mhirsch
04-15-2006, 11:09 AM
Hi, All
I'm designing multilayer PC boards. My understanding has been that the preferred construction is prepreg on the outer layers. then core alternating with prepreg. So an 8-layer board would be
prepreg
core
prepreg
core
prepreg
core
prepreg
I believe this is also known as the "foil" method
The place I'm currently working seems to do things the reverse way
core
prepreg
core
prepreg
core
prepreg
core
I believe this is known as the "capped" method
They insist that's the right way to do it. I spoke to the production manufacturer at a well regarded shop. If I understood correctly, he told me that the "foil" method was much preferred these days, but that both methods were valid. He also told me that the "capped" method was normally specified by old-school military contractors, and that shops would advise them to switch drawings to "foil" construction.
So my first question....any thoughts on the above? Which is the right way to go these days?
Second and related.... How does the choice of method related to available blind and buried via sets (if it does at all??)
For example, using the capped method, I understand that normal blind sets would be 1-2, 1-4, 1-6. In other words, the first and last layer of the blind set is core. I think this is understandable. Is this right so far?
Now how about blind sets in foil construction? What are allowable blind sets? I'm supposing (now here I'm unsure...) that the allowable blind sets are as above: 1-2, 1-4, 1-6. In this case, the first and last layers are prepreg. But then how do you build the remaining layers? By a normal stack up, the next layer would have been core...How is this done? Do you use two prepreg layers in a row? Or??
Any clarification greatly appreciated. Thanks!
I'm designing multilayer PC boards. My understanding has been that the preferred construction is prepreg on the outer layers. then core alternating with prepreg. So an 8-layer board would be
prepreg
core
prepreg
core
prepreg
core
prepreg
I believe this is also known as the "foil" method
The place I'm currently working seems to do things the reverse way
core
prepreg
core
prepreg
core
prepreg
core
I believe this is known as the "capped" method
They insist that's the right way to do it. I spoke to the production manufacturer at a well regarded shop. If I understood correctly, he told me that the "foil" method was much preferred these days, but that both methods were valid. He also told me that the "capped" method was normally specified by old-school military contractors, and that shops would advise them to switch drawings to "foil" construction.
So my first question....any thoughts on the above? Which is the right way to go these days?
Second and related.... How does the choice of method related to available blind and buried via sets (if it does at all??)
For example, using the capped method, I understand that normal blind sets would be 1-2, 1-4, 1-6. In other words, the first and last layer of the blind set is core. I think this is understandable. Is this right so far?
Now how about blind sets in foil construction? What are allowable blind sets? I'm supposing (now here I'm unsure...) that the allowable blind sets are as above: 1-2, 1-4, 1-6. In this case, the first and last layers are prepreg. But then how do you build the remaining layers? By a normal stack up, the next layer would have been core...How is this done? Do you use two prepreg layers in a row? Or??
Any clarification greatly appreciated. Thanks!