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jcw

Member Since: 11 Sep 2016
Location: Gloucestershire
Posts: 168

2007 Defender 90 Puma 2.4 HT Stornoway Grey

Key Fob Circuit Board - Re-soldering Tiny SMD Capacitor?

I have a key fob circuit board that has a micro SMD capacitor that has detached and needs re-soldering.

The capacitor is tiny, around 2mm x 4mm x1mm and position on the board similarly small, although fortunately, there are no other components too close by.

Although I’m ok at soldering on a ‘normal’ scale, not sure how I should go about this - online advice suggests using solder paste and a hot plate or hot air source carefully directed to melt the solder, although I’ve also seen videos using a very fine tipped soldering iron in combination with the solder paste pre-applied to the pads on the board.

I think it’s a ceramic capacitor by the look of it, which I believe means no polarity?

Does anyone have any experience / advice of how best to go about this?

Click image to enlarge

30th Jun 2024 8:36am

MadTom

Member Since: 10 Sep 2013
Location: Olomouc
Posts: 614

No need for solder paste and reflow, much better and safer for the rest of components is just solder the two.pads with same fine tip solder. Key is to use some flux - look for RMA-223. Solder paste is not enough for contact soldering. Some toothpick is enough to apply the flux to board. "Drobek" = The Small One - Discovery 2, "Blufínek" = The Blue Thing - Defender 130, and for me at least Ford Mondeo

30th Jun 2024 5:38pm

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20265

There is liquid flux as well, the issue I think is the very fine solder tip needed.

Possibly tweezers to hold the capacitor and very quickly on low a mini gas torch just enough to heat and off, though I’m not sure how safe an option that would be. The above is the safest.

It’s tricky due to its size, you could possibly with tweezers put the tiniest dot of superglue under it to keep it in place but keep it away from contacts, or a tiny bit of hot glue just to keep it where you want.
The latter here can come off easier.

I’d tend to try and keep the capacitor in place, then solder it, far easier, it’s that (the cap) moving around that will be your problem otherwise.

30th Jun 2024 8:45pm

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6601

2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

I think you’re pretty close to me despite being 2 counties over

So if you wanted it doing instead of buying kit and consumables for one tiny job let me know

1988 90 Td5 NAS soft top

2015 D90 XS SW

1st Jul 2024 5:43am

jcw

Member Since: 11 Sep 2016
Location: Gloucestershire
Posts: 168

Thanks all, just the type of guidance I was looking for.

Martin, yep Hook Norton’s a stones throw from me, that’s a very kind offer and that would avoid me potentially making a pigs ear of it and rendering the circuit board scrap

I’ll drop you a PM to sort out arrangements

Jonathan

1st Jul 2024 11:09am

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