Stength Of Soldered Joints

Browsing round Tandie the other day I noticed they had some lead free solder for sale 99.5% tin 0.5% Copper, also what they called silver solder 95% tin 4.5% Silver 0.5% Copper. This got me thinking how strong the joints would be from these types of solder. So her's the ? does any one know where you can find on line a data sheet showing the mechanical properties of joints made with this type of solder.

I'm thinking it may be a cheaper substitute for higher % silver solder, for fabricating parts.

Stew

Edited By Stewart Hart on 21/03/2013 12:14:57

Stew,

The material you saw labelled "silver solder" is in no way equivalent to "real" silver solder as used for silver brazing at 600 deg C plus. It is just a lead free soft solder which has a tiny amount of silver added to give it the desired properties.

David

Something like this ?

Stew its probably similar to the Harris "staybrite" where the silver is added to compensate for the lead being removed, they give strengths on their site. Click the resorses tab and then spec

**LINK**

Edited By JasonB on 21/03/2013 13:38:56

 Stew,

We in the avionics industry have been forced to move to SnAgCu solder. Mechanically a SnPb (tin-Lead or Eutectic joint) is ductile and flexible. SnAgCu (Lead-Free) joints are stiff and brittle. this is caused by the tin-lead forming a 2 phase structure where as the Lead free forms an inter-metallic compound suspended in the Sn Matrix.

Long and short of the new stuff: It fractures much easier than classic soft solders, electrically has a nasty habit of growing whiskers over time which causes short circuits. If you see some good old fashioned soft solder at a car boot sale: buy it. The "lead free silver solder" is only desigend to replace soft solder do not confuse it with silver solder.

Jo

Edited By Jo on 21/03/2013 14:48:57

Edited By Jo on 21/03/2013 14:49:43

Edited By Jo on 21/03/2013 14:54:53

Here (Canada) the lead free solder was mandated for potable water plumbing. I think it's 95% tin 5% antimony. As far as I know ordinary 50/50 lead-tin is still ok for electrical and other work. I've seen "silver solder" 95% tin etc advertised but as far as I'm concerned it is deceptive advertising as real silver solder has a definite set of uses and cannot be replaced by the 95% tin stuff.

Ken

Thanks for the info,

I new it was different to silver solder but didn't know how diferent it was, I did find some information on line, but what with the units being in PSI or N or kg/mm3 they were also talking about tear strength/ UTS/shear/brittle fracture etc it started to do my head in and give me a migrane.

What got me thinking was this thread **LINK** a contributer talks about using 99% tin solder for fixing parts to shot guns, and I was reasoning if it strong enough for that aplication it may be ok for fabricating engine bits.

What Jo said bout the 5%% silver stuff fracturing makes it a non starter:--- is the jury is still out on the 99% tin stuff?

Great minds Jo I've got a good stock of leaded solder all obtained from car boot sales.

Thanks for you're input folks

Stew

Edited By Stewart Hart on 21/03/2013 15:28:53

Tin/lead solder is still available from professional electronics distributors. I don't think there's a ban on its use per se; what is banned is use in equipment put on sale within the EU after a given date. As always there are exceptions, including large scale fixed industrial equipment, exclusively military equipment and some medical devices.

To be pedantic the exemptions for medical devices were removed in 2011, but there are moratoriums in place for 3 or 5 years depending upon the precise use of the equipment. You wouldn't want a duff joint in your pacemaker!

Regards,

Andrew

I believe the 5% silver loaded tin solder is for use in electronics with surface mounted capacitors to stop the silver being leached off the contacts. This caused many failures in the early days of surface mounted components.

Russell.

Hi Stew,

The informaton you seek is basically unavailable because joint strength is not only dependent on the bulk strength of the alloy (which may be available) but more importantly on how and where it is used. A manufacturer or supplier has no control on these factors and therefore cannot quote any figures.

For instance the strength of a butt joint in tension is dependent entirely on the bulk strength of the filler metal - assuming that is higher than the strength of the parent material! Although soft and silver solders are sometimes used in this manner - they are not intended to be so.

These fillers metals should be used such that the joint is designed to operate in shear ie using capillary attraction to make the joint. Even then there are considerations.

Joint gap - narrow gaps = stronger joints

joint length - too long = possibility of voids / too short = insufficient area to carry the load

degree of penetration - dependent on heating technique

joint design

fluxing

No supplier can control these factors hence there are no figures. The only solution is for the user "to suck it and see". If it gives you the result you want then use it. Generally speaking there is a technical reason why silver solder is used in place of the cheaper soft solders.

eg its melting temperature,

corrosion resistance

potentially higher joint strength

ability to join dissimilar metals etc

An F1 car can reach speeds of 200mph(?) but not with a 15 stone driver, roof rack, and pulling a caravan. But that is not what it s designed for - hence the ford escort et al.

Finally, when selecting silver solders, the last consideration is joint strengh. Used properly they will all produce joints stronger than the parent metal.

keith

The 95% tin solder was mandated for potable water plumbing because there was lead leaching out of the 50/50 solder into the drinking water so opening up the possibility of lead poisoning if someone drank enough of it. This was discovered in school fountains--the water contained detectable amounts of lead after sitting in the pipes all night; once the pipes were flushed out it was ok for the day. It's one place where the "precautionary principle makes some sense although I'm not sure anyone knows if the actual amount of lead was a hazard.

Don't forget that lead poisoning from the early tin cans soldered with lead solder was one of the things which doomed the Franklin expedition to find the northwest passage 150-160 years ago.

--That plus a refusal to learn how to live from the native Inuit

Ken

I'm not sure anyone knows if the actual amount of lead was a hazard.

I don't know, having hard water was agood protection, once the pipes furred up.

There was a statistically significant shortfall in kid's educational attainment clustered around the M6 and spaghetti junction in the days before lead-free petrol.

Neil

Hi Chaps

The move to unleaded soft solder was driven by the amount of electronics equipment winding up in landfill and possible contamination of ground water. The 'ban' if it can be called that is the restriction on electronics manufaturers use of leaded solders in commercial equipment. The silver in the unleaded solder replaces the lead to get the right flow characteristics and melting point. Leaded solder is still freely available and probably will be so long as there is a big enough market for it.

Often it's disposal of substances that cause problems rather than intrinsic hazard in use. An example is plasterboard (Gypsum) which when disposed of in landfill with organic waste can generate Hydrogen Sulphide which is poisonous. Apart from which it is a valuable resource and can be recycled into new plasterboard.

regards Martin

As jo says about difficulties with lead free solder in avionics, I can see lives lost because of this.

The local second hand shop here often has tin lead solder, and I'm getting quite a collection of it, two reasons, one it could get difficult to obtain, two, they sell it at a fraction of the normal retail price.

Ian S C

reading this thread has reminded me of attending a PCB soldering course at Marconi College in Chelmsfoord in the 1970s. I can still hear the lecturer say " Clean the board with IPA" in a cockney accent, this phrase was repeatted about 100 times a day.! True to life we never had IPA where we worked. The end of course test, was to solder some 18 SWG brass wires through .1" diametre copper lands on a PCB. The resulting joint was then subjected to a "pull off" test and if my memory is correct a minimum weight of 3 kG was needed to be hung on the wire before the joint failed, or you failed!

Tektronix used to include a little reel of silver bearing solder on the chasis of their instruments. This was used to repair them. Their construction was to have strips of ceramic with grooves in them to anchor the component leads which were silvered. If you used non silver bearing solder to resolder a component, the silver on the ceramic would disolve into the tin/lead solder leaving the component leads soldered togather, but flapping in the breeze.

Frank