Correct pin naming of BGA and DIL chips
Typically ICs with pins on the edges have numbered pins. That's DIL, but also QFP, DFN and even SOT23. You start at the pin 1 marker and follow the contour. IIRC PLCCs have their pin 1 in the middle of one of the sides, but normally pin 1 is one of the corners.  

You'll see alphanumeric pin IDs whenever you've got some kind of grid, where there could be confusion about which are rows and which are columns. Usual suspects are BGA, PGA, and variants like WSP (WaferScale Packaging), but also this one:  

  

One found this one recently, it's called a "Staggered Dual-row MicroLeadFrame® Package (MLF)". Like some BGAs where only the outer pins are used this one numbers the outer pins as "A*", and the next round as "B*".