pcbsoldering
I recently came across a pcb.
This is the picture of the aforementioned PCB.
As you can see, some solder points seem burnt. The copper trace has been removed.
Does this mean the PCB is dead? If I solder the component on the solder points, will it work?
Maybe I should do prework, like remove pieces of solder with solder wick?
Solder bridges mean you need more/better/fresh flux.
(Either iron or hot air will work fine. Heat is heat. I prefer iron for clearing shorted pins: wipe iron on sponge, apply to pins, repeat. The excess solder will stick to the tip.)
Remove the third lead, this will let you clear/prepare the pads for re-soldering.
It's probably best to flick the old solder off the leads; do this by heating and bending the lead with the tip of the iron and letting it spring back, DO NOT DO THIS TOWARDS YOUR FACE!
You can buy solder with a flux core. Also, if you can get it, buy lead solder, it is MUCH nicer to work with.
Yes the guy tins his iron to remove the leads, you should always tin (add solder to your iron tip) before you do anything, it stops the tip oxidising. It also helps when melting old solder.
To clean the pads generally I would put a bit of new solder on, then wick it off to give a nice clean and shiny surface.
He is applying flux, this will stop the solder "balling up" and sticking to stuff it shouldn't. You can do this, but if you are careful, and have flux core solder, you wont need to.
As regards the rest of your questions, this is just about technique. The guy seems to tack solder (a connection made to hold it in place) the leads at first. When the whole lead is tack soldered he goes around and tidies up the job.
Remove the lead - Tin and clean the pads and flick the old solder off the end of the lead (NOT TOWARDS YOUR FACE!)
Add a little solder to each of the pads
Place each lead above the pad and push down gently whilst touching the tip of the iron to the solder you placed on the pad. Make sure you remove the iron before removing the pressure.
When all connections are made, get some tweezers and push down on each lead in turn, melting the solder on the pad with the tip of the iron so the lead is properly flat on the pad.
Remember! Before you touch the iron to anything, make sure you have applied some solder to it and wiped it off on a sponge.
Also, if you are buying new equipment, when you first turn the iron on, keep adding solder to the tip and wiping it off. You need to thoroughly tin/protect the tip before you start using it. You can get little pots of hard flux, this is useful and it will help remove the crud on the tip due to oxidation. Also, tin it and DON'T wipe it off when you are done, the tip will still be hot for a while after you switch it off.
Best Answer
This horrific butchering 'repair job' can be repaired with time and patience, assuming the reasonable skills are there. The person who did this can be immediately disqualified by virtue of the latter requirement.
Presumably the part removed is known- maybe a SIP audio amplifier IC or a switch. The part needs to be replaced with a good one (hopefully that's all that is wrong). The pads are all lifted, including the ones that were for primarily mechanical reasons. For the latter perhaps epoxy to provide the mechanical support, but that can wait until it is working.
First, clean the board with a mild solvent such as 99% isopropanol and one of those manual toothbrushes that the dentists give you at every visit (obviously it should be new, clean and not used for teeth afterward). Then inspect the damage.
I would run a thin (eg. AWG30-AWG24) insulated wire back to the nearest pad that used to be connected to those missing pads- follow the traces to where they went. This is a single-side paper-based phenolic board, so all the circuit is visible. The pads are also very weakly attached to the substrate. Make absolutely sure you get the connections to the right place- a mistake at this point could greatly compound the disaster. You can see that some traces are peeled back by the ham-fisted thug that worked on it.
Use a sharp Xacto knife or similar fine blade to trim off the loose ends of the ripped traces so they can't get into trouble.
Make sure that the big pins or tabs are connected to the proper places in the same way (with wires) as the copper around those pads is missing or compromised (lifted). Looks like they were connected together and to a ground (?) pour via a thermal relief(s).
If you get the device working, make sure you provide mechanical support with something like epoxy.
Some of the unrelated component leads look a bit like cold solder joints, it might not hurt to carefully touch them up. If the device was intermittent that might have been the root cause.