Siltamäki is a Finnish surname meaning "bridge hill" or the hill on a bridge. It was conceived in the 19th century when a village in Finland was populated with too many families sharing the same surname "Frante". This caused much confusion with the postmaster so some villagers adopted the name Siltamäki while others chose other new surnames. Siltamäki's scattered around the world may not even be related.
References
Siltamäki (name) Wikipedia(Text) CC BY-SA