Intermetallic Issues With Wire Joining by Thermocompression

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Intermetallic Issues With Wire Joining
by Thermocompression Soldering Dr Henning
Leidecker Goddard Space Flight Center, Code
562 Parts, Packaging, and Assembly Technologies
Office Henning.W.Leidecker_at_nasa.gov 301-286-9180
21 Oct 2003
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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

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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. gt DO NOT FEAR COTS
BUT BE WARY lt
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Gold-Indium Phase Diagram
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Optical Cross-section of a ball bond
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SEM intermetallic at base of bond
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SEM cross section
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Note Cracks
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Familiar Intermetallic?
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Carbon Exuding From Grain Boundaries
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Intermetallic Remaining
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Normal and Carbon-Sensitive Images
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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/no
  tes/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)
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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 (--gt 100) of the joins breaking.
• The short-term attractiveness of Indium as a
  solder induces repeated lessons learned!

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Wedge Bond of 1 mil Au to In
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Wedge Bond of 1 mil Au to In
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Au changing into Au-In compound
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Au wire with In attack side view
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Au wire with In attack top view
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Indium Solder and 1 mil Gold Wires
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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/photonic
  sdocs/LDreliability.htm