Flip chip bonding is a cutting-edge semiconductor packaging technology that offers numerous benefits for electronic devices. It involves directly bonding an unpackaged integrated circuit (IC) chip onto a substrate or another chip, enabling optimal electrical connections between them.
Semiconductor packaging technology
Those who are engaged in the semiconductor industry, especially the semiconductor packaging industry, always meet several packaging processes, that is, chip bonding, wire bonding, and flip-chip connection technologies.
In particular, wire bonding and flip chip bonding are the most common, because the tape carrier bonding technology (TAB) has certain limitations, and this technology is gradually eliminated in packaging.
Flip-chip technology is to directly interconnect the components downward to the substrate, carrier or circuit board through the bumps on the chip. The connection method of wire bonding is to connect the chip to the circuit board through a wire (usually a gold wire) with the front side of the chip facing up.
Wire bonding, tape connection, and flip chip bonding each have their own characteristics. Among them, flip chip bonding is more and more widely used in the packaging industry due to its compact structure and high reliability.
What is flip chip technology?
Flip-chip technology originated from IBM, which developed a flip-chip welding process for making bumps on chips in 1960. Electroplated NiAu bumps are surrounded by 95Pb5Sn bumps. Later, PbSn bumps were made, using Controlled collapse Component Connection (C4 technology for short), which was originally a highly reliable packaging technology developed for its own mainframe computer. The C4 chip has excellent electrical and thermal properties, and the fatigue life of the package is at least 10 times higher.
Since IBM developed and successfully applied C4 technology, in the subsequent technological development, some semiconductor companies have optimized and upgraded C4 technology, including the AI bump developed by Fairchild and Au bump technology developed by Amelco.
Semiconductor packaging technology has also developed from QFP (Quad Flat Package) packaging process to BGA (Ball Grid Array ball grid array) packaging, to the latest CSP (ChipScale Package wafer level) packaging.
With the gradual reduction of the volume of semiconductor chips, the requirements for chip packaging technology are getting higher and higher, and the packaging technology is developing towards wafer and packaging.
With the mature application of flip-chip technology, the annual consumption of flip-chip in the world exceeds 600,000 pieces, and it is growing at a rate of about 50%. 3% of wafer packaging is used for flip-chip bump technology. It is expected to exceed 20% in the future.
Flip-chip components are mainly used in semiconductor equipment. Some components, such as passive filters, detection antennas, and memory equipment, have also begun to use flip-chip technology, because the chip is directly connected to the substrate and the carrier through bumps. Therefore, to be more precise, flip chip is also called DCA (Direct Chip Attach) .
Advantages and disadvantages of flip chip technology
(1) Advantages of flip-chip connection technology
(a) Small size: Small IC pin pattern (only 5% of the flat package) reduces height and weight.
(b) Function enhancement: The number of I/Os can be increased by using flip chip bonding. I/Os are not limited in number like wire bonds are located around the chip. Area arrays can interconnect more signals, power, and electric drive Benchrnarker power supplies in a smaller space. A typical flip chip pad can have up to 400 pads.
(c) Increased performance: Short interconnect distances reduce inductance, resistance, and capacitance, ensuring reduced signal delay, better high frequency, and better thermal access from the backside of the die.
(d) Improved reliability: Epoxy filling of large chips ensures high reliability. Flip-chip reduces the interconnect pin count by two-thirds.
(e) Improved heat dissipation: the flip chip has no plastic packaging, and the back of the chip can be effectively cooled.
(f) Low cost: Bulk bumps reduce costs.
(2) Disadvantages of flip-chip connection technology
(a) Bare chips are difficult to test.
(b) Limited adaptability of bump chips.
(c) PCB technology is facing challenges as the pitch decreases and the number of pins increases (d) X-ray inspection equipment must be used to detect invisible solder joints.
(d) Poor compatibility with the SMT process.
(e) It is difficult to operate and hold the bare wafer.
(f) High assembly precision is required.
(g) Current use of underfill requires a certain cure time.
(h) Some substrates are less reliable.
(i) Difficult or impossible to repair.
Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting dies such as semiconductor devices, IC chips, integrated passive devices and microelectromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads.
For adhesive flip chip interconnection systems, nonoxidizing gold is widely used as bump material and combined with, e.g., a titanium–tungsten UBM. Thereby, the gold bump is either electroplated or provided by a ball wire bonder in the form of a so-called stud bump (i.e., a ball bond with short wire tail).
Since wire bonding connects the chip and the substrate with a wire, the active surface of the chip was the upper surface. On the other hand, in flip-chip bonding, the active surface faces downward and is mounted facing the board surface.
