Not all SSOPs Are Created Equal
Iturns out making assumptions about chip variants is a bad idea.
As I already mentioned, I ran into a little trouble when I assumed the SSOP-28 and SSOP-36 versions of the MAX6957 LED driver were basically the same size, with the 36-pin version being just a little bit longer. This turned out not to be the case at all, since the lead pitch is different. On the 28-pin version, pins are 0.65mm apart on center; on the 36-pin version, the distance is 0.8mm.
Here’s a close up picture illustrating the difference:
When you bring the chip and board together, the mistake is pretty dramatic: