Altium footprint wizard LQFP offset issue

[diyaudio]

Hi

I'm practising creating footprints in Altium, However im stuck and have a few questions.

Using the Altium Designer footprint wizard, (I'm not using the IPC wizard as I just need a basic footprint and I don't need all the mechanical layers.)   

* How do I calculate the pin offset for the LQFP-176? see land pattern attachment. (The land pattern doesn't specify the offsets, and im not getting the correct offsets see my calculation)
I tried using the calculation as follows:
0.5mm (pitch) * 43 (number of lead spaces) = 21.5
SQ (24.10) - 21.5 = 2.6mm offset 

* The lead length of the component is 0.75mm, however I use 1.33mm, what is the recommend lead length for hand soldering vs production?   

   

[diyaudio]

Okay I think I figured it out.

REF = 21.50mm (0.5mm (pitch) * 43 (number of spaces) = 21.50mm) 
SQ = 26.20mm (see land pattern pin to pin)
User Defined Lead Length = 1.30mm
Find mid point Length 26.20mm + 1.30mm = 24.9mm

Now calculate the package offset..

24.9mm - (21.50mm) REF / 2 = 1.95mm

Note Ive overridden the solder mask expansion as well and gave it 2mil.

See attachment for the results.
 


 

[T3sl4co1l]

Why wouldn't you use the mechanical layers?  If you don't use them, they don't matter anyway.  If you do, you should want as much information, and accuracy, as possible.  Anything else is negligent or half-assed.

It's worth looking up IPC-7351 specs to see what the general guidelines are.  That way you also have some idea which way to allow for errors, given the part and PCB tolerances, plus any other allowances like soldering or clearance or anything else you might want to cover.

Tim

[diyaudio]

Why wouldn't you use the mechanical layers?  If you don't use them, they don't matter anyway.  If you do, you should want as much information, and accuracy, as possible.  Anything else is negligent or half-assed.

It's worth looking up IPC-7351 specs to see what the general guidelines are.  That way you also have some idea which way to allow for errors, given the part and PCB tolerances, plus any other allowances like soldering or clearance or anything else you might want to cover.

Tim

Hi Tim

The reason why I didn't include the other mechanical layers was 2 things, 1) I just needed a the footprint for a simple test home PCB layout assembly (so the other mechanical properties wasn't of value), I'm also a newbie(I also did the basic Alitum course by Robert Fedeve and they only covered the footprint wizard not the IPC wizard).
 
However I do understand your point and its a good one, I will practice using the IPC wizard as well and look into the IPC-7351.