[sdiy] There is no fun analogue chips anymore!

Barry Klein barryklein at cox.net
Fri Jun 29 16:47:41 CEST 2012


Wow, nice papers.  If I had come across those back when I worked on this I wouldn't have had to spend 3 weeks on it.  I discovered this behavior when we suspected we had some bad caps.  I then went through a variety of them that we commonly used and saw the variation. In the process I used several LDR meters - from HP/Agilent/Hioki etc.  What really bugged me was how poorly the measurements correlated between the various instruments.  The trends followed but the values given didn't match within any reasonable tolerance.  I was evaluating the Hioki testers as a more cost effective solution for my lab as I didn't feel the higher expense was justified for the HP as I rarely had to test for component values.  I had an old boat anchor HP LCR system that I had started with - it has the DC bias module and accessories to handle SMT parts - but it gave different readings each day even though it met calibration.  I ended up not getting the Hioki as it was just as variable - but different.  We have a dedicated Components Engineering team but they were off testing stuff from the drive side and I was off on my own testing for the Branded Products side.  We now have a qual. process where all such capacitors go through their instrument (Agilent) and are tested at a couple percentages of rated voltage and all results are put on a spreadsheet for any engineer to see.   From this we came up with some parts that we use all over in multiples - one I think is 10uf 25V.  If we need 22uf 25V the two 10uf's give better ESR and less cap/DC variation than the 22uF.  Plus since we buy higher volume the total cost is lower.  Thus if you look at our USB controller boards you will see these in parallel strings in a few places.  

Barry

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Paul Schreiber
Sent: Friday, June 29, 2012 06:14
To: 'sdiy diy'
Subject: Re: [sdiy] There is no fun analogue chips anymore!

Required reading:

http://www.electrical-integrity.com/Paper_download_files/EPEP03_cap_models_poster.pdf

http://www.electrical-integrity.com/Paper_download_files/DC11_13-TH2Paper_Novak.pdf

or as I like to call it "What they leave off the data sheets".

Paul S.
/former TDK capacitor FAE
//Shhhh...it's a secret.....sigh......




-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Dan Snazelle
Sent: Friday, June 29, 2012 8:08 AM
To: Barry Klein
Cc: sdiy diy
Subject: Re: [sdiy] There is no fun analogue chips anymore!

On Jun 28, 2012, at 4:19 PM, Barry Klein <Barry.L.Klein at wdc.com> wrote:

> Many designers don't realize that effective capacitance drops often 50% with DC across multilayer type ceramics - and this varies between manufacturers and voltage ratings.
> I hadn't come across any that got worse over time though.  Any background on this - a particular vendor?
> 
> Barry
> 
> 


Woa! This sounds like a potential nightmare.

So does this mean that I should not use ML caps in parts of my circuits where Dc exists? Can you explain this more? 

Are plain old (cheap brown disc) ceramics at risk also?


Thanks



> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Gordon JC 
> Pearce
> Sent: Thursday, June 28, 2012 12:26 PM
> To: sdiy diy
> Subject: Re: [sdiy] There is no fun analogue chips anymore!
> 
> On 28/06/12 20:16, Pete Hartman wrote:
>> So I have displayed my ignorance publicly again :-)
>> 
>> Thanks for the pointers.  Glad to see it's not as complicated as I 
>> had thought from some long past exposure to things like "flowing 
>> solder with a toaster oven".
>> 
>> Pete
> 
> http://www.gjcp.net/~gordonjcp/capacitor.jpg
> 
> That was taken with a cheapy USB microscope.  It's an 0.1F ceramic capacitor in a Kenwood HT, part of the mic preamp, and like all little ceramic caps prone to going leaky if there's a DC voltage across them - like, uh, the preamp bias voltage.  The replacement in the picture was hand-soldered, cleaned up with some flux cleaner, and you'd hardly tell it had been touched.  I used a fairly pointy soldering iron tip and some tweezers that I'd reshaped a little to be better at picking up tiny grain-of-sugar components.  I didn't use the USB microscope because it is too "laggy" to update.
> 
> Now, I don't need glasses, but I'm 38 and I can tell my eyesight isn't 
> as sharp as it was ten years ago ;-)
> 
> It's not that hard...
> 
> --
> Gordonjcp MM0YEQ
> 
> 
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