Hello.
A hint to distinguish one from the other:
fino a --> until to
finché non --> finché(=fino a che) non --> until to that moment, point you don't
So you _cannot_ use them interchangeably.
"fino a" identifies temporal or spatial or acting limits
fino a domani/until tomorrow
fino a qui/until here
fino a cadere/until falling
but its use is more limited than "finché non"
Look the same example with both :
a) fino a
Leggi FINO A qui.
Read until here
b) finché non
(?)(?) Leggi FINCHE' NON qui (?)(?)
(?)(?)Read until you don't here.(?)(?)
Do you feel it misses something?
It should be :
Leggi FINCHE' NON *arrivi* qui.
Read until when you don't *arrive* here. (*reach this point* would sound better in English)
The best sentence would be "Leggi finché non sei arrivato fin qui" (fin qui=fino a qui)
But how can I use "fino a" with a similar meaning of "finché non" (I guess your confusion comes from this)
When, at example, one inserts an adverb (quando/when) after "fino a"
Leggi FINO A *quando* NON ARRIVI qui.
But, like you can notice, you still need the NON, negative form, and the VERB for the secondary sentence.
Is it clearer now?
:-)