Page 53 - Chip Scale Review Sep Oct_2022-digital

with the die is smaller (~2.6ppm/
K for silicon). However, because of
copper’s hardness, it is not possible
to directly perform wedge bonding
without breaking the die. This last
issue is solved with the Die Top
®
System (DTS ), which provides a
mechanical protection to increased
u l t r a s o n i c p o w e r a n d b o n d i ng
force. It also further benefits from
Table 1: Overview of properties used for FEM simulation. wedge bonding, which is the most
conductivity and thickness) to the
resu lt (t her mal resist a nce). T he
intervals for the parameters used for
simulation are shown in Table 1.
The thermal conductivity of the
braze metal layer is defined by its
composition, which is approximated
by a bronze of composition CuSn x
[6]. Typical variations of the braze
m e t a l l aye r t h ic k n e s s e s a r e o n LEADERS IN
the order of 20 to 60µm and were
e s t i m a t e d b y c r o s s s e c t io n s of MICRO DISPENSING
samples and subsequent secondary
electron microscopy analysis. TECHNOLOGY
The correlation between thermal
conduct iv it y of t he br a ze met al SMALL REPEATABLE VOLUMES
layer, the thick ness of the braze ARE A CHALLENGE, BUT NOT
metal layer and the corresponding IMPOSSIBLE IF YOU HAVE BEEN
thermal resistance can be observed CREATING THEM AS LONG AS WE HAVE.
in the surface plot in Figure 10.
The main inf luencing factor is the
thermal conductivity of the braze
metal layer. The strongest change of TO DO IT WELL,
R th is observed in the region towards WE PROVIDE THREE THINGS:
lower thermal conductivities while
the inf luence is reduced for higher
values. The R th values extracted from
Figure 10 vary between 0.088 and
0.104K/W using the input from the Dispensing Expertise in a variety of microelectronic
table. Comparing this theoretical packaging applications.
possible range with the measurement
results of (0.13 ± 0.03)K/W shows that Feasibility Testing & Process Verification based
experimental and simulated values on years of product engineering, material flow testing
are in agreement. It can be stated that and software control.
an overall thermal understanding of
the substrate was accomplished. Product Development for patented valves,
dispensing cartridges, needles, and accessories.
Challenges of replacing aluminum
with copper
Copper is the ideal replacement
for aluminum for bonding wires or
ribbons. It has higher electrical and
thermal conductivities (x1.7 higher Our Micro Dispensing product line is proven and trusted by
fo r b o t h). It c a n t ol e r a t e m o r e manufacturers in semiconductor, electronics assembly, medical
st ress in the elastic defor mation device and electro-mechanical assembly the world over.
regime and bears more deformation www.dltechnology.com.
before breaking. Also, with a lower
CTE (~18ppm/K against ~23ppm/ 216 River Street, Haverhill, MA 01832 • P: 978.374.6451 • F: 978.372.4889 • info@dltechnology.com
K fo r a l u m i n u m) t h e m i s m a t c h

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