While we’re on the subject, can someone recommend a good, inexpensive hands-on soldering practice kit? Something like this.
A completely free one is a random piece of old enough junk electronics to have through-hole parts. Strip them from the boards, and either put them together to some simple circuits or just solder little pieces of art from them.
Or, possibly simplest, strip some copper wires, string them between a couple nails to a grid, and you have a lot of joints to make. (Not proper joints as for them you want the wires to go at least parallel for a few millimeters, if not twisted together - the solder alloy is not mechanically strong enough - but for the practice and simplicity it is good enough.) Dad taught me this way. Then, once I had the basics, I proceeded with the salvaging way.
Or you can solder together random wires. Then pull the finished joint apart (and feel how much force it takes), then examine the rupture surfaces - you want the joint to give way through the solder. If the joint fails at the solder-wire interface, you did it wrong.
Watch the temperature. Too low, and wetting will be poor. Too high, and the surfaces will oxidize, the flux will burn, and the wetting will be poor. Use enough flux to form a layer on the molten solder or at least all over the solder-metal interface. The flux’s role is to disrupt and dissolve the surface oxides (the solder also dissolves some) and prevent oxidizing of the hot metal (which goes appalingly fast otherwise).
Also, for learning, make sure you go with a lead-tin alloy, preferably eutectic 63-37 one but 60-40 is close enough, preferably with activated flux (more corrosive but also more aggressive; here you want to get rewarding, motivating work experience and long-term reliability in harsh environment is less of a concern).
The lead-less substitutes handle like crap and need higher temperature, and are dull so you won’t get the proper shiny bead (with lead-tin a dull bead means oxidizing or moved during solidifying or otherwise wrong) and it impairs visual inspection of joint quality.
A jewellery loupe or a stereomicroscope is a friend. Will let you see where the solder does not properly wet the substrates. The wetting angle has to be low. If it sits on the metal like a mercury drop on the floor, it’s wrong. Usually you have cold solder, oxidized solder, too little flux, or grossly oxidized or contaminated substrate.
Beware of soldering on things like metal pins in thermoplastic part. They WILL move. Hold them in the opposite-gender connector and solder for the shortest time needed to make a proper joint. This is a little higher school than a plain joint, so graduate to these after you master (or at least apprentice) the basics.
Once you consistently get a good joint, go for a cheap kit. Then you’ll just blaze through the assembly, without having to chase cold joints.
[quote=“shaddack, post:3, topic:62210”]Once you consistently get a good joint, go for a cheap kit.[/quote]While I appreciate the advice, the selection of a cheap kit is the step I am currently at.
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