August 2006
www.semiconductor.net/packaging
Jetting Small Dots
of High Viscosity Fluids for Packaging Applications
Alec J. Babiarz,
Asymtek,
Carlsbad, Calif.,
www.asymtek.com
1. The mechanical jet is
designed to mitigate flow
out of the nozzle under
fluid pressure alone and
eject a dot based on the
nozzle size, ball size and
seat geometry.
A
pplications for various fluids in electronics assembly have increased at a
rapid pace over the years. In the 1970s,
the packaging of die was completed
using a leadframe, die bonding, wire
bonding, and plastic molding process.
Printed circuit board (PCB) assembly
used wave soldering equipment and IC inserters. The
two fluid dispensing applications were die attach and
temporary solder masks. With the growth of hybrid
assembly and surface-mount technology (SMT), the
dispensing applications expanded to solder paste, surface-mount adhesives, die-attach materials, glob top,
temporary solder mask, and die coating. In the late
1980s, the demand for higher speed and performance
drove semiconductor packaging advances to area-array
packages, which brought applications for dam and fill,
encapsulation and the first large production volume
applications for flip-chip underfill. As the market
demands more performance in terms of smaller size,
lower power, lighter weight, greener components,
higher functionality and higher speed, the applicaMECHANICAL JET
Step 1
Ball
Step 2
Seat
Step 3
Nozzle
tions for more types of fluids, adhesives, coatings,
encapsulants, pastes and fluxes increase.
In the past, the application of fluids was looked on
as a process to eliminate because of the tough nature of
applying fluids in the assembly process. Today, fluids
are becoming integral parts of the electronics package
as evidenced by liquid crystal displays (LCDs), biotechnology labs on a chip, lenses, and MEMS devices. The
transition of wire harnesses to PCB to SMT to systemin-package (SiP) modules drive more new fluids and
applications. Similarly, there is an evolution in the
technology for applying fluids from needle/contact
methods to jetting/non-contact methods. This transition is as important in our niche market as the
transition from contact/pin printing to inkjet printing
for computer printers. Change is inevitable, and new
customer requirements drive the automation market to
innovate and develop new technologies, such as jetting
fluids used in assembly.
Types of jets
Thermal inkjets are the most common jets available
today. The device is very appropriate for the
consumer market because it can be manufactured in volume with semiconductor and
thin-film techniques at very low production
prices. The technology jets small dots of lowviscosity inks, particularly acceptable in the
printing industry.
The history of thermal inkjets goes back to
using thin-film resistors for thermal printing
on special thermal paper. At one point, it was
recognized that the hot resistor could be used
to boil an ink and create dots. The thermal
inkjet works by rapidly heating a small resis-
COVER STORY
At a Glance
Jetting adhesives
for electronics and
semiconductor packaging
has provided enabling
technology for highthroughput underfilling,
small fillets and other
applications for small,
discrete amounts of
material used in
packaging.
tor to create a bubble at the
resistor by initiating boiling,
then turning off power to the
resistor and allowing the surrounding ink to cool and the
bubble to collapse. The
action of bubble formation
and subsequent collapse
imparts momentum to the
fluid directly above the bubble. Having a hole above the
resistor or nearby provides an
easy escape path for the fluid.
Consequently, a dot of ink is
expelled from the orifice.
The advantages of this technology are the size of dots,
speed of operation, insensitivity to entrapped air,
low-cost manufacturing of
heads, and the ability to
package many nozzles closely together. However, the
thermal technology is difficult to extend into other
areas beyond inks. The technology works best with low-viscosity fluids below 30
cps. Also, the process of heating fluids to boiling creates many opportunities for unwanted chemical
reactions in the fluid and at the resistor.
There are several piezoelectric actuated jets and
non-contact spraying technologies that are finding
applications in electronic assembly. The first class
of piezoelectric jets is used in printing applications
as a competing technology to thermal inkjet printing. These jets use a piezoelectric disk, beam or
tube to change the volume of a chamber containSP-2 䡲 Semiconductor PACKAGING
ing a fluid. The piezoelectric jets in this configuration can work at rates of up to 20 kHz. The forces
can be quite high, but the deflections are small.
