Solder rot

[D.M. Procida]

My Christmas present to the children was a Commodore 64.

I picked it up a couple of months ago, and ran it for several hours to test it; it was all fine.

On Christmas Eve I tested it again; after a few minutes it would start throwing junk all over the display and then lock up, and I realised that the difference was the house at room temperature where it crashed, and the much cooler garage where it wouldn't.

We've repaired it now (mostly), by resoldering many of the pins on the PCB where the solder seemed to have developed holes. I've never noticed this phenomenon before, even in much older equipment. I assume that it wasn't like that after manufacture.

What causes it?

Presumably, a 30-year-old computer would have had proper lead solder, not this tin-whiskery lead-free stuff.

Actually it can't have been the soldering alone that fixed it because it continued to crash; I also used a hot air gun to try to identify the component that was failing after warming - I only once managed to get that to trigger the fault, but since then, it hasn't crashed again.

So the crashing is fixed, but the next thing to tackle is the sound output, which is barely audible.

Anyway, the children have been happily playing The Hobbit and Attack of the Mutant Camels from tapes that have been sitting in boxes for nearly three decades, which isn't bad going.

Daniele

[Owain]

...

You do realise that when the children do their "What I did over the christmas holidays" essays the social workers will be round accusing you of deprivation and asking why you didn't buy them a Wee like the chavvy children got, don't you?

Owain

[NT]

I've occasionally seen examples of other products from that era where teh soldering was dire, but somehow it worked. Over time the solder surface oxidises, then contact is no longer good and it fails. Cause: substandard soldering.

NT

[JonH]

Fault finding is probably better assisted by a can of Freezer Spray from the local Maplins or equivalent.

The solder rot is probably extant because the OEM used solder with a highly active or acid flux and lousy cleaning (if the board was cleaned at all) to overcome oxidation of plating on cheap and nasty PCBs and the terminations of cheap and nasty components to increase the yield but at the expense of medium to long term reliability. (I opened up a Sinclair ZX Spectrum once, it looked like a rat had cr@pped the solder onto the board.)

Reflow the joints with some good honest 60/40 Lead based solder (still legal for repairs) and a decent temperature controlled soldering iron. Clean the reflowed joints with Isopropyl Alcohol - if you can get hold of it - and a stiff brush followed by de-ionised water. Ensure the board is completely dry before re-applying power.

Regards JonH

p.s. If you look diligently on the web, you should be able to find US military handbook MIL-HDBK-2000 (Previously MIL-STD-2000 and WS-6536) which goes into much more detail and is in the public domain. It's successors, the IPC 6100 series of workmanship standards are ruinously expensive.

[Huge]

Readily available on eBay. To my surprise.

[brass monkey]

I've occasionally seen examples of other products from that era where teh soldering was dire, but somehow it worked. Over time the solder surface oxidises, then contact is no longer good and it fails. Cause: substandard soldering.

We used to get a lot of Apricot F1's with joints like this on the power conns -

[D.M. Procida]

Is there any problem mixing lead and lead-free solder?

Daniele

[Dave Plowman (News)]

Using leaded to repair a lead free joint is fine. Only a madman would do it the opposite way round.

[<me9]

I got my last lot from CPC about a year ago.

[Jules Richardson]

TVs seem to be about the worst culprits IME. I've found soldering to typically be good on vintage 'home' computers - less so on the games consoles of the era.

cheers

Jules

[The Natural Philosopher]

Not really.

[geoff]

In message , Huge writes

Why so ?

Its been discussed to death in the past - about £6 /litre from CPC for example

[the_constructor]

Not really a surprise as you can often purchase it from you r local pharmacy like I do. Reminds me, I have juist run out..... Jim G

[JonH]

Depends on the alloy. Some of the Lead-free solders currently available contain high quantities of Zinc. While they flow and melt like 60/40, they are prone to corrosion.

Other mixes don't perform well at low temperatures (especially high Tin alloys) or under vibration. Probably OK for most domestic applications, not good at all for aerospace.

Your equipment will almost certainly have been made using Tin/Lead solder.

Regards JonH

[Brian Gaff]

Yes indeed. Well solder joints get dry due to oxide forming on the component wires where the solder did not take correctly to start with.

The effect used to hit pcbs before plated through holes where rivets used to do that job and of course under a high powered magnifier you could see the furryness forcing its way under the solder. Another thing I encountered recently via a sighted person was that some of the chips of that era had poorly plated pins and in some cases they actually oxidised completely through causing all sorts of problems. OK if its a z80 or 6502 etc, processor there are still some made but some of the custom chips like in the 64 you are stuffed. With regard to sound. Are you using a modern analogue tv to get the sound out? Most of these are digitally tuned and the modulators in these computers tend to drift. In the old sets the afc followed the drift, but not the newer models. Often, its better to wire up a monitor lead and get the sound out as audio. some of these older machines have psu faults. The ripples on the picture or hum on sound make it rather obvious that the capacitors have dried out. You can get new ones fairly cheaply of course. Brian

[Brian Gaff]

So what is in the lead free solder to replace the lead, and can we look forward in a few years to learn this new substance is more dangerous than the lead... Brian

[D.M. Procida]

No, it's not the modulator - I get it on the audio out too. And I don't think it's the amplifier either, as a tone from a signal generator on the right pin of the sound chip socket comes through very clearly.

Daniele

[John Williamson]

Tin, 3.5 percent silver and 0.7 percent copper (Roughly), with some having a minute amount of zinc to reduce the melting point.

The main known problems are the mechanical strength and formation of whiskers in hand work if temperature isn't correctly controlled. The melting point is also about 20 degrees higher than Tin lead solder.

[Frank Erskine]

Just curious - what type of solder (if any) IS used in the aerospace industry these days?

I think I've got enough tin/lead (grade K) to see me out anyway :-)

[Tim Watts]

Leaded I would imagine, seeing as the automotive industry is exempted from the lead free requirement, so moreso the aerospace industry.