show the trade off between adding mass and stiffness in a pwb assembly design

1. PC Graphics card : a simple lesson
in basic vibration resonances
2/13/2018 rev A
Don Blanchet
3B Associates
dwb3298@verizon.net
Prepared for Meech Group LTD Ontario, CA
Sample high performance
Graphics card for a PC
chassis

2. Basic vibratory motion
f hz

3. Simple Design Goals:
 Increase the natural frequency of the
graphics card assembly.
– Increase stiffness K
– Decrease mass M
– Increase the ratio of K/M
 Result – Lower displacement and thus
decreased potential for damaging
stress in the printed wiring board

4. Base pwb design model
SOLIDWORKS SIMULATION 2018

5. Base board analysis: f1 =16hz
CARD INSERTED IN MOTHERBOARD

6. Add card retention bracket :
front panel f1 = 18hz

7. Add aluminum heatsink assembly
with plastic fans: f1= 32 hz
Weight = 2.47 lbs

8. Result summary
CASE RESONANT
FREQUENCY
HZ
WEIGHT
LB
STIFFNESS
normal to pwb
K
LB/INCH
BASE PWB 16 1.25 33
PWB WITH
FRONT BRACKET
18 1.48 49
TOTAL ASSEMBLY
WITH
HEATSINK
& FANS
32 2.47 260

9. Conclusions
 In this design doubling the weight by
adding a stiff heatsink structure
resulted in doubling the natural
frequency of the total assembly.
 The heatsink serves cooling and
vibration control functions.