Intrinsic Failure Rate (IFR)

Product	Result at 1000 hrs	Stress Dev Hrs at 150°C	Equiv Dev Hrs at 55°C	IFR
ABT, ALVT, LVT	0/2,660	2,660,000	689,472,000	1.33 FIT
AHC	0/536	536,000	138,931,200	6.62 FIT
ALVC, LVC	0/918	918,000	237,945,600	3.87 FIT
FAST	0/630	630,000	163,296,000	5.63 FIT
HC	0/536	536,000	138,931,200	6.62 FIT
HEF4000	1/1,188	1,188,000	307,929,600	2.99 FIT
LV	0/347	347,000	89,942,400	10.23 FIT
MCU	0/1,250	1,250,000	324,000,000	2.84 FIT
PicoGate	0/1,080	1,080,000	279,936,000	3.29 FIT
Total	0/9,145	9,145,000	2,370,384,000	0.39 FIT

The IFR is obtained by accumulating the test-results of SHTL and DHTL stresses over a period of 12-months, with readpoints beyond 170 hours of stress. The FIT values are calculated with a 60% Confidence Level (Poisson statistics) and rated at 55°C by using an Arrhenius activation energy of 0.7eV.

The floor of the failure rate curve consists of random failures, and the failure rate is relatively low and constant. This behavior is seen in large populations of mature components and is commonly referred to as the useful life of the product. The intrinsic failure rate is usually defined by the Failure-In-Time (FIT)—a FIT being 1 failure in 1 billion device hours of operation.

The formula for calculating the Intrinsic Failure Rate, expressed in Failures-In-Time (FITs), is:

IFR = n_c(n) * 10⁹
_{¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯}
N * t * A

Where:

IFR	=	Intrinsic Failure Rate [FIT]
n	=	Observed total number of failures during the test excluding early failures
nc(n)	=	Corrected number of failures (using a 60% confidence interval with Poisson statistics)
N	=	Number of units tested
t	=	Duration of test at elevated temperature in hours
A	=	Arrhenius acceleration factor (Ea = 0.7eV at Tref=55°C)

The following table is used to determine the corrected number of failures n_c(n), using a 60% confidence interval with Poisson statistics, derived from the Poisson Chi-square distribution.

n	nc(n)	n	nc(n)	n	nc(n)	n	nc(n)
0	0.916
1	2.022	11	12.553	21	22.867	31	33.113
2	3.105	12	13.589	22	23.894	32	34.136
3	4.175	13	14.624	23	24.920	33	35.157
4	5.237	14	15.658	24	25.946	34	36.179
5	6.292	15	16.690	25	26.971	35	37.201
6	7.343	16	17.722	26	27.996	36	38.222
7	8.390	17	18.752	27	29.020	37	39.242
8	9.434	18	19.782	28	30.044	38	40.263
9	10.476	19	20.811	29	31.067	39	41.283
10	11.515	20	21.839	30	32.090	40	42.303