lead free solder

If you are just doing repairs or mods to PbF stuff then use SAC (Tin

+Silver+Copper) solder, the cost would be prohibitive for complete new build soldering.

As I would not use a pound every few years, the cost would not be a problem for me. For the very small solder I doubt I would use a pound of the lead free solder for the rest of my life.

As it is just for my own use at home I am not worried about the legal Rohs part.

While the above seems like dumb questions, I find it is easier to ask than spend all day looking for the answers.

I did see where some of the water clean up flux says that it can be left on and some of it says it is safe for a few dys so I am going to stay away from that. Reminds me of the old acid flux. May be ok to use if cleaned off, but absolutly can not be left on if used. Even then I wold never use it on anything but pumbing.

Ralph-

I sympathize!

The problem with using tin-lead solder with SMD, is that lead "amalgamates" with the silver contacts of surface mount devices, resulting in a non-conductive layer between the device and the circuit.

While tin-lead-copper solder may help, it would be better to use lead-free. It may work better if you use a temperature-controlled iron, capable of higher temperatures than your old iron.

Fred

Ok Fred, thanks for explaing the 'amalgamates' part. Looks like I will be getting some of the lead free solder. I know the old gold plated RF power transistors gave a lot of problems due to the gold plating of the leads, so guess the lead free boards are doing something similar.

I do have a couple of temperature controlled irons. Also bought one of the hot air gun and soldering pencil stations. Just an inexpensive one for about $ 65 off Ebay. Seems to work well on the regular leaded SMD boards. I have been running the irons up much higher to match the lead free boards.

I have been looking at a lot of the Youtube vids about the SMD soldering and they make it look easy. The boards with the tin/lead solder I have been practicing on usually turn out very well, not so much for the lead free stuff. I do have one small tube of solder that has some silver in it but not sure what else. I need to look it up on the internet and see what it is actually made of. It is some from some samples we got when I was working and no one ever used. The tube does not state the makeup, just thatit has some silver in it.

OK, just for your own use, you can do repairs with PbSn solder on assemblies made originally with Pb free. I do this all the time, never had a problem.

You can also, in most cases, do repairs on gear that was made with PbSn solder using SAC305. This does require higher temperatures, but when hand soldering one lead at a time, usually there's no harm.

Jon

Actually, if it amalgamates, you are fine. That essentially means it has made an alloy. Pbf component leads usually do NOT have silver on them, just Tin. Now, GOLD is a problem, a certain percent of gold dissolved into a solder joint can cause brittle structures that fracture under thermal or mechanical stress. They call this intermetallics. But, I've never heard of this with silver. I've done tons of boards with SMDs using PbSn solder, and had no trouble with it. One time ONLY, I got talked into trying gold flash plating on the circuit boards, and had HUGE problems with joints that never flowed, or became brittle. The fix was, desolder, lift the lead, scrape the pad down to bare copper, tin the pad, fold the lead back down and solder. UGGGH! Still gives me nightmares!

Jon

I have ran into the gold problem. Only "simple" cure I know of is to just scrape it to the base material. I never gave the solder any other thought before just use the 60/40 or beter if around 63/37 and rosin flux, but now with that lead free stuff comming in and components having to be made to the Rohs standards it is time to do some asking about the mechanics of it. Seems there are about half a dozen or more mixes now without the lead. There is one other problem I have seen , not with solder, but tin plated items. The tin "whiskers'. Probably will be a problem with the tin/silver and no lead solder. I have read that the military and space agencies still use the tin/lead to not have that problem.

I know I have to use a lot more heat on the irons on that lead free stuff.

"Amalgamates" *Does Not* mean that an alloy has been formed. An Amalgam is essentially a solid colloid whereby the *separate* properties of the compon ents makes a mixture that does not behave as either. The best example of th is that is easily understood is Dental Amalgam, which is a mixture of silve r, tin, copper and zinc, indium and other materials *as a powder* mixed 1:1 with mercury. The mix is pressed into place, whereupon the mercury is disp laced and the rest of the mixture hardens. But, it is NOT an alloy. The var ious components partially dissolve in the mercury and bind to each other as a result. Kinda-sorta like sticky bits of candy would bind to each other i f made wet. But, the individual bits of candy never dissolve entirely, and except at the direct interface, could never be described as an alloy. Or, i f you must, somewhat like concrete. The components, sand, gravel, water, an d cement *cure* (NOT dry) into an amalgam - but they are NOT an alloy.

This is an obscure point, but important in this context. The potential for a non-conductive oxide to form is real as each component of the amalgam rem ains discrete in its behavior at the chemical level.

The reason that gold is used is that it is more resistant than any other of the noble metals to 'dissolving' into anything, forming an oxide or otherw ise degrading. If it is attacked by something, that something will be quite toxic or dangerous in its own right. Those compounds would include chlorin e, mercury, cyanide and reactants of same. Gold often does not solder well, true, but that depends much on how how it is alloyed and its purity. 24 ka rat (pure) gold tends to solder quite easily, if gotten hot enough, but is also very expensive, very soft and for those reasons seldom used. 10 karat gold - the lowest that can still be called 'gold' solders badly unless very high silver-content solder is used, and typically requires a flame. Silver Brazing would be a better description.

