Thermosonic Flip-Chip – a solder-free interconnection technology requiring lower temperature and force, ideal for delicate materials and maximum precision.
Thermosonic Flip-Chip bonding is an advanced, solder-free technology for area-array interconnections. In this process, ICs with gold bumps are precisely connected to gold-plated pads on the substrate. The method is simple, clean, and dry—similar to thermo-compression bonding but with significantly lower bonding force and temperature thanks to the use of ultrasonic energy.
Originally known from wire bonding, the thermosonic process also offers major advantages for die-attach applications. While pure thermo-compression welding often requires temperatures above 300 °C—a risk for packaging materials, laminates, and sensitive chips—thermosonic bonding combines the benefits of thermo-compression and ultrasonic welding. This allows temperature and bond force to be greatly reduced, typically to 100–160 °C and 20–50 g per bump, enabling gentle, reliable, and highly precise connections for microelectronics.
The thermosonic process begins with the substrate placed on a heated stage and held in position by vacuum. The chip is held by the vacuum pick-up tool. After alignment using the beam-splitter optic (Figure 3), the chip with its Au bumps is brought into contact with the substrate. Once the required bond force is reached, an ultrasonic vibration is applied for a predetermined duration to complete the process.
The parallelism of the ultrasonic tool relative to the substrate is a critical parameter for achieving a good result. Misalignment can lead to uneven force distribution, resulting in a strong bond on side A but an insufficient bond on side B (Figure 4). Dr. Tresky’s True Vertical Technology™ ensures stable and precise parallelism throughout the entire Z travel (Figure 5). Combined with active force measurement, it delivers perfect results at every height (Figure 6).
Force, time, temperature, and ultrasonic power are critical parameters that significantly influence the bonding process and can be individually programmed on Dr. Tresky systems. In general, higher bonding force, increased temperature, stronger ultrasonic power (greater vibration amplitude), and longer vibration duration result in greater collapse of the bumps, leading to higher