When performing mods that require soldering, it is very very important to use FLUX, it helps the solder flow nicely and gives you good well soldered connections, if you do not use FLUX then you are essentially applying excessive heat to the solder pads which you are soldering to, risking lifting them away or completely burning them off !,  you will create yourself a whole heap of problems if you do not use a good FLUX paste.

This FLUX is a 'no clean' variety and low odour, when using you will get a lot less sticky residue which makes it much easier to clean up after your work is done, giving you a much more professional finish.

Comes with plunger to push flux out and needle attachment for precise application.

AMTECH NC-559-ASM BGA PCB No-Clean Solder Paste Welding Advanced Oil Flux Grease 10cc 
Soldering Repair Tools Capacity: 10CC 
Brand : AMTECH
Model: NC-559-ASM 

Features: 

Product is no-clean solder paste, very little residue, without washing. 

The residue is colorless and transparent.

Free plunger and needle attachment.