I have a design that,due to space constraints, requires stacking microvias (L1-
L2) directly on top of (in line with) drilled buried vias (L2-L7, L2-L11).  I am 
receiving conflicting information about this strategy being reliable (storage 
temp. range -50C to 110C, operating temp. range -40C to 85C) because of 
the different CTE's of the via fill material used in the L2-L7/L2-L11 vias and 
the board material (FR406, 170Tg). While the board shops that will fab this 
admit they prefer the vias be staggered (not very pratical in this design), they 
claim they have produced boards of this type without negative feedback or 
issues.  The CM that will be assembling this is extremely hesitant about using 
this via strategy.  Does anyone have experience using a stack-up similar to 
this?  Would this be reliable?  Is there a plugging paste material that very 
closely matches the CTE of FR406, 170Tg?  Any and all comments are 
welcome.

Thanks,

Mark Focht C.I.D.+
Pole/Zero Corporation
5530 Union Centre Dr.
West Chester, Oh  45069-4821

Voice:  513.870.9060 X173
FAX:    513.870.9064
Email:  [log in to unmask]

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