MECHANIC X6 Rosin Flux Solder Paste BGA PCB PGA SMD Soldering Paste Flux For Electric Soldering Iron Welding Fluxes

It's flux. It works like it should.
It's more dense than many fluxes I've used, which is good, that means it will take less for the same job.You can thin rosin flux and use it as a liquid, all you need is a solvent like isopropyl alcohol or acetone and add a little flux until it's the consistency you want, then use it.