Here is a link to the Philips App Note AN212. This shows the advantage of having the power and ground leads of an high speed logic IC in a DIP package on the middle of one side of the package as opposed to the corner pins. This example shown is for a 20-pin DIP. Just imagine the effects of the 40-pin dip where the length of the lead frame to the corner pins about twice as long as those of the 20-pin package.

The picture below shows the relative size comparison of a 40-pin DIP to a 48-pin TQFP. The red and green areas show where the Vcc and GND of the microcontroller in each respective package are located. I only show one each of the power and ground on the small package but often these packages have multiple power and ground connections. You can see immediately why the small package is has such advantages over the 40 pin DIP for high speed applications.



Michael Karas