Key Documents for Fabrication and Assembly

June 11, 2019 John Watson

I come from humble beginnings - a long line of farmers in central Pennsylvania. It is amazing how one can take a simple seed, place it in the ground, and tend to it. Before long, you have a mature plant with a variety of uses: food for people, feed for livestock, and most importantly, more seeds for the next growing season.

With so much riding on the seed, it is no wonder why you want to guard and protect it.

Your PCD Designs are like that simple seed. We plant initial sensitive data that go into them. After tending to them through the design process, they become our mature plant, our final PCB design we send for fabrication or assembly.  In a way, I am as amazed by that process as I was standing in a field of corn. How is that the underlying complexity is even possible in the first place?

The data we use throughout the process depends on the specific roles we have for the design. We see this whole thing differently when everyone works in their respective roles together. PCB Design is layered with complex processes, and we cannot talk about sensitive data without bringing in those roles.

Initial Data and the PCB Design Development

The lifeblood of every PCB design is the electronic component. Everything starts and ends from there.

At one time, because electronic systems were not as complicated as they are today, components were much more straightforward. They consisted of a schematic symbol, a footprint, and a few basic parameters. A common practice was to copy a component throughout the design with different values. Over time, more complex components became necessary with much more information and details to support cutting-edge systems.

At a minimum, we should include the following information with every component: schematic symbol, footprint (Decal), 3D Model, circuit simulation (Optional), parametric information, sourcing and supporting documents.

At this point, there are three roles: the Electronic Engineer, Librarian, and the PCB Designer. As we see in the chart below, a specific role uses data. Of course, I am aware that these are not absolute and there may be some crossover.

Throughout this design process, you use specific data at certain points. For example, the EE uses parametric information to pick the design’s primary component. The selected component goes over to the Librarian to build the necessary part. The PCB designer uses the component in a schematic pushing it over to the PCB layout.

At critical points in the design, I make sure to bring several other people to the party. They include the Mechanical Engineer (ME), Purchasing and Quality. They use specific data to fulfill their roles. Our chart is growing, but these individuals are a little more specific about the data they want.

PCB Output Data

We can now look at the output data of our PCB Design. Probably more importantly and, I might add, nerve-racking, we are ready to build our output data packages.

Yes, you read that right package(S). There are two data packages. Our first package is the Fabrication package which includes the required data needed to fabricate the board. Secondly, the Assembly Data package (as you guessed) is for the assembly of the PCBs. Just a word about data security, understand these two data packages ultimately have all the necessary information to build a PCB design. As a common practice, we have two data packages so we can send them to multiple vendors. No single vendor (of course unless you fully trust them) gets both packages. The one document that never goes out under any condition is the schematic. With that, anyone can copy your design.

Knowing the specific needs of your fabrication and Assembly comes in handy. The industry is ever-changing, and there are multiple output data formats available. It is more comfortable when you know which is the best to use. What is offered here is typical, but your mileage may vary, as they say. Much can be said regarding each item. Each of them has a purpose.

Fabrication Drawing

This detailed drawing should include the critical items your Fabrication house needs including drill dimension, drawing of the board, Drill chart, Layer Stackup, special fabrication needs such as transmission line tables (used for controlled impedance lines), and detailed fabrication notes. Keep in mind, this is just a guideline. If you do not include specific details in the document, they will not happen.

Assembly Data

The Assembly Drawing guides the assembly house. On this document, you should overstate things rather than understate them. Not giving specific requirements will most likely delay the build. Provide accurate information primarily for the BOM. Errors at this point compound significantly.

Conclusion

Every piece of data in the PCB design process has its place and purpose. If you know why and what they are, your team, fabrication, and Assembly house will thank you. They are the seeds we plant to bring about some amazing things, but only when we know how to use them and, more importantly, why.  

Would you like to find out more about how Altium can help you? Talk to an expert at Altium.

About the Author

John Watson


With nearly 40 years in the Electronic industry with 20 of them being in the field of PCB Design and engineering, John has stayed on the cutting edge of the PCB industry as a designer/Engineer and more recently as a trainer and mentor. His primary work has been in the Manufacturing field but it has also expanded to several PCB Service arenas. As a veteran, he proudly served in the Army in the Military Intelligence field.

John is a CID Certified PCB designer. Presently pursuing his Advance CID certification. Now as the Senior PCB engineer at Legrand Inc, he leads the PCB Designers and Engineers in various divisions across the United States and China.

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