HI, Sir Werner,

I can see how filling a PTVH with solder will strengthen the barrel against
collapse under pressure from X-Y expansion/shrinkage/pull-away (your
two-tank analogy (ish)), but the Z-direction still bothers me. Expansion
and contraction in this direction causes the relative (to a given datum)
positions of the internal layers to move up and down as the'yre carried
with the board material. At the same time, the copper plating in the
interconnecting holes has to "give" to accommodate this and minimise the
displacement between the layer in the board and the point to which it
connects to the barrel.

If the "give" (ductility) is constrained by the hole being full of solder,
the displacement between a layer and its connection point to the barrel
increases, increasing the risk of shearing the joint between barrel and
layer .... unless a solder-filled hole has a LCTE in the Z direction more
closely matched to that of the board material than does a plated barrel
alone (?).

Maybe the risk of failure of the barrel-to-layer connection is
significantly greater from x-y compression and tension from expansion and
contraction than the shear effects in the Z axis - I don't have any
comparitive figures to judge from. It may be that, overall, hole
reliability IS improved by filling them with solder, I can't tell, but
welcome any further education of this subject.

BR's
Peter



Werner Engelmaier <[log in to unmask]>    01/10/2002 11:46 AM
Sent by: TechNet <[log in to unmask]>

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              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: Re: [TN] PCB design with mask over vias.








Hi Peter,
The theory is wrong. Think about it--what the solder in the PTV does is
strengthen the PYV barrel. It is like submerging two tanks, one filled with
water, the other empty--which one do you think will collapse.

Werner

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