[SI-LIST] Re: PCB thin dielectrics
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Steve Weir" <weirsi@xxxxxxxxxx>, "Bowden, Ivor" <ibowden@xxxxxxxxxxxxxxxxx>
- Date: Fri, 18 Dec 2009 10:16:34 -0800
Problem with most of these materials is they are single source with all
that entails. I do just fine with standard laminates by using thin
prepregs between the power planes. This does not result in single
sourcing. I know that puts a crimp in those companies that offer special
materials, but an engineer's job is to do what he can to avoid single
sources when doing designs.
Sorry Steve! Didn't mean to step on you here.
Lee Ritchey
> [Original Message]
> From: steve weir <weirsi@xxxxxxxxxx>
> To: Bowden, Ivor <ibowden@xxxxxxxxxxxxxxxxx>
> Cc: <si-list@xxxxxxxxxxxxx>
> Date: 12/18/2009 9:24:18 AM
> Subject: [SI-LIST] Re: PCB thin dielectrics
>
> 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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