Hardware: Flux - the Solder Magnet

I'm just finishing off a 6 page article on the EeePC for Custom PC Magazine at the moment, and part of it involved cracking open the EeePC and doing some soldering - much like my Bit-Tech article. This time I decided to add Bluetooth support, as well as the 32GB of extra space. To do this, I dismantled a USB 2.0 hub and integrated this to give me a couple more USB ports - I don't trust myself soldering to those tiny pins (yet).

In the process I discovered how much difference flux makes to soldering. I've always been led to believe that there is enough flux mixed into the solder not to need it, but decided to give some a go after seeing a video on Hackszine. I brushed a little onto the contact, and some more on to the wire, popped some solder on the tip of the iron and touched the wire. A short "fizz" and the solder was just instantly attracted to the wire. I then put the wire to the contact and heated it up. Another short "fizz" and I had the neatest and strongest looking solder joint I had ever seen.

Why has nobody suggested to me before that I should try flux? It has bought a whole new life to my soldering and has left me with the yearning to do some more soldering!

I found some nice information on flux on this site. To quote a little:

Circuit Rework

This is accomplished by the flux action which is very corrosive at solder melt temperatures and accounts for flux's ability to rapidly remove metal oxides. In its unheated state, however, rosin flux is non-corrosive and non-conductive and thus will not affect the circuitry. It is the fluxing action of removing oxides and carrying them away, as well as preventing the reformation of new oxides that allows the solder to form the desired intermetallic bond.

Much like any other self respecting geek, I have a cupboard full of things that I intend to repair at some point. One of these things, is a 400GB hard drive that blew up while I was at Trusted Reviews. Identifying the blown component was pretty difficult, as it turns out SMD components use a code that doesn't tell you a lot. Mine said "15A 451". After quite a bit of Googling, I decided that this was infact a 15A Fast Fuse. As I didn't need to save any space, as you usually do with SMD, I figured a 13A house fuse might do the job, with a worst case scenario of it just blowing again. I'm not entirely sure how much faster a "fast fuse" is...

A neat job, but unfortunately, I saw a lovely red glow from the fuse as soon as I powered it up. Homebase and B&Q didn't turn up at 15A fuses - only 15A fuse wire. The gauge of the fuse wire was so thick, I felt I may as well have been soldering the joint across!

This time around, the fuse held up, but I saw a red flash from near the SATA power plug, and was left with a warm SATA connector and slightly scorched pins. I can only assume that the fuse had blown because of another fault with the drive, rather than a freak voltage spike. Still - nothing ventured, nothing gained

Spode, perhaps a little help with something I do know about and I'm not being patronising! Firstly a fast blow SMD fuse is fast because it blows at very nearly it's rating. A standard 13 AMP mains fuse doesn't blow until around 30 AMPS. 15 AMP fuse wire blows and around 45 to 50 amps!
This is done that way because of the surge current that can be drawn from a single phase motor (A high wattage vacuum cleaner for example) when it's first switched on. Domestic irons have a similar problem although from the wattage it would seem a 5 AMP fuse would suffice, but the stat opening and closing would soon blow it.

Soldering is something that needs to be learned and taught by professionals. The method is to place the two parts to be soldered together as firmly as possible and some heat applied to both parts, then apply the solder to the joint, the correct gauge solder is also important. I mostly use the 1 mm lead free stuff and carefully stretch it if I need it thinner. This must be done as quickly as possible for obvious reasons. Solder used like glue melted on to the iron first does not work too well as the flux in the solder will burn away before you get to the joint.

On electronic devices a non mains, low voltage iron must be used as the high magnetic field and resulting circulating currents can blow the crap out of CMOS and the like devices. Some of the gas driven irons are great for this as they have no magnetic fields and the temperature can usually be controlled, that is very useful.

I use an ANTEX gas iron that has a needle point bit that is so useful for very tiny joints. Flux is very handy for re working and curing dry joints. (A solder joint that has not been soldered correctly and looks dull, also old joints that have oxidised over the years) Fluxes need to be cleaned off with a proprietary cleaner as they tend to be corrosive even if they say they are not. Cleaning up the gack after also stops any bad joints or shorts from hiding under it. I see you have some magnifying glasses in your photo, great stuff, absolutely essential with small work as solder bridges across joints can occur that are so small deem themselves invisible to the naked eye.

I hope that makes sense Spode and I hope none of that made you feel insulted. I was properly apprenticed in electronics and used to repair a build hearing aids, you can't get much smaller than that! I also hope you find this helpful, if not you can give me a thump when we next meet.

Can I say well done for the brilliant efforts modding the devices most would shy well away from. Great stuff Spode keep it up, you sir are a true pioneer.

I know it can be a real pig trying to hold three things at once Spode. I bought a very useful gadget called helping hands from Maplin HERE This tool is indispensable when you need extra help.

Yes, this "helping hand" (I know something similar called "3rd hand" can be very useful. Soldering really doesn't seem to be made for human anatomy...

I have never tried to use additional flux as I thougt that the one that comes with the solder would be sufficient. But maybe I'll have a try now. For me, it's sometimes difficult to get a good contact between the components an the solder within the estimated time (I have been told that a good soldering should be done within one second or temperature sensitive components could be damaged.). I know that the contacts need to be clean and fat-free, but sometimes the solder just doesn't stay where it should anyway.

For quick soldering and for tougher components or simple wires, I take a quick soldering "gun" (I don't know how you call it in english). That may be neiher professional nor made for all purpose ( I guess it would rather be a bad idea to use it for soldering micro electronics), but it's really fast. It gets hot within some seconds and cools down as quick as that.

I haven't tried gas-powered soldering irons yet. How long can you work with one charge of gas?

I have seen the battery powered soldering pens and they are good for big stuff like audio wiring and such. The manufacturer does not recomend them for electronic components. That's the only thing keeping me from buying one.