Do I need to free char array of fixed length? [duplicate]

This question already has an answer here:

• Can I free() static and automatic variables in C? 2 answers

As far as I can tell from the answers to other SO questions, I don't need to free fixed-length arrays like the following:

unsigned char buffer[16];

But in general one has to free memory whenever calling malloc, memcpy, etc.

My Question is: Do I need to call free in the following scenario:

unsigned char buffer[16];
memcpy(buffer, source, 16);
...
free(buffer); // needed?

To be more precise: Is the decision, whether heap or stack is used, based on the declaration or initialization of a variable?