- Buyers Guide
Dinosaurs and Fab Drawings
One frustration of making printed circuit boards these days is trying to make a board without a clear, respectable fabrication drawing. Apparently they have gone the way of the dinosaurs and are now extinct. In the old days, a board house wouldn’t quote a job, much less build it, a without a fab drawing. Back then I schlepped around big plastic-wrapped sets of film with giant “D” sized drawings, while talking on a mobile phone the size of a brick. In those days, jobs didn’t start without a drawing, period! (Thank goodness those days are gone, along with my big 80’s hair!)
These days everything is smaller, more efficient, PCBs are far more complex, but fab drawings have been lost along the way—I assume due to time constraints. What we receive, along with the Gerber files, is usually some sort of README file that has a few notes of instruction—and that’s on a good day. We nearly always have to call or email the designer to clarify instructions before we begin the job.
On frontdoor.biz I found a site call How to PCB. Here is what they had to say about the purpose of a fabrication drawing:
The Fabrication Drawing fulfills several important functions to support the circuit board manufacturing process:
- It provides enough information about the design for the bare board fabricator to prepare a quote
- It adds all the extra details about the build that aren't easily incorporated into the data files, like material and final finish
- It lists the criteria by which the finished product will be evaluated for acceptability
- It serves as a tool to be used during final inspection
- It is a record or document to store the history of a product by title, part number and revision; physical dimensions, and lists the name of the designer and possibly several other supporting entities as well as the company name and address, etc.
- The notes area is like an Instruction Manual for manufacturing your product. Many of them will reference acceptability requirements
Here is a sample of a very simple, but thorough fab drawing: http://www2.keck.hawaii.edu/inst/nirc2/%5Bfab%5D.pdf
Fabrication notes create clarity, accountability, and reference for both designer and fabricator, and the lack thereof hurts them both. This is especially true when it comes to RF and Microwave boards. Some minor assumption or oversight can dramatically affect the performance of these boards. For these reasons, I thought I would share my concerns, as a fabricator, and also share some helpful resources to help you create a good, solid fab drawing. So, check out the links below, and if you don’t already, do yourself a favor by providing a decent fab drawing to your fabricator. I promise it will save you critical time and money in the long run, and earn big points with your fab house!
Design for Manufacturablity. Includes instructions for making a good fab drawing
How to PCB. Has good notes about a fab drawing in the Data sectio
IPC-2524 Evaluation tool for grading a data package/fab drawin
PCB Design and Fab Institute: has a nice section about Fab drawing
Best Wishes, Judy
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