This is a quick-and-dirty method that can rapidly reproduce existing PCB boards if a 3D model is not already available. It's especially useful for quickly reproducing breakout boards to do component fit checks, or for last-minute nice renders.
1) Gather any manufacturer information you can find, or any existing drawings or 3D models.
2) Take photos of the front and back of the board, making the photos as square as possible.
3) Use any available documentation to build the base board shape in Fusion 360.
4) Use Inkscape, Illustrator, or some other graphic design program to prepare the photos.
5) Use the photos as a canvas to lay out components. Extrude your components.
6) Use the same photos as decals to improve the aesthetic of your model. This will also make the model more quickly recognizable while in use.
A couple of *important notes*:
(A) This process is not highly accurate! We are trading precision for speed if we take this approach. With that said, resistors and other small components that are soldered to a board via reflow often differ a bit from board to board anyway.
(B) Only do this if you can't find a 3D model or high-quality documents from the manufacturer!
(C) There will always be camera lensing effects when you take a photo of the board. The closer you are to the board, the more distorted the edges of the photo will be.
Step 1: Check for Existing 3D Models & Other Documentation
First, look for a datasheet! Most datasheets will have the most important dimensions shown in a drawing, which is a great place to start before adding smaller components like on-board resistors. You can also think about opening any existing EAGLE files to pull dimensions out there.
If you're sourcing, say, breakout boards from Adafruit or Sparkfun, they might have a 3D model already available. If not, it's worth quickly checking GrabCAD to see if anyone else has already put the time in to create a model of the board you're working with. Make sure to vary your search terms when you're checking.
Just remember that if you need extremely tight precision to make the board work with your design, you're better off with a manufacturer's file than something made by a random GrabCAD contributor - you never know how accurately the user measured components and distances!
Step 2: Take Top and Bottom Photos
When you do this, try to get good lighting, and more importantly, you need to make sure your camera is perpendicular to the board to avoid excessive warping of the image!
I did this with my cell phone camera, holding my cell phone flat against a square block of wood to make sure it was parallel to the table surface.
In the case of this board, a little lump of solder on the back side meant that the board wasn't flush to the table. I used some laser-cut gears as standoffs to deal with this issue on both sides.
Step 3: Create the Board Outline in Fusion 360
Fusion 360 has PCB tools that can integrate with EAGLE. But we're not going to use them, since we just want a quick-and-dirty representation of an existing board type.
We're going to model the board as a base body, and each component as another body so that it's easy to change their appearances. Since there was an EAGLE screenshot on the Adafruit website, we'll use that to dimension our board perimeter and the mounting hole locations.
Follow Rule 1 of Fusion 360: Make the board a new component when you make your design!
Then import the schematic as a canvas to quickly create the board body.
Extrude the board body, and you're ready to drop a photo onto it for component placement.
Step 4: Prepare Your Images in Inkscape
Use Inkscape to remove everything outside of the board, and to rotate your image as needed. You can then size the page to perfectly fit the board. Don't make your image the proper size in Inkscape, or it will export the image at low quality.
Export the image as a .png file and you're ready to drop it into Fusion 360!
Step 5: Use the Photos As Canvasses to Populate Components
Apply the canvas to the face of your PCB. It will be sized automatically by Fusion 360!
Now create a sketch, and name it so you can reference it later. Start dropping in rectangles and using rectangular patterns to automatically set up distances and constraints between them.
How much time you take in this part of the process will largely decide whether your resulting PCB is really quick-and-dirty, or whether it's pretty accurate.
Use the same process, with rectangular sketch patterns, to create all the soldering vias on the board. I highly recommend that you measure these distances with calipers, rather than relying on the photograph! Flow-soldered components vary in location quite a bit, but vias less so.
Extrude all of your components, and cut your via holes either by extruding them or by using the "hole" tool. You can save lots of time by extruding any components of the same height together, as I show in the screencast below. Choose whether you want the whole board to be one body, or whether (as I've shown here) you want each component to be a separate body so that it's easy to change its color.
Step 6: Use the Photos As Decals to Improve the PCB's Appearance
Now re-apply the photo you took of each face, manually scaling and placing it.
Okay, brace yourself. This is where it's going to become clear that any photo you take with a cell phone camera is going to be warped, even if you did a good job of making the lens parallel to the part. The farther away you were from the part, the less of this warpage you should see. Look how the holes on the edges all look stretched out from the center in the photo!
This is why it's important that any measurements you're definitely going to use, like the mounting hole locations or the outer board diameter, should be taken either from manufacturer drawings or using calipers.
After some adjustment, we get a model that looks pretty good and aligns with manual measurements. This should be good enough for my purposes, and the overall process should only take about 20 minutes.