Special packaging feature: Imbedded Component/Die Technology: Is it ready for mainstream design applications?
sion/CTE of quality. The material is sup-
the material plied in a syringe for use on
over a wider automated dispensing equip-
temperature ment and is typically stored at
range
5
. -40ºC to prevent changes in the
• Material material performance.
purity—Low
Thermal cycling fatigue or overstress
ionic con-
failures are detected through alternating ex-
taminants
posure of the assembly to extreme tempera-
and alpha
tures with short transition times between
particles emit-
extremes. The test vehicle was placed in
ted will aid
a thermal shock chamber to evaluate the
in increasing
resistance to temperature excursions of the
the reliabil-
assembly materials and process parameters
ity of the bare
used to manufacture the test vehicle.
die. Industry
The assembly was placed on a tray that
recommends
transitions from a cold chamber to a hot
chloride (Cl-), chamber (air-to-air) within a specified time.
Figure 3. High-resolution image of the test coupon final assembly.
sodium (Na+), Test conditions were changed periodically
potassium during the thermal shock test. Test condi-
• Conformal Coating: Parylene
(K+), and tions included: 1000 cycles from -55°C
C
fluorine (F-) levels of less than to 85°C, 250 cycles from -55°C to 125°C,
• Encapsulant: silicone gel
5-10 ppm in order to decrease
200 cycles from -55°C to 85°C, followed
• Lid: laminate with top/bottom
the opportunity of corrosion
6
.
by 4200 cycles from -55°C to 125°C. The
copper plane layer
Industry recommends less
test vehicle was subjected to over 175 days
than 0.001 particles/cm
2
/hr in
of thermal shock cycling. Critical materials
Material properties found on the technical
order to minimize irradiating
evaluated during this analysis included the
data sheets were reviewed prior to selec-
particles found in encapsulants
following.
tion of die attach, conformal coating, and
that can cause soft errors in
encapsulant candidates to include in the
logic and high-density memory
Critical Packaging Materials
test matrix. Materials were identified that
• Die Attach Adhesive—deter-
minimize coefficient of thermal expansion
devices such as DRAMs and
mine effect of stress-related
(CTE) induced stress on the devices and
SRAMS
7
.
cracking of silicon die due to
interconnects and to reduce the thermal
• Voiding—Voids, or air pock-
mismatch in CTE of die and
resistance between the die junctions and
ets, in the material result in
laminate/copper core
substrate/heat sink. Certain characteristics
increased localized stresses
• Conformal Coating—determine
are desirable for all materials comprising
which can lead to premature
aging characteristics of Parylene
the assembly. Materials with a glass transi-
delamination, or loss of
after repeated exposure to
tion temperature (T
adhesion to the die and/or sub-
g
) outside the fielded
environment range are desired in order
strate. The material is no
to minimize thermomechanical stresses
longer an effective stress
Daisy-Chain Cycles Wire Cycles
induced by a material’s state change from buffer with voids present,
Wire Group Group
glassy to rubbery. Die attaches, underfills, and the material’s thermal
and encapsulants with low ionic contami- resistance is increased
1 3,057 16 none
nates are desired to minimize opportuni- due to air’s poor ability to
2 4,507 17 none
ties for corrosion in harsh environments. transfer heat.
3 4,507 18 none
Thermal and electrical performance of the
• Moisture Absorption—Due
4 4,947 19 none
materials are equally as important in order
to use of organic substrate
to meet system-level performance require-
materials, a hermetically
5 5,102 20 none
ments. Materials meeting the following
sealed assembly cannot
6 5,656 21 none
specifications were selected to be included
be achieved. Thus the 7 5,656 22 none
in the test matrix.
materials selected should
8 none 23 none
be hydrophobic or ‘water
Critical Material Properties
repelling’ in nature
8
.
9 none 24 none
• Cure temp—The type of cure
• One-part system—One-
10 none 25 none
(snap cure versus a step cure)
part materials are easily 11 none 26 none
and cure temperature affect
integrated into the manu-
the cured material properties
12 none 27 none
facturing and assembly
including the glass transition
13 none 28 none
process. All components of
temperature. The glass transi-
the material (resin and cur-
14 none 29 none
tion temperature should be
ing agent) are premixed, 15 none 30 none
significantly above the upper
eliminating handling by
operating temperature range of
Table 1. Thermal shock failure data for the daisy-chain test
the operator to ensure
the assembly to decrease expan-
vehicles with imbedded die.
product uniformity and
30 – Global SMT & Packaging – September 2009
www.globalsmt.net
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