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The latest qualification methods standard for SMT clears up confusion over CSP reliability.

IPC-SM-785, Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments, has been in use for more than a decade. But confusion over claims by users of that document has led to an update of IPC-9701, a specification that now covers advanced BGA and CSP technology.

According to Dr. Reza Ghaffarian of Jet Propulsion Laboratory and chair of the IPC-9701A task group, IPC-SM-785 did not set testing requirements or a performance standard. As such, he says, it led to some "extravagant claims" for product reliability - for CSPs, for example. The upshot of this is that considerable resources and time could be wasted to generate failure data that are unrelated to solder attachment. Dr. Ghaffarian cites the example of a novice user or supplier testing a surface finish that might induce interfacial rather than solder joint failure.

Thus, the task group set about to respond, authoring IPC-9701A, Performance Test Methods and Qualification Requirements for Surface Mount Solder Attachments. The draft document is currently being ratified by IPC membership.

Updates to IPC-9701 include guidelines for Pb-free solder alloys. Testing includes thermal cycling, power cycling, moisture and mechanical stress. An appendix describes guidelines for the modifications required for Pb-free solder joints.

Still, there is work to be done, as Dr. Ghaffarian points out: "[O]nly limited data and insight are available to determine acceleration factors and acceleration models for Pb-free." Data on the impact of various thermal cycle profiles on the results of accelerated testing in comparison to eutectic SnPb solder are still being gathered.

Acceleration thermal cycle test results are sometimes inaccurately assumed to be the same as product reliability. Correlations between acceleration testing and product reliability for SnPb have been established through years of investigation and product use; however such correlations remain to be established for the less understood Pb-free solder attachments. Thus, says Dr. Ghaffarian, it is not currently possible to properly estimate product reliability from accelerated tests for Pb-free solder joints.

The revision aims to help suppliers and users decide how to gather test data and determine the key processing and test parameters that must be controlled in order to generate valid data.

IPC-A-610 and J-STD-001 handbooks released. Last year, IPC released revision "D" of its popular IPC-A-610 standard covering the visual qualification and acceptance of electronic assemblies. Revision D received ANSI approval in April and has since been adopted by the U.S. Department of Defense.

What did the revision add? "The changes are in and there is a lot of new information in revision D, including over 730 new and updated illustrations of acceptability criteria," says Jennifer Day, co-chair of the IPC-A-610 task group and a training instructor at Sanmina-SCI. "The document's sections have been reformatted, and there is additional information on BGA requirements, as well as new criteria for PQFNs and DPAKs." The revision also added acceptance criteria for Pb-free solder connections.

According to Day, "The task group worked diligently to ensure clarity and accuracy. We also made a major effort to make sure IPC-A-610 was not in conflict with the main industry soldering standard, J-STD-001. Although there remain sections in IPC-A-610 that J-STD-001 is silent on, this is not considered a conflict."

The committee is taking a short recess before beginning review of recommendations for the next revision. In the meantime, a list of reported errata to the print version of IPC-A-610D is available at ipc.org; from the online store, use search term 610 and click on the link to A-610D.

In October, new handbooks were published for both IPC-A-610 and J-STD-001. Jack Crawford, director of IPC certification, notes the importance of these releases: "When a standard is updated, users need an easy way to review the changes. This is important, one, to assess whether to adopt the document revision and two, to determine what process changes may be needed if the new revision is adopted." He believes IPC-HDBK-610 with Amendment 1 fills that need with its cross-referencing and version-to-version change information.

Sharon Ventress, chair of the IPC-HDBK-610 task group, adds that "the content of the handbooks didn't change, but both handbooks now included B-C-D comparisons." From now on, both handbooks will only include revision comparisons.

The committee is beginning work on a new handbook, and held meetings during IPCWorks in November and Apex in February.

Robin Norvell is associate editor of Circuits Assembly; rnorvell@upmediagroup.com.

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