importantly, like our amphibious friend, what is the purpose of each part? I get this question all the time: What should be in my components? Let’s take a look.

For the past several months, we looked at the five pillars of our library; we’re now ready to load that library up with some components. First, of course, we all know the importance of our library, but even more important is what exactly you store there and the quality of those components.

I sat down to enjoy an apple the other day. I spent some time cleaning and polishing it, and it looked great. I took a big bite, and do you know what’s worse than finding a worm in an apple? Finding half a worm. Although everything looked nice and shiny on the outside, on the inside it was rotten. That story is an excellent example of many of our libraries. They may be nice and shiny on the outside, but on the inside, we have worms because we have poor quality components.

Component Overview
With technology and innovations in our industry constantly changing and advancing, we can easily see this on display with the number of available components. Depending on the source, the variety of electronic components on the market is almost endless. Octopart has over 19 million, and IHS Markit exceeds 900 million. But with so many options, there is cohesion with every PCB component. We see that every component is made of the same essential parts and structure when examined.

In the early days of our industry, designs got done with components with just basic information of a schematic symbol, footprint, and some basic parameter information. Now components have massive details and information; everything needed for the entire design, fabrication, and assembly process is all capsulized in a small convenient package.

Every component is divided into two main categories. The first is information, and the second is the models. As we will see, it is essential to have all the various parts of the component since each part has its purpose and use in the design process.

We begin by looking at the information side of our component. Information drives our industry. Having the best information helps avoid duplicating components and knowing that you have the correct and best part for what you are designing.

Name and Description
What you intend to call a particular component is where everything begins. I highly recommend perusing my July 2020 column, PCB Components Naming Convention. In that piece, we discussed the specific naming standards for your schematic components and models and how to ensure that they are organized to find things easily and not create duplicates.

There are several common mistakes made here. First, many designers provide too much information in the name field. Instead of showing only the essential information, it becomes a pseudo description field. Keep in mind that when searching for a specific component, you have both the name and the description to find what you’re looking for, so it is unnecessary to duplicate the information. Instead, look at the name as a hook of essential information; the description holds the details.

A second mistake commonly made is using part numbers for the name. That works great if you have a complex component; for example, a specific component from a manufacturer. You can easily use the MFG part number as the name and what I usually do (because I am lazy) is copy the description of the component right off the datasheet. But it would help if you avoided that with general components, which are mainly your discrete. The discrete components have several manufacturers and suppliers, and distinguishing them by a single MFG will cause problems. Also, as your part choices will constantly change because of shifts in the supply chain or depreciation, you don’t want to tie them to a specific part number. For example, call a resistor by its basic information of value, tolerance, and size. More details can go in the description field.

The other reason is that it is difficult to decipher what a part number is saying. For example, knowing what CPF0603B1M0E1 represents is difficult, if not next to impossible. If you were wondering—it is a Resistor Thin Film 0603 1M Ohm 0.1% 1/16W ±25ppm/°C Molded SMD Paper T/R.

Parameter Information
The parameter information is the components’ details, which are very subjective according to the type of components. So, for example, you won’t have the same parameters for a chip resistor as a 4608 cells 402.58MHz FPGA. But as we remember, our library organization is broken down into categories of families and sub-families. So, a common rule would be to have the same parameter configuration for all the components in a family and sub-family. Then all the specific components in a family/subfamily are together and can quickly compare based on the same information.

Sourcing
Up to this point, most of the information attached to our components is static, meaning that they most likely won’t change. But with the sourcing information, we break into the dynamic side. Connecting the manufacture(s) and supplier(s) allows for the creation of your bill of material (BOM). As we are probably aware, that is like nailing Jell-o against the wall right now with supply chain shortages. That is even more reason to have excellent sourcing information for every component and should have both multiple part choices and alternate components.

A multiple-part choice is another component that exactly matches the form-fit-function (FFF), or another term often used is a drop-in replacement. The alternate components are ones that first meet the FFF criteria of your circuit, but may vary in some of the electrical parametric specifications. Use both to strengthen your component as much as possible. That broadens the options when going through the perils of part procurement.

Datasheet
Lastly, connect multiple datasheets to the component (with emphasis on multiple). When available, do not trust just a single datasheet. I know it may come as a shock to some, but datasheets have been known to be wrong. Many times the problem is not caught until it’s too late. So, attach all the information with all the datasheets available to reference. Comparing various parts from various manufacturers will flag any potential problems early. Your EE will thank you.

In my next column, I will take a deep look into your component models and the industry standards to use when creating them.

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

For more educational information from Altium, be sure to download The Printed Circuit Designer’s Guide to… Design for Manufacturing by David Marrakchi. You can also view other titles in our full I-007eBook library here.