
Example of Failure Rate Calculation:
Assume a device operating 8 hours/day, 5 days a week. The utilization factor, given 168 hours/week is:
(8 hours/day) x (5 days/week)
÷
(168 hours/week)
=
0.25
The point failure rate per year (8760 hours) at 25
°
C ambient temperature is:
(0.021%/1K hours) x 0.25 x (8760 hours/year) = 0.045% per year
Similarly, 90% confidence level failure rate per year at 25
°
C:
(0.081%/1K hours) x 0.25 x (8760 hours/year) = 0.177% per year
Table 2.
Point Typical
Performance
[1]
in Time
Failure Rate
MTBF
[1]
(%/1K Hours)
457,000
643000
920,000
1,344,000
2,006,000
3,066,000
4,809,000
Performance in Time
[2]
(90%Confidence)
Failure Rate
MTBF
[2]
(%/1K Hours)
118,000
165,000
237,000
346,000
516,000
788,000
1,236,000
Ambient Temp.
(
°
C)
85
75
65
55
45
35
25
J unction Temp.
(
°
C)
115
105
95
85
75
65
55
I
F
30
0.219%
0.156%
0.109%
0.074%
0.050%
0.033%
0.021%
0.850%
0.605%
0.423%
0.289%
0.194%
0.127%
0.081%
Notes:
1. The point typical MTBF (which represents 60% confidence level) is the total device hours divided by the number of
failures. In the case of zero failures, one failure is assumed for this calculation.
2. The 90% confidence MTBF represents the minimum level of reliability performance which is expected from 90% of all
samples. This confidence interval is based on the statistics of the distribution of failures. The assumed distribution of
failures is exponential. This particular distribution is commonly used in describing useful life failures. Refer to
MIL-STD-690B for details on this methodology.
3. A failure is any LED which does not emit light.
Table 3. Environmental Tests
Units
Tested
10
2600
Units
Failed
0
1
Test Name
Solder Heat Resistance
Temperature Cycle
Reference
MIL-STD-883 Method 2003
MIL-STD-883 Method 1010
Test Conditions
260
°
C, 3 seconds
-55
°
C to 100
°
C, 15 min. dwell,
5 min. transfer, 20 cycles
85
°
C, 85% RH, 168 Hours
16 Hours steam aging followed by
solder dip at 260
°
C for 5 seconds
35
°
C, 24 Hours
Humidity Storage
Solderability
JIS C 7021 Method B-11
MIL-STD-883 Method 2003
252
10
0
0
Salt Atmosphere
MIL-STD-883 Method 1009
10
0
Table 4. Mechanical Tests
Units
Tested
11
11
22
Units
Failed
0
0
0
Test Name
Terminal Strength
Lead Strength
Vibration Variable
Frequency
Reference
MIL-STD-883 Method 2004 Cond. A
MIL-STD-883 Method 2004 Cond. B
MIL-STD-883 Method 2007
Test Conditions
1 lb. for 30 sec.
3 X 90 degree bend, 8 oz.
2 Hours for each X, Y, Z axis at
20 Gs, 10 to 2k Hz; 20 min. sweep
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