Here is an excerpt from the datasheet for Kester 245 no-clean solder which is what I primarily use.

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I do use the flux pens which are great stuff. Not cheap, but they last a long time and they are the opposite of messy. The no clean flux is much better than activated fluxes that have to be cleaned off. Even if you are going to clean the flux, you don't have to worry about missing something.

The Kester 44 is the RA flux version. It can be very useful for hard to solder items like cell terminals, etc. But it does need cleaning afterwards.

 

My Weller soldering iron has temperature control and is 54 years old. My soldering iron at work was the same.
I have only used a 700 degrees F tip.
I clean it with a damp sponge and only use 63/37rosin-core solder. Each solder joint takes about 1 second.

 

82 posts and the TS still hasn't done a successful solder - either the TS is just not suited for soldering or the TS is just wanting attention. By five posts the TS should have sufficient information on how to make a successful solder joint.

Unwatched.