Mister Multicultural wrote:
[...]a friend[...]was explaining , theres a oven type device
that is used in the electronics industry[...]used for fixing mother boards
[...]as a lot of them require to be reheated for dry joints etc.

Usually called *cold joints*.
To expand on what Richard said (his spelling isn't the greatest)
http://www.google.com/images?q=conveyor-oven+re-flow

[...]i'd of thought it would melt all the plastic parts ,
as its bound to heat up so much that it would melt them ?

It can be an issue.
You have to check the spec sheets for the parts.

Does anyone have any links to such a device and typical cost ?

They don't come cheap.
Delivery times can be another issue.