[SI-LIST] Re: PCB thin dielectrics
- From: steve weir <weirsi@xxxxxxxxxx>
- To: "Bowden, Ivor" <ibowden@xxxxxxxxxxxxxxxxx>
- Date: Fri, 18 Dec 2009 09:24:15 -0800
Ivor, there are about four materials to know about:
Except for exotic applications the big thrill in thin dielectrics is
reduction in inductance. This lets you get rid of a bunch of bypass
caps, and/or yield lower impedance to the power attachment of your IC
package, and in a number of cases do things like reduce layer counts
depending on the specifics of your power distribution scheme. With
proper design a thin dielectric lets you use far fewer bypass capacitors
to cover the frequency ranges from about 5MHz up to around 100MHz -
300MHz where the bypass network impedance crosses over into the
interconnect impedance. Above the crossover, the thinner dielectric
gives you lower impedance period. For unloaded materials the impedance
improvement is almost linear to the ratio of the thickness: IE 1mil
material is about 1/3 the impedance of a 0.0035" glass epoxy cavity.
The impedance peaks caused by modal resonances come down faster than the
thickness ratio.
In the thinner than 0.0035 camp there is:
$ BC2000 50um
$$ DuPont HK04 24um polyimide / Oak Mitsui BC24 24um epoxy
$$$DuPont HK04 18um polyimide
$$$$Dupont HK04 12um polyimide / Oak Mitsui BC12 epoxy
$$$$$$OakMitsui BC12T BT loaded epoxy / Oak Mitsui BC8 8um epoxy / 3M
Cply BT loaded epoxy
I provide application support to DuPont for HK04 materials. The 24um
material is cheap enough now that in many applications it reduces total
cost versus an equivalent performance bypass system using thicker
dielectric.
Best Regards,
Steve.
Bowden, Ivor wrote:
> Hi SI people,
>
>
> Could I get some comments on the use of "thin" (<0.0035") dielectrics in
> PCBs, in terms of available materials, cost, reliability, dielectric
> strength, trace width vs dielectric constant, power plane capacitance,
> stories, studies, useful web links, any other pertinent issues? Base question
> is, could this be a practical way to increase PCB layer count while
> maintaining overall PCB thickness?
>
>
>
> Any / all information / comments welcome.
>
>
>
> Thanks,
>
>
>
> Ivor Bowden
>
>
>
>
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