does any one use multilayer glass dielectric capacitors for recapping motherboards?

[weepis]

i just wanted to ask?

[ratdude747]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

I doubt they have the right ESR. I don't think anybody has tried it, nor do i think it would work.

[weepis]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

WHY wont they work?? and imagine what would be the benefits?

[Th3_uN1Qu3]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

I don't see anything larger than 1200pF in an appnote i found. They also are pretty big. Good luck fitting enough of them on a typical mobo.

[Longbow]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

Using glass as a dielectric produces a cap that is maximized for no or very low leakage. Glass caps can stay charged indefinitely. One example of a glass cap is the standard television tube which has 2 layers of conductive carbon (aquadag) separated by the crt glass envelope. That cap is part of the high voltage filter system for the crt anode. A few pf at 50 KV or more. Tradeoff: using glass for a dielectric is only practical for very small capacitance values and definitely not in the microfarad range. Once in a while you see glass caps used in precision timing circuits, but these have largely been replaced by digital and software based designs. To get an idea of practical sizes of various caps, have a look at a chart of dialectric values - that will tell you what is practical in terms of physical size. Ever seen a 1 microfarad polymer (non-electrolytic) cap? Huge.

[linuxguru]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

Yup, no advantage in using low-K materials like glass or porcelain, which are optimized for low loss in the microwave region. However, X5R ceramic is now available in reasonably large values (4.7uF..22uF) in very small sizes (0603) for motherboard and general digital bypassing, and I've used these successfully for mobo upgrades. The only minor drawback is that the ESR is not very low (4.7uF measured 0.4 ohm), but it still works well especially when several are used in parallel.

[Uniballer]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

How big would a 820uF 6.3V capacitor be? What kind of ESR would you get?

[linuxguru]

Re: does any one use multilayer glass dielectric capacitors for recapping motherboard

How big would a 820uF 6.3V capacitor be? What kind of ESR would you get?

You get 47uF and 100uF/6.3V in 1206 (maybe also 0805) size these days. If you parallel 8 of the 100uF, you get 800uF/6.3V. Assuming an ESR of 0.1 ohms for the 100 UF, the paralleled ESR will be ~0.0125 ohms - fairly competitive with ultra-low ESR electrolytics, and possibly about half to one-quarter the physical volume.