fvtx substrate fea

FVTX substrate FEA 1

FVTX Substrate FEA

C. M. LeiMarch 02, 2006


Goals

• To use FEA as a design tool to understand what kind of adhesives and substrate should be used for achieving a mimimal thermal displacement.– Options of substrate

• cf/TPG/cf• aluminum

– Options of adhesives• Silicone glue (E = 2 Mpa)• Epoxy glue (E = 500 ~ 6,900 Mpa)


The Layup of the Multi-chip Module

substrate


FEA Model

Half Modules with 4 chips

(took advantages of symmetry and all modules evenly positioned)

Bump bond layer were modeled as a continous layer with adjusted properties based on an area ratio 21.33 (with eutectic solder bond diameter 0.035 mm assumed).

Effective Heat flux from ROC = 5.868 mW/mm^2Effective heat flux from sensor = 0.25 mW/mm^2Total heat load = 2.8W for half model

Cooling contact area 5mm wide at +7C


Material Library Used in this FEA

70 # # 292080 # # 343290 # # 3784

100 # # 3984150 # # 3624200 # # 2600250 # # 1960

273.2 # # 1784300 # # 1600350 # # 1352400 # # 1168500 # # 904600 # # 744

Temp in K K in W/m-K

All materials were assumed to be isotropic with constant properties except - TPG in which the thermal conductivity varies- Anisotropic carbon fiber facing and bump bonds

Young’s modulus E, MPa

Poison’s ratio Thermal k, w/m-K

CTE

HDI 30e3 0.30 0.26 17e-6

Silicone glue 2 0.36 0.24 100e-6

Silicon sensor 110e3 0.30 141 2.6e-6

Silicon ROC 110e3 0.30 141 2.6e-6

Epoxy (silver filled)

500 ~ 6,900 0.36 1.59 49e-6

TPG 83e3 0.20 table -1e-6

Eutectic solder 32e3 0.051 24.7e-6

TPG Thermal K

Carbon fiber 0/90facing:Einplane = 1.48e5 Mpa, Eout-of-plane =7445 Mpa, kinplane = 55.85 W/mK, kout-of-plane = 0.69 W/mK, ainplane = -0.04e-6 ppm/K, aout-of-plane =30.17e-6 ppm/KEutectic solder bump bond layer: Ex = Ez = 0.15 Mpa, Ey = 1500 Mpa, kx = kz = 0.33e-3 W/mK, ky = 2.38 W/mK, a = 24.7e-6 ppm/K


Silicone as substrate glueEpoxy as electrical glue

Overall ∆T = 19.9CFrom +7C to +26.9C

RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDS, 4 Combinations of AdhesivesEpoxy thermal k = 1.59W/mK, cte = 49 ppm/K; silicone thermal k = 0.24W/mK, cte = 100 ppm/K

Silicone as substrate glueSilicone as electrical glue

Overall ∆T = 22.0CFrom +7C to +29C

Epoxy as substrate glueEpoxy as electrical glue


Heat Load = 2.28W , Half Model with 4 chips

Epoxy as substrate glueSilicone as electrical glue

Overall ∆T = 20CFrom +7C to +27.0C


RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSUBSTRATE GLUE IS SILICONE (E=2 Mpa )ELECTRICAL GLUE VARIETY AS SHOWN BELOW

E = 500 Mpa (epoxy)Max resultant disp. = 2.09 microns

E = 1,200 Mpa (epoxy)Max resultant disp. = 2.23 microns



E = 2 Mpa (silicon)Max resultant disp. = 3.66 microns


RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSUBSTRATE GLUE IS EPOXY (E=500 Mpa )ELECTRICAL GLUE VARIETY AS SHOWN BELOW




E = 2 Mpa (silicon)Max resultant disp. = 15.4 microns


Silicone as substrate glueEpoxy as electrical glue


RESULTS WITH ALUMINUM SUBSTRATE 1/16” (1.5875 mm)COOLING AT ENDS, 4 Combinations of AdhesivesEpoxy thermal k = 1.59W/mK, cte = 49 ppm/K; silicone thermal k = 0.24W/mK, cte = 100 ppm/K


Epoxy as substrate glueSilicone as electrical glue


Epoxy as substrate glueEpoxy as electrical glue


Silicone as substrate glueSilicone as electrical glue




RESULTS WITH ALUMINUM SUBSTRATE 1/16” (1.5875 mm)COOLING AT ENDSSUBSTRATE GLUE IS SILICONE (E=2 Mpa )ELECTRICAL GLUE VARIETY AS SHOWN BELOW



E = 2 Mpa (silicone)Max resultant disp. = 22.2 microns




E = 1,200 Mpa (epoxy)Max resultant disp. = 57 microns

RESULTS WITH ALUMINUM SUBSTRATE 1/16” (1.5875 mm)COOLING AT ENDSSUBSTRATE GLUE IS EPOXY (E=500 Mpa )ELECTRICAL GLUE VARIETY AS SHOWN BELOW

E = 2 Mpa (silicone)Max resultant disp. = 29.2 microns


RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mm


RESULTS WITH ALUMINUM SUBSTRATE 1/16” (1.5875 mm)

Displacements higher than those of cf/TPG/cf substrate


Quick Conclusions

• Cf/TPG/cf substrate performed better with less thermal displacement

• Silicone glue should be used for the thermal substrate.

• Basically any epoxy can be used for the electrically conductive adhesive, but flexible one with lower modulus is preferred.


