I see the .gif, but I don't have protel handy so I don't know what the relative pad
sizes are. Would be interested to know.
Using an IPC-7352 land pattern calculator and data for a panasonic 1% 0402 I get:
least nominal most
Pad Width 20 24 28
Pad Length 24 31 39
Pad C-to-C 39 47 55 mils
How does that compare?
Gary Crowell
Micron Technology
> -----Original Message-----
> From: Ian Wilson [mailto:[EMAIL PROTECTED]
> Sent: Monday, March 15, 2004 9:26 PM
> To: [EMAIL PROTECTED]
> Subject: [PEDA] An example why IPC footprints are often sub-optimal
>
>
> One to stir up the hornets nest a little...and a little off
> topic maybe
>
> http://www.considered.com.au/ProtelFiles/images/Phycomp_vs_IPC.gif
>
> shows the Phycomp (the old Philips, now part of Yageo) reflow 0402
> footprint versus the 0402 footprint from the Altium P2004
> Chip Resistor
> library (in the ../Library/PCB folder) which I think is based on IPC.
>
> You can see the ridiculous difference. The one on the left
> is based on
> reflow with a +/-0.15 mm placement accuracy. I need maximum packing
> density - IPC in this case is not on for this application.
>
> The problem with one size fits all (and an oversize like the
> IPC postage
> stamp footprints) is that assemblers and others can grab onto it as a
> pseudo-standard and say "we only accept IPC footprints". Instead of
> attempting to understand the pressures on the product and adapting
> processes they simply take the easy way out. Sure, using
> small footprints
> may reduce yield and increase costs - in some applications this is
> appropriate. By *blind* use of overgenerous footprints I
> think designers
> are loosing the ability to optimise their products globally -
> they are
> reduced to local optimisation only. And yes, this is
> probably a skill that
> is developed over time and with experience - but newcomers to
> the industry
> should be told, in no uncertain terms, that "IPC footprints are an
> appropriate starting point and since they are designed to
> cope with many
> soldering processes are necessarily not optimum for any.".
>
> I am not keen on any library that thinks wave footprints are
> the same as
> reflow. Does SMTplus makes the distinction?
>
> Ian
>
>
>
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