UK Changing micro switch on car key

[AlexBuz]

Hi everyone, I need some advice about changing the micro switch on my car key please. I'm not an electrician but I have a soldering kit as I build little robots sometimes as a hobby.

The button stopped clicking, probably the spring in it is done now and I want to change it. The board has some sort of gel covering the soldering from the micro switch as well and could use with some advice. What is that gel and what's the best way to desolder that microswitch? I've attached a picture in the link below with the board, many thanks!

 

[brianmoooore]

For removing old switch: https://cpc.farnell.com/duratool/d03332/pump-desoldering-esd/dp/SD01153 plus god quality fine bit soldering iron.
For replacing coating: https://cpc.farnell.com/electrolube...r-cpl-200ml/dp/SACPL200H?st=confirmal coating

 

[ImpededLoop]

There's someone on ebay that'll do it for you for £25. I had the same problem and it got sorted with no problems.

 

[Lucien Nunes]

That's probably a blob of silicone over a couple of critical parts. Just cut it away with a scalpel or craft knife around the pad of the switch.

Touch the iron and some solder on one pad, so that a little blob of solder forms. When it has flowed over the pad, lift that side of the switch just off the board, letting the other leg bend. Then repeat for the other leg. There may be a dot of glue behind the switch - make sure the solder is properly molten before you pry the switch up or you won't know if you are working against the glue or about to lift the track off the board. Each side should take about one second.

Once the switch is off, if you have some desolder wick, press it against the pads for 1 second with the iron tip to level the surface. If not, wipe off the solder as best you can while molten.

Place a small blob of fresh solder on one pad, not too thick. Let it cool, check it has flowed. Place a dot of adhesive behind the switch if there was one. Place the new switch in position with one leg on top of the solder. Press the leg down with the iron and position the switch with your finger as it melts through. Don't press so hard that the leg bends. Again max heating time 1 second. When cool, check switch position, if wrong reflow the solder and adjust. When happy, solder the other leg. Check the position again. Finally reflow each leg pressing the switch down firmly.

Manipulating surface mount with a regular soldering iron is a skill that takes time to acquire, so don't be surprised if it doesn't go perfectly first time. I've been doing SMD repairs for decades and I still occasionally break parts, lift tracks or create dry joints.

 

[telectrix]

myself, i cut the legs above the board then solder new component to the bits of leg left in the board. saves unsoldering both sides of board and risking camage to track/s.

 

[Lucien Nunes]

Yes that can be a good trick, also for removing surface mount parts like this, Cut the legs first, then remove them separately from the pads. With SMD one needs to have very sharp and fine cutters, there is probably 1mm of leg to cut here. Here the pads need to be completely cleaned off as the switch must lie flat and accurately in position within 0.5mm or it probably won't line up with the plastic case moulding.

 

[AlexBuz]

That's probably a blob of silicone over a couple of critical parts. Just cut it away with a scalpel or craft knife around the pad of the switch.

Touch the iron and some solder on one pad, so that a little blob of solder forms. When it has flowed over the pad, lift that side of the switch just off the board, letting the other leg bend. Then repeat for the other leg. There may be a dot of glue behind the switch - make sure the solder is properly molten before you pry the switch up or you won't know if you are working against the glue or about to lift the track off the board. Each side should take about one second.

Once the switch is off, if you have some desolder wick, press it against the pads for 1 second with the iron tip to level the surface. If not, wipe off the solder as best you can while molten.

Place a small blob of fresh solder on one pad, not too thick. Let it cool, check it has flowed. Place a dot of adhesive behind the switch if there was one. Place the new switch in position with one leg on top of the solder. Press the leg down with the iron and position the switch with your finger as it melts through. Don't press so hard that the leg bends. Again max heating time 1 second. When cool, check switch position, if wrong reflow the solder and adjust. When happy, solder the other leg. Check the position again. Finally reflow each leg pressing the switch down firmly.

Manipulating surface mount with a regular soldering iron is a skill that takes time to acquire, so don't be surprised if it doesn't go perfectly first time. I've been doing SMD repairs for decades and I still occasionally break parts, lift tracks or create dry joints.

Thanks for the tips Lucien, that helps a lot. Much appreciated!

 

[w0z]

Yes that can be a good trick, also for removing surface mount parts like this, Cut the legs first, then remove them separately from the pads. With SMD one needs to have very sharp and fine cutters, there is probably 1mm of leg to cut here. Here the pads need to be completely cleaned off as the switch must lie flat and accurately in position within 0.5mm or it probably won't line up with the plastic case moulding.

Having first ensured that the leg spacing on the new one is correct...
If you have a solder sucker the trick is to support the board very firmly copper side up, and suck the solder off

If you don't have a solder sucker or braid to absorb the solder another method is to cut the old switch off with very sharp side cutters so you don't stress the board (nibbling is fine), then hold the board very firmly copper side towards a flat surface and when the solder is melted copper side facing the hard surface bang your hand down hard and the solder will fly off. Then , with a judicious use of the iron you can clear the holes.
Needs must if you don't have the tools.