Investigators: J. R. Manning, W. J. Boettinger, F. W. Gayle, C. A. Handwerker, D. Josell, U. R. Kattner and M. E. Williams

Technical Description:

To meet the need for improved solder joint reliability, NIST is developing measurements, test techniques and scientific guidelines that U.S. manufacturers can use (1) to evaluate components for solderability before committing them to the production line and (2) evaluate solder joint designs for their manufacturability and reliability. For this purpose, measurements and modeling of wetting balance solderability tests, area-of-spread solderability tests, and solder wetting phenomena are underway.

Technical Objectives:

• To develop improved solderability tests using steam aging techniques to allow reliable accelerated testing.

• To analyze solder wetting phenomena that influence area-of-spread and wetting- balance solderability tests.

• To identify conditions that lead to poor reproducibility in presently-used solderability tests.

Anticipated Outcome:

• Improved solderability test methods will be developed which will lead to increased manufacturability and reliability in microelectronic devices. Such increased reliability and predictability for solder joints will be essential for U.S. industry in producing surface mount and ball grid array interconnects, where limits on visual inspection of the solder joint make rework of improperly soldered connections difficult or impossible.

Accomplishments for FY 1995:

• NIST research on wetting-balance solderability tests identified conditions that provide high sensitivity to wettability factors in these tests. These results were incorporated by the Institute for Interconnecting and Packaging Electronic Circuits (IPC) Wetting Balance Test Group into the IPC Joint Industry Standard document on Solderability Tests for Component Leads, Terminations, Lugs, Terminals, and Wires.

• A workshop on Concurrent Design of Advanced Interconnection Technology, held at Amelia Island, FL, Nov. 14-16, 1994 was organized in collaboration with Sandia National Laboratories to obtain views of the microelectronics industry on needed measurement programs in this area.

• Predictive models were developed for the rate and extent of reactive wetting of solder during area-of-spread and wetting balance solderability tests. Complicating factors in these models are solute diffusion and the Marangoni flow from temperature gradients expected under these conditions.

Impacts and Technical Highlights:

• NIST wetting balance measurements have shown how intermetallic formation and oxidation can affect solderability. These results are being used to design improved solderability tests, particularly accelerated tests. Since industry finds that the presently used wetting balance tests are not sufficiently reliable, improved tests are needed. A NIST-designed accelerated test using steam-aging techniques to allow more rapid testing is under consideration by IPC.

• Collaboration of NIST researchers with an industrial consortium on printed wiring boards led by the National Center for Manufacturing Sciences (NCMS) contributed to new solderability tests being developed by this consortium. Members of the consortium are AT&T, IBM, Hamilton Standard, Sandia National Laboratories, and Texas Instruments.

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Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister