Salaam Koosha,

The purpose, and action, of the flux during soldering is to chemically remove that oxide layer and allow the molten solder to physically bond with the metal pad. This is why reflow (thermal) profiles specify maximum ramp rates and minimimum dwell times leading up to the melting temperature of the solder. These provide the necessary time and temperatures for the flux to activate and do its cleaning work.

You should also understand that the reason the flux and solder need to comingle during the reflow/soldering process is to ensure that the molten solder contacts clean metal. In other words, there is no air beteen the flux and solder. If air gets to freshly cleaned metal, even for an instant, new oxide forms. In other words, even if you chemically clean the copper before soldering, there will still be some oxide present by the time you do solder.

I'm not sure what you mean by "soldering grease," but if you mean flux, then the cleaning you're doing is unnecessary. On the other hand, if you have pads that are heavily oxidized, or that are macroscopically coated with other contaminates, then you will need to clean them before soldering. In the final analysis, if you end up with solid solder joints, you did okay.

By the way. If you are not using "No Clean" (NC) solder paste (flux), you will need to clean the board after soldering. Residual flux will corrode the solder joint just like it did the oxide layer, and can lead to unreliable joints. I use NC solder paste. If you want shinier solder joints (because they look better maybe), you can use "Water Soluable" (WS) solder paste (flux) and clean it with clear running water. If your solder paste (flux) does not specify either NC or WS, then you will need to clean it with an appropriate saponifier.

Good luck,

Joe