Mechanical resonances in microwave integrated circuits

and packages

Above 2000 hz who cares ??

9/14/2016

Don Blanchet

3B Associates

dwb3298@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 Grmsresponse 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.