Jetting fluids in non-traditional packaging and assembly applications
Operation i/b Step Sq. Ft. Man UPh #Mch Str. CT
ductors deposited by standard deposition
techniques. In some designs the platinum
Die attach 1 i DA1 32 0.5 420 2 789
and ruthenium (Pt and Ru) catalyst are de-
(Mother + 25µm DAF)
posited as well. But in most cases a porous
Die attach 2 i DA2 32 0.5 460 2 720 catalyst layer laden with carbon particles,
(Daughter + 10µm DAF) that have Pt and Ru attached, is deposited
Plasma 1 (Pre WB) b PL1 18 0.25 1 600
or placed on the anode. In some cases the
layer is a separate sheet of carbon catalyst
Wire bond 1,2 (Std. + RBSoB) i WB1 20 0.25 140 4 2366
film placed in intimate contact with the
Plasma 2 (Pre FOW) b PL2 18 0.25 1 600
anode. Figure 10 shows nine steps to fabri-
cate a typical semiconductor DMFC.
Die attach 3 (Daughter + FOW) i DA3 32 0.5 460 2 720
The proton exchange membrane
Die attach 4 (Daughter + 10µm i DA4 32 0.5 420 2 789 (PEM) is composed of Nafion. Nafion is a
DAF) DuPont product that is a perfluoro sulfo-
nic acid polymer with low gas permeability
Cure FOW b CR1 18 0.25 1 24600
and high proton conductivity. The cathode
Plasma 3 (Pre WB) b PL3 18 0.25 1 600
side uses basically the same catalyst and gas
Wire bond 3,4 (Std. + RBSoB) i WB3 20 0.25 100 5 3312
diffusing layers. The cathode semiconduc-
tor side may have channels and or holes
Plasma 4 (Pre FOW) b PL4 18 0.25 1 600
to allow oxygen in and water out. In a
Die attach 5 (Daughter + FOW) i DA5 30 0.5 460 2 720
DMFC, the anode side requires water. An
optimally designed device reuses the oxida-
Die attach 6 i DA6 30 0.5 420 2 789
tion side’s water byproduct at the anode
(Daughter + 10µm DAF)
reduction side. Also, it is possible to design
Cure FOW b CR2 18 0.25 1 24600 the device for passive flow of fuel, water
Plasma 5 (Pre WB) b PL5 18 0.25 1 600
and air (oxygen) so no external pumping
is required. There are many papers on
Wire bond 5,6 (Std. + RBSoB) i WB5 20 0.25 100 5 3312
different configurations of mDMFC using
Plasma 6 (Pre FOW) b PL6 18 0.25 1 600
semiconductors
3,4,5,6,7
.
In some devices the catalyst layer
Die attach 7 (Daughter + FOW) i DA7 32 0.5 460 2 720
is dispensed as a carbon black ink and
Die attach 8 i DA8 32 0.5 420 2 789
the Nafion polymer PEM is dispensed
(Daughter + 10µm DAF)
as a fluid in solution with a solvent. It
is challenging to apply these materials.
Cure FOW b CR3 10 0.25 1 24600
The carbon particles in the ink tend to
Plasma 7 (Pre WB) b PL7 18 0.25 1 600 settle or conglomerate, causing jet nozzle
Wire bond 7,8 (Std. + RBSoB) i WB7 20 0.25 85 6 3896
clogging issues. The solvent-based Nafion
flashes off quickly causing clogging issues
TOTAL (FOW) 22 1084 16 46 39
in the jet nozzles. In addition, the Nafion
Steps Sq. Ft. Men Mach. Hours
contains an active sulfonic acid that reacts
Table 1. Stacked wire bonding process—8-die 1mm FOW NAND.
with most wetted dispensing parts causing
poisoning, bubbles and deterioration of
the dispensing system.
Operation i/b Step Sq. Ft. Man UPh #Mch Str. CT
In addition there are challenges with
Die attach 1 i DA1 32 0.5 590 1 561
the fluids’ various interactions with the
(Mother + 25µm DAF)
substrates. The carbon ink may not wet
to improperly prepared surfaces. The wet-
Die attach 2-8 i DA2 32 0.5 115 5 2880
ting issues can be resolved with standard
(Daughter + 10µm DAF)
substrate cleaning by plasma or alcohol/
Plasma 1 (Pre-coat) b PL1 18 0.25 800 1 414
acetone washes. However, as the ink dries
it becomes brittle. If the ink layers are too
Parylene coat b CT1 60 0.5 1 7500
thick, the outer layer dries much faster
Laser ablation i LS1 60 0.5 416 2 796 than the inner layers, causing cracking
Plasma 2 (post-laser/pre-ViP) b PL2 18 0.25 800 1 414
similar to water-based conformal coatings.
Ink jetting heads have been used to apply
Vertical interconnect process i VI1 20 0.5 140 4 2366
the carbon catalyst inks. Unfortunately,
Cure ViP b CR1 18 0.25 1 3600
ink jets apply ink with very small drops
(8 picoliters), requiring more time to
TOTAL (VCI) 8 258 8 16 8
dispense. This problem was solved by using
Steps Sq. Ft. Men Mach. Hours
jet valves from the underfill dispensing
Table 2. Jetted interconnect for stacked die—8-die 1mm VCI NAND.
applications. The jet valve can apply ink in
adequate thicknesses in one or two
www.globalsmt.net Global SMT & Packaging – May 2009 – 17
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