Material Selections• Carbon fiber facing – 2 plies,0o and 90o Bryte

K139-BT250, 55 gsm, 0.12 mm thick• TPG – 0.38 mm thick• Substrate adhesive – NEE001 silicone glue• Module adhesive – MasterBond MB21 TDXSFL.

(Minimum order is 20 grams @ $25 per gram. If too costly, can use Tra-duct 2902 which is currently being used at Sidet and has a higher thermal conductivity at 2.99 W/mK.)

More plots follow based on these selections.



RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSubstrate Glue: Silicone; Module Glue: 500 Mpa Epoxy


∆T, sensor/ROC = 3.3CFrom +23.6C to +26.9C

Mid-section all layersOverall ∆T = 8.3CFrom +18.6C to +26.9C

22.0C26.5C 26.9C

∆T across HDI (from 22C to 26,5C) = 4.5C

19.7C

sensorTPG HDI


Stress Z Plot (out-of-plane 900direction)


TPG LayerMax Resultant Stress = 0.9 MpaMax Stress_Z = 0.1 Mpa

Flexural Strenth = 36.7 Mpa Z = 38.5 Mpa //

Tensile Strength < 0.69 Mpa Z = 6,897 Mpa //

RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSubstrate Glue: Silicone; Module Glue: 500 Mpa Epoxy OK!


Carbon Fiber LayerMax Resultant Stress = 0.7 MpaMax Stress_Z = 0.2 Mpa

Flexural Strenth = 669 Mpa 00

Tensile Strength =1950 Mpa 00

= 28 Mpa 900





Silicone Glue Layer between HDI and Substrate(E = 2 Mpa)

Max Stress = 0.02 Mpa

Strength_NEE001 = 1.1 Mpa




HDI Layer


Tensile Strength_Kapton = 166 MpaTensile Strength_Copper = 320 MPa




Module Glue Layer(E = 500 Mpa)


Shear Strength_MB21 TDCSFL = 6 Mpa






Sensor and ROC Layers


Strength_Si = 120 MPa


Bump Bond Layer

Max Stress = 0.34*21.33 = 7.2 MPa

Strength of eutect solderTensile Yield = 43 MpaUltimate = 52 MPa




When heat load = 0, Temperature everywhere at +7CMax resultant disp. = 42.2 microns


RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDS, POWER OUTAGESubstrate Glue: Silicone; Module Glue: 500 Mpa Epoxy







RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDS, POWER OUTAGESubstrate Glue: Silicone; Module Glue: 500 Mpa Epoxy OK!





= 28 Mpa 900


Heat Load = 2.28W , Half Model with 4 chipsOK!



Silicone Glue Layer between HDI and Substrate(E = 2 Mpa)






HDI Layer






Module Glue Layer(E = 500 Mpa)


Shear Strength_MB21 TDCSFL = 6 Mpa

Heat Load = 2.28W , Half Model with 4 chips OK!



Bump Bond Layer




Resultant stress in most area = 0.030*21.33 = 0.64 Mpa…OK

Resultant stress in most area = 0.006*21.33 = 0.13 Mpa…OK

Max resultant stress = 3.04*21.33 = 64.8 Mpa

Resultant stress at corner = 0.97*21.33 = 20.7 Mpa…OK

Could fail at cornerslocally


Updates on FEAwith

Silicone Glue for Substrate and Modules

March 23, 2006


RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSubstrate Glue: Silicone; Module Glue: Silicone


∆T, sensor/ROC = 2.9CFrom +26.1C to +29.0C

Mid-section all layersOverall ∆T = 10.3CFrom +18.7C to +29.0C

∆T across HDI (from 22.1C to 26.6C) = 4.5C

sensorTPG HDI

Overall ∆T = 22CFrom +7C to +29.0C



Max resultant disp. = 3.66 micronsMax displacement of silicon = 3.02 mircons

RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSubstrate Glue: Silicone; Module Glue: 2 Mpa silicone


When heat load = 0, Temperature everywhere at +7CMax resultant disp. = 86.8 micronsMax displacement of silicon = 55.3 mircons


RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDS, POWER OUTAGESubstrate Glue: Silicone; Module Glue: 2 Mpa silicone


Bump Bond Layer



RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSubstrate Glue: Silicone; Module Glue: 2 Mpa silicone


OK!






OK!Heat Load = 2.28W , Half Model with 4 chips

RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDSSubstrate Glue: Silicone; Module Glue: 2 MPa silicone








= 28 Mpa 900




Silicone Glue Layers between HDI and Substrate and between HDI and Module






HDI Layer




Bump Bond Layer



RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDS, POWER OUTAGESubstrate Glue: Silicone; Module Glue: 2 Mpa silicone


OK!







RESULTS WITH CF/TPG/CF SUBSTRATE 0.62 mm (0.12+0.38+0.12) mmCOOLING AT ENDS, POWER OUTAGESubstrate Glue: Silicone; Module Glue: 2 MPa silicone








= 28 Mpa 900




Silicone Glue Layers between HDI and Substrate and between HDI and Module






HDI Layer




Conclusions• Comparing results between 500 MPa-Epoxy and 2 MPa-

silicone as the module adhesive, all stresses using silicone adhesive were all well within corresponding yield stresses at a cost of increasing displacements.

– 3.66 mircons vs 3.02 microns in normal operation– 86.8 microns vs 42.2 microns in power outage case.

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