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Old 12th Nov 2018, 1:16 pm   #1
Al (astral highway)
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Default Mounting SMT electrolytics?

Hi folks,

I’m now used to soldering IC’s in a SOIC package without too much challenge, I enjoy the concentration needed.

But I’m foxed by electrolytics, typically as shown.

These have been around for years now, I note from some commercial circuits and development boards.

The problem is they have PVC or similar plastic bases next to the bit we need to solder and with a conventional (not hot air) soldering station , there’s no headroom to solder the adjacent connectors. Copious fluxing and pre-applying a shiny blob of solder are useful but the plastic is easily damaged.

Any tips gratefully received.

Thank you
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Old 12th Nov 2018, 2:41 pm   #2
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Default Re: Mounting SMT electrolytics?

Pre tin the pads, use a small tip side on, melt solder on one pad and position cap, press down on top of cap as you melt the solder on the other pad.
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Old 12th Nov 2018, 2:50 pm   #3
Paul JD
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Default Re: Mounting SMT electrolytics?

Found this youtube video showing a method of doing it https://www.youtube.com/watch?v=o3BdfJPIBmA. However the American gentleman demonstrating the technique appears to be using something called "sodder" to attach the component - not sure if the same technique will work with solder!!
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Old 12th Nov 2018, 3:19 pm   #4
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Default Re: Mounting SMT electrolytics?

Al... I think the caps you have show have "hidden" pads, which would make conventional "soddering" LOL impossible.... these are usually for soddering in wave soddering or hot oven reflow.
I shy away from SMD electrolytic caps and prefer to use Radial caps...mostly the same footprint but obviously taller. Works for me.
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Old 12th Nov 2018, 3:51 pm   #5
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Default Re: Mounting SMT electrolytics?

Here at work we use solder paste, apply to the pin & the pad then heat the pad with a soldering iron, works a treat. You don't need a lot of paste, a little goes a long way.
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Old 12th Nov 2018, 4:20 pm   #6
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Default Re: Mounting SMT electrolytics?

Pre-Tin just one of the Pads. Keep heating that pad whilst placing the Cap, with only the one Pad Tinned the Cap can be placed 'flat'.
Then solder the other exposed part of the Pad.

Try getting them OFF without the 'proper' tool. A nightmare !!!

James.
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Old 13th Nov 2018, 1:01 am   #7
Al (astral highway)
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Default Re: Mounting SMT electrolytics?

Hello wonderful people,

Too many replies to acknowledge individually but some great tips and links here, thank you. I haven’t tried soldering paste before but now have some on order.

Thanks again!
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Old 13th Nov 2018, 5:20 am   #8
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Default Re: Mounting SMT electrolytics?

To remove them is easy enough, you can cut them away with sharp cutter (destroying the part) until you can get at the pins to un-solder them. Apart from the obvious difficulty soldering these in, I avoid them like the plague as they are the type that cause more leakage and destruction to pcbs than any other type of electro. When I see these in my own equipment I generally replace them with surface mount Tants, which are dead easy to solder in and won't leak corrosive liquid to the pcb.
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Old 13th Nov 2018, 7:04 am   #9
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Default Re: Mounting SMT electrolytics?

The key to hand-soldering these is to have large enough pads on the board that some metal peeps out from under the capacitor and is accessible to a soldering iron. I use a chisel shaped bit to contact as much area as is available.

You can get liquid flux in felt-tip pen form. Watch out for the limited shelf life of solder paste - it tends to dry out in its applicator. I just use cored solder on the pads before mounting the component.

Tants are currently showing terrible failure rates. Modern parts have minimal amounts of tantalum due to ramping price, and the reliability is what pays the price. Industry is avoiding them as far as possible.

There are conductive polymer aluminium electrolytics which don't dry out and don't leak.

On the ceramic front there is big trouble. The large manufacturers have shut a few big plants, more than slow markets justified, I think. There are now shortages, parts are on allocation and lead times are going out far beyond a year. Take a look through Farnell and RS websites at SMT ceramics and you'll see hundreds of parts with "Waiting for delivery" or very low stocks. Prices are shooting up. Cynics are saying it's an OPEC-like ploy to put prices up to cash in on the upturn in the industry. Oh, and they're saying they will drop 'larger' SMT packages and concentrate on 0402, 0201 and smaller sizes.