There are several commercially available jets for
OEM applications. The primary advantage of this
technology is that arrays of jets can be manufactured and small dots of material ejected at high
rates. The jets come in arrays of 125, 256 and up to
300 nozzles. A successful commercial application
of this technology in the electronics industry is in
the manufacture of organic light-emitting diodes
AUGUST 2006
Underfilling a flip-chip
in package, the Asymtek DispenseJet DJ9000 jet shows how jetting provides a new
way to apply adhesives
and package electronics in smaller spaces.
JET VS. NEEDLE DISPENSE
JETTING DOTS FOR LINES
Start
Compress
Jet nozzle
30 gage needle
No flow
More compress
200 µm
100 µm
Further compress
Die
3. Jetting dots merge on compression between two substrates to form seals (patent
pending).
2. A 100 µm jet
nozzle has a length
of 0.5 mm and can be
positioned 2 mm
above the surface of
the die. An equiva lent needle would
need to be posi tioned down below
the die edge, in creasing the
chances of clipping
and chipping the die,
shown in the above
top view.
(OLEDs). Dimatrix (formerly Spectra) and Epson
heads are used to jet organic dyes into the LED cells
to create the red, green, blue and white diodes. This
is a very viable production tool and application of jetting in electronics assembly.
This style of jet is typically limited to low-viscosity
fluids below 30 cps. Also, since the deflections are
small, any entrapped air in the chamber being
squeezed by the piezoelectric significantly dampens
the response and prevents material from being ejected
from the nozzle. Piezoelectric technology is more
chemically inert than thermal inkjets, and this author
believes it has a significant advantage over thermal
inkjets for applications beside ink.
Another practical way to create a jet is to rapidly
open and close an orifice. In this method, a fluid is
put under relatively high pressure (>0.2 mPa for fluids in the 30 cps range and significantly higher for
more viscous materials), then an orifice is opened. A
stream of fluid starts to flow out the orifice, which
then closes. The rapid closure cuts off the flow, and
the stream momentum carries the fluid away from
the nozzle. Piezoelectric actuators attached to a lever
system allow a rapid means of valve actuation. Rapid
and repeatable actuation is required to accurately
control the amount of material streamed out of the
orifice. Also, to form small dots, small nozzles are
required with higher pressures and faster actuations.
This process is completely dependent on the fluid viscosity, and is similar to an air-over-valve actuation.
This jet technology has found good success in applying ultraviolet-curable adhesives for electronics
encapsulation. Jets of this type are available from
Picodostec, Delo and Vermes.
Another new jet technology was recently introduced
by Mydata. This technology uses a piezoelectric rod as
an excitation device in a semi-closed chamber. The
chamber is open to a supply line that feeds in solder
paste from a rotary positive displacement pump
(RPDP). As material is pushed into the chamber, the
pumping action of the piezoelectric standing wave propels consistent-sized dots of material from the nozzle at
rates up to 500 dots/sec. This type of piezoelectric jet is
new to the industry, but seems promising in providing
a new means of applying solder paste as an alternative
to stencil printing in prototype or high-mix production
lines. This technology has the advantage of having a
positive displacement component because of the addition of the RPDP.
The mechanical jet works in another unique
manner (Fig. 1). In this case, fluids are fed into a
chamber at a relatively low pressure. Typically,
underfill adhesives are pressurized at <0.1 mPa and
lower-viscosity materials, such as liquid crystal, at
0.01 mPa. The mechanical jet is designed to mitigate
flow out the nozzle under fluid pressure alone and
eject a dot based on the nozzle size, ball size and seat
geometry. The advantage of this technology is that it
creates very high local pressures at the nozzle and is
able to jet very high-viscosity fluids. The disadvantage is that the dot sizes are much larger than
piezoelectric or thermal inkjets. However, the
mechanical jet has found many applications in jetting adhesives and fluids typically found in
electronics assembly, such as underfill, epoxy, flux,
surface-mount adhesive, and liquid crystal. Almost
every type of fluid used in electronic assembly has
been jetted with this technology.
www.semiconductor.net/packaging
JETTING SMALL DOTS OF HIGH VISCOSITY
Theory of operation
The supply pressure is used to refill the ball/seat area.
The jet works by moving the ball away from the seat
to allow fluid to fill the seat area. As the shaft moves
up, it makes the first chamber larger; consequently,
fluid flows into the chamber from the fluid supply.
