In the development of packaging of electronics the aim is to lower cost, increase the packaging density, and improve the performance while still maintaining or even improving the reliability of the circuits. Flip chip microelectronic assembly is the direct electrical connection of face-down electronic components onto substrates, circuit boards, or carriers, by means of conductive bumps on the chip bond pads. Flip chip is also called Direct Chip Attach (DCA), since the chip is directly attached to the substrate, board, or carrier by the conductive bumps. Flip chip has advantage in size, performance, flexibility, reliability, and cost over other packaging methods. There are three stages in making flip chip assemblies: bumping the die or wafer, attaching the bumped die to the board or substrate, and, in most cases, filling the remaining space under the die with an electrically non-conductive material. Several varieties of flip chip assembly are solder bump, plated bump, gold stud bump, and adhesive bump suit flip chip which are used in a wide range of applications. Applications of flip chip include low to high-end workstations, routers, switches, components in graphics, DSP processors and ASIC devices.

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FLIP CHIP
 method for interconnecting semiconductor devices
 Controlled Collapse Chip Connection, C4 .
 IBM introduced flip chip interconnection
HISTORY
 Introduced commercially by IBM in the 1960s.
 DEC followed IBM's lead,but failed.
 In the 1970s it was taken up by Delco Electronics, and has since become very common in automotive applications.
FLIP CHIP PROCESS
1. Integrated circuits are created on the wafer.
2. Pads are metalized on the surface of the chips.
3. Solder dots are deposited on each of the pads.
4. Chips are cut.
5. Chips are flipped and positioned so that the solder balls are facing the connectors on the external circuitry.
6. Solder balls are then remelted (typically using hot air flow).
7. Mounted chip is “underfilled” using an electrically insulating adhesive
Need for BUMPING
 It is very difficult to directly attach to thin aluminum or copper IC pads.
 To provide a standoff that can produce a controlled gap between the chip and the substrate.
 To provide a good electrical connection.
 A thermally conductive path to carry heat from the chip to the substrate.
 Provides a spacer, preventing electrical contact between the chip and substrate conductors
FLIP CHIP JOINING
1.By Thermocompression
i. bonded to the pads on the substrate by force and heat applied from an end effectors'.
ii. requires gold bumps on the chip or the substrate and a corresponding bondable surface
iii. the process is limited to rigid substrates such as alumina or silicon.
iv. the substrates must have a high planarity
2.By Thermosonic
i. using ultrasonic power.
ii. benefit of the method compared to thermo compression is lower bonding temperature and shorter processing time
iii. One potential problem associated with thermo sonic bonding is silicon cratering; such damage are due to excessive ultrasonic vibration

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Abstract
he intense competition in the electronics industry generally serves to drive down the size and cost of electronic products while improving their performance, flexibility, and reliability. As a part of this effort, packaging methods are constantly being improved and new, innovative methods are being developed. One area of focus is highly integrated chip-level electronics assembly, using multiple unpackaged dies and electrical components in a single package. One of the most popular methods is known as flip chip assembly.
Advancements in the packaging of semiconductor devices traditionally use wire bonds to provide the interconnection from device to substrate or to other active devices. Flip chip offers advantages over traditional interconnect schemes. A smaller overall footprint can be realized, better thermal heat transfer, and improved performance especially at higher frequencies are all enabled through the use of flip chip technology.
The assembly process has proliferated in many applications, including automotive electronics, smart cards, radio frequency identification (RFID) cards etc………………………!
Introduction
In the development of packaging of electronics the aim is to lower cost, increase the packaging density, improve the performance while still maintaining or even improving the reliability of the circuits. The concept of flip-chip process where the semiconductor chip is assembled face down onto circuit board is ideal for size considerations, because there is no extra area needed for contacting on the sides of the component. The performance in high frequency applications is superior to other interconnection methods, because the length of the connection path is minimized. Also reliability is better than with packaged components due to decreased number of connections. In flip-chip joining there is only one level of connections between the chip and the circuit board. Potentially flip chip technology is cheaper than wire bonding because bonding of all connections takes place simultaneously whereas with wire bonding one bond is made at a time. In practice, however, this price benefit is not always achieved due to immature processes, e.g. the cost of die bumping with current processes can be significant, especially in low volumes. Flip-chip joining is not a new technology. The technology has been driven by IBM for mainframe computer applications. Many millions of flip chips have been processed by IBM on ceramic substrates since the end of 60`s. At the beginning of 70`s the automotive industry also began to use flip chips on ceramics. The number of flip chips assembled was over 500 million in year 1995 and close to 600 million flip chips were consumed 1997. Over the past ten years major advancements have been made in flip chip development in the commercial silicon industry and in many cases the manufacturing infrastructure has been put in place and is being exploited. DELCO was a pioneer in silicon flip chip in the eighties. Today flip chips are widely used for watches, mobile phones, portable communicators, disk drives, hearing aids, LCD displays, automotive engine controllers as well as the main frame computers.
FLIP CHIP
Flip chip microelectronic assembly is the direct electrical connection of face-down (hence, "flipped") electronic components onto substrates, circuit boards, or carriers, by means of conductive bumps on the chip bond pads. In contrast, wire bonding, the older technology which flip chip is replacing, uses face-up chips with a wire connection to each pad.
Flip chip components are predominantly semiconductor devices; however, components such as passive filters, detector arrays, and MEMs devices are also beginning to be used in flip chip form. Flip chip is also called Direct Chip Attach (DCA), a more descriptive term, since the chip is directly attached to the substrate, board, or carrier by the conductive bumps.
IBM introduced flip chip interconnection in the early sixties for their mainframe computers, and has continued to use flip chip since then. Delco Electronics developed flip chip for automotive applications in the seventies. Delphi Delco currently places over 300,000 flip chip die per day into automotive electronics. Most electronic watches and a growing percentage of cellular phones, pagers, and high speed microprocessors are assembled with flip chip.
Worldwide flip chip consumption is over 600,000 units per year, with a projected annual growth rate of nearly 50% per year. Semiconductor manufacturers currently bump for flip chip assembly about 3% of wafers produced, and are expected to be bumping 10% within a few years.
Flip chip, also known as Controlled Collapse Chip Connection or its acronym, C4, is a method for interconnecting semiconductor devices, such as IC chips and Micro electromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads. The solder bumps are deposited on the chip pads on the top side of the wafer during the final wafer processing step. In order to mount the chip to external circuitry (e.g., a circuit board or another chip or wafer), it is flipped over so that its top side faces down, and aligned so that its pads align with matching pads on the external circuit, and then the solder is flowed to complete the interconnect. This is in contrast to wire bonding, in which the chip is mounted upright and wires are used to interconnect the chip pads to external circuitry.
Reasons for USE of FLIP CHIP.
The boom in flip chip packaging results both from flip chip's advantages in size, performance, flexibility, reliability, and cost over other packaging methods and from the widening availability of flip chip materials, equipment, and services.
 Smallest Size
Eliminating packages and bond wires reduces the required board area by up to 95%, and requires far less height. Weight can be less than 5% of packaged device weight. Flip chip is the simplest minimal package, smaller than Chip Scale Packages (CSP’s) because it is chip size.
 Highest Performance
Flip chip offers the highest speed electrical performance of any assembly method. Eliminating bond wires reduces the delaying inductance and capacitance of the connection by a factor of 10, and shortens the path by a factor of 25 to 100. The result is high speed off-chip interconnection.
 Greatest I/O Flexibility
Flip chip gives the greatest input/output connection flexibility. Wire bond connections are limited to the perimeter of the die, driving die sizes up as the number of connections increases. Flipchip connections can use the whole area of the die,accommodating many more connections on a smaller die. Area connections also allow 3-D stacking of die and other components.
 Most Rugged
Flip chip is mechanically the most rugged interconnection method. Flip chips, when completed with an adhesive "underfill," are solid little blocks of cured epoxy. They have survived the laboratory equivalents of rocket liftoff and of artillery firing, as well as millions of cumulative total hours of actual use in computers and under automobile hoods.
 Lowest Cost
Flip chip can be the lowest cost interconnection for high volume automated production, with costs below $0.01 per connection. This explains flip chip’s longevity in the cost-conscious automotive world, pervasiveness in low cost consumer watches, and growing popularity in smart cards, RF-ID cards, cellular telephones, and other cost-dominated applications.
HISTORY
The process was originally introduced commercially by IBM in the 1960s for ICs being used in the mainframe systems. DEC followed IBM's lead, but was unable to achieve the quality they demanded, and eventually gave up on the concept. It was pursued once again in the mid-90s for the Alpha product line, but then abandoned due to the fragmentation of the company and subsequent sale to Compaq. In the 1970s it was taken up by Delco Electronics, and has since become very common in automotive applications.
In the development of packaging of electronics the aim is to lower cost, increase the packaging density, improve the performance while still maintaining or even improving the reliability of the circuits. The concept of flip-chip process where the semiconductor chip is assembled face down onto circuit board is ideal for size considerations, because there is no extra area needed for contacting on the sides of the component. The performance in high frequency applications is superior to other interconnection methods, because the length of the connection path is minimised. Also reliability is better than with packaged components due to decreased number of connections. In flip-chip joining there is only one level of connections between the chip and the circuit board. Potentially flip chip technology is cheaper than wire bonding because bonding of all connections takes place simultaneously whereas with wire bonding one bond is made at a time. In practice, however, this price benefit is not always achieved due to immature processes, e.g. the cost of die bumping with current processes can be significant, especially in low volumes. Flip-chip joining is not a new technology. The technology has been driven by IBM for mainframe computer applications. Many millions of flip chips have been processed by IBM on ceramic substrates since the end of 60`s. At the beginning of 70`s the automotive industry also began to use flip chips on ceramics. Today flipchips are widely used for watches, mobile phones, portable communicators, disk drives, hearing aids, LCD displays, automotive engine controllers as well as the main frame computers. The number of flip chips assembled was over 500 million in year 1995 and close to 600 million flip chips were consumed 1997

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Flip Chip Technology
Introduction
Advancements in the packaging of semiconductor devices  traditionally use wire bonds to provide the interconnect from device to substrate or to other devices
Along with the rapid advances in microwave and millimeter wave subsystem development
 a growing interest concerning chip interconnection techniques has developed.
The importance of quality of these interconnects
 a large impact on the performance of the entire subsystem, especially at high frequencies.
Flip chip offers advantages over traditional interconnect schemes.
 A smaller overall footprints, better thermal heat transfer
Wire Bonding
Flip Chip Interconnection
Flip Chip Interconnection
Flip Chip Interconnection
Proximity Effect in Flip-Chip Structure
Why Flip Chip Technology?
Comparison
Stud Bump Bonding Technology
Micro Bump Bonding Technology
Conclusion
The need for smaller packaging
Flip chip interconnect process → more compact fashion
Improved electrical performance
Reduced interconnect length → lower inductance and reduced signal loss → lower power requirements
The demands of high frequency applications
Limitation of the wire interconnect → flip-chip bump connection