Gold is seldom used in soldered components as there is no reason to do so. The only real reason for gold (as it is a poor conductor relative to silver or copper) is its resistance to corrosion on contact-type connectors - ja cks, plugs and switches. Soldering *to* a gold-flashed lug or pad is asking for trouble for all sorts of reasons, some obvious, some not so much.

This is basic high-school chemistry - at least when I was in school.

Peter Wieck Melrose Park, PA

Within the EU; hobby use and repairing originally lead solder equipment is among the exemptions.

Never bothered swotting up on the laws elsewhere, but I think America and Asia comply with RoHS purely so they can export to the EU.

RoHS certification is expensive enough, but certification guaranteeing that cross contamination can't happen in a manufacturing plant that uses both processes, is much more costly - its much cheaper to impose blanket compliance with RoHS, even for goods that don't have to comply.

Mixing them depends on individual compositions - visual appearance of the finished joint is a good indication whether you got away with it.

it is alloyed and its purity. 24 karat (pure) gold tends to solder quite easily, if gotten hot enough, but is also very expensive, very soft and for those reasons seldom used. 10 karat gold - the lowest that can still be called 'gold' solders badly unless very high silver-content solder is used, and typically requires a flame. Silver Brazing would be a better description.

I know gold is used in contacts because it is resistant to oxidation. They really found that out when computers and memory chips were put together with the tin contacts instead of gold. I have a ham radio repeater made by GE that has some cards in it with the tin edge connectors. About once or twice a year I have to pull them out and give them a good cleaning. The low level audio stages seem to be the worse and I have rewired the circuits to byapss those weak points. What I never did understand is why most of the RF power transistors seem to have gold leads. Most are soldered in and that solder joint often goes bad for the reason you stated. Then you have to scrape off the gold and remove the old solder and put fresh solder on.

I think I have mentioned "purple plague" here before.

I learnt about it decades ago when working on experimental conducting films.

I thought that gold was tricky to solder precisely because it did tend to dissolve unless the solder was already loaded with gold.

Mike.

Pure tin solder, if not processed hot enough to anneal the Tin, can get REAL bad. Part of the reason for the tin/silver solder is to reduce the whisker formation, and it seems to work. I had some Xilinx chips which had pure tin lead plating, and I was processing them at PbSn temperatures, and the LEADS, not the solder joints, had whiskers at the bends in the leads, as this is where the stressed tin was. Xilinx suggested hotter soldering temps.

Jon

Not really. Gold is also somewhat lubricious - and things flow well on it. BUT, they do not STICK well to it. Solder will flow and appear to be nice and tight, until it peels off like cheap tape. But it takes more than heat to cause gold to dissolve.

Peter Wieck Melrose Park, PA

** In fact gold dissolves readily in tin and hence solder.

Normally, gold plated parts have a nickel underlay which does not readily dissolve to form an alloy with solder. This results in joints that have poor mechanical strength.

.... Phil

Me too, the amalgamate talk makes me wonder though.

George H.

Reworking lead free with 60/40 sometimes gives a grainy finish that looks even more dodgy than the original lead free.

When I was in TV repair, most Asian manufacturers had converted before most people in the UK had even heard of RoHS. (but it took the Asian manufacturers a lot longer to get it right).

My introduction to lead free solder was a steady stream of TVs with bizzare random faults that defied any attempt at logical diagnosis - going over the soldering fixed them as if by magic.

With Hitachi sets; you could push down on a component and the whole solder fillet would detach from the other side, that revealed a thin black layer of oxide on the copper.

On Sony sets; the solder looked as good as lead free ever can - but going over the soldering fixed over 90% of all faults.

During that time I routinely used 60/40 - I didn't get many bounced repairs, and not many of those had anything to do with solder.

I had a RCA (think that was the brand) that had a classic case of bad solder around the tuner. This was in the days before the internet,but there was the FIDO net that I found the solution of the problem. Went over the solder around the tuner and it was good for about 2 years and then had to do it again. Not sure what kind of solder was used way back then as it was over 20 years ago. Seems that RCA had many solder issues around tht period of time. Should have been a total recall for them. Last thing I bought with the RCA name on it.

AFAICR: RoHS came in about 96. It probably isn't law in America and Asia, but they have to comply if they want to export to Europe.

Certification is expensive - and much more expensive if they also run a non RoHS production line, as they have to prove that cross contamination cant happen.

Last time I checked - RCA had been taken over by the French Thomson firm.

Last Hitachi I looked inside; the innards were made by the Turkish Vestel company - while researching servicing info; I learned that quite a few big name manufacturers stick their badge on the very same chassis I found.

That is one big problem for me. I never know who or where anything is really made. I was repairing some CB radios for friends around 1970 and found even then the same insides were put into different cabinets for different brands. Sometimes even the same color wires were used.

The Brand names are often sold and moved to a different country so the quality may or may not be worse.

Sometimes it gets as bad as the Jeep. From what I heard you almost need to know the day it was made to find out what kind of engine or transmission was used in it.