Presentation:
Bonding with your Semiconductor: Understanding Ultrasonic Welding
Lee Levine, Process Solutions Consulting, Inc.
Abstract
With more than 15 trillion wire bonds produced annually and
volume still growing the reliability and productivity of wire
bonding makes it the dominant chip interconnection method.
Estimated wire bond interconnection volume exceeds 90% of market
share. But that does not mean that rigorous attention to details
can be ignored. New products must be fully qualified and periodic
testing of the weld intermetallic is an important part of assuring
high quality bonds. Process changes, materials changes and tool
changes must all be tested and reliability confirmed. Long-term
aging studies using accelerated high temperature storage, thermal
cycling and temperature/humidity tests are not only initial
qualification requirements but should be a part of any review
when materials s and encapsulation changes are required.
Wire bonding is a welding process where an intermetallic weld
nugget (an alloy of the wire and the bond pad or substrate surface)
is formed by the deformation of the ball or wire (wedge bonding).
Ultrasonic energy unlocks easy slip mechanisms within the crystal
lattice of the deforming materials allowing deformation at lower
force and temperature than the materials would otherwise require
for deformation. Deformation mixes the wire and substrate to form
the initial bond. Subsequently diffusion allows the mixture to
resolve into the equilibrium compounds of the phase diagram. The
intermetallic compounds each have different physical properties
and behavior. During the life of a wire bond it is normal for
transformations to occur, where one intermetallic transforms to
another because diffusion has increased (or decreased) the
concentration of one of the elements. Transformations can
generate large strains in the lattice structure, even resulting
in bond failures at the interface between adjacent intermetallic
compounds.
This talk will discuss the ultrasonic welding mechanism and its
effect on wire bond reliability
Biography
Lee is a consultant for Process Solutions Consulting, Inc. where
he provides process engineering consultation, SEM/EDS analysis,
and wire bond training. Lee's previous experience includes 20
years as Principal and Staff Metallurgical Process Engineer at
Kulicke & Soffa and Distinguished Member of the Technical Staff
at Agere Systems. He has been awarded 4 patents, published more
than 70 technical papers, and has won both the John A. Wagnon
Technical Achievement award and the Daniel C. Hughes award from
the International Microelectronics and Packaging Society (IMAPs).
Major innovations include copper ball bonding, loop shapes for
thin, small outline packages (TSOP and TSSOP, and CSPs) and
introduction of DOE and statistical techniques for understanding
semiconductor assembly processes. He is an IMAPs Fellow and a
senior, life member of IEEE.
Lee is a graduate of Lehigh University, Bethlehem, Pa where
he earned a degree in Metallurgy and Materials Engineering.