Some comments on repairing stuff

[ajay_m]

I have managed over many years with fairly basic kit; a good temperature controlled soldering iron with a range of bits, the usual array of screwdrivers and whatnot, along with some other things more useful when I'm creating new stuff, like a taper reamer for enlarging holes, a nibbling tool for making nice clean neat cuts out of thin metal or plastic etc.

Recently though after a somewhat challenging repair job involving some rather small SOIC chips, as well as stuff involving materials that won't take kindly to normal soldering temperatures, I've been looking around at what's available.

Firstly I decided to fork out on an SMT hot air rework station. Apart from being (hopefully) a slightly less lethal approach to shrinking heatshrink plastic tubing, where I traditionally relied on an Iroda gas soldering iron with a hot air attachment, it also offers the possibility of being able to remove SMT components and also of course assemble with them, using solder paste. This is not something I'm skilled at but it is an interesting thing to tinker with.

Turns out there are a lot of very dodgy products (surprise!) out there and you want one with the hot air blower in the main case, not in the handset, as these units don't work very well and are quite fragile, if you accidentally drop the handset even a short distance. The one to get for a price that doesn't make you suck your teeth appears to be the Quick 859, which'll go from 100 degrees up to 500 degrees, precisely temperature controlled and with 100 air volume steps as well. It's about £80 - but look out for fake knockoffs. I found a reliable eBay seller, luckily. If the 'Quick' brand is obscured in the pic, it's fake.

Anyway, it works well and comes with three tips but there's a huge range of specialised nozzles available if required. Set to max temperature it scares me, and I'd probably want to wear protective gloves, as it can send out a searing blast of heat for a short distance which will instantly char paper and probably start a fire, but of course at lower temperatures it's somewhat less risky; still, a tool, like a bandsaw or a lathe that I will treat with enormous respect and care, I think.

I also took a look at solder. Although most of the time I'll just use unleaded solder or for some things, Ersin multicore leaded solder, there are some interesting specialist solders available now. One of the most interesting is Tin/Bismuth solder paste which contains flux and melts at 138 C. This will tin copper foil quite nicely and offers an approach for repairing stuff at lower temps (like mylar ribbon cables, though I haven't tried this yet).

Also it is apparently useful to bring the melting point of an existing normal solder joint down, by mixing with the solder and creating a new alloy. Then you can apparently more easily remove the part because the joints will stay molten quite a bit longer and you can use braid or a solder sucker to remove solder.

This stuff is quite cheap - about £8 for 40g which is quite a bit of paste. It will also I think allow SMT components to be potentially soldered using a standard oven at, say, 170 degrees, like a reflow oven. I haven't tried this and I do know that the joints are more brittle, but it's an interesting idea.

You can purchase this solder in wire form but unlike the paste, it does not contain flux; the application is to reduce the melting point of an existing joint, not to solder with it. There's another alloy that melts at only 58 C called 'chip quick' I think. It's expensive; a six inch long piece of solder wire will set you back £7 or so. Again it's not for soldering but to reduce the temperature down drastically that an existing joint remains liquid to allow easy part removal. I have some but haven't experimented yet with it.

Another thing I'd like to do in some cases is stick two things together with some kind of conductive glue. This turns out to be interesting. Although Amazon and ebay are rife with listings for 'conductive silver glue' this appears to be silver-loaded paint and has poor reviews; also, it has no real adhesive properties. I have tried a couple of products and for the classic repair scenario e.g broken track on flexible circuit board etc, Loctite 3863 is a superior product; not cheap, over £20 for a weeny little bottle but it has a long shelf life and is a quality product.

There's also some carbon-based products sold for purposes like repairing remote controls. To be honest I didn't have great success with this product. Although I followed the instructions religiously, the carbon coating wasn't very durable and little crumbs fell off and caused all manner of weird issues in the remote I did fix. Also the product has a short shelf life once opened and turns into a block of rubber despite carefully keeping the top tightly on the bottle.

I wonder whether silver-loaded paint might have worked better, to be honest; I'll see next time.

Anyway, glue. Well it turns out there are conductive epoxy resins. The one part resins cure at around 80-90 degrees, something that in theory could be achieved by putting stuff on the heated bed plate of one of my 3d printers. But the products have a short shelf life and several people have complained that the product they received was unuseable because it had already cured.

There are also two part conductive resins. The prices of these will definitely have you sucking your teeth - £80+. There's one super-annoying vendor on Amazon who has a range of products for what initially look like reasonable prices but shipping is a staggering £130 from the US. Clearly dishonest but what can you do.

