Transcript Undergraduate Admissions & College of Engineering

Packaging
ECE/ChE 4752: Microelectronics
Processing Laboratory
Gary S. May
April 8, 2004
Outline
 Introduction
Test Structures
 Final Test
 Package Types
 Attachment
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IC Manufacturing
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Manufacturing = process by which raw materials are
converted into finished products
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IC manufacturing:
 Inputs = wafers, insulators, dopants, metals
 Outputs = ICs, systems
 Processes = oxidation, deposition, photolithography,
etching, doping, etc.
Other Key Processes
Electrical testing: necessary to ensure
conformance to specifications and the
reduction of any variability in the
manufacturing process
 Packaging: set of technologies that connect
ICs with electronic systems (Analogy:
“brain” = IC; “body” = package).
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Outline
Introduction
 Test Structures
 Final Test
 Package Types
 Attachment
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Process Control Monitors
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Special structures used to
assess the impact of defects
Include single transistors,
single lines of conducting
material, MOS capacitors,
and interconnect monitors
Product wafers contain
several PCMs distributed
across the surface
Interconnect Test Structures
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Used to assess presence of defects, which can be inferred
by shorts or opens found using resistance measurements.
 Meander: facilitates the detection of opens
 Double comb: used to detect shorts
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Various combinations of widths of lines and spaces in
these test structures allow the collection of statistics on
defects of various sizes.
Outline
Introduction
 Test Structures
 Final Test
 Package Types
 Attachment

Functional Testing
Final arbiter of process quality and yield
 Automated test equipment (ATE) used to
apply a measurement stimulus and record
the results
 Major functions of ATE:
 Input pattern generation
 Pattern application
 Output response detection
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Schmoo Plot
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Outlined shaded region = where the device is
intended to operate
Blank area outside = failure region
Cell Maps
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Show failure patterns and defect types.
Die Separation
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After functional testing, ICs (or dice) must be separated
from the substrate.
 Substrate wafer is mounted on a holder and scribed in
both the x and y directions using a diamond scribe.
 Wafer is removed form the holder and placed upsidedown on a soft support.
 Roller used to apply pressure, fracturing wafer along
scribe lines
This must be accomplished with minimal damage to the
individual die
Modern processes use a diamond saw, rather than a
diamond scribe
Separated dice are ready to be placed into packages
Outline
Introduction
 Test Structures
 Final Test
 Package Types
 Attachment

Packaging Hierarchy
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Level 0: on-chip
interconnections
Level 1: inter-chip
interconnections
Level 2: chip-to-PCB or
chip-to-module
Level 3: board-to-board
interconnections
Levels 4, 5: connections
between sub-assemblies
and systems (i.e.,
computer to printer)
Dual In-line Package (DIP)
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Package most people
think of when they
envision ICs.
Developed in the
1960S, has long
dominated the
packaging market.
Can be made of plastic
or ceramics
Surface Mount Package
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Developed in 1970s and 1980s
Leads don’t penetrate the PCB; so package can be
mounted on both sides of the board, allowing
higher density.
EXAMPLE: Quad flatpack (leads on all 4 sides to
increase possible I/O connections)
Pin/Ball Grid Arrays
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PGAs have I/O
density of ~ 600
BGAs have densities >
1000 (compared to ~
200 for QFPs).
BGA takes up less
space than QFP, but is
more expensive to
manufacture.
Chip Scale Packages
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Defined as packages no larger
than 20% greater than the size
of the IC
Designed to be flip-chip
mounted
Manufactured in a process that
creates power and signal I/O
contacts and encapsulates the
die prior to dicing.
Provide an interconnection
framework so that before
dicing, each die has all
functions (i.e., external
contacts, encapsulation) of a
fully packaged IC.
Outline
Introduction
 Test Structures
 Final Test
 Package Types
 Attachment

Bonding
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An IC must be mounted and bonded to a package.
Package must be attached to a PCB
Methods of attaching ICs to PCBs are part of
Level 1 packaging.
Techniques used to bond a bare die to a package
have significant effects on the electrical,
mechanical, and thermal properties of the fianl
system.
Bonding Methodologies
(a)
(b)
(c)
Wire bonding
Flip-chip bonding
Tape-automated
bonding
Wire Bonding
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Oldest attachment method and still dominant for ICs with
< 200 I/Os
Requires connecting Au or Al wires between IC bonding
pads and contact points on the package
ICs are attached to substrate using thermally conductive
adhesive with bonding pads facing upward.
Au or Al wires attached between pads and substrate using:
 Ultrasonic,
 Thermosonic, or
 Thermocompression bonding.
Although automated, the process is time-consuming since
each wire must be attached individually.
Thermocompression Bonding
(a)
(b)
(c)
(d)
(e)
Fine wire (15-75 mm diameter)
fed from a spool through a heated
capillary.
H2 torch or electric spark melts
end of wire, forming a ball.
Ball is positioned over the chip
bonding pad, capillary is lowered,
and ball deforms into a "nail
head".
Capillary raised and wire fed from
spool and positioned over
substrate; bond to package is a
wedge produced by deforming the
wire with the edge of the
capillary.
Capillary is raised and wire is
broken near the edge of the bond.
Ultrasonic Bonding
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Problems with thermocompression:
 Oxidation of Al makes it
difficult to form a good ball.
 Epoxies can’t withstand high
temperatures.
Ultrasonic is a lower temperature
alternative
Relies on pressure and rapid
mechanical vibration to form
bonds.
Approach:
(a) Wire fed from a spool through
a hole in the bonding tool
(b) Wire lowered into position as
ultrasonic vibration at 20-60
kHz causes the metal to
deform and flow.
(c-d) Tool raised after the bond to
the package is formed,.
(e) Clamp pulls and breaks wire.
Thermosonic Bonding
Combination of thermocompression and
ultrasonic
 Temperature maintained at ~ 150 oC
 Ultrasonic vibration and pressure used to
cause metal to flow to form weld
 Capable of producing 5-10 bonds/sec
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Tape-Automated Bonding
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Developed in early 1970s
ICs first mounted on flexible polymer tape (usually
polyimide) w/ repeated Cu interconnection patterns.
Cu leads defined by lithography and etching
After aligning IC pads to metal interconnection stripes on
the tape, attachment occurs by thermocompression
Au bumps formed on either side of the die or tape used to
bond die to the leads.
TAB Process
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Advantage: all bonds
formed simultaneously,
improving throughput.
Disadvantages:
 Requires multilayer
solder bumps with
complex metallurgy.
 A particular tape can
only be used for a chip
and package that
matches its
interconnect pattern.
Flip-Chip Bonding
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Direct interconnection
where IC is mounted
upside-down onto module
or PCB
Connections made via
solder bumps located over
the surface of IC
I/O density limited only
by minimum distance
between adjacent bond
pads
Flip-Chip Process
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Chips placed face down on the module substrate
so that I/O pads on the chip are aligned with those
on the substrate
Solder reflow process is used to simultaneously
form all the required connections,
Drawback: bump fabrication process itself is fairly
complex and capital intensive.
Solderless flip-chip technology is another
alternatve; involves stencil printing of organic
polymer onto an IC.