Anybody knows AMD Sempron 140 can unlock to Dual Core?  

Wow! really, can semplron single core unlock to dual core. So how about my dual core 5600 can i unlock it to quad core? Amazing what kind of motherboard should it be possible to do the unlocking?

Certain motherboards.
Expensive ones mostly too.

The money you may spend on the motherboard to do this plain and simply doesn't justify the chances that you are taking in order to do this. For the motherboard list, Google for it to get an idea.

Now, what happens with these CPUs is no different than what happens in graphic cards. Lower model cards aren't always made with the intuition of covering a market share, but rather they are selling not fully functional equipment since the GPUs on those cards still aren't refined for 100% usage.
This translates in that the Sempron 140 has a second core, yes, however there is no guarantees that it's fully functional or at all, depending on the revision of the fabrication procedure.

The money you'll spend on a adequate motherboard is better spend on a cheaper motherboard and a proper CPU; if you already have a motherboard that supports this though there should be not much harm in this. Damage may occur, but more frequently than not what you'll see is the computer crashing if the second core isn't stable enough and the applications start trying to use it too intensively.