Customers have now started putting out parallel orders to see which turn up first, then cancelling the others. Suppliers are threatening that people doing this will be dropped in priority. Customers are threatening to remember. It's getting nasty.

Shades of the days of memory on allocation.

David
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Old 13th Nov 2018, 2:50 pm   #10
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Default Re: Mounting SMT electrolytics?

Quote:
Originally Posted by Radio Wrangler View Post
On the ceramic front there is big trouble. The large manufacturers have shut a few big plants, more than slow markets justified, I think. There are now shortages, parts are on allocation and lead times are going out far beyond a year. Take a look through Farnell and RS websites at SMT ceramics and you'll see hundreds of parts with "Waiting for delivery" or very low stocks.
David
Oddly I just noticed that a few days ago trying to order some SMT ceramic caps for a digital delay line and I really had to hunt around. It sounds like a bit of a worry.
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Old 13th Nov 2018, 3:16 pm   #11
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Default Re: Mounting SMT electrolytics?

David,

These sound like ominous signs of the times indeed. It seems unthinkable that such structural absurdities could exist in the supply chain.

I feel lucky for the time being to have some mil spec caps - wet tantalums- and also plenty of high quality ceramics.

Thanks for the soldering hint- I’ll try to find a more delicate bit . I haven’t used solder paste before and will give it a try but also noting its limitations .
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Old 13th Nov 2018, 3:19 pm   #12
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Default Re: Mounting SMT electrolytics?

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Originally Posted by Argus25 View Post
Apart from the obvious difficulty soldering these in, I avoid them like the plague as they are the type that cause more leakage and destruction to pcbs than any other type of electro.
Thanks Hugo, is never have realised they were such a liability . I’ve seen them in a very high quality Austrian development board that is ten years old and still goin strong so I assumed they were treble A star rated !

I have radial electrolytics and mil spec tants to use instead , fortunately.
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Old 13th Nov 2018, 3:30 pm   #13
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Default Re: Mounting SMT electrolytics?

I have found they vary in quality quite lot, the type used in Sony monitors of 15 or 20 years ago would frequently pack up after a couple of years, some other type are much better.

I find when using solder paste it makes life a lot easier if you gently warm the pad area first with a hot air gun - this makes the paste stay in place better.
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Old 13th Nov 2018, 3:31 pm   #14
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Default Re: Mounting SMT electrolytics?

In the past I've replaced bad SMD electrolytics with quality sub miniature leaded electrolytics (from Rubycon or Chemicion etc). I form the leads at right angles (outwardly), slightly away from the rubber seal, to mimick the flat leads of the SMD caps. This can be a bit fiddly but so are the SMD caps... if needed you can secure the cap in place with a little spot of some type of (removable, non aging) glue.
I find the leaded caps much more reliable than the SMD types.
Of course, space may be tight so the above might not be a suitable idea..!
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Old 13th Nov 2018, 8:44 pm   #15
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Default Re: Mounting SMT electrolytics?

I've taken this approach with DAT servo boards, nearly all made in the heyday of dodgy surface-mount electrolytics. Having cleaned up all the fishy muck and bridged the corroded tracks, I wasn't about to let myself in for the same problems further down the line.
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Old 13th Nov 2018, 10:30 pm   #16
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Default Re: Mounting SMT electrolytics?

Quote:
Originally Posted by astral highway View Post
Thanks Hugo, is never have realised they were such a liability .
It might be that the more modern versions are better. I struggle to forgive them for the diabolical damage they have done to multiple A5 logic and control pcb's in the Tektronix 2465B scopes (my favorite scope model). The A5 pcb's that were fitted with Tants, practically never give any problems, even nearly 30 years later.
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Old 14th Nov 2018, 9:01 pm   #17
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Default Re: Mounting SMT electrolytics?

Various Japanese camcorders and the head amp boards for various DCC recorders (the ones made by Marantz using Japanese SMD electrolytics) had a particularly bad reputation for leaking all over the place. Most people repairing those DCC head amps wash the board very well and then mount conventional electrolytics. In camcorders, this wouldn't be so easy. I wonder which brand electrolytics they used, as some seem worse than others (DCC head amps and some brands of camcorders had a near 100% failure rate).
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