miniaturized microwave circuits assumed to be beyond the frequency range of vibration testing are in fact susceptible to damage induced by hammer blows used in HALT/HASS equipment
1. Mechanical resonances in
microwave integrated circuits
and packages
Above 2000 hz who cares ??
9/14/2016
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.
16. FEA of sample small
Microwave components
Determine resonant frequency
Sine sweep characterization 5-35000 hz
Wideband random “vibration” hammer
blows
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.