by Simon Althoff, Jan Neuhaus, Tobias Hemsel, Walter Sextro
Abstract:
In order to increase mechanical strength, heat dissipation and ampacity and to decrease failure through fatigue fracture, wedge copper wire bonding is being introduced as a standard interconnection method for mass production. To achieve the same process stability when using copper wire instead of aluminum wire a profound understanding of the bonding process is needed. Due to the higher hardness of copper compared to aluminum wire it is more difficult to approach the surfaces of wire and substrate to a level where van der Waals forces are able to arise between atoms. Also, enough friction energy referred to the total contact area has to be generated to activate the surfaces. Therefore, a friction model is used to simulate the joining process. This model calculates the resulting energy of partial areas in the contact surface and provides information about the adhesion process of each area. The focus here is on the arising of micro joints in the contact area depending on the location in the contact and time. To validate the model, different touchdown forces are used to vary the initial contact areas of wire and substrate. Additionally, a piezoelectric tri-axial force sensor is built up to identify the known phases of pre-deforming, cleaning, adhering and diffusing for the real bonding process to map with the model. Test substrates as DBC and copper plate are used to show the different formations of a wedge bond connection due to hardness and reaction propensity. The experiments were done by using 500 $\mu$m copper wire and a standard V-groove tool.
Reference:
Althoff, S.; Neuhaus, J.; Hemsel, T.; Sextro, W.: Improving the bond quality of copper wire bonds using a friction model approach. Electronic Components and Technology Conference (ECTC), 2014 IEEE 64th, 2014.
Bibtex Entry:
@INPROCEEDINGS{Althoff2014,
author = {Althoff, Simon and Neuhaus, Jan and Hemsel, Tobias and Sextro, Walter},
title = {Improving the bond quality of copper wire bonds using a friction
model approach},
booktitle = {Electronic Components and Technology Conference (ECTC), 2014 IEEE
64th},
year = {2014},
pages = {1549-1555},
month = {May},
abstract = {In order to increase mechanical strength, heat dissipation and ampacity
and to decrease failure through fatigue fracture, wedge copper wire
bonding is being introduced as a standard interconnection method
for mass production. To achieve the same process stability when using
copper wire instead of aluminum wire a profound understanding of
the bonding process is needed. Due to the higher hardness of copper
compared to aluminum wire it is more difficult to approach the surfaces
of wire and substrate to a level where van der Waals forces are able
to arise between atoms. Also, enough friction energy referred to
the total contact area has to be generated to activate the surfaces.
Therefore, a friction model is used to simulate the joining process.
This model calculates the resulting energy of partial areas in the
contact surface and provides information about the adhesion process
of each area. The focus here is on the arising of micro joints in
the contact area depending on the location in the contact and time.
To validate the model, different touchdown forces are used to vary
the initial contact areas of wire and substrate. Additionally, a
piezoelectric tri-axial force sensor is built up to identify the
known phases of pre-deforming, cleaning, adhering and diffusing for
the real bonding process to map with the model. Test substrates as
DBC and copper plate are used to show the different formations of
a wedge bond connection due to hardness and reaction propensity.
The experiments were done by using 500 $\mu$m copper wire and a standard
V-groove tool.},
doi = {10.1109/ECTC.2014.6897500},
file = {Althoff2014.pdf:Althoff2014.pdf:PDF},
keywords = {adhesion;circuit reliability;deformation;diffusion;fatigue cracks;friction;interconnections;lead
bonding;van der Waals forces;Cu;adhering process;adhesion process;ampacity
improvement;bond quality improvement;cleaning process;diffusing process;fatigue
fracture failure;friction energy;friction model;heat dissipation;mechanical
strength;piezoelectric triaxial force sensor;predeforming process;size
500 mum;total contact area;van der Waals forces;wedge copper wire
bonding;Bonding;Copper;Finite element analysis;Force;Friction;Substrates;Wires}
}