microwave mic resonances
TRANSCRIPT
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Mechanical resonances in microwave integrated circuits
and packages
Above 2000 hz who cares ??
9/14/2016
Don Blanchet
3B Associates
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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.
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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.
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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
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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 Grmsresponse to display to the test engineer.
This is falsely represented as random vibration to manufacturing and quality test engineers.
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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.
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Measurements from HALT/HASS vibration
testingevidence of shock pulse components > >2000 hz
References from COTS Journal
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Halt test statistical analysis many strikes above 3 sigma a poorly controlled test
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Significant numberof high G measurementsIn the HIGH FREQUENCY
Range > 2000hz ,Up to 100 Khz !
measured ona 6 dof HALT
hammer blow machine.
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High frequency excitationfrom hammer blows
PSD
Shock pulses
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Random excitation above 2Khz measured on HALT fixture!
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HALT machine also known as 6 degree of freedom test is
capable out to 20Khz !
Air driven hammers
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COTS Journal June 2009measurement out to 10khz
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Solidworks SimulationAdvanced Dynamics
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FEA of sample small Microwave components
Determine resonant frequency
Sine sweep characterization 5-35000 hz
Wideband random “vibration” hammer blows
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Case #1Covered header package
Formed lid
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Model formed lid
f1= 7100 hz
ResonantFrequencyFrom FEA
Lid oil canMode
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Cover 1g sine sweep
Q=14.5 @ 7100 hz
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Cover sine sweep displacement at cover center
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Cover response to HALT machine hammer blows input
at 15 g rms
6 sigma displacement = 3.0 e-04 inches
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Case #2Gold ribbon bond wire
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model
.002 x .012 x 0.23
f1 = 5300 hz
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Ribbon 1g sine sweep
Q=107 @ 5300 hz
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Other susceptible components
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VCO circuit
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T-pack amplifier
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MIC mixer brick
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Laser welded hermetic cover
Thin aluminum seal coverthickness = .020 inch
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Semi-rigid coaxial cable
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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.
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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.