Dimension tolerances by creating own SMD

[Onedust]

Hi,

I have a question regarding dimension tolerances, which are given by manufacturers. For example this ceramic capacitor: https://www.mouser.com/catalog/catalogusd/646/1018.pdf . The one I choose is 0603 in imperial. The tolerances for the Length and Width are +/- 0.1mm. The lead width is 0.35mm +/- 0.25mm. it's about 70% tolerance. Since I'm designing my first PCB, I don't have much experience with it.
Can someone explain to me if I should take exactly 0.35 mm or better to take larger width? Should I add to overall length i.e 1.6mm + 0.1mm?

best regards

den

 

[emresel]

Hi;
I am not an expert on PCB design but some manufacturers advise pcb footprint as reference. See below links.
https://www.vishay.com/docs/28745/soldpads.pdf
**broken link removed**
Hope helps

 

[Mattylad]

If you use the IPC-7351 footprints then it should not be a problem, choose the one that fits.

However going back even further - just find a footprint that it fits on at its largest tolerance.
Generally - if it fits it works, there is no real need to have several different 0603 footprints, 1 will generally do.

Ceramic caps get a little taller with the capacitance so require a bigger land for good soldering, so you can pick the biggest and use for all - if they fit it works (generally).
You can also consider the pads being narrower than the component ends to reduce the stress on the component and reduce the possibility of the component fracturing.

If you are making 100,000+ boards then you may consider each individual value cap and adjust pads accordingly for the very best soldering however for small quantities then a one size fits all is more than adequate.

Try the IPC-7351 calculator from mentors website (LP Viewer) however it is old and you have to jump through hoops to get it, the PCB Wizard Lite from PCB libraries can give you the correct pad sizes when you enter the component dimensions.
And the best thing is (AFAIK) its free and can output a single component archive that you can import into your PCB program. (Its also written by the same team that did the other and is much better.)