how do we decide on dimensions of masks and layers

[ahsoka]

Hi,
can anybody tell me how do we decide on dimension of drill,top layer,solder mask,paste mask

EX:
if the drill dia is 'a'
then what is top layer,solder mask,paste mask dimensions

thanks in advance

 

[Anonymous_Ricky]

Pad size (or top layer as you define here) is generally taken to be 0.6-0.8mm bigger than drill with 0.8 being prefered so if we take drill to be "a" tahn pad size will be"a+0.8".
Solder mask is .25 mm more than the pad size so it will be"a+0.8+0.25".
for drilled pads you need not ro provide paste mask.

 

[cyberrat]

You have to consider annular ring for the hole to pad dimensions.

Solder mask has to be slighly oversized to allow for slight misalignment, historically it has been 0.008" ish, it can be smaller but that makes it harder for the manufacturer & that costs more.

On fine pitch IC's you may have a block of missing solder mask rather than individual pads.

for paste, SMT pads - leave 1:1 and the screen manufacturer will reduce them as required.
pth pads - as they are generally round - identify that they ned removing from the screen.
or if you can reassign a zero size in your CAD package that will ensure they are not used when making the Gerber.