Problem with Soldermask Spread

Hello, i am a student from Spain who is finishing his final studies proyect and this is my first PCB outside the university.

I'm going to order my pcb soon, but i have 1 problem.

I will use www.pcb-pool.com to get a prototype board with SM. In their technical page i can find this
Soldermask Spread 0.15mm (6mil)
This is the diameter of the Soldermask pad minus the diameter of the Copper pad.


My question is...

I use the Orcad libraries but they have a Soldermask Spread of 0mm (SM PAD = Copper PAD), so... if i use this footprints, my board will be totally wrong?
Will they use their minium spread while making my board? There is any fast way to change all the padstacks to meet the requirement in Orcad Layout?


Thanks in advance.

Hola,
I think you do not have to worry about this. Usually, this soldermask spreading is used because at the PCB production there can be small missalignment placement of the solder mask, and if the soldermask have the exact form and dimension as the component pad, an overlap between these two will occur. Adding a small spreading in the soldermask will avoid this effect. However, this aspect is a concern only in high precision PCBs with very fine pitch pads. If you have relatively big components like 1206 and SO packages, then all is ok.

/pisoiu

If by "spreading" they mean enlargement, then your soldermask aperture should always be larger than your actual finished pad size because of the tolerances in the registration process when it is applied. 0.15 <> 0.4mm is a reasonable amount for an enlargement depending on the board technology.

This should be defined in your rules, where you have pads with fine pitch leads, then the chance is that the remaining soldermask between these pins may be less than the minimum printable size and you should simply block remove all SM along these pins.

If you want you could actually make the soldermask smaller and define your finished pad size that way instead, but I have never seen this done in hooby or project boards, just high volume production and of course lower volume boards with BGA's.

John

Thanks for both replies

I understand this now.

I only use DIP's with big pads so i think i will have no problem with the missalignament. Anyway i asked the manufacturer if i MUST change the values or if they are fine.

Thanks again