#1. Incorrect Gerber File Format for Stencil Paste
Fix: The gerber format MUST be RS274X (opposed to RS274D). The RS274X format is the most current industry standard and includes aperture information in the gerber itself instead of requiring a separate aperture file.. (Google for “RS274X format”) All current version CAD programs can generate the -X format although some may default to the older format for the sake of backwards compatibility. If you need to convert from 274D to 274X, try out dcone@earthlink.net Their web site is: http://www.d03.com/
#2. Missing a gerber file for stencil paste for one or both sides
Fix: We need a paste layer in order to generate a paste stencil. (if you have 2 sided SMT, then there will be 2 paste layers) This is not the same gerber as the solder mask. A normal paste layer/gerber will contain ONLY SMT PAD features. A paste gerber will seldom include: un-tented vias, holes for axial or radial leads, or mounting holes with annular rings. Also, a paste gerber does NOT need a board outline, dimensioning marks, labels, or company logo/info boxes.
Note: The solder paste layer may have to be generated separately
The complete guide can be be obtained below
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