2.1 Flip-Chip Mechanism
Flip Chip technology (shown as Figuare.2.1) is a connection between the chip and substrate of the packaging technology. In the process of packaging, the chip will be flip over to connect the pads above the chip and the substrate. As the cost and process factors, the flip chip bonding product usually are divided into two forms, one is the low I / O number of FCOB (Flip Chip on Board, flip chip assembly) and the other is the high I / O number of FCIP (Flip Chip in Package, flip chip packaging).
Flip Chip Technology makes use of the substrates including ceramics, silicon, polymer laminates, and glass. Its applications include high-level computers, PCMCIA cards, military equipment, personal communications products, and liquid crystal displays. Using Flip Chip technology has two benefits:
1.Can reduce the chip and substrate of electronic signal transmission distance, high-speed devices for packaging.
2. Can be reduced the chip size package, making the chip package about the size is same after the bonding.
Traditional flip chip machine is using the pneumatic cylinder to drive the vacuum suction plant to move upward by the feedback control.
But the feedback control is limited by the stick slip effect of the pneumatic cylinder. So it is difficult to obtain exact force accuracy. And the traditional flip chip machine positioning mechanism on the x- axle, y-
axle, and rotational are complex, and the transmission chain exists the backlash in the position feedback control, it is difficult to precisely control because the nonlinear elements.
Stick-slip effect (shown as Figuare.2.2) is caused by the surfaces alternating between sticking to each other and sliding over each other, with a corresponding change in the force of friction. Typically, the static friction coefficient between two surfaces is larger than the kinetic friction coefficient. If an applied force is large enough to overcome the static friction, then the reduction of the friction to the kinetic friction can cause a sudden jump in the velocity of the movement.
2.2 The Improve Flip-Chip Mechanism
The improve flip-chip mechanism (shown as Figuare.2.3) include three parts：Micro-stepping mechanism、Self-Aligned mechanism and Force Positioning mechanism. These three mechanisms are synthesized by many of the sensors and the actuators. The following is the structure of the whole flip chip machine：
(1) IP camera：Having the CS Mount lens can be replaced, remote monitoring, as long as you can browse the web, or send images via
Email or FTP. The image Specification as follows：
Compression format: MPEG4/MJEPC Video format: AVI
Number of shots: 30fps
Image resolution: 320 x 240
(2) IDM：Precise positioning for flip chip mechanism
(3) Electromagnet: Control the size of the load bearing between the suction of the carrying platform through the electromagnet and the magnet.
(4) SmartMotor：This servo SmartMotor represented for the Sensitive Stone company, as shown in Figure 2.4. The communication between servomoter and computer take RS232 9600 bps, no parity, 8 bytes, 1 stopbit
(5) Power Supply：It is an programmable Power Supply PR9000. It offers the RS232 interface to use the computer to control it. As long as input the instructions specified via the rs232, we can control by the computer. The communication between Power Supply and computer take RS232 9600 bps, no parity, 8 bytes, 1 stopbit.
(6) Solenoid valve：Be the switch of the air pump and the suction machines
(7) Relay：R1-00, as shown in Figure 2.5, Coil Voltage 5V, can control the solenoid valve’s state.
(8) Force sensor：Measure the strength of the value of platform.
(9) Heater：Use to heat the chip.
(10) Computer: The control center
(11) Leader-5017：It is an ethernet-based 8-CH isolated analog input module. The specification as follow：
Channels: 8, differential
(12) PCI8516: As shown in Figure 2.6 has the analog output and the digital I/O.
The mechanism is a modified impact drive mechanism (IDM) [2]
which belongs to the stick slip device of pulse type. The general operating principle of IDM receives the asymmetric voltage triangle waveform. The PZT actuator is connected between slider and counter-mass of IDM and then the IDM causes a series of stick-slip motion powered by PZT actuator on the guide way. Three PZT actuators on a circular plate will compose a planar, as shown in Figure 2.7. We
change the duty-ratio and frequency of the triangle wave in the three IDM to let the circular plate move or rotate.
2.2.2 Self-Aligned Mechanism
The Self-Aligned Mechanism [3], as shown in Figure 2.8, constitute by the gas bearings, springs and pneumatic cylinders. It minimizes the friction by air pressure. It is easy to adjust the upper and lower substrate to match each other, so that the upper and lower substrate is coplanar. It can prevent the non-coplanar problems when the flip chip bonding. There are the solenoid valves to control the switch of the air pump and the aspirator. Let the air pump and the aspirator alternate open to make the upper and lower substrate is coplanar.
2.2.3 Force Control Mechanism
The flip-chip machine is designed the Z-axis localization and the force control organization. Using the SmartMotor actuates the lead screw to do the platform moving in the first stage. The second stage use electromagnet and spring to slowly rise the platform to the position of the pressure, then recombines load cell which display the pressure value, makes the force feed back to control magnetic force size of the electromagnet to reach the expected force resolution. The localization and the force control organization contain the lead screw, the step motor, the compression spring, the load cell, the electromagnet. In the second stage, the main linkage strength is depended on the electromagnet current to decide. The force control mechanism as shown in Figure 2.9.