[SI-LIST] Re: PCB thin dielectrics
- From: steve weir <weirsi@xxxxxxxxxx>
- To: leeritchey@xxxxxxxxxxxxx
- Date: Fri, 18 Dec 2009 14:21:16 -0800
Lee, the DuPont HK04 polyimide and Oak Mitsui BC24 are fairly
interchangeable.
Best Regards,
Steve.
Lee Ritchey wrote:
> 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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