noun
the whole face; all of one's face
Literal noun for the entire face. It is more written or descriptive than everyday 顔中, and often appears with に to say that sweat, color, etc. covers the face.
彼は満面に汗を浮かべて戻ってきた。
He came back with sweat all over his face.
adverb, noun which may take the genitive case particle 'no'
all over one's face; with one's whole face
Used adjectivally with の or adverbially with に, most famously in 満面の笑み, meaning that an expression is spread across the whole face.
彼女は満面の笑みで迎えてくれた。
She greeted me with a broad smile.
優勝が決まり、選手たちは満面に笑みを浮かべた。
When their victory was decided, the players smiled all over their faces.