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June 1999

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Subject:
From:
"Alderete, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 23 Jun 1999 14:53:14 -0700
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Frank-

Been buried at work the last week or so, and I don't know if your question
was ever answered. I wanted to recommend a vibration text by D. Steinberg
<1>, but couldn't find my copy [nor any of our Library's copies] for a
couple of days.

I finally copied applicable sections of the Steinberg text; I can fax all
sheets to you, if you send a FAX number [13 sheets].

Basically, Dave Steinberg presents the Rayleigh Method for finding the
natural frequency of a PWB (assembly). After deriving the equations, they
are summarized in a Figure depicting 21 possible PWB configurations, where
each configuration is a unique set of mechanical constraints applied to
rectangular PWBs. The 3 edge constraint types are free, supported edge, and
fixed edge.

Supported may apply to a mated daughterboard/motherboard connector set on
one edge of the PWB. Fixed is usually used on PWB edges held by card
guides/locks, etc.

One of the equations, for example:

(top) edge free, side edges (2) are fixed, and bottom edge is supported.
Then natural freq. approximated by-

f_n = pi/1.74 { (D/rho) [  {4/(a^4)} + {1/(2* a^2 * b^2)} + {1/(64 * b^4)}
] }^(-1/2)


WHERE:

f_n = natural freq

pi = 3.1416....

D = a plate stiffness factor, which is a simple function of PWB Modulus of
Elast., PWB thickness, and Poisson's ratio for PWB [Steinberg gives typical
values for each of these!]

rho = mass per unit area [which Steinberg also shows you how to calculate]

a = length of PWB

b = width of PWB


All this reads much easier in the text!


This text by Steinberg, and his companion text for themal analysis of
electronic equipment, are handy references for this type of stuff.

Regards,

Michael Alderete
Aerojet


<1> "Vibration Analysis for Electronic Equipment", by Dave S. Steinberg, 2nd
Ed. (1988), Wiley-Interscience Publication [John Wiley & Sons], TK 7870
S8218 1988, ISBN = ?





Frank Frimpong wrote...
-----Original Message-----
From: Alderete, Michael
Sent: Wednesday, June 16, 1999 6:39 AM
To: Alderete, Michael
Cc: '0 AlderetePENET'
Subject: Vibration Analysis [Question: PWB natural freq = ?] <IPC TN>


------------------------------

Date:    Tue, 15 Jun 1999 15:31:33 +0000
From:    "Frank K. Frimpong" <[log in to unmask]>
Subject: Vibration Analysis

Hi netters
I've been struggling with this for a while, and then it suddenly occurred
to me that if the guys.....and gals of cause, from technet cannot help me
with this then no one else can. How does one determine the natural
frequency of a PC board?

With best Regards
Frank Frimpong.

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