Early Failure Rate (EFR)

Product	Result	EFR
ABT, ALVT, LVT	0/12,939	70.8 fpm
AHC	0/10,789	84.9 fpm
ALVC, LVC	0/7,404	123.8 fpm
FAST	0/10,717	85.5 fpm
HC	0/10,789	84.9 fpm
HEF4000	0/12,172	75.3 fpm
LV	0/6,322	144.9 fpm
MCU	0/5,775	158.7 fpm
PicoGate	0/2,250	407.2 fpm
Total	0/79,157	11.6 fpm

The EFR is obtained by accumulating the test-results of SHTL and DHTL stresses over a period of 12-months, with readpoints upto 170 hours of stress. The "fpm" figures are calculated with a 60% Confidence Level (Poisson statistics).

Components typically have an initially high, but rapidly decreasing, failure rate. The Early Failure Rate (EFR), sometimes referred to as Infant Mortality Failures (IMF) or Early Life Failures (ELF), represents this small fraction of the population of components which contain defects that do not immediately fail but will fail in a relatively short time interval.

The formula for calculating the Early Failure Rate, expressed in Failures-Per-Million (FPM), is:

EFR = n_c(n) * 10⁶
_{¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯}
N

Where:

EFR	=	Early Failure Rate [FPM]
n	=	Observed total number of failures during the test
nc(n)	=	Corrected number of failures (using a 60% confidence interval with Poisson statistics)
N	=	Number of units tested

It is often useful to normalize the Early Failure Rate based upon die area, especially for large die. This methodology allows for scaling of Early Failure Rate FPMs based upon die area as follows:

EFR_N = n_c(n) * 10⁶ * A_{N
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯}
Σ[(N₁*A₁) + … + (N_n*A_n)]

Where:

EFRN	=	Normalized Early Failure Rate for AreaN [FPM/mm²], for example, FPM/25mm²
Nn	=	Number of units tested of die Area An
Anc(n)	=	Area of die tested [mm²]
AN	=	Area to Normalize or scale FPM [mm²], for example, 25mm²