By Mark Thompson | Published on: March 26, 2018
One of the biggest issues PCB fabricators face is the completeness of the data output package received from customers on a new part. In this column I am going to present what is needed, from a fabricator’s perspective, for a good output package and why.
My colleague Dan Beaulieu recently published in his column “The Perfect Customer” that fabrication packages are frequently incomplete, delaying the quote process. This is absolutely a true statement for ALL board fabricators at this time! He pointed out that many larger customers that previously had their own in-house PCB fabrication no longer have that ability, and as such, much of the “tribal” knowledge that was shared between their in-house fabrication and the engineering group in those days has disappeared. So a lot of the board fabrication knowledge has not been passed on to the new generation of engineers and designers. This leads to incomplete or inaccurate output packages that end up having clarification questions prior to quote. Thus, delaying the quote process....
In this column, I will be discussing what files are needed for fabrication and why.
Let’s start with the obvious.
The 4 most common and accepted are the following:
This is the file with the Hole sizes, plating status (plated or Not) and the X and Y hole coordinates.
Usable file types for the NC drill file are as follows:
Drawings should include at a minimum:
Here are some examples of discrepancies or conflicting notes on a drawing that would require clarification:
Should you have either an AS9102, IPC class 3 6012 multilayer or even just a simple 2-layer board and you want to make sure the files emulate the electrical design parameters...
Please provide an IPC net-list for Net-comparison.
As fabricators we are obligated to run an IPC net-list against your provided Image data for any class 3 6012 or AS9102 parts or any parts that specify a net-list compare to be done on the drawing.
What is an IPC Net List? The IPC net-list is an electrical version of your design parameters to be compared with your exported Image data. It is not a file to be “generated” by a fabricator based on your Image data. If we create a net-list based solely on your Gerber data, at NO point would we ever find a mismatch, which may result in boards successfully being built, tested and shipped that are nonfunctional.
Care should be taken to not assign net-points to things that should not be electrical nets, things such as Non-plated holes or targets.
Before any fabrication edits have been performed, a Net-list compare is done. Any known or otherwise intentional shorts or opens should be noted on a “read –me” file word doc or on the drawing itself. Example: “AGND to DGND short net000 is intentional by design”
Then after any manufacturing edits such as drill compensations or etch compensations are performed the net-list is again ran to ensure the fabricators has not created any electrical anomalies. Some of the most common net list types for fabrication are IPC D356, IPC D356A or a mentor neutral file.
Lastly, any specific panelization requirements such as the addition of text for part marking, fiducials of a specific size or sub panel tooling of a specific size should be negotiated with the fabricator prior to quote. If no sub-panel drawing can be provided, you will want to, at the very least, indicate to a board fabricator areas of either part overhang or feature proximity where you DO NOT wish frame tabs to exist. This will minimize having to go back into CAM to move tabs or add cutouts in the frame.
PCB fabricators are an extension of their customers, and for this relationship to be successful both sides need to work collaboratively, and it all starts with the output package. Following these guidelines is the critical first step to assuring product quality and reliability.
As I've said before, your best bet is to communicate with your fabricator early on.
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