FreeLists / si-list / [SI-LIST] Re: PCB layer stackup

[Ed Linke <ed@xxxxxxx>]

Hi Stuart,

    Your stackup #2 is the correct choice to prevent warpage especially 
if this is a substrate for a device package with buildup outer layers.

    In stackup #1 with build up technology, layers #4 and 5 are the core 
layers. With routing on 1 layer, it stress relieves that layer cousing 
possible warpage. In Stackup #2 layers 4 and 5 are balanced and cancel 
one another.

    The outer layers with buildup technology are of less concern.

    Ed. L.

Symon wrote:

>Hi Stuart,
>To the best of my knowledge, and IME, I think you're mistaken. As long as 
>the cores and prepregs etc. are symetrical there won't be a warpage problem. 
>The copper planes per se don't matter. The designer can even use copper 
>balancing if they're paranoid!
>HTH, Syms.
>
>----- Original Message ----- 
>From: "Stuart Brorson" <sdb@xxxxxxxxxx>
>
>
>  
>
>>Forgetting about any minor SI advantages/disadvantages, stackup 1 has
>>the major disadvantage that the plane layers are unbalanced, which can
>>lead to board warpage.  That is, the planes will strain the top
>>layers of stackup 1 more than the non-plane bottom layers, which can
>>lead to bent, warped boards.  The problem would become acute over wide
>>temperature ranges.  I'd stick with stackup 2.
>>
>>Stuart
>>
>>    
>>
>>>I need to specify a 8layer board. Fastest edges on the board are on the
>>>600Mbit LVDS channels : about 500ps. I have two stackups in mind :
>>>
>>>                 stackup 1              stackup 2
>>>---------------------------------------------------------
>>>L1                routing                routing
>>>Substrate
>>>L2                power plane            GND
>>>Substrate
>>>L3                power plane            routing
>>>Substrate
>>>L4                GND                    power plane
>>>Substrate
>>>L5                routing                power plane
>>>Substrate
>>>L6                routing                routing
>>>Substrate
>>>L7                GND                    GND
>>>Substrate
>>>L8                routing                routing
>>>      
>>>
>
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