Electronic – Solder paste not wetting at all

I have an issue with solder paste, I would like to know its origin so I can fix the problem and solder by components properly.

I use a lead free Sn42/Bi57.6/Ag0.4 solder paste, manufactured by ChipQuick.

Here is the datasheet.

The syringe I'm using was opened three weeks ago and stored at ambient temperature until now. (I close it with the protective cap between each use, of course.)

I ran some tests before actually using it to solder components. I simply deposited several bits of it on a copper board, which I previously wiped with alcohol.

I have at my disposal a soldering oven (not some salvaged toaster, a real oven designed for this application).) However, it works like regular timer-ovens: set a time with one button, and set a temperature with another.

This is the process I used so far:

1. I put the board in the oven, at ambient temperature
2. I start the oven at 90°C and I wait one minute
3. I set it to 140°C and wait for two minutes
4. I set it for 180°C and wait for the solder paste to "melt" and get transformed to actual solder
5. Finally, just after the activation, I turn off the oven and open the door to allow a quick return to ambient temperature.

Problem is, I always end up with a nice sphere instead of observing spread solder across the copper face.
Exactly like this :

I want to know if I am doing something wrong during the process, or if this is linked to the storage conditions of the solder. Note that the manufacturer indicates a good "shelf life" but I don't know if it implies that the container should not be opened.