6 degree of freedom testing machines impart shock pulses to delicate electronics, many folks refer to it as random vibration, controlled random vibration cannot be produced with hammer blows

1. Mechanical shock applied to
delicate microelectronics
6 degree of freedom halt/hass
machines are shock testing
9/28/2016
Don Blanchet
3B Associates
dwb3298@verizon.net

2. Known
 From inception 1930’s-40’s vibration
testing is limited over the range of
10hz to 2000hz.
 At 2000hz and above the response
displacements are very small as well
as component stresses.
 Small Parts with high resonant
frequencies rarely experience any
fatigue failures.

3. Known (con.)
 Electronics design has evolved from
thru-hole mounting to much smaller
surface mount technology
 Microwave electronic circuits can
experience signal noise due to
vibration and shock excitation.
 Microwave integrated circuit
components are very small and exhibit
very high mechanical resonant
frequencies.

4. Known (con.)
 If testing rarely exceeds 2000hz where
is the source of the mechanical noise ?
– Severe shock events
 Gunfire
 Missile steering pulse rocket motors
 Missile stage separation
 Repetitive hammer blows such as those
in HALT/HASS 6 degree of freedom
quality control test machines.
Shock pulse

5. Problems
 Design of HALT/HASS machines
include digital control that treats the
repetitive shock as random “vibration”.
 The output control loop filters above
2500 hz and calculates a Grms
response to display to the test
engineer.
 This is falsely represented as random
vibration to manufacturing and quality
test engineers.

6. Potential Problem for
microwave designers
 Repetitive hammer blows do contain high
frequency components.
 The machine control loop can’t undo a
hammer blow !
 Repetitive strikes tend to be additive and
“ring up” the high frequency input to the
test fixture and unit under test.
 Significant electrical noise and possible
fatigue damage can be expected over the
duration (hours) of these lengthy 6 dof
tests.

8. Measurements from
HALT/HASS vibration
testing
evidence of shock pulse
components > >2000 hz
References from COTS Journal

9. Halt test statistical analysis
many strikes above 3 sigma a
poorly controlled test

10. Significant number
of high G measurements
In the HIGH FREQUENCY
Range > 2000hz ,
Up to 100 Khz !
measured on
a 6 dof HALT
hammer blow machine.

11. High frequency excitation
from hammer blows
PSD
Shock pulses

12. Random excitation above 2Khz
measured on HALT fixture!

13. HALT machine also known as 6
degree of freedom test is
capable out to 20Khz !
Air driven hammers

14. COTS Journal June 2009
measurement out to 10khz

15. Solidworks Simulation
Advanced Dynamics

16. FEA of sample small
Microwave components
 Determine resonant frequency
 Sine sweep characterization 5-35000 hz
 Wideband random “vibration” hammer
blows

17. Case #1
Covered header package
Formed lid

18. Model
formed lid
f1= 7100 hz
Resonant
Frequency
From FEA
Lid oil can
Mode

19. Cover 1g sine sweep
Q=14.5 @ 7100 hz

20. Cover sine sweep
displacement at cover center

21. Cover response to HALT
machine hammer blows input
at 15 g rms
6 sigma displacement = 3.0 e-04 inches

22. Case #2
Gold ribbon bond wire

23. model
.002 x .012 x 0.23
f1 = 5300 hz

24. Ribbon 1g sine sweep
Q=107 @ 5300 hz

25. Other susceptible components

26. VCO circuit

27. T-pack amplifier

28. MIC mixer brick

29. Laser welded
hermetic cover
Thin aluminum seal cover
thickness = .020 inch

30. Semi-rigid coaxial cable

31. Conclusions
 Multiple references have shown that
there is significant excitation > 2000hz
in 6 degree of freedom HALT/HASS
machines using repetitive hammer
blows.
 Mechanical resonances of small
components such as those found in
microwave integrated circuits do exist.
 These resonances can induce electrical
signal noise and potentially metal
fatigue fracture.

32. Opinion
 Micro electronic surface mount
assemblies and high frequency
assemblies should be screened for
defects at the board level using
traditional well controlled
electrodynamic shakers.