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IRAUDAMP6 REV 1
.0
AMP6 Thermal pad pressure control calculation
PCB thickness=1.6mm
Heatsink thickness=2.54mm Weight=27.1g
(DCC58375837L-18B
http://www.alphanovatech.com/c_dcc5837ue.html
)
Thermal Pad thickness=2.03mm
(BER164-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_butto
n&KeyWords=BER164-ND+)
Spring : S001YJ1D FL=6.4mm SL=2.9mm (http://www.alphanovatech.com/c_springe.html)
Pressure Required:10-50psi(Fig21)
Clearance between push pin and heatsink:
1, Without Spring:
Pin height-PCB thickness-heatsink height(substructure height)-thermal pad thickness
=8.5-1.6-2.54-2.03=2.33mm
2, With Spring:( Assumption: pressure=50pci strain=30% according to Fig22)
Pin height-PCB thickness-heatsink height(substructure height)-thermal pad thickness*70%
=8.5-1.6-2.54-1.421=2.939mm=expected length
Spring length change=Free length-expected length=6.4-2.939=3.461mm
Spring strength= Spring length change*spring rate=3.461*5.19=17.96N
Strength to PCB=4* Spring s(heatsink weight*0.00098)=4*17.96+27.1*0.00098=
71.87N
To have 50psi pressure we need strength as below:
1kg/cm^2=14.21psi; 1g/cm^2=0.0098N/cm^2
=>50psi=3.51kg/cm^2=3.51*1000*0.0098nN/cm^2=34.398N/cm^2
Heatsink S=5.79*3.68cm^2=21.31cm^2
Total strength we need=34.398*21.31N=
732.93N>>71.87N
=>So spring does not have enough strength support push pin more than solid height.
Then, spring height=solid height
Clearance between push pin and heatsink=2.9mm
Pin height-PCB thickness-heatsink height (substructure height)-thermal pad thickness*
X %
X=72%
According to Fig22
When Strain=28%, Stress=45psi within the required range 10-50psi