The jet nozzle is small enough and the supply pressure is great enough so that air is not drawn into the
nozzle. The ball is then moved down rapidly with a
known velocity to impact the seat. As the shaft moves
down, fluid is displaced. Fluid in contact with the
shaft moves with the shaft, but fluid in the center of
the space between the shaft and wall of the chamber
moves back toward the supply. This process continues until the ball approaches the seat. At the point
just prior to contact with the seat, a volume of fluid
leaves the jet nozzle and impacts the surface. Therefore, one uncontrollable variable is eliminated;
consequently, the reliability, repeatability and process window gets better.
Another advantage is that the small geometries of
the jet orifice allow for small streams and relative high
steam velocity (1.5 m/sec). The physics of flow in a
nozzle tube and needle are the same (Equation).
Q=
␲dn 4
(P 2 − P3)
128 ␮n1n
However, the 100 µm jet nozzle has a length of
0.5 mm and can be positioned 2 mm away from a surface. An equivalent needle would be 32 gage and
need to be >2.5 mm in length. Given the same fluid
pressures, the jet delivers 53 more fluid. The jetting
stream is unconstrained. The needle provides a casing all around the
ONE-DROP FILLING
fluid to the point of delivery. ConVacuum injection
ODF technology
TFT
sequently, the position of the fluid
TFT
C/F
C/F
is dependent on the position of the
needle, which may be bent or out
of the closed-loop position of the
positioning robot. Furthermore,
LC dropping
Seal dispense
Seal dispense
the needle may not wet the substrate consistently and cause the
fluid to be biased to one side of the
needle or another, contributing to
UV
additional positional errors on
deposition. At this point, one must
LC filling
ask why the needle is bent, which
alludes to the point that it hit something. This attribute to needle
dispensing gave rise to “die clipping,” which means
4. Jetting is
is trapped in the seat and finds its only exit path out the edge of a flip-chip was damaged by an errant neereplacing timethe nozzle orifice. The fluid pressures become dle. Jetting can never chip a die (Fig. 2).
consuming vacuum
Jetting dots to make lines for seals provides
techniques for extremely high, and fluid is jetted out of the orifice
advantages that are not initially obvious. A series of
filling a flat panel in a stream. However, the source of additional fluid
dots at the correct spacing will make an almost
display with liquid is already cut off, and the final impact of the ball on
crystal. (Source: the seat snaps the fluid stream.
perfectly straight and non-scalloped line once comShin-Etsu).
pressed between two parts. As the dots are
Jet vs. needle
compressed, they initially make bigger circles as the
The various jetting technologies all provide advan- fluid flows out equally. However, once the dots
tages over needle dispensing by solving the needle’s touch one other along the line axis, there is an equalinherent weaknesses. The process of depositing mate- ization of flow symmetrically at the point of contact
rial with a needle requires that the needle, substrate (Fig. 3). As the dots are further squashed, the fluid
and fluid are all in contact with each other at the flows toward the unrestricted boundaries. At first, the
same time. Deposition occurs after the flow from the boundary is scalloped. As the dots are compressed
needle is stopped and the needle is extracted away for further, the fluid will take the shortest path, which is
the surface. As the needle moves up, the break off and to the deepest scallop. Consequently, the flow equalamount of material that remains on the surface and izes along the free surface to a straight line. This has
needle is uncontrolled. In the case of the jet, the fluid real advantages in making seals for OLED, LCOS
SP-4 䡲 Semiconductor PACKAGING
AUGUST 2006
www.semiconductor.net/packaging
and flat panel display (FPD) assemblies. Since the
beginning and end of a rectangle or continuous
shape made with equally spaced dots is unrecognizable, there is no beginning or ending blob in the
dispensed line. This condition is next to impossible
to achieve with needle dispensing.
Enabling technology
All jetting applications have enabled new packaging
technology. The ability to place fluids in smaller
spaces provides new ways to use adhesives and
package electronics in smaller spaces. Flip-chip on
flex (FCOF) is used in many hand-held devices, cameras and hard disk drive assemblies. Flexible circuit
substrates have been growing faster than rigid PCBs
for the past few years, and will continue to find more
applications in packaging.
In the case of small flip-chip die, the ability to
apply underfill quickly enables the end product introduction. In order to meet cost goals, the
manufacturer must meet high units per hour (uph)
throughput on the production line. If a single 1 mm
die required four dots of underfill, a jet could apply
the dots at 200/sec, which equates to 50 pps. If a needle process was used at the high rating of 14 dots/sec,
the throughput would be 3.5 pps. When considering
the other parts of the process, jetting provides >33
the advantage in throughput — therefore, at least 33
the machine utilization.
The FPD assembly market has unique applications that use the inherent advantages of noncontact dispensing. FPDs are made on large panels of
glass. The latest generation of glass called Gen 7 is a
substrate 2 3 3 m. Even in much smaller panels, needles are traditionally used to dispense a bead
of sealant around each display. Good needle dispensing requires the distance between the needle and
substrate to be tightly maintained to make a good
deposition. Complicated mechanics and servo controls are required to meet these demands. Fortunately,
jetting does not require tight height controls. The jet
applies fluid over substrates that vary 1 mm, therefore
higher dispense speeds with less costly mechanics provide lower-cost manufacturing of displays.
In the application of underfill chip-scale packages,
new challenges occur as the wireless applications
become more prevalent. The new, sophisticated, highend personal data assistant/cell phones usually require
electromagnetic interference shielding. If a shield
needs to be placed over a component that requires sec-
ondary underfill, the shield may not be applied until
the underfill operation is complete. This would
require an additional solder reflow of the shield onto
the board, which is highly undesirable, expensive, and
subjects the almost-finished product to undue stress.
Fortunately, a small hole in the shield placed above a
corner of the component requiring underfill will solve
the problem. Since the jet can deliver high flow rates
in the range of 20 mg/sec with 100 µm stream size, jetting the underfill material into the hole provides a
viable production process. Depositing underfill in one
location along the edge or corner of the part will provide adequate underfilling.
Another enabling technology is the process called
one-drop filling (ODF). The name is somewhat of a
misnomer because more than one drop is used.
However, the usual way to fill the space between
the glasses of an FPD was to apply a vacuum to
one end of the display and draw the liquid crystal
in from a supply tray. As screens got larger, this process could take a day. The new method is to jet the
liquid crystal in an array and then laminate the display in a vacuum. This method increases the
throughput of the process on large displays from
24 hours to 3 hours (Fig. 4).
Conclusion
Jetting is rapidly becoming the standard method for
applying the various fluids used in electronics assembly, semiconductor packaging and FPD assembly.
It may be easy to predict that automated needle dispensing will decrease to niche processes in the future
because of the inherent advantages of jetting and its
enabling features. The small size, tighter tolerances,
and high speeds of jetting allow newer and smaller
products because the manufacturers can produce the
higher-performance components economically. •
Acknowledgement
This article is based on a paper presented at the SMTA
Pan Pacific conference in January 2006.
Alec J. Babiarz is senior vice president and a co-founder of
Asymtek. He is a co-developer in 31 patents worldwide for fluid
dispensing equipment and has written more than 15 papers on
fluid dispensing and jetting. He received a B.S. in engineering
from Arizona State University, and a master’s degree from
Stanford University in mechanical engineering and electrical
engineering.
E-mail: [email protected]
Posted from Semiconductor International, August 2006. Copyright © Reed Business Information, a division of Reed Elsevier, Inc. All rights reserved.
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Do you need faster,
lower cost, better dispensing?
It’s called, “Jetting.”
Jetting can achieve 400%
speed increases over needle
dispensing and improve
yields with better accuracies.
Non-contact jetting solves challenges
in assembling the most advanced
packages and assemblies:
• Stacked die
• Folded package
• Flex circuits
• 3-D packaging
• OLED
• MEMs
• Small die
• PCB assemblies
If you’re dispensing underfill,
encapsulation, flux, UV-cure adhesives,
surface mount adhesives, and conductive
epoxies, jetting improves yield and
adds capability. Get into production and
to the marketplace faster with jetting.
Find out what you can
achieve with jetting now:
Americas:
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Japan:
China:
Email:
+1-760-431-1919
+31-43-352-4466
+ 81-3-5762-2801
+8621-5899-1879
[email protected]
www.dispensejet.com
Dispensing problems typically
associated with needles such as
die clipping, broken wires, bent
needles and dripping are
eliminated with jetting technology.
With jetting, you have fewer
problems, higher yields and
a better process.
The jet shoots a fluid stream as
small as 100µm and achieves wet
out areas as small as 250µm —
allowing tighter die spacing.
Jetting has been proven to deliver
higher thoughput compared to
needle dispensing for die sizes
from under 1 mm to over 20mm.