Soldermask Compensation

2017/2/26 17:05:48

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?