Both Fab and assembly drawings are useful to communicate various information to your vendors. The fabrication drawing contains information on how to build the printed circuit board (PCB). While your assembly drawing depicts details on how several components are going to fit on the raw PCB.
However, there are certain standards that you must follow, so your vendors can understand the instructions.
Basics of Fab and Assembly Drawings
First, whether it is a fabrication or assembly drawing, you will begin from the same place in both cases. Here are some general items you will need for both Fab and assembly drawings.
It is the outline for the design of your circuit board from a layout database. Typically, it includes cutouts and slots to define dimensions on your fabrication drawing. You will also use this outline to reference components on an assembly drawing.
While some of the CAD systems may require you to utilize a library part as a drawing format, others will auto-generate a drawing format. It does not matter which of these methods your CAD system executes. You will have to combine this produced format with your PCB layout to build your drawing.
Usually, the drawing format will have one or multiple areas to add a drawing identification number, board name, revision level, contact data, creation date, and corporate address.
Now let us look at the specifics needed for both Fab and Assembly drawings.
Key Elements for Both Drawings
Elements for Fab Drawing
We will look at the fabrication drawing first. Here are some of the key features that you must include in your Fab drawing.
Every hole in the board for vias or pars needs representation in your drawing. Your CAD system usually auto-generates these holes diagrams. However, your fabricator will be using the NC drill file sent for actual holes’ locations.
This chart is also known as the drill schedule. It associates each hole size via using a unique drill symbol.
Board Layer Stackup
This one provides a cut-away view of your board with its layer structure. Pointers detail the width and configuration of all conductive layers on the board, including any associated core layers and prepreg.
Dimensions and Notes
Dimensions show the overall size of your board, along with different features within and around the board’s outline. The notes give specific instructions to the fabricator that it cannot include elsewhere.
Elements for Assembly Drawing
Let us look at what standards you must follow for an assembly drawing.
It is best to display the shapes of all the components along with the reference designators for soldering onto your board. It also includes mechanical parts that will need press-fitting or attachment with mounting hardware.
Sometimes, these parts might not get accurate representation in the footprint library. So it may require a little drafting and drawing efforts from you.
These are usually required in double-sided boards as they need a view of both back and front. Both views are a part of one assembly drawing. You can also include expanded views with details of mechanical parts.
All manufacturing labels, including assembly tags and barcodes, will need identification via pointer and must have a reference in the assembly notes.
These entail manufacturing instructions, including industry specifications and standards, assembly details, and locations of special features. You can also add a list of all parts on the manufacturer’s request.
You can always modify or change the elements mentioned above for Fab and assembly drawings as per your requirement. Creating a checklist will ensure that you have not left out anything.
If you have any questions about the standards/elements that every Fab and assembly drawing must adhere to, we’re here to help. Reach out to us today!