Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Soldermask Compensation

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Soldermask Compensation | 13 November, 2012

I am looking for opinions on how much larger soldermask pads should be versus the copper. I am aware that some pcb manufacturers can hold tighter tolerances than others but is there an IPC recommendation? Some shops we deal with can hold .002 per side over the copper (ie. .014 mask, .010 copper) but some of the shops we work with ask for .004 per side (.018 mask, .010 copper) does that sound reasonable for 2012. I remember when we were screening mask we needed that kind of increase but is it realistic in today's market to expect .008 mask over copper increase?

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Soldermask Compensation | 13 November, 2012

I expect that suppliers can just about always hold solder mask registration within a true position of 3 thou. That's the old SMT padstack think ... make the solder mask openings extend 3 thou larger than the copper. That way, even if the copper and the solder mask are misregistered by 3 thou, there won't be solder mask on the pad. 

Suppliers that have invested in technology might be able to hold 0.002".

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