APPENDIX A
PRINTED WIRING BOARD NATURAL FREQUENCY
EQUATIONS
The following is a list of PWB conditions with their respective natural
frequency equation. The first series of equations are for rectangular PWBs
with varying edge conditions, and the second series of equations for odd
shaped PWB configurations. These equations, when evaluated, will provide the
user an approximation of the natural frequency (f_{n}).
The parameters for these equations are as follows:
where: 

E = modulus of elasticity of PWB t =
thickness of the PWB µ = poisson’s
ratio of the PWB; if unknown, use a value of 0.3 D = stiffness
factor of the PWB p = mass per unit area of the W = weight
of the PWA area = area of PWB material equal to a times b for
rectangle a = long side of the PWB b = short side of
the PWB g = force of gravity: 32.2 ft/sec^{2 }or 386
in/sec^{2} 
"1">
NOTES: 1) The above equations apply to thermal planes as
well as
PWAS.
2) For oddshaped PWAS, use the plate that best fits the actual
PWA.