On 05:43 PM 12/08/2002 -0700, Brad Velander said:
>Ian just for reference here is the SMT Plus sizing.
>
>         This is for the standard SOT23. (SMT Plus has over a dozen SOT23
>variations covering metrics and all the other minor variations.)
>
>Reflow
>X+2E pad edges: 2.87mm
>Z pad edges 2.82mm
>
>Wave
>X+2E pad edges: 2.87mm
>Z pad edges 3.48mm
>
>         So your pattern and Philips would be very close for overall sizing.
>There could be significant differences in the pad sizes by what I have seen
>in the past for manufacturer's or others land patterns. SMT Plus follows
>some pretty stringent rules for pad sizing and now, ten years after I took
>the course, I still see SMT Plus following the same rules time and time
>again in their new footprints.

Well, I think I like the SMT Plus designs better than IPC, in that 
case.  At least they are considering process technology.

I have also seen manufacturers recommended pad sizes varying - but unless 
they get so big, and take up so much of the available space under the 
device that you have to put the vias outside the area of the component, the 
outer dimensions are a fairly good measure of packing density.  I was just 
including one outer dimension as an example as to why IPC are *way* off 
optimum for high density designs.

Thanks,
Ian


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