Master Thesis - OUFTI-1

Figure 4.4: Illustration of the experimental set-up for a torsion test [44]
If the PCB mass and dimensions are known, the density of the PCB is easily found
using Equation 4.2.2.
ρ P CB = m P CB
V P CB
(4.2.2)
where m P CB is the mass of the PCB and V P CB is its volume. It is important to note that
this equation is based on the implicit assumption that the thickness is constant over the
entire PCB (which it is not always the case as it can be observed in Figure 4.2).
An other important fact to keep in mind is that all the tests must be performed on the
etched PCB because, as it was already mentioned, manufacturing will induce changes in
the PCB properties, like loss of mass or stiness.
4.2.4 Choice of mesh element
After the denition of the PCB properties, it remains to choose the type of mesh
elements which will be used to mesh the PCB. In accordance with the particular geometry
of this type of structure, two possibilities can be pointed up:
• Volume elements
• Shell elements
In this particular case, the shell elements are the best solution because a PCB can be
linked to a thin structure. Indeed, these elements allow to obtain results as accurate as if
volume elements were used, but they require less computation time and memory, which is
a great advantage in the current world of industry.
To convince ourselves of this fact, let us use the two solutions on a simple example.
Consider a steel plate with an area of 10×10 cm. The properties of this particular material
are well known:
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