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Blind Via and Via-In-Pad fabrication steps

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rcasciola

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I am looking at the fabrication artwork for a reference design. It is a four layer, 1mm thick PCB with 0.4mm pitch BGAs. They use blind vias and VIP for connections from Layer 1 to Layer 2, with 0.1mm silver filled holes. But the stackup calls for core and foil construction, with an FR4 core, 1080 Pre-preg dielectrics and copper foil outer layers. The drill file shows that the blind vias and VIPs have holes only between Layers 1 and 2.

My questions are:

1. Do they laminate the Layer 1 foil to the Prepreg and then (laser) drill for the blind vias and VIPs before then laminating to the core?

or

2. Do they laminate the whole stackup and then laser drill only to the depth of the thickness of the 1080 Pre-preg?

Seems like if they do (2.), that would be kind of tricky to get the depth correct. If they do (1.), I didn't realize that uncured Pre-preg could be drilled, and also I thought that the foil/prepreg/core went to the press all together, not in stages.

Or is it done some other way?

Is the filling of the vias with silver done after all lamination?

Thanks,

Randy
 

marce

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Download this book and have a look at chapter 6.
The HDI Handbook

In your case I would liase closely with whoever is making the board, and get their opinion of the stack and whether they want foil or cap construction.
When drilling laser vias you have a target (a copper pad) on the layer below, this controls the drilling depth, and drilling has to be done on a cured board (ie laminated and pressed).
I believe that currently laser vias (HDI construction) involes a sequential build up of the PCB, with your structure they may have fun, as I presume you have standard drilled holes from layers 2 through to 4?
 

rcasciola

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Download this book and have a look at chapter 6.
The HDI Handbook


I believe that currently laser vias (HDI construction) involes a sequential build up of the PCB, with your structure they may have fun, as I presume you have standard drilled holes from layers 2 through to 4?

Actually, there will be standard vias between layers 1-4. I don't plan to have blind vias between 2-4 or 3-4, nor any buried vias between 2-3.

Thanks for your help!

Randy
 

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