difference between scan flop and normal flop(non scan flop).

difference between working of scan flop and normal flop . how it effect the current design
Scan flop and non scan flop .
if any good docs on this topic . please share it here.

The size difference really depends on what type of non-scan and scan flip-flop you are talking about.
In general, the mux-D scan flip-flop has the smallest area increase (a single mux), but if you have a dedicated scan output, then there is some bufferring involved.
The next area-efficient flip-flop is the clocked scan, where you usually have a separate scan clock which is edge triggered. This can usually be done with an additinal latch stage.
The more expensive flip-flop is the LSSD type, where there are normally one or two extra latches, and two scan clocks, but it is the safest because you eliminate any hold time isses with the two non-overlapping scan clocks.
So in general, the difference can be anywhere from just a few percent area increase to almost double the size of the flip-flop. Usually you can tell by looking at the datasheet of your standard cell library.
check these
https://www.eng.auburn.edu/~agrawvd/TALKS/VDAT05_anand.pdf
The history and future of scan design
**broken link removed**