gerber data vs bare board

hello

having a problem with one customers bare boards not matching my stencil apertures. i design stencils based on gerber data and reduce up to 15% on some pads. do some board houses reduce pads after receiving gerber data???why would they do that anyway? had to reorder stencil because of poor gasketing on fine pitch causing bridging. 20mil qfp pads were 7-9mil in width, pretty puny if you ask me. thanks for any input

wayne sanita

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| hello | | having a problem with one customers bare boards not matching my stencil apertures. i design stencils based on gerber data and reduce up to 15% on some pads. do some board houses reduce pads after receiving gerber data???why would they do that anyway? had to reorder stencil because of poor gasketing on fine pitch causing bridging. 20mil qfp pads were 7-9mil in width, pretty puny if you ask me. thanks for any input | | wayne sanita | | | Some houses reduce, or otherwise modify (move, enlarge, etc.) pads. Micro-modifiers were a great asset to board shops some time back. Some still use them to gain better clearances and to better drill through pad centers, as best they can, in MLB's.

If this is happening to you, you need to specify very clear requirements concerning pad sizes and their location. Don't forget, Gerber data is exact or perfect. It starts out simply as X-Y locators for all holes, pads, and other physical features. From there, much changes perfection and the board fab process is difficult enough.

Gerber data has noting to do with a pad's size - only its location. Other data, as part of the Gerber data determines all else. How well a board is laid out is of concern, followed by photoplotting, micro-modification (if practiced), imaging, etching, lamination, drilling, etc. If all physical features (pads, holes, etc.) are not properly located with reference to an X-Y datum, there's no chance any process following will be effective.

Typically, qualified board shops have no problem doing as you require provided information, as notes and graphics, are properly called out on the master drawing - first. After that, acceptance specifications take precedence followed by artwork.

Have a serious discussion with your fabricator about your problem. If nothing positive is forthcoming, qualify another shop.

See my latest, and last article concerning PCB fabrication and other.

Earl Moon

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| | hello | | | | having a problem with one customers bare boards not matching my stencil apertures. i design stencils based on gerber data and reduce up to 15% on some pads. do some board houses reduce pads after receiving gerber data???why would they do that anyway? had to reorder stencil because of poor gasketing on fine pitch causing bridging. 20mil qfp pads were 7-9mil in width, pretty puny if you ask me. thanks for any input | | | | wayne sanita | | | | | | | Some houses reduce, or otherwise modify (move, enlarge, etc.) pads. Micro-modifiers were a great asset to board shops some time back. Some still use them to gain better clearances and to better drill through pad centers, as best they can, in MLB's. | | If this is happening to you, you need to specify very clear requirements concerning pad sizes and their location. Don't forget, Gerber data is exact or perfect. It starts out simply as X-Y locators for all holes, pads, and other physical features. From there, much changes perfection and the board fab process is difficult enough. | | Gerber data has noting to do with a pad's size - only its location. Other data, as part of the Gerber data determines all else. How well a board is laid out is of concern, followed by photoplotting, micro-modification (if practiced), imaging, etching, lamination, drilling, etc. If all physical features (pads, holes, etc.) are not properly located with reference to an X-Y datum, there's no chance any process following will be effective. | | Typically, qualified board shops have no problem doing as you require provided information, as notes and graphics, are properly called out on the master drawing - first. After that, acceptance specifications take precedence followed by artwork. | | Have a serious discussion with your fabricator about your problem. If nothing positive is forthcoming, qualify another shop. | | See my latest, and last article concerning PCB fabrication and other. | | Earl Moon | | | Forgot,

Though I did mention the imaging process, it must be said this is critical. Very columnated, high intensity light must clearly be focused on the artwork pattern (usually on .007" thick "mylar") or distortion, or image growth or reduction occurs.

Concerning etch: An over etched condition could also cause your problems. Again, process management in the board shop is key.

Earl Moon

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