Small Tiny SMD Caps, soldering technique, values and polarity?

[dicky96]

Hi guys
Me again - learning fast

OK I have a couple questions, I'm working on a Western Digital WD10EURS controller board. I found a short circuit cap on the 5V rail and removed that.

What I would like to know is how would I identify the value of the faulty cap? It appears to me to be a decoupling cap on the 5V rail (as it connects between te rail and ground) and I'm tempted to either think it is something like a 100nF cap, or just try the drive without it.

While finding the fault, I removed a diode from across the 5V SATA connection to 0V. I've removed one of these before on a drive of mine which went short circuit when the computer PSU blew up (with a flash, a bang and a little fire!) and I think these are avalanche diodes for protection, anyway that drive worked OK without it.

I also removed a SMD cap near the 5V pins on the SATA connector. This one again was between 5V and 0V

OK so the questiond:

1. I want to resolder the diode and cap. The diode polarity is obvious but the cap reads 10uF on my meter so would that mean it is polarised like an electrolytic? In which case how to find the polarity - there are no markings I can see. Actually it reads 10.00uF exactly in one polarity and 9.84uF the other way round - on my Fluke. Is that telling me something?

2. What is the technique for replacing the tiny little short circuit cap. I've soldered SMD caps and resistors before but on this drive controller board they are tiny - considerably smaller than anything I tried to solder before such as SOT23 or SOIC chips which I am OK with.

I only have an illuminated bench magnifier probably 2-3X and a 10x / 20x double ended jewelers loop

Pics are on this thread, to save me reposting again here: https://www.badcaps.net/forum/showthread.php?t=61761 post #12.

Rich

[diif]

Re: Small Tiny SMD Caps, soldering technique, values and polarity?

Ceramic SMD caps aren't polarised. You can solder them either way round.
To attach i'd use either my hot air station or my iron and small curved tip (T12-JS02). Some decent flux is a must. I use Amtech 559. A paste that allows for plenty of rework time before it burns up.
I also use a stereo microscope for SMD work, it makes things so much easier and enjoyable.

[dicky96]

Re: Small Tiny SMD Caps, soldering technique, values and polarity?

Thanks Diif

Will solder the SMD cap back either way then. You guys have to realise I was brought up on valves and stuff though I have moved on a bit since then.

A Stereo Microscope is on my list of must gets next time i am back in the UK (in 3 weeks or so).

For Flux I use a tin of this 'Pasta do Lutowania' stuff which I have to melt with my soldering iron tip but it does wonders with desolder braid and rework in general.

However I have seen videos on youtube where they use some sort of liquid flux and apply it with a small paint brush or dropper?

I do worry about resoldering small smd components in densely populated parts of the PCB. I would think I might desolder other parts by mistake in the process?

Rich

[diif]

Re: Small Tiny SMD Caps, soldering technique, values and polarity?

Low air speed so nothing blows away and plenty of practice on scrap boards. That worry will soon subside.
I prefer the thicker paste to the runny flux. I also have some cheap China Kingbo flux in a tub that i have used to full an empty syringe.