The carbon provides a high specific strength and stiffness and the thermal properties to control and reduce the thermal coefficient of expansion
of the composite.
Quartz is suited to applications requiring a minimal coefficient of expansion
and ultra-low level of contaminants.
"The coefficient of expansion
is similar for the materials," he says, "and our longer fibers means there can be a greater panel curvature before there is any tearing." However, there are problems to be overcome.
Some minor distortion occurs in BGA components and circuit boards when heated, due to the thermal coefficient of expansion
(TCE) of the materials.
Semitron ESd 420 is said to offer just the right combination of properties for the job: static dissipation, low coefficient of expansion
, and high strength and heat resistance.
The substrate is bonded to a metal base, which has a thermal coefficient of expansion
closely matched to that of the beryllium oxide.
In the past, the acrylics had a high shrink rate and coefficient of expansion
. Therefore, early work with rapid prototyping outputs for investment castings provided marginal results.
If it were desirable, ceramic can have a very low coefficient of expansion
(as low as 2.0 X [10.sup.6]/deg K for silicon nitride, used in some earlier gage blocks), but they chose zirconia because its expansion coefficient (10 X [10.sup.-6]/deg K) more closely matches that of steel (11.5), the material usually being measured.
This design allows for low resistance values and a closer match in temperature coefficient of expansion
to the substrate when compared to traditional thick film resistors constructed with ceramic substrate.
The constant of proportionality is [[Tau].sub.L], the linear coefficient of expansion
Silicon--increases the fluidity of molten aluminum, decreases hot cracking tendency and solidification shrinkage, improves pressure tightness and reduces the coefficient of expansion