Calculating the footprint dimensions

[rajasekaran]

hi,

While creating the foot print, Mr.Robert uses some reference values in the Orcad course. for example, while creating the footprint for SMD capacitor 1210, he uses the following values.
Terminal pin spacing (e1) = 3.1mm
Package width (E) = 4.9mm
Package length (D)=3.3mm

As per the datasheet, the package width (E) is 2.8mm and package length (D) is 2.6mm.

1. May I know how Mr.Robert calculating the values for the components ( like do we have any reference procedures like add 0.1 or 0.5 mm to the values specified in the datasheet) ?
2. How to calculate the value for terminal pin spacing (e1) ? (is it distance between two pins?. i am getting e1 value as 1.85mm for the 1210 smd capacitor)

Thanking you.

Thanks & regards,
Rajasekaran

[robertferanec]

Usually if board is hand soldered, I print the footprint on a paper and compare it with physical component. Then, I adjust the footprint based on what looks like will be the right footprint for hand soldering - no special rules for the values.

You can always use the values from datasheet first. Then after you print the footprint, you will see if you will be able to solder it by hand - many times the pads are very small and that is reason why I adjust them. Once you adjust pad size, you need to adjust also e1 (the middle of pads is moved).

If you are not sure, I recommend you use the numbers from datasheet. Once you print the footprint, you will see if you would like to adjust it or not. You do not have to adjust it .... if you are not sure, you can always use the values from datasheet, that is just fine.

[rajasekaran]

Thank you