Finally there is one miracle product I only just found out about. Adhesive copper foil I've used on several occasions for various purposes but most of these have non-conductive adhesive on the back, which means that if you wanted to, say, bond a broken track, you'd have to then apply silver loaded paint on the edges of the joins, which kind of negates the whole purpose, when you could have just done the repair without using the copper foil. But it turns out you can purchase copper foil with a conductive adhesive for about the same price as regular copper foil (on Amazon). I was sceptical but purchased a roll and lo and behold, if you stick two bits to each other then my multimeter confidently reports a connection between the two.

So this could be very useful indeed in some scenarios. One mystery to me is that if they can put conductive adhesive on the back and not charge you any more, how come I can't buy little bottles of the stuff, which could be very useful. This is one of life's great mysteries alas, and despite assiduous googling I have been unable to locate whatever wonderful product they are using.

[resistorman]

Thanks! Good info

[Tomás Mulcahy]

THis is great, thank you. The shipping cost is probably legit, it has become crazy expensive from US. Nothing to do with Trump tarrifs.

[Drew Stephenson]

I propose this post for the Useful Information Archive.

[Martin Walker]

Ooh - conductive adhesive copper foil is INDEED a most useful material to know about

Thanks ajay_m!

EDIT: Ironically though, having had a look on Amazon it seems more common than I expected - even slug repellent copper tape has conductive adhesive (pesky slugs!)

[Nazard]

Ooh - conductive adhesive copper foil is INDEED a most useful material to know about

I have an unused free gift of Cir-kit, courtesy of the April 1969 edition of Practical Wireless, (I was a not very old schoolboy then). Cir-kit may be the original self-adhesive copper foil.

There were instructions for use and the interesting bit was: "CIR -KIT, which is the invention of Mike Wheals, is produced by his company "Peak Sound (Harrow) Ltd. ". As you will see from your free sample, it comprises 99-5% pure copper strip one- sixteenth inchwide. This copper strip, which is only two -thousandthsof an inch thick, is backed by a layer of special adhesive, protected by easily removed silicon release paper. The surface of the copper is covered by a flux assist lacquer making soldering easy".

[tomas]

Elektor currently has a discount on an SMD rework station.

https://www.elektor.com/products/zd-896 ... rk-station

[ajay_m]

Re: shipping costs from the US. I have purchased a number of vintage HP calculators over the last few months from the US and the cost each time was around USD30 in shipping (plus, unfortunately, VAT in some cases, which is charged on the item cost PLUS shipping). Unfortunately some Amazon and eBay vendors charge ridiculous shipping costs in order to make their products look cheap and come to the top of a price sorted list.

Incidentally eBay's international fulfilment service is glacially slow and it can easily take an item a whole month to travel from the US to the UK, a journey it makes via a tortuous series of hops around the US before being assigned to Asendia, the carrier of last resort (look at its online reviews). Finally the item is (hopefully) handed to Royal Mail for the last leg of the journey.

Some sellers dispatch directly using Fedex or USPS. Fedex has poorer reviews than USPS and recently managed not to be able to deliver a package to my address, despite several previous successful deliveries, then it disappeared into some kind of black hole. I was luckily able to pop down to the Slough dispatch centre and a very helpful man spent 30 minutes tracking it down, but still.. having to do all this is like having a dog and barking, surely...

I will say that in general eBay is a more reliable and cheaper source for most electronic bits and pieces than Amazon these days, and I have found it utterly reliable, albeit delivery times are a bit longer than Prime. The Chinese vendors often offer extremely good prices with often free postage, and they are also surprisingly reliable - it typically takes about 3 weeks for things to arrive but they will be often half the price of a UK seller. For example I picked up 4 X 1.3 inch OLED displays for £10 all up. I love these for little projects as they are quite a bit bigger than the 0.96 inch displays and can display a LOT of information (about 8 lines of text for instance). They arrived each packed into its own little plastic protective case, which is quite impressive.

Anyway we certainly live in a wonderful world when it comes to obtaining components and bits and pieces these days - and things like soldering stations, DVMs, function generators and other test equipment are incredibly cheap compared to when I was young.

I wonder whether SOS ought to set up a dedicate forum topic for questions relating to gear repair, to be honest, you could add some sticky topics for reputable parts suppliers, electrical safety, etc. Just a thought....

[ajay_m]

Elektor currently has a discount on an SMD rework station.

https://www.elektor.com/products/zd-896 ... rk-station

Nice little unit, but only 300W; the Quick is 580W and even this is regarded as on the lower side for some work, where units like the Atten provide up to 1000W. On the other hand I'm not sure all that power is absolutely necessary and the price is very attractive; I might have gone with this had I seen it, especially with the nifty little stand, that's very nice.

[Drew Stephenson]

I wonder whether SOS ought to set up a dedicate forum topic for questions relating to gear repair, to be honest, you could add some sticky topics for reputable parts suppliers, electrical safety, etc. Just a thought....

https://www.soundonsound.com/forum/viewforum.php?f=35