i have a few soldering questions before i begin a project

if i use rosin core solder,dose that have flux in it or if not how do i add it?
if i wire in an opamp to a mousbot kit(See make magazien’s youtubechannel an mousie the junkbot for more details) is thatsurface mount soldering or if not can you tell me hout to do it(real basicly though no need for great detail)
on solarbotics hydro x solder how do i wash it off with watter so i dont damage anyrthing?
what size tip do you sugest for things like small robots andarduino?

my final question,
if i need extra flux what kind do you sugjest for the things i said i was doing?

Rosin is the most popular and oldest form of flux—they found artifacts that some believe indicate rosin flux was being used back in 2500 B.C. (“Basics of Soldering, Armin Rahn, p.2). Back to things you care about, YES, rosin-cored solder has flux built inside, you shouldn’t need extra. The flux inside the solder should be fine. This isn’t true for surface mount soldering, though…

The opamp in the mousebot kit, LM386, is a through hold component, which means it has widely-spaced pins that fit into holes. It also comes as a surface mount component but that’s not what’s in the kit. If you’d like to get an intro to surface mount soldering, and see what surface mount chips look like, check out our “surface mount soldering guide”http://www.curiousinventor.com/guides/Surface_Mount_Soldering and surface mount soldering 101 intro video

On Solarbotic’s hydro x solder: Rinsing with warm water for a minute is the best way to clean off the flux residues. You must clean off the residues; they are conductive and corrosive.

Now for reasons not to buy that solder, or any other water soluble solder, or any other multicored solder.

The flux integrated into the middle of that solder is water soluble, not rosin based. Water soluble solder is typically only used in industry for difficult to solder surfaces (heavily oxidized, older parts). Water soluble flux’s ability to remove tough oxides comes at a price: the residues are corrosive and conductive, so cleaning is a requirement. Rosin flux, on the other hand, depending on the manufacturer and type, usually leaves behind residues that are both non-conductive and non-corrosive, and doesn’t require cleaning. I recommend rosin flux since there is some risk you won’t clean up all the water soluble flux residues, especially under chips. This is why water soluble flux is not used in military, life support, etc. devices.

The Solarbotics page selling that solder says that the joints will looks shinier than with rosin based flux. First of all, the shininess does not necessarily mean the joint will be stronger or weaker (unless it’s completely dull and rough). Leadfree solder isn’t shiny at all. 2nd, the shininess depends on flux, the underlying metals, technique—lots of stuff, not just the flux.

The hydro X solder is also multicored, which has multiple “cores” of flux on the inside. There used to be problems manufacturing a consistent fill of flux inside wire solder. Often you’d have gaps that would wreak havoc on the soldering process. Multicore solder was developed to reduce the likelihood of these gaps. However, modern manufacturing processes (at least for Kester) have addressed this shortcoming. I can’t speak for RadioShack solder.

And one last thing, Solarbotics doesn’t publish specifications on just what exactly that solder is made of, just like RadioShack doesn’t provide specs. This bothers me, but I might be the exception.

Having said all this, just about any ‘cored’ solder you get your hands on will probably work fine for these kits :) You’re not making something you want to last for 5 years, so I wouldn’t lose sleep over choosing the solder.

I recommend a 1/16” chisel or screw driver tip for through hole soldering and a 1/32” chisel / screwdriver tip for surface mount soldering. For through-hole soldering, again don’t lose sleep over the tip if you’re just starting out. About anything will work, just be sure to keep the tip clean.

And one more point to include in my rant against water soluble solder: The aggressiveness of the flux will also reduce soldering iron tip life.