Chip Scale Review May • June • 2019[ChipScaleReview.com]
onsider the most expensive
wire bond failure in history.
In 1997, NASA experienced
a failure in the solid-state data recorder
aboard the Hubble Space Telescope,
which at the time was roughly 350 miles
above the Earth’s surface (
The data recorder contained multi-chip
stacked dynamic random access memory
(DRAM) modules that were connected
to circuit boards with 25µm gold bond
wires. Apparently, several of these
bonds fractured from a combination of
poor initial quality and fatigue from
subsequent vibration in service.
Wire bonds to the moon and back
Each year, the electronics industry
creates over ten trillion semiconductor
i n t e r c o n n e c t s – mo r e t h a n 10 0 0
interconnects for every human on Earth.
At ~3mm length apiece, that would
amount to 30 million km of wire – enough
to go to the Hubble Telescope and back
over 27,000 times. For the last 50 years,
the vast majority of these connections
were made with wire or ribbon bonds,
so one might conclude that, by now,
the process is in a state of near perfect
reliability. Unfortunately, wire bonding
still suffers failures during processing,
as well as failures in the field during
use. Direct printing of semiconductor
interconnects with finely-sprayed inks
containing conductive nanoparticles is a
promising alternative to wire bonding in
Non-contact micro direct printing
t e c h n o l o g y h a s p r o v e n t o b e a
mo r e ge nt le me t hod of p r oduc i ng
interconnects, which is of particular
interest for those packaging fragile
parts such as gallium arsenide (GaAs).
Furthermore, this direct printing process
is not limited to planar arrangements.
ICs can be st acked or a r ranged on
curved surfaces to save space or improve
How wire bonds fail
Wire bonds can fail in a number of
). The U.S. Department of
Defense, in MIL-STD-883F Method 2011
, lists eight common failure modes for
wire bond interconnects:
1. Wi re break at neckdown poi nt
(reduction of cross section due to
2. Wire break at point other than
3. Failure in bond (interface between
wire and metallization) at die.
4. Failure in bond (interface between
wire and metallization) at substrate,
package post, or other than die.
5. Lifted metallization from die.
6. Lifted metallization from substrate
or package post.
7. Fracture of die.
8. Fracture of substrate.
Ma ny of t he f a i l u r e
modes listed above are
exacerbated by the wire
b o n d e r ’s i n j e c t i o n o f
contact energy — either
t hermal or mechan ical
— into the bond pads of
the die or the substrate.
The die or substrate can
crack and the pads can
d e l a m i n a t e f r om t h e
i n t e n s e u l t r a s o n i c o r
thermosonic zap from the
Even when the pads, the
die and substrate are not
damaged from the bonding
process, there is a chance
for wire fracture at the
neckdown point from the
residual bending stresses
in the wire loop. Higher
wire loop heights reduce
the stresses in locations
1 and 3; however, t h is
i nc rea se s t he requ i red
package height and can degrade the
signal acuity and coupling efficiency.
Furthermore, the higher loop heights
can result in lower mechanical resonant
frequencies in the wire itself. In fact, in
the case of the Hubble Telescope failure,
the resonant frequency of the failed
bond wires was below 1kHz—within
the operating range of the electronics’
Low-impact, printed interconnects
For many applications, getting rid of
the wire bond entirely with a printed
interconnect is worthy of consideration.
A printed interconnect does not require a
static or oscillating force to be applied to
fragile components, pads or substrates.
It is essentially a non-contact process.
I n fact, some non- cont act pr i nt i ng
processes can print the conductor from
Avoiding the downfalls of bond wires with
By Bryan Germann
A bond wire failure in your home PC is one thing, but in the
case of the Hubble Telescope at its current altitude, the service call had
a price tag of around $1 billion. SOURCE: NASA Hubble Space Telescope
(Courtesy NASA/JPL-Caltech [www.jpl.nasa.gov/imagepolicy])
How wire bonds fail.