Ok where do I start   first the problem as questioned was does high temp
effect  or damage the board, yes  how? by slow degration over time and temp
extreams. the second remark put out was that most PCB people do not know how
close we come in damaging the plating in the holes and vias with large temp
extreams such as soldering.  First the T/G is so missused its is a wide
imaginary point at which the epoxy starts to become soft and increases its
expansion rate/temp  noticably. this expansion  force has enough power to
lift pads and crack copper in the holes. The T/G has nothing to do with a
max operational temp or a max usable temp, it is way above were you want to
run a board at.Some materials such as Kapton have no noticalbe T/G. The
copper in the hole has a lot to do with how many cycles of soldering you get
before the via cracks. The ductility of the copper does effect it, as does
its thickness. if you are just below 1 oz and the board is a 4 layer mult
.125 thick you may not even see 3 cycles before the vias crack.  The
thickness and build also play a effect in the cycles.
Can you improve it? yes  as I stated I found that a little bit more copper
realy helps the situation doubling or even tripling the numbers, this
doubling takes you out of the scary area of 3-4 cycles which is not uncommon
today with mixed components.  The statement was put forth that you cant
plate 3 oz of copper and have 10:1 ratios well not so . Where do you think
the 1 oz copper came from we so dearly hang on to   from the 60's when the
only copper we could buy was 1 and 2 oz , it worked so we used it,  To plate
more copper in the holes  lets say 2 oz is easy start with 1/4 oz and use
thicker dry film ( you will be amased how accrate it can resolve) and drill
ever so slightly over and plate 2 oz the board will now be out of the danger
zone .
But I have found many people have there head stuck firmly in the   "cant do
that" arena of life.

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