5.4.4.2 Metal Can Type Parts
5.4.4.2 Metal Can TypeParts
The another part type to consider in lateral vibration is the metal can
type parts, including transistors and small hybrids. They are usually mounted
perpendicular to the PWB surface, have no lead bends, and can have any number
of leads. The calculation for this part is similar to the lateral vibration
for axial lead parts with a few minor changes. The parameters required to
perform this calculation are represented in Figure 56 and defined as the
number of lead wires (n), the length of the lead wire from the part to the PWB
in inches (1), the weight of the part in pounds (W), and the length from the
edge of the part body to the center of gravity of the part in inches (a). The
first step in this procedure is to calculate the deflection of the part due to
its self weight using Equation 533. Once the deflection is known, the natural
frequency of the part can be calculated as shown in Equation
534.
"1">
Figure 56. Metal Can Type Part

"1"> 
Eq. 533
Eq.
534 
The stress applied to the lead wires due to the static load can be
calculated using equation 535. This is the amount of stress that is
applied to the lead wires while it is motionless on the PWB.
where: I =
.049d^{4}
Using the natural frequency calculated for a static load, a value for Q
equal to 62.5, and the PSD level (w_{o}) equal to
0.04, the G_{out} level can be determined using the Crandall equation
shown as Equation 536.
The stress on the lead wires due to vibration is calculated by multiplying
the stress for static loading by the G_{out} level as shown in
Equation 537.
The maximum allowable G level for this part can then be determined by using
the endurance limit of the lead wire material from Appendix B and the stress
applied to the lead wires using Equation 538. The maximum allowable PSD level
is determined as shown in Equation 539.

"1"> 
Eq. 538
Eq.
539 