Interesting pinout

[AlphZeta]

I was working on an old piece of equipment and it was using an AT45D041 (4Meg Flash). What is interesting about this chip is the pinout (see http://www.datasheetcatalog.org/datasheets/120/131280_DS.pdf). The SOIC packaging uses 28 pins, but 8 through 22 are all NCs.

What puzzles me is why would any one design an 28 pin IC and leaves the right half all NC (take a look at the first page of the PDF you will understand what I am referring to)? Wouldn't it be easier and cheaper just make it a 14 pin device? It would still be pin-wise compatible. What am I missing?

[SeanB]

Probably the internal die is too big to fit in the smaller leadpack, so they put it in one that fits, even though they have so many unused pins. The lower pin count frame has more metal inside the package, and probably they could not fit the internal spacing and route to the bonding pads on the die with the 14 pin leadframe. to fit. As well the other packages use less plastic filler and are thinner and thus lower cost.

[AlphZeta]

Code: [Select]

Probably the internal die is too big to fit in the smaller leadpack, so they put it in one that fits
Right.... I forgot that this chip was manufactured at least 20 years ago and back then the dies were much larger. That totally makes sense!