Need some help soldering Binding posts.

UPDATE: Sonic Craft has recently told me that they always loop the hookup wire through the little hole in the tip of the Cardas binding post before soldering. So, I apologize to those whom I disparaged. 

However, Sonic Craft still commands that a 250 watt+ soldering iron be used. I can verify that the post heats up so quickly with that wattage iron that within a matter of perhaps 30 seconds the solder literally flows even more quickly than water. Just use enough to hold the connection. Do not fill up the tube with solder as I think it deadens the sound and I know for certain that doing so wastes a ton of solder. Additionally, I would say after having filled up 18 Cardas binding posts with solder (7.2 system with passive subwoofers) while using a 60 watt iron, installing them all to the speakers, then uninstalling them, heating the posts, dumping the solder, and then re-soldering using a 250 watt iron after laying down some extra flux and just enough solder to solidly hold the connection, that the improvement in sound quality is amazing.

The rule in my day as a tech were to make the connection physically sound, and then solder. Do not use solder as a glue.

Don’t forget to prepare the mating surface of the binding post before soldering by lightly sanding or wire-brushing. This, as well as a modest amount of rosin flux (never use acid flux) will ensure the solder “wets” correctly. This provides as close to a molecular bond as possible. And yes, wrap the wire firmly around the post, or double fold it over if inserting in a tube before soldering. This will give you the required mechanical integrity that is necessary for long term reliability. A good soldering iron or station with the correct (1/8” or larger) tip should be sufficient to heat the post and wire. My preference is the Weller WTCPS or WESD50. 

There are so many images of improperly soldered Cardas binding posts on the internet that I decided to change my profile image to that of a somewhat correctly soldered Cardas binding post. I say "somewhat" because when I have the time I am going to redo mine by first looping the wire through the little hole and then soldering. I did not do this initially because I needed to be able to remove the nut, however, now I do not because I switched to Cardas mounting plates that mount over small cutouts in the back of my speaker cabinets. 

This solder was done with a Weller 300/200, Cardas solder and extra flux. The solder will flow like water when heated with an iron having the correct wattage. A 60 watt iron  ill heat the Cardas binding post sufficiently to melt the solder and make the connection. However, it will be a cold solder and will not sound as good as a wet solder. I know this from experience.  

Hi Craig: I see that you’re still trying to improve your workmanship for soldering wire to a binding posts. Your plan to loop the wire into the binding post hole and then solder is a good one.

A couple things. From what I can see from the picture you show, this soldering job would not pass industry standards (IPC). The wetting angle is not correct and there is no strain relief to the solder joint.

The difficulty, as you know, with soldering anything to a binding post is to get it hot enough. Your choice of solders exacerbates the problem. I would use Sn63/Pb37 alloy which melts at 183C instead of something like SAC 305 which melts at 217C. That way, you don’t have to get the binding post so hot. All electronics prior to 2006 (RoHS) where fabricated with Sn/Pb solder. There is no difference in SQ.

As for technique, you should coat the wire and post with rosin flux prior. Then hold your iron up against the outside of the binding post by the hole the wire is looped thru. Feed your solder to the inside of the binding post at the post/ wire interface. When done, the solder joint should have a smooth fillet (proper wetting) and not be a big blob.

The IPC solder standards are not in the public domain but there are some boot legged copies on the web.