Transcript Slide 1

General Semiconductor Packaging Process Flow
Wafer Backgrinding, Die Preparation, Die
Attach, Wire Bonding, Die Overcoat, Molding,
Sealing, Marking, DTFS, Lead Finish,
Electrical Testing, Tape & Reel, Dry Packing,
Boxing and Labeling.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die Attach
•
Die Attach (also known as Die Mount or Die Bond) is the process of
attaching the silicon chip to the die pad or die cavity of the support
structure (e.g., the leadframe) of the semiconductor package
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General Semiconductor Packaging Process Flow
Typical Die Attach Process Flow
In high-volume production, die attach is performed on fully automated
assembly equipment. The basic die attach steps, some of which are
performed simultaneously, are:
• A robotic loader picks up a lead frame from a stack and places
it on the input area of the workholder.
• The lead frame is moved from the input position to the
dispense position. Depending on the required placement
accuracy, mechanical or optical alignment points are used to
define the dispense position.
• Epoxy is dispensed in a pattern and volume appropriate for the
chip size.
• A sophisticated vision system inspects the lead frame,
dispensing pattern and bond pads before the substrate is
transported to the bonding position.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Typical Die Attach Process Flow
• In the meantime, a pattern recognition system locates a good
die on the sawn wafer.
• A vacuum pick-up tool mounted on a bond head grabs the
aligned die from the wafer and places it on the programmed
and pre-dispensed bond position on the substrate.
• Appropriate bonding time and bonding force result in a strong
bond, according to the specified process requirements. An
additional optical inspection is performed to ensure that
placement position and epoxy bleed-out requirements are met.
• Each bond pad on the lead frame or substrate goes through
this process before it is unloaded into an output magazine.
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General Semiconductor Packaging Process Flow
Die Attach
There are two common die attach processes, i.e., adhesive die
attach and eutectic die attach. Both of these processes use special
die attach equipment and die attach tools to mount the die.
For high-powered applications, the die is usually eutectic bonded onto
the package (for good heat conduction). For low-cost, low-powered
applications, the die is often glued directly onto a substrate using an
epoxy adhesive.
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General Semiconductor Packaging Process Flow
Die Attach
Die
Process of attaching the die
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die Attach
Leadframes
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General Semiconductor Packaging Process Flow
Adhesive Die Attach
• Adhesive die attach uses adhesives such as polyimide, epoxy
and silver-filled glass as die attach material to mount the die on
the die pad or cavity.
• The adhesive is first dispensed in controlled amounts on the die
pad or cavity.
• The die for mounting is then ejected from the wafer by one or
more ejector needles.
• While being ejected, a pick-and-place tool commonly known as
a 'collet' then retrieves the die from the wafer tape and positions
it on the adhesive.
• All of the above steps are done by special die attach equipment
or 'die bonders'
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die attach equipment or 'die bonders'
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die Attach Tools
Assignment 2 Group A1
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Adhesive Die Attach
Advantages - Widely use as die attach materials in low-cost
packaging application or plastic packaging. They are bonded at
lower processing temperatures, reducing stress and
providing a thermally and electrically conductive path from
chip to the leadframe.
Disadvantages of adhesive die attach material are that they are
not thermally stable and absorb moisture, hence cannot be
used in hermetically sealed package.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Adhesive Die Attach
• The mass of epoxy climbing
the edges of the die is known as
the die attach fillet.
• Excessive die attach fillet may
lead to die attach contamination
of the die surface.
• Too little of it may lead to die
lifting or die cracking
Photo shows the D/A adhesive as the grainy
material between the die and the die pad.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Adhesive Die Attach
Another critical aspect of adhesive die attach is the ejection of
the die from the wafer tape during the pick-and-place system's
retrieval operation.
The use of inappropriate or worn-out ejector needle and
improper ejection parameter settings can cause die backside
tool marks or microcracks that can eventually lead to die
cracking.
DMT 243 – Chapter 3
M.Nuzaihan
General Semiconductor Packaging Process Flow
Adhesive Die Attach
Another critical aspect of adhesive die attach is the ejection of
the die from the wafer tape during the pick-and-place system's
retrieval operation.
The use of inappropriate or worn-out ejector needle and
improper ejection parameter settings can cause die backside
tool marks or microcracks that can eventually lead to die
cracking.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Eutectic Die Attach
Assignment 2 Group B1
DMT 243 – Chapter 3
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Die Attach-related Failure Mechanisms
Die Lifting - detachment of the die from the die pad or cavity.
Common Causes: contamination on the die pad or cavity, die backside
contamination, excessive die attach voids, incomplete die attach coverage,
inadequate die attach curing.
Die Cracking - occurrence of fracture anywhere in the die.
Common Causes: in the context of Die Attach: excessive die attach voids, die
overhang or insufficient die attach coverage, insufficient bond line thickness,
excessive die ejection force on the wafer tape, absence of die attach voids
Adhesive Shorting - electrical shorting between exposed metal lines, bond pads,
bonds, or wires as a result of adhesive accidentally dripping on the surface of the
die (sometimes called 'epoxy on die').
Common Causes: incorrect die attach material viscosity, incorrect adhesive
dispensation
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die Attach-related Failure Mechanisms
Bond Lifting - lifting of the first or second bond from the die or leadfinger,
respectively. From the die attach process point of view, this is often due to resin
bleeding of the die attach material into the bond pads or leadfingers, inhibiting good
intermetallic formation. See also Wirebonding.
Die Scratching - inducement of any mechanical damage on the die, as when an
operator scratches a die with tweezers due to mishandling.
Common Causes: insufficient operator training, worn-out or contaminated pick-andplace tool, disorderly workplace, use of improper tools
Die Metallization Smearing - depression or deformation of any metal line on the
die surface.
Common Causes: dirty or worn-out die attach pick-and-place tool, wafer
mishandling
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die Attach-related Failure Mechanisms
Lateral crack on the failed units
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Die Attach-related Failure Mechanisms
Crack on die
Adhesive shorting
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Die Attach-related Failure Mechanisms
Scratches on die (optical)
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Scratches on die (SEM image)
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General Semiconductor Packaging Process Flow
Die Attach-related Failure Mechanisms
Die Lifting
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Wire Bonding
•
Wire bonding is the process of providing electrical connection between the
silicon chip and the external leads of the semiconductor device using very
fine bonding wires.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Wire Bonding
DMT 243 – Chapter 3
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Wire Bonding
DMT 243 – Chapter 3
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Terminologies - Wire Bonding
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Wire Bonder – Close up
camera
wire clamper
capillary
EFO
DMT 243 – Chapter 3
window opening
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General Semiconductor Packaging Process Flow
Wire Bonding
There are two main classes of wire bonding:
• Ball bonding
• Wedge bonding
Ball bonding usually is restricted to gold and copper wire and usually
requires heat.
Wedge bonding can use either gold or aluninium wire, with only the gold
wire requiring heat.
In either type of wire bonding, the wire is attached at both ends using some
combination of heat, pressure, and ultrasonic energy to make a weld.
Wire bonding is generally considered the most cost-effective and flexible
interconnect technology, and is used to assemble the vast majority of
semiconductor packages
DMT 243 – Chapter 3
M.Nuzaihan
General Semiconductor Packaging Process Flow
Wire Bonding
The wire used in wirebonding is usually made either of gold (Au) or
aluminum (Al), although Cu wires are starting to gain attention in the
semiconductor manufacturing industry.
Wire diameters start at 15 µm and can be up to several hundred
micrometres for high-powered applications
There are three types of wire bonding ( thermocompression, ultrasonic
and thermosonic ) which can be divided into two common wire bond
processes: ball bonding and wedge bonding.
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Wire Bonding
There are three basic wire bonding techniques:
•
Thermosonic bonding: utilizes temperature, ultrasonic and low
impact force, and ball/ wedge methods.
•
Ultrasonic bonding: utilizes ultrasonic and low impact force, and the
wedge/wedge method only.
•
Thermocompression bonding: utilizes high temperature and
high impact force, and the ball/wedge method. No ultrasonic is
used during bonding. Use in special application such as
bonding of GaAs devices
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Thermosonic bonding
Assignment 2 Group A2
DMT 243 – Chapter 3
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Ultrasonic bonding
Assignment 2 Group B2
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General Semiconductor Packaging Process Flow
Thermocompression bonding
Assignment 2 Group A3
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Ball/Wedge Connection
Side View Ball/Wedge
Connection
Top View Ball/Wedge
Connection
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General Semiconductor Packaging Process Flow
Wedge/Wedge Connection
Side View Wedge/Wedge
Connection
Side View Wedge/Wedge
Connection
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General Semiconductor Packaging Process Flow
Ball-Stitch Bond
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Wedge Bond
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General Semiconductor Packaging Process Flow
Wedge Bonding
DMT 243 – Chapter 3
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Wirebond - Important Parameters
Assignment 2 Group A1
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Wirebond – Advanteges of Ball/Wedge
and Wedge/wedge
Assignment 2 Group B1
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Wirebond-related Failure Mechanisms
Assignment 2 Group B3
DMT 243 – Chapter 3
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General Semiconductor Packaging Process Flow
Next:
Wafer Backgrinding, Die Preparation, Die
Attach, Wire Bonding, Die Overcoat, Molding,
Sealing, Marking, DTFS, Lead Finish,
Electrical Testing, Tape & Reel, Dry Packing,
Boxing and Labeling.
DMT 243 – Chapter 3
M.Nuzaihan