mttf calculator users guide

7/28/2019 MTTF Calculator Users Guide

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MTTF Calculator MTTF Calculator

User User ’ ’ s Guides Guide

10/4/07



Nitronex Confidential

MTTF(TJ) Formula

1.6 1.8 2.0 2.2 2.4

100

101

102

103

104

105

106

107

108

260C

285C

M T T F ( h o u r s )

Ea = 2.0eV

310C

Operating at 150C

leads to MTTF>107

NRF1

y = 5E-17 * e23192x

R2 = 0.9988

Ea = 2.0eV

“x” is 1/Tj in

Degrees K




CW MTTF Code

Calculate Pdis, TJ from user input

MTTF formula parameters derived

By S.Singhal from ID(Q) Drift

(electromigration formula)

Dim TF, POUT, GAIN, DE, RJC, TJ, MTTF, PDIS As Double

TF = TFbox.Value

POUT = POUTbox.Value

GAIN = GAINbox.Value

GAIN = 10 ^ (GAIN / 10)

DE = DEbox.Value

DE = DE / 100

RJC = RJCbox.Value

PDIS = POUT * (1 / GAIN + 1 / DE - 1)

TJ = TF + RJC * PDIS

MTTF = 5E-17 * Exp(23192 / (TJ + 273.16))

MTTF = MTTF / 24 / 365

PDISbox.Text = Round(PDIS, 1)TJbox.Text = Round(TJ, 1)

MTTFbox.Text = Round(MTTF, 0)

End Sub




CW Section

Select a product from the list to

set default “Input” values for flange T,

POUT

, gain, DE, and thermal resistance.

Press CalcCW to calculate PDIS, TJ, and

MTTF.

Each time you change any of the

“Input” boxes, press CalcCW to

Recalculate TJ and MTTF.




TJ

Contours (NPTB00040B)

An example of results from TJ

data generated using calculator.

NPTB00040B




TJ

Contours (NPTB00080B)

NPTB00080B

An example of results from TJ

data generated using calculator.




Pulsed Section

Enter the desired duty cycle and pulse-

width in s.

Each time you change either of the

“Pulsed Input” boxes, press CalcPulseto recalculate Peak TJ, average TJ,

and MTTF, as well as the time-TJ(t)

Profile.

One can also go back and change the

CW “Input” boxes. Press CalcCW or

CalcPulse to update their corresponding

sections.

*To re-enable to product selection list,

Press the CW/Pulsed button

If either NPTB00025 or 50 are selected

then the CW/Pulsed button is able

to turn on the “Pulsed Input” section.




Pulsed MTTF Notes

The fits for pulsed operation are done for

30,40, and 50% DE at the device defaultPout and other values.

Fits were made for a simulated device with

the default JC. User changes in JC arehandled by dumb scaling.

Going outside of these fitting ranges, onecan quickly get non-physical results.

Pulsed calculator is a general guide only.




Appendix

Pulsed Reliability Calculator Explanation




Simulated Pulsed Operation

36mm 100W 50% DE (2.78 W/mm)

4 mil Si, 1mm CPC (k=240 W/m-K)

300

320

340

360

380

400

420

-10 590 1190 1790 2390 2990

Time (s)

T e m p e r a t u r e ( K )

403.9K

308.6K (+8.6°)

410.2K (+6.3°)

312.3K (+3.7°)

413.8K (+3.6°)

314.7K (+2.4°)

The pulsed behavior was generated

from Finite Element simulation

using the full device structure and its

relevant thermal environment. The

heat flow equation is solved

in solids with user defined temperature-

dependent thermal conductivity,

heat capacity (T-dependent for Si),

and density.

Software used:

ESI Group’s CFD-ACE+




50% DE (25W PDIS) Sim.Turn-on

3 Exponential Fits to Simulated Device Turn-On

100

120

140

160

180

200

220

240

0.1 1 10 100 1000

Time (s)

J u n c t i o n T e m p e r a t u r e ( ° C )

fit1 fit2

fit3




Fitting

Divided into three ranges with fits of the form:

0.1 to <3 s TJ=4.1568*ln(time)+136.31

3 to 40 s TJ=11.777*ln(time)+126.76

>40 to 500 s TJ=21.905*ln(time)+92.07

Repeat procedure for 30%, 40% DE

Now…fit to the fitting parameters! So we have the fitting

parameters as a function of dissipated power.

1. Calculate PDIS from user input

2. Calculate TJ formula fitting parameters based on PDIS

3. Calculate TJ at any time in the turn-on with TJ formula




Pulsed MTTF Calculation

MethodologyDivide the turn-on into 10 slices

(pulse width-0.1s)/9

Calculate TJ and “MTTF based upon that TJ” at each slice

(shift by user entered TF)

Combine using Matthiessen’s rule:

1/MTTF=1/MTTF1+1/MTTF2+…1/MTTF10

Divide by duty cycle (10%10*MTTF)

mttf calculator users guide

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