Hi TechNet List Gurus,

If I have several different serial daisy chains undergoing accelerated reliability testing per IPC-SM-785, can I apply partition correction (IPC-SM-785 Eq. 16) to calculate an "effective" Nf @test (X%) for each daisy chain?  Each chain only has a single component type, but there are different numbers of components in each chain.

For example, if the first chain has 10 two-terminal leadless SMT components (assume BETA=4), and the first IPC-SM-785 failure occurs at 800 cycles, then per Eq. 16:

Nf (component) = Nf (m partitions) * [1/m] ^ (1/BETA)
                        = 800 * (10) ^ 1/4
                        = 1422

So with 10 components in the first partition or daisy chain, then Nf @test (component) = Nf @test (10%) = 1422.

A more conservative analysis neglecting the partition correction would be to say Nf (10%) = 800.

Which way makes the most sense?

From Nf @test (10%) and BETA, I can calculate Nf @test (50%), then apply the acceleration factors to get Nf @use (50%), then extrapolate to get Nf @use (1%) and Nf @use (0.1%).

Best regards,

John Nieznanski


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