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Design rules dictate the complete set of physical design constraints to ensure that the board is manufacturable. For example, this is where you would define the minimum trace width and spacing, component clearances, etc. JLC’s capabilities improve every so often and are listed on their site, however you can grab this template (maintained for now by f39zhou) and load it through Design → Rules, right click Design Rules in the tree on the left and click Import, click ctrl + A to select all, and then load the 2L 1oz rule file. Hit Yes to the prompt about clearing existing rules prior to import.
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