Page 17 - Chip Scale Review_January February_2023-digital

When comparing the two packages,
the T/C stress corresponded to the
comparison data of lower warpage and
CTE value.

Electrical characterization
I n t h i s s t u d y, t h e e l e c t r i c a l
performance of the HIFOM package
ha s been i nvest igated u si ng a n
Table 2: Comparison of package CTE. e l e c t r i c a l s i m u l a t i o n . A h i g h -
frequency structure simulator (HFSS)
the W/B package, and 48.14ºC for the
HIFOM package, respectively. The
thermal resistance junction to ambient
(θ JA ) of the HIFOM package was
23.1ºC/W, and the thermal resistance
junction to board (θ JB ) was 8.4ºC/
W. Looking at the W/B package, the
θ JA was 25.1ºC/W, and the θ JB was
9.0ºC/W. Simply speaking, the HIFOM
package had a 6~7% improved thermal
dissipation ability compared with a
normal W/B package; this result is
presumed to be due to the thinner
package height.
Package warpage was also measured
by the shadow moiré interferometry.
For the W/B package, the warpage was
over 40µm with the “crying shape” at We Take Care of the
30ºC and at -20µm; the smile shape
was at 260ºC (see Figure 7a). Its Fine Work
warpage difference at both room and
reflow temperatures was very high.
However, the HIFOM package had
no remarkable changes at room and Wafer Level Packaging
reflow temperatures and its warpage
difference was around 20µm (see
Figure 7b). These results can be
explained by noting that no organic
substrate resulted in a lower warpage
in the HIFOM packages.
T h e c o e f f i c i e n t o f t h e r m a l
expansion (CTE) of a package was
also measured and compared using a
COMPONENT ASSEMBLY
thermomechanical analyzer (TMA). REDISTRIBUTION LAYER COPPER PILLAR COMPONENT ASSEMBLY WAFER METALLIZATION
A Q400 from TA Instruments was
u sed for t he T M A mea su reme nt
a n d i t s t e m p e r a t u r e r a ng e wa s
20ºC to 260ºC; its ramp rate was
10 º C/m i n. As noted i n Table 2,
t h e p a c k a g e C T E o f a H I F O M
p a ck a ge i s 2 . 5 ~ 3 .8 p p m / º C
less than that of a conventional W/B ELECTROLESS PLATING SOLDER BUMPING WAFER THINNING WAFER DICING
package. With measured package CTE
and warpage, thermal cycling (T/C)
stresses at the BGA ball area were also
evaluated by finite element analysis.
As a result, the T/C stress in the
HIFOM package was 28% lower than
for the conventional W/B package. pactech.com

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