Solder Mask Sliver

[ozarif]

Hi,

I am designing a prototype with 40-QFN 5x5mm and 14-LGA 2.5x3mm chip.

There are some errors like clearance constraint and minumum solder mask sliver constraint , i wonder the firm can manufacture it even if i change the constraints.

when I dropped smd pad constraints 0.2 to 0.15 mm, it fixed the clearance constaint error but LGA pads distance is very close. If my manufacturer cant do it,

could u suggest me any proper manufacturer or do u have a suggestion for pads distance.?

Thanks

[robertferanec]

Normally I try to use minimum 0.1mm sliver in mask, it is possible to manufacture 0.075mm. We talked about that a little bit in this video: https://youtu.be/FM3pRM0CxGw

[ozarif]

But i draw it from datasheet. what can i do about it, i cannot change pads size, right ?

[robertferanec]

What datasheet?

You can make the mask opening smaller, make it 0.075 - that may help.

PS: PCB manufacturer will still be able to manufacture it, only ... some will simply draw a big rectangle over the all the pads, instead of making openings for individual pads. However, that is not the best approach for soldering (there is higher chance, that there will be short circuits between the pads)

[ozarif]

Its less than 0.075, qfn 40 5x5 mm also less than 0.075 mm. Actually, there are more chips like that dimensions, right. I think, this might be a common challenge, i wonder the general approach.

[robertferanec]

0.075 should be ok. The space between pads is 0.25, then divide by 3 (mask opening / mask sliver / mask opening) = 0.083, so when you go for mask opening 0.075 it should be ok. Or, am I calculating something wrong?