Part 3: Documenting Your PCB for Assembly

Zachariah Peterson
|  Created: February 16, 2022  |  Updated: February 28, 2022
Part 3: Documenting Your PCB for Assembly

With your fabrication (bare board) requirements documented, it is now time to move on to an equally important stage — documenting the instructions for component placement and final assembly. It is in the assembly stage where your bare board is brought to life with all the components you specify in your Bill of Materials. This chapter will cover what you need to know to have your board successfully assembled and will cover assembly drawing requirements, adding notes, and placing cautionary markings.

If you would like to skip to different chapters in this series, use the Table of Contents links below:

Assembly Drawing Requirements

Your design documentation is arguably one of the most important aspects of your design process. Even the greatest PCB design will go to waste, if you are not able to clearly communicate design intent to your manufacturer. With your master drawing completed, you now have everything you need to get a bare board produced by your chosen fabricator. In the next chapter we will explore the last piece of the documentation puzzle for the final assembly of your PCB.

Location of components

Reference dimensions for envelopes

Conformal coating requirements

Reference designations for all parts

Component mounting and spacing installation requirements

Mechanical hardware including latches and mounting hardware

Orientation and polarity of components

Masking requirements

Cleanliness requirements

Required structural details for support and rigidity

Electrostatic discharge label

Workmanship specifications

Requirements for markings and lead forming

Electrical test requirements

 

Specific soldering requirements including solder paste

Eyelets and terminals

 

Required Assembly Documentation

The required assembly documentation consists of a number of assembly drawing templates that you will need to include with your final design including schematic prints and a finalized BOM. In addition to your notes, these drawing templates will allow your manufacturer to clearly understand your design intent for final component placement and assembly. Also, learn more about how to Enhance Your Design Efficiency with Project Templates (WP).

Schematic Prints

The schematic prints outline your intended board component connections and are necessary to define and establish your required test points. During the final testing process, your board tester may be able to find your test points on the physical PCB, but for greater clarity they’ll utilize your schematic prints to understand how those test points connect to your network of circuitry. Test points are shown in the sample schematic below.

Schematic Prints

Bill of Materials

The Bill of Materials will include a detailed and sourceable part list that includes all necessary part supplier information. Providing a BOM to your manufacturer with included component designators and supplier information ensuring your design will be manufactured with the appropriate parts. The BOM is covered in depth later in the guide. The drawing sheet below shows a sample BOM with some of the necessary part information you will want to include:

Bill of Materials

Cautionary Markings

Cautionary markings are very important for safe handling of your board. As part of your assembly documentation, you will need to include the electrostatic discharge markings shown below if your board requires special handling due to static sensitivity.

Electrostatic Discharge Markings

In addition to the symbols above, the notes in the table below need to be placed above or as close to the title bar as possible. The notes used depends on the class of your board, and markings can be applied using copper etching or silk screening.

Class 1 & 2 Boards

“ELECTROSTATIC DISCHARGE CONTROL PROGRAM FOR PROTECTION OF ELECTRICAL AND ELECTRONIC PARTS, ASSEMBLIES AND EQUIPMENT SHALL BE IN ACCORDANCE WITH MIL-STD-1686, CLASS _____ AND MIL-HDBK-263.”

  • Class 1 - Devices sensitive to voltages of 2,000 or less
  • Class 2 - Devices sensitive to voltages between 2,001 and 4,000

Class 3 Boards

“ELECTROSTATIC DISCHARGE CONTROL PROGRAM FOR PROTECTION OF ELECTRICAL AND ELECTRONIC PARTS, ASSEMBLIES AND EQUIPMENT SHALL BE IN ACCORDANCE WITH MIL-STD-1686, CLASS 3, AND MIL-HDBK-263”

  • Class 3 - Devices sensitive to voltages greater than 4,000

 

Notes

Assembly drawings, like fabrication drawings, require their own set of notes. These notes include information about the merging of the board with its components, including assembly standards, handling instructions and solder specifications. There’s no such thing as too much detail in your assembly documentation. If you think your manufacturer needs to know something about a specific component’s placement or assembly requirements, make a note for it. Below are some examples of assembly notes as seen in IPC-A-325A[8-1]:

  1. Workmanship to be equal to and compliant with the requirements of IPC-A-610.
  2. Mark group (or dash) number, revision and serial number as shown; marking to be 0.10’’-high characters using item no. 6, white epoxy ink, per MILI-43553, type II.
  3. This assembly contains electrostatic discharge (ESD) sensitive devices; static-free handling is required per MIL-STD-1686, class 2
  4. Conformal coating is not required.
  5. Designations are for reference only and do not appear on individual parts.
  6. Dimensions shown specify maximum envelope limits for the finished assembly.
  7. Orientation of polarized capacitors is denoted by a plus (+) sign. Polarity is identified on the part.
  8. Dot identifies pin #1 location and device orientation when viewed from the top.
  9. Using solder paste screen, apply solder paste, item #4, to primary side of board.

Completing Your Design Documentation

Draftsman is a sophisticated yet easy to use drawing tool that is integrated within Altium Designer, for the creation of fabrication and assembly drawings. Draftsman is a built-in extension that can be installed or removed manually by going to the Extensions and Updates page. You can access the Extensions and Updates page by clicking on the user icon on the top right of the Altium Designer window.

The next time you need to create fabrication documents for your PCB project, use the Draftsman utility in Altium Designer®. This powerful, easy-to-use feature is included in Altium Designer and it will help you speed through the document creation process. When you’re ready to release your board fabrication files and drawings to your manufacturer, the Altium 365™ platform makes it easy to collaborate and share your projects.

We have only scratched the surface of what’s possible with Altium Designer on Altium 365. Take a look at our flexible licensing options for Altium Designer + Altium 365 today.

About Author

About Author

Zachariah Peterson has an extensive technical background in academia and industry. He currently provides research, design, and marketing services to companies in the electronics industry. Prior to working in the PCB industry, he taught at Portland State University and conducted research on random laser theory, materials, and stability. His background in scientific research spans topics in nanoparticle lasers, electronic and optoelectronic semiconductor devices, environmental sensors, and stochastics. His work has been published in over a dozen peer-reviewed journals and conference proceedings, and he has written 1000+ technical blogs on PCB design for a number of companies. He is a member of IEEE Photonics Society, IEEE Electronics Packaging Society, American Physical Society, and the Printed Circuit Engineering Association (PCEA), and he previously served on the INCITS Quantum Computing Technical Advisory Committee.

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