Soldering issue with arduino I am trying to solder arduino nano onto a perfboard/solderable breadboard using rosin core solder. The connection is only working some of the time, when I check with a multimeter (+) at pin 29 (in image below) I and (-) at pin 17 there is power at the top of the pin sticking out of the via/hole but there is 0 volts if I check at the actual joint (lower portion of the pin). I see a little flux residue around pin 29 that could indicate a little burning around the area could that be causing this, it is only very minor .. anyway I can fix it?





Also is it normal  to have a little yellow residue left over on the joints? I am new to soldering so not sure if a little flux reside is a bad thing on the joint...
Fair play, that is a lot of flux residue. I am assuming you are using some quite chunky solder with lots of flux in it.

Flux is non-conductive, so the residue will be forming an insulating layer on the outside of the solder. That doesn't mean the joint is bad, only that you can't get to the joint because the flux residue is in the way.

If there is a conductive path between the tip of the pin and the pad next to it then all is fine. The fact that you can't see the signal through the outside layer of flux is neither here nor there.

If you want to clean it off you can use isopropyl alcohol (AKA PCB cleaner, AKA "rubbing alcohol") and use, for instance, a tooth brush to scrub it off.