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

Third Pillar: A is for Architecture
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. 

The library is your central source of truth and is vital to a company's success. Everything begins and ends with that library. A small error could cost a company an untold amount, which is like a kick to the gut to the company's profitability. Therefore, it’s vital to understand the importance of your library and how it is controlled.  

This acronym helps to remember the five pillars. It is called the SMART rule. 

S: Singularity  M: Managed  A: Architecture  R: Review  T: Traceability 

• S is for Singularity: Nothing destroys a PCB Design faster than rogue libraries. Therefore, I would say that a single source of truth is vital to succeeding with the other pillars. 
• M is for Managed: The specific tools available to manage our library are component revisioning and lifecycle schemes. To keep those components at top-notch quality, understand what revision and lifecycle your components are. Furthermore, the ability to revert if needed to another modification is a must. 

Library Structure Prerequisites
Before doing a swan dive into the details of our library structure, let’s consider some prerequisites. First, you want a library that grows with your company. So often, libraries are organized to handle what a company needs and where they are at today, without consideration of where they will be years from now. Every company in existence hopes to grow to make money (with some exceptions), which means new technologies for different resources in your library. We should expect and prepare for those changes—new components coming "online," with old ones deprecating and finally going obsolete. Library structure shifts to meet the company needs. We must have a library that allows for this sort of variability.  

Another prerequisite for your library has a structure that easily and quickly finds the correct component. That involves where you put things and the naming conventions used. At best, using obscure or unclear naming conventions for your components is problematic. It's like pushing the proverbial Ark of Covenant into the warehouse at the end of the “Raiders of the Lost Ark.” Fortunately, many of the PCB software platforms (at least the good ones) allow for detailed searches either by name/description or parameter information done on your library. But you need to nail down the naming convention you intend to use, and everyone agrees. It's an essential prerequisite because if you cannot find the exact component you need, you'll most likely believe it does not exist and create a duplicate component. Then you quickly lose control over managing your components.

Keep in mind that your library structure will be unique to your company. Every single library is different. So, don't feel as if you need to "lock" yourself into how someone else did theirs. The library is very subjective. You must allow for flexibility to meet your company's needs. What I offer below is only a suggestion. 

Lastly, don't re-invent the wheel as they say. Much of the work regarding your library structure is already done, you just need to follow the example that the component providers had set up. Also, depending on standards. I would especially have available IPC-7351, which is the Generic Requirements for Surface Mount Design and Land Pattern Standard and IPC-7251 Generic Requirements for Through-Hole Design and Land Pattern Standard. These are your go-to specifications when it comes to your library components.  

I hate to estimate how many components there are in the electronic industry. IHS Markit claims to have close to one billion different components. With that many components, how to organize them can be a daunting task. But it turns out that every one of them has the same organization. They all have a category, family, and sometimes a sub-family. 

Categorizing the Components 
First, there is no need to re-invent the wheel. The reason being is the excellent component sites have already categorized every component. I use Octopart.com. That old saying from Ben Franklin, "A place for everything and everything in its place." 

Every component has a category, then families, and some are broken down further into sub-families (Figure 2).

For example, looking at Passive Components (category), the families of capacitors, crystals and oscillators, EMI/RF components, inductors, resistors, and transformers. Those families break down further into subfamilies, so there will be three levels to a good library structure. From that, we use it as a  blueprint to construct our library.  

Library Structure Numbering Scheme
Having a numbering scheme on components is strictly up to you. I have seen some companies do it; others do not. But it would help if you consider it to keep your library organized into its category, families, and subfamilies. 

With our library's framework now up, we can give a further level of organization by having a numbering system for each category and family. Each category will be on a 100-base level, and the families would be singular. For example, we see that the category of Passive Components is 0800; the next category would be 0900. Each family under the Passive Components will use the singular number format. 

That results in: 

• Capacitors (0801) 
• Crystals and Oscillators (0802) 
• EMI/RFI Components (0803) 
• Inductors (0804) 
• Resistors (0805)
• Transformers as (0806) 

This sort of numbering system has several advantages. It will allow you to quickly identify the component as its category/family and wherein the library it resides. 

Home for the Models
The models of your components consist of the schematic symbol, footprint, and simulations. They make a significant part of each component. There are various strategies to managing these models in your library. My views on the model folder have evolved over the years. I used to believe that a model folder was attached to each category of components. But, I now see that becomes very difficult to manage. So, I currently support having a single model folder.

But I do believe some organization is needed to keep it from becoming just a piled-up mess. With the Footprint models, I highly recommend allowing IPC-7351 to help you here. IPC has categorized footprints into types (Figure 3).

Under my Footprint model folder, I create a subfolder for each package type. Organizing them this way keeps all the same package types together and manageable.

One of the prerequisites we discussed earlier was the ability for the library to grow. When you set up the library in this way, new components come online in a design. Therefore, you can first identify if you already have a specific category, family, or sub-family and if not, just add it. Furthermore, you can better manage the components and remove them when they go obsolete. 

I hope you found this helpful, and I look forward to continuing the series in my next column. 

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

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