495

Outdoor temperature [°C] -25 -20 -15 -10 -5

0

5

10 15 20 25 30

Days per year

5

10 10 20 25 30 45 50 50 50 35 35

Load cycles per day

2

2

2

2

2

2

2

2

2

2

2

2

Load cycles per year

10 20 20 40 50 60 90 100 100 100 70 70

Load cycles in15 years

150 300 300 600 750 900 1350 1500 1500 1500 1050 1050

T

op,min,Diode

[°C]

-25 -20 -15 -10 -5

0

5

10 15 20 25 30

T

op,max,Diode

[°C]

126 126 126 126 126 126 126 126 126 126 126 126

∆

T

op,Diode

[K]

151 146 141 136 131 126 121 116 111 106 101 96

n

Stress

293 521 462 814 893 936 1220 1170 1004 855 506 424

Example of the derivation of the required test cycles based on the

temperature swings, resulting from the climatic considerations, for a cycling test under

the existing application requirements

To what extent the climatic conditions need to be considered depends on the specific

application. Ingeneral, the climatic valuesmatter in all applications operatedoutdoors.

The necessary number of test cycles for this example is 21494, composed of the

respective results of the active and climatic calculation. In both calculations the same

acceleration parameters t

on,Stress

, I

Stress

,

∆

T

Stress

andT

j,min,Stress

were used.

For the calculation of the required test cycles the following equations were used, based

on theCoffin-Mansonmodel:

1

op

Stress

load

test

T

T

n n

β

∆

∆

⋅

=

4

3

op,

mean ,j

Stress ,

mean ,j

2

op

Stress

op,on

Stress ,on

K273

T

K 1285

K273

T

K 1285

op

Stress

load

test

I

I

t

t

e

e

T

T

n n

β

β

+

+

β

⋅

⋅

⋅

∆

∆

⋅

=

escribes the relationship of test cycles to the number of load cycles as a

function of the respective temperature fluctuations

∆

T

Stress

and

∆

T

op

. This is valid when

examining the thermal cycling tests to investigate the system solder.

applies

to the power cycling test to investigate the bond wire connections. As influencing

parameters in addition to the temperature swings

∆

T

Stress

and

∆

T

op

also the following

additional factors are of importance:

•

Minimal temperatureT

j,min,op

andT

j,min,Stress

per cycle

•

Time t

on,op

and t

on,Stress

for the component per load cycle

•

Operating current I

op

and I

Stress

for the time t

on,op

and t

on,Stress

The numerical values

β

1

to

β

4

used i

an

generally vary from one

manufacturer to another and from product to product and they result from amultitude of

tests carried out. The correct or recommended values have to be requested from the

manufacturer before implementinga lifetime calculation.

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