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Visitor liuhangyu
Visitor
474 Views
Registered: ‎09-29-2019

what prepreg metarial is used in kc705 evaluation board

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The design files of kc705 evaluation board show that the material of PCB core is NELCO 4000-13EP SI. But I don't find any descriptions to illustrate the material of pre-preg.

So I want to know what material is used as pre-preg.

In addition, what's the unit of the thickness of board 0.062" ?

Thanks!

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12 Replies
Scholar drjohnsmith
Scholar
451 Views
Registered: ‎07-09-2009

Re: what prepreg metarial is used in kc705 evaluation board

Ive not seen that doc before,

   but it does seem to be broken ,

for instance,

  look at the top copper, its direct onto a pre preg.

     this sort of implies they made the copper without a core, and aligned it to the layer below !

 

Sort of wrong ..

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Visitor liuhangyu
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Registered: ‎09-29-2019

Re: what prepreg metarial is used in kc705 evaluation board

XTP133 zip file includes a PDF file which depicts the PCB layout of KC705 evaluation board. You can find the PCB stack structure in the first two pages.
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Scholar drjohnsmith
Scholar
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Registered: ‎07-09-2009

Re: what prepreg metarial is used in kc705 evaluation board

Is that the picture of the structure you posted,

   If so , its wrong due to the comment above.

 

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Visitor liuhangyu
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Registered: ‎09-29-2019

Re: what prepreg metarial is used in kc705 evaluation board

No, it's not wrong. In PCB with multiple layers, the top and bottom coppers are directly aligned to the pre-preg. My question is what material is used as pre-preg(adhesive).
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369 Views
Registered: ‎07-23-2019

Re: what prepreg metarial is used in kc705 evaluation board

0.062" has units. ["] means inches. Also expressed as 62 mil (mili inches) and is about 1.5 - 1.6 mm, the standard thickness for a PCB

368 Views
Registered: ‎07-23-2019

Re: what prepreg metarial is used in kc705 evaluation board

You are lucky for having so many details. You can work out the prepreg details with the specified impedance.

If you use Altium Designer, for example, you can set up a layer stack as that one and specify copper thicknesses and core thicknesses and material (epsilon, the dielectric constant). Then you specify impedances on different layers to match those in the doc. Then you try different dielectric materials and thicknesses to match everything (even total thickness)

Scholar drjohnsmith
Scholar
366 Views
Registered: ‎07-09-2009

Re: what prepreg metarial is used in kc705 evaluation board

Agree with your quesotion about what pre preg, sorry I dont have answer to that,

    as others say , you could reverse engineer the material properties to some degree off of the impedane and size given,

 

My question to you is more on lines of please talk to your PCB manufacturer,

I've seen alot of baords over 40 years, and I'm always willing to learn , but I have not seen foil directly attatched directly to pre preg,

prepreg is horrible "gungey" stuff, more akine to hunney than a board. It sticks like babies output to nappies...  !!

the foil has to be etched and drilled, and I cna not see a sheet thinner than aluminium kitchen foil being etched and drilled on a pre preg backing.

Pleae let us have more details , but I don't think even laser cutting would work in this situation,

I have only ever seen copper on core material.

which is why your layer stacke layer is normaly

copper

core

pre preg

copper

core

copper

pre preg

etc.

 

 

 

 

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Visitor liuhangyu
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Registered: ‎09-29-2019

Re: what prepreg metarial is used in kc705 evaluation board

Thank you for replying the second question! About the first question, I will try what you said. I think there should be some fixed compositions of lamination & prepreg materials when use NELCO 4000-13EP SI as PCB core. I really want to know what materials is used as adhesive when using NELCO 4000-13EP SI as PCB core? By the way, what do you mean about "lucky"? I just download a zip file from xilinx official website for free named as XTP133 in which there is a PDF file that depict the KC705 PCB layout information and stack structure.

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Visitor liuhangyu
Visitor
333 Views
Registered: ‎09-29-2019

Re: what prepreg metarial is used in kc705 evaluation board

@drjohnsmith Well, many websites show this structure in which top and bottom coppers are directly aligned to pre-preg. You can just search "multilayers PCB stack structure" in google to learn something.
328 Views
Registered: ‎07-23-2019

Re: what prepreg metarial is used in kc705 evaluation board

@liuhangyu 

With "lucky" I meant that such PCB details are not frequently available. Actually... cloning that PCB is not much useful, you probably won't make it cheaper, so they are safe in that sense. Also, Xilinx's business is not making and selling dev boards.

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Scholar drjohnsmith
Scholar
323 Views
Registered: ‎07-09-2009

Re: what prepreg metarial is used in kc705 evaluation board

 
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Scholar drjohnsmith
Scholar
322 Views
Registered: ‎07-09-2009

Re: what prepreg metarial is used in kc705 evaluation board

Well,

I stand amazed,

thank you , as I said I'm always open to learn, technology of PCB's has moved on ..

 

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