Intermetallic Issues WithWire Joining by

Thermocompression & Soldering

Dr Henning LeideckerGoddard Space Flight Center, Code 562

Parts, Packaging, and Assembly Technologies OfficeHenning.W.Leidecker@nasa.gov

301-286-9180

21 Oct 2003

Outline

● Wire Bonding Au-Al● Intermetallics – Equil.● Intermetallics – Rates● Degradation/Failure● GFSC Websites

● Wire Soldering Au-I● Intermetallics – Equil.● Intermetallics – Rates● Degradation/Failure● GSFC Websites

But first, a bit about COTS ...The “Commercial Off-The-Shelf” (COTS) market is huge and competitive: the stakes are high. Hence, some of the best designers in the world develop COTS parts, sharply focused on a “target” market. Often, they hit this market with exquisite precision.

But trade-offs are usually made in this target-focused design, and the resulting parts may not be apt for a different market whose needs differ from the target.

Reliability over long times (5+ years) is a prime example.

==> DO NOT FEAR “COTS” BUT BE WARY <==

Gold-Indium Phase Diagram

Optical Cross-section of a ball bond

SEM – intermetallic at base of bond

SEM – cross section

Note Cracks

Familiar Intermetallic?

Carbon Exuding From Grain Boundaries

Intermetallic Remaining

Normal and Carbon-Sensitive Images

GSFC Websites about this topic

● NASA/GSFC Wire Bond Website:

● Selected Topics of Interest to GSFC “Parts”

● http://nepp.nasa.gov/wirebond/Index.htm

● Richard Katz Website:

● http://klabs.org/richcontent/fpga_content/pages/notes/fpga_reliability.htm

● Pay special attention to Horsting's work on the effects of impurities on the bonding pad; see also

“Issues with Gold Electroplating for Microelectromechanical Systems Applications”, by C. A. Kondoleon, et al.Materials Research Society Symposium Proceedings 2002, 687 (143--148)

Indium Solder and 1 mil Gold Wires

● Before there was “wire bonding” (e.g., thermocompression), there was “soldering”

● Pb-Sn solder dissolves gold; not good for 1 mil.● About early 1950's, Indium was used to solder

thin gold wires --- Initial success, followed by high frequency (--> 100%) of the joins breaking.

● The short-term attractiveness of Indium as a solder induces repeated “lessons learned”!

Wedge Bond of 1 mil Au to In

Wedge Bond of 1 mil Au to In

Au changing into Au-In compound

Au wire with In attack: side view

Au wire with In attack: top view

Indium Solder and 1 mil Gold Wires

GSFC Websites about this topic

● NASA/GSFC

● Technology Validation Assurance Web Site:

● http://misspiggy.gsfc.nasa.gov/tva/

● Reliability of Laser Diodes for Space Flight Applications:

● http://misspiggy.gsfc.nasa.gov/tva/meldoc/photonicsdocs/LDreliability.htm