EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: gnif on January 25, 2019, 02:47:29 am
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Bought some cheap Chinese monolithic caps from ebay and just out of curiosity figured i'd cut some open and see how they are made. Really not surprised by the result, but interesting for those that want to know. One is a 22pf, the other is 10uf. The measure just fine so are fine for my use, audio and power decoupling :).
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Yup, as I stated I am not at all surprised that it's done this way. The last time I cut one of these open was nearly 20 years ago and it wasn't hiding a SMD :). Just figured i'd share :)
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Oh, that's cool.
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I didn't know that, thanks for sharing :)
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Leaded MLCC capacitors have been built that way at least back to the 70s. Initial axial packaged parts even used the hermetic DO-7 glass package (shown below) usually associated with germanium diodes which made them unusually reliable unlike later plastic packaged axial and radial parts.
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I sense a business opportunity here. Someone should make a generic case that holds any 0603 SMD part, two versions, one with the leads facing downwards and one cylindrical one with the leads facing outwards. That way if a through hole part dies in some old gear it can be substituted with an SMD part easily.
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If one were that determined to replace a through-hole part with SMD, why not just replicate this method of packaging? Can't be too difficult to solder on a couple of leads and dip the thing in some epoxy.
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If one were that determined to replace a through-hole part with SMD, why not just replicate this method of packaging? Can't be too difficult to solder on a couple of leads and dip the thing in some epoxy.
I'm thinking a small PCB that solders into the through hole footprint and gives a pair of SMD pads to work with. Hard to sell something like that for much, however.
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VERY interesting ! Thank you !
I guess I haven't opened one of these caps up for a very long time !
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If one were that determined to replace a through-hole part with SMD, why not just replicate this method of packaging? Can't be too difficult to solder on a couple of leads and dip the thing in some epoxy.
I'm thinking a small PCB that solders into the through hole footprint and gives a pair of SMD pads to work with. Hard to sell something like that for much, however.
They already make these. You can buy them on eBay, but specialist companies that make lots of specific versions have much bigger selections, albeit at frankly outrageous prices.
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Why not just re-layout the board to use SMD and reduce board size by 4x while you're at it?
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What is nice about these is they don't suffer the fragility issues that are characteristic of new MLCC capacitors when being soldered. They're a lot more tolerant of abuse.
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Why not just re-layout the board to use SMD and reduce board size by 4x while you're at it?
For a new product you definitely would. But for rework/repair you need to fit into the existing board.
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That's the way I've been making my TH caps and resistors too...
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So, does manufacturing them that way now make them inferior quality or unsuitable for certain applications. I'm not all that good with how they were constructed before hand??
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Just means you have to do the same thing you do with any other ceramic, and always have needed to, really: check the C(V) curve for suitability.
Proof that I'm not taking the piss -- a salvaged "203Z" (20nF, Z5U temp code) ceramic disc, about 8mm dia.
(https://www.seventransistorlabs.com/Images/Z5U_CV_Plot.png)
Annealing was holding both leads at soldering temperature (~300C) for ten seconds, during which the ceramic dip coating bubbled and oozed (it's a wax-impregnated coating, which inevitably adsorbs some moisture -- this is normal). As you can see, it recovered some value, although not the full nominal value. The side-of-barn tolerance that Z5U has, means it was never outside of spec, so it technically doesn't matter, but the voltage change remains.
The main differences these days are:
1. Dielectrics are thinner than ever, meaning you're ever more likely to see a problem related to C(V) variation, even for low voltages (e.g., logic supply bypass);
2. You're probably more likely to see curves from the manufacturer describing this. Characterization is still really spotty (maybe 10% of all type 2 ceramic capacitors provide this?), but I'm guessing it was near 0% back in the day. Y'know, back in the days when this was still just as relevant anyway, because you might've used a 500V capacitor to bypass a tube radio IF strip, or something.
Tim