Post on 16-Apr-2017
Mechanical shock applied to delicate microelectronics
6 degree of freedom halt/hass machines are shock testing
9/28/2016Don Blanchet3B Associatesdwb3298@verizon.net
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.
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.
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
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.
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.
Measurements from HALT/HASS vibration
testingevidence of shock
pulse components > >2000 hz
References from COTS Journal
Halt test statistical analysis many strikes above 3 sigma a poorly controlled test
Significant numberof high G measurementsIn the HIGH FREQUENCY
Range > 2000hz ,Up to 100 Khz !
measured ona 6 dof HALT
hammer blow machine.
High frequency excitationfrom hammer blows
PSD
Shock pulses
Random excitation above 2Khz measured on HALT
fixture!
HALT machine also known as 6 degree of freedom test
is capable out to 20Khz !Air driven hammers
COTS Journal June 2009measurement out to 10khz
Solidworks SimulationAdvanced Dynamics
FEA of sample small Microwave components
Determine resonant frequency
Sine sweep characterization 5-35000 hz
Wideband random “vibration” hammer blows
Case #1Covered header package
Formed lid
Model formed lid
f1= 7100 hz
ResonantFrequencyFrom FEA
Lid oil canMode
Cover 1g sine sweep
Q=14.5 @ 7100 hz
Cover sine sweep displacement at cover center
Cover response to HALT machine hammer blows
input at 15 g rms
6 sigma displacement = 3.0 e-04 inches
Case #2Gold ribbon bond wire
model
.002 x .012 x 0.23
f1 = 5300 hz
Ribbon 1g sine sweep
Q=107 @ 5300 hz
Other susceptible components
VCO circuit
T-pack amplifier
MIC mixer brick
Laser welded hermetic cover
Thin aluminum seal coverthickness = .020 inch
Semi-rigid coaxial cable
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.
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.