6.4.5.3.3.2 Sample
Calculation
The best way to illustrate the stress analysis prediction
technique is to perform a sample calculation. The example is; a 60,000 gate
dualinline 64 pin digital bipolar microcircuit which will be operated in a
ground fixed environment. General commercial practices apply to the
manufacturing which has been ongoing for two years. The formula for
determining the failure rate of the microcircuit is from MILHDBK217 (Ref.
[11]):
l_{p} = (C_{1}p_{T} + C_{2}p_{E})p_{Q}p_{L}
where:
l_{p} 
=

bipolar failure rate in failure per 10^{6} hours

C_{1} 
= 
complexity factor for 60,000
gates

p_{T} 
= 
temperature factor based on junction
temperature

C_{2} 
= 
complexity factor for the package
type

p_{E} 
= 
operating environment
factor

p_{Q} 
= 
quality inspection and test
factor

p_{L} 
= 
the learning factor based on years in
production 
STEP 1: Given: 60,000 gate bipolar microcircuit,
with 64 pin nonhermetic dualinline package, to be operated in a ground
fixed condition. The manufacturing has been ongoing for 2 years and is
considered good commercial practices. The case temperature is expected to be
no greater than 45°C, and the thermal resistance factor is 11 degrees
centigrade per watt. The microcircuit maximum power dissipation is 200
milliwatts.
STEP 2: Determine C1: From MILHDBK217, the complexity
factor for a 60,000 gate digital microcircuit is 0.08 as shown in Table
6.412.