Soldermask and pastemask dimensioning

[vsnute]

pastemask

Hi everybody,

I'm switching from Mentor PADS 2007.2 to OrCAD. I'm trying to build my first padstack in OrCAD but I don't know how much I have to oversize the soldermask and pastemask with respect to the pad size, since Mentor PADS does it automatically. Does anyone have any suggestion?

Thank you in advance.

 

[kender]

paste mask solder mask

I make the pastemask the same dimension as the PAD and oversize the soldermask diameter by 0.005 inch. I've also noticed that the soldermask isn't oversized in the OrCAD's own layout footprint library.

 

[cyberrat]

solder mask paste mask

As Kender says.
Although here there is a historical oversize of 0.008" for solder mask, but it all depends upon your manufacturers capabilities & these days they are a lot better & our pads are a lot smaller.

Orcad may not oversize is solder mask on the assumption that you can just as easily provide your manufacturer with 1:1 solder mask & they will simply increase the aperture sizes for it. (easy enough to do).

Same for the paste mask, you provide 1:1 with instructions on what reduction you want.

When adding this to libraries you have to consider that things may change, percentages can vary depending upon thickness of the paste screen. As such its best to set them to 1:1 for the paste & then you can do all reductions with the Gerber data without having to edit every component in your library.

 

[M!k]

paste mask vs solder mask

Same for the paste mask, you provide 1:1 with instructions on what reduction you want.

What are typical values for the reduction of the paste mask and under which conditions are they varied?

 

[mhawary85]

soldermask pastemask

i do this and it works for me

if the pad size<1mm the add to solder mask .08 mm and decrease from solder
paste .08 mm

if the pad size>1mm the add to solder mask .1 mm and decrease from solder
paste .1 mm

example square pad size with length 1.5 then SM=1.6 and SP=1.4

 

[Anonymous_Ricky]

how to make pcb soldermask pastemask

Hi,

I increase 10mil solder mask for through hole and 5 mil for SMD (may very to 8-6 and 4-3 mil respectively depending on the pitch).

For slder paste it is zero for Thru Hole and 5-4 mil lesser depending on the pad size for very small pin size you can make paste mask equal to pad size.

Regards,

Ricky

 

[vsnute]

pastemask soldermask pcb

Ok. I think that for a standard size pad a 1:1 pastemak/pad and soldermask/pad ratio should fit as for the other packages in the OrCAD libs. Upon generating the gerber files I'll set it if needed according to my manufacturer's capability.