here is the flux i use.
http://www.mgchemicals.com/products/solder/fluxes/rosin-flux-835/
http://www.amazon.com/dp/B004RIF3BM/ref=cm_sw_su_dp
http://www.mgchemicals.com/products/solder/fluxes/rosin-flux-835/
before that i used this stuff for years:
Witch amazon still sells.
http://www.amazon.com/dp/B004RIF3BM/ref=cm_sw_su_dp