Don't take this the wrong way but some of those solder joints looks a little rough. I'm not sure this is your issue but you need some soldering practice. Solder joints should be bright and shiny and should completely cover the pad.
I can tell by the joint on pin 16 you didn't get it hot enough or the solder would have flowed to cover the entire pad. Some of the other joints look like they were overheated. Does your soldering iron have a temperature control? Experience will help you know when to turn it up and when you can get by with a lower temperature. Is your tip too large or needs replacing?
There's lot's of soldering how-to videos out there but no substitute for practice, practice, practice and then practice some more. :)