Arrgh - PCB footprint pad dimensions!

[Leon Heller]

Why is it that the manufacturers' footprints for SM devices nearly always
give the dimensions between the edges of the pads? I thought it was standard
engineering practice to give the dimensions between centres, which is what
is required by the PCB package I use, so I have to do a few calculations
every time I create a new SM footprint.

Leon

 

[Leon Heller]

Why is it that the manufacturers' footprints for SM devices nearly always
give the dimensions between the edges of the pads? I thought it was
standard engineering practice to give the dimensions between centres,
which is what is required by the PCB package I use, so I have to do a few
calculations every time I create a new SM footprint.

Further to the above, I've just seen a footprint which has *one* dimension
between the *centre* of a central pad and the edge of another with *all* the
others between the edges!!!

Leon

 

[Simon Peacock]

they do that so you can learn how to use a calculator!

 

[Bob Stephens]

Why is it that the manufacturers' footprints for SM devices nearly always
give the dimensions between the edges of the pads? I thought it was standard
engineering practice to give the dimensions between centres, which is what
is required by the PCB package I use, so I have to do a few calculations
every time I create a new SM footprint.

Leon

One of my pet peeves as well. So far I haven't screwed up the offset
calculations on a board, but it's only a matter of time...

Bob

 

[Spehro Pefhany]

One of my pet peeves as well. So far I haven't screwed up the offset
calculations on a board, but it's only a matter of time...

Bob

I always try to print it out 1:1 and lay the part overtop with a new
footprint. If there's no samples in hand, that's when problems (this
and other kinds) tend to occur.


Best regards,
Spehro Pefhany

 

[James Jackson]

Using my CAD software, when creating Patterns like this - I will usually
also place the Package Outline information on an Assembly Layer -
superimposing it onto the Pad Layout. I will also create little square pads
on the Assembly Layer - that way... if something looks 'odd' it will usually
jump out at me, and I can investigate further, correcting if necessary.

I had a Pattern recently - for a SIM Card - that dimensioned to the plastic
edges... and the Pad edges. That was a challenge. I think mechanicers like
to pose interesting challenges when it comes to dimensioning parts.

Regards,

James Jackson
Oztronics

I always try to print it out 1:1 and lay the part overtop with a new
footprint. If there's no samples in hand, that's when problems (this
and other kinds) tend to occur.


Best regards,
Spehro Pefhany

http://www.speff.com

 

[Slav Mit.]

Hello, everybody.
In my opinion it is worth to visit www.pcblibraries.com and try their PCB
Libraries Navigator. It is free (demo) for a month period. It helps to
design land patterns properly concerning all tolerancies. I would appreciate
any opinions about it.
Best Regards.
Slav.