Thermal Expansion Coefficient:
Copper expands @ 17E-6/K
Resin mainboard expands @ 4E-6/K
Difference in expansion 13E-6/K
So, yes, the copper expands more than the mainboard's resin..
And thus the part that 'glues' the two together will have to give as
reaction to this expansion.
Over time it will settle at the new length of the copper, and then
rapid cooling will break the copper circuit.
It's fact, not supposition.
The circuit was repaired later by bridging the connection alternately..
(And it was truly broken, with this error mechanism being the cause..)
(And yes, the 'fix' can help alleviate such breakage, since chance for breakage
is directly linked to the length of the circuit, in a straight line,
across the mainboard.)
(The longer the circuit the greater the sensitivity for rapid temp fluctuations..)
(It's already being tested and has already shown appreciable alleviation of the error mechanism..)
Laterz..
Note: I will not be watching this any longer..
@ hoola: It's not visible to the naked eye, the amount of stretch/shrink required to sever the circuit is in the order of microns.
Re-examine the figure, and you'll figure the reason why..
You'll also see why the zig-zag will prevent a circuit from beraking when it's cooling rapidly,
or at least you oughta be able to..
Also, the srinking of the resin happens very slowly over time as it tends to dry out still more,
thus shrinking..but that's a 'permanent' shrinkage, which doesn't involve the cooling 'cycle'..
In engineering for circuitboards meant for use in space, the 'zig-zag' may prevent many repairs..
In space things heat rapidly, while being on the nightside, it will cool also rapidly..
The only alleviation of heat in space is heat emision, through light, not heat transfer,
like atmospheric, and yet, sunlight or no sunlight will still rapidly heat or cool..
Anyways, it's usefull, even in Earthly settings, where the temp delta is well in the range
of 60K, specially with stuff like fans around..
I also believe that this error mechanism may also occur on Si-SiO processor types,
but in a different way, more like contributory to electron migration.
(electron migration can be mitigated this way, and thus also processing equipment
for use in outer space may be 'hardened' a little that way, albeit
at a cost of a tiny bit of processing power, in the order of 2-3%..
But THAT right now for me is just a calculated guess..
For those who are interested:
A very long circuitboard (1 meter long with a single circuit, in a straight line, and one more
with the 'zig-zag'heated to 363K, over a month, then rapidly cooled..)
The straight one failed, the zig-zag held..
Each circuit was 0.5 mm wide..
The stretch was visible to the naked eye on the test subject.(I didn't measure it though,
I was more interested in the result of the rapid cooling..)