Hi List Gurus,

I have a few questions on these standards that I could not answer on my own after some research. If there are links or archives that cover these topics, I will be happy to pursue this off list. To refresh our memories:

- The IPC-SM-785 (1992) and IPC-9701A (2006) failure criteria is met anytime there are 10 failures (~1 microsecond events) on any channel with all of the failures occurring within a number of cycles that is 10 percent (10%) of the cycle number at the first failure on that channel.

- The JESD 22-B111 failure criteria is met anytime there are 3 failures (~1 microsecond events) on any channel with all of the failures occurring within 5 cycles after the first failure on that channel.

- The JEDEC standard is application specific "Board Level Drop Test Method of Components for Handheld Electronic Products" while the IPC standard is only specific to SMT devices, regardless of application.

- In both cases, the standards call out 1000 ohm thresholds are to be used based on possible sensitivity to false failures from electrical noise when loop resistance thresholds are set lower than 1000 ohms.

Q1. What is the basis for allowing 10 events within 10% of first event (for IPC) and 3 failures within 5 cycles (for JEDEC)? This allows small numbers of infrequent events to occur before counting them as failures. This may provide a false sense of security, quality and reliability to the end user that may not always be justified.

Q2. Is this a statistical argument (a "few" events occurring in a relatively "small" sampling window are likely to be correlated, not random or noise generated), an application dependent argument, both or neither?

Q3. Is it common to tailor these criteria for the application and/or customer at hand? For example, it seems that a low impedance analog circuit or 100 ohm differential signaling application may be more sensitive to interconnect events below 1000 ohms than a traditional single ended digital switching circuit with megohms of input impedance.

Thank you for your time.

Regards,
John Nieznanski


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