By Mark Thompson | Published on: October 07, 2013
A Net-list compare is again the comparison between the provided Gerber data PRIOR to any manufacturing edits and the provided IPC 356 Design net-list. A “1 up compare” is done after manufacturing edits are performed at CAM stage to ensure that no edits performed have the changed the electrical functionality of the boards. This ensures that we the fabricator have not changed the electrical functionality of the boards by bridging features due to an etch compensation for instance. If I have not mentioned it before, the “etch compensation” is done in fabrication at the CAM stage. Generally speaking, for every half ounce of starting copper a half mil of etch compensation is associated. So that after etch your desired line size is maintained.
Getting back to why I brought up the difference between a CAM 1 up compare and a net list compare: many times there will be a drawing or read me callout for net-list compare and when a net-list file is not provided and the customer is contacted they indicate they merely wanted a 1 up compare to make sure WE have not changed the function of the part by our manufacturing edits. Sometimes our customers will ask for test based upon the provided net-list files. Test file generators for modern test machines generally use the customer Gerber files for test point generation and NOT the customer supplied IPC net-lists. Having said that, the requirement is still being met as in both CAM and then again when the TEST files are generated, a net-list comparison between the Gerber files and the provided IPC net-list is performed and any mismatches communicated to the customer.
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