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Layout design and stackup

joniengr

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Hi,

I need to change the layout design from 8 to 12 layers. I already have 1.6 mm thickness in 8 layer design. If I increase the layers to 12 then I also have to increase the total thickness of the board which will be around 2.2 mm for 12 layers. What are the pros and cons of increasing thickness of the PCB ?

Another question, I have seen some designs on which 35 um copper is used on outer layer and 18 um copper is used on inner layers but on planes they still have 35 um copper. Is this standard or there is another arrangement that could have more advantages ?
 

barry

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1) increasing the number of layers doesn’t necessarily have to increase the overall board thickness, you have choices on the thickness of your core/prepreg/copper.
2) there are no absolute pros or cons on a thicker board. A thicker board is thicker, that’s it. It may not fit mechanically, or it may make no difference. It may change the parameters for trace impedance If layer spacing changes. Obviously a thicker board will be more rigid.
3) I generally use 1 oz.(35 um) on all layers. Sometimes I’ll go to 2 oz for increased current handling. Maybe thinner copper will save some cost?
 

joniengr

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If a manufacturer has minimum 5 mil core/prepreg dielectric that can be manufacture using their facility, does this also means that they can also manufacture a PCB with 10 mil or 15 mil core/prepreg dielectric instead ? Do they put 5 mil core/prepreg on the top of the other to make 10 mil or 15 mil core/prepreg dielectric ?
 

barry

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You really shouldn’t be asking us, you should be asking the manufacturer. Different manufacturers have different standard stackups, some are more flexible, I.e., will do custom work. Many manufacturers show stack ups on their website.
 

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