When an assembly is up issued there can be many reasons for the change - some of which will affect the surface mount process and some will not.
The component placement program is one aspect of the process that may need to change but only if neccessary - the reason for the up issue may only be a tracking change in the PCB in which case there will be no difference to the placement program.
The type of changes could be:-
- Part number change/addition/removal
- Circuit board reference change/addition/removal
There are many ways of comparing documents and one in particular which is quick, easy and the software is free to download is called MELD - available to download here or link below:-
The image below shows the software in use to find the differences listed above