Duane Benson over at Screaming Circuits has a great blog post from Nov 14, 2011, on creating stencil opening for QFN parts. Here's the link to the actual post. Duane's post talks about EAGLE specifically, but the general idea can be used for other CAD tools as well. Nevertheless, it's worth quoting a couple key ideas here; they bear repeating: 1. In Eagle, open the part that you want to customize in the Eagle Library editor. 2. Open up the package for that component. 3. Now, select "i" on the left side and click on the center pad. You might need to turn off the "tcream" layer in order to select the pad. 4. In the Properties dialog box, un-check the check box for cream. That will get rid of the standard stencil layer. 5. Now you can use the rectangle tool to add in stencil cut-outs as you want them. Make sure you set the layer for the rectangle to be "tcream" and remember that you are drawing the cut-outs of the stencil, not the blocked part. And that's it, really. Here at Sunstone, we highly recommend the Screaming Circuits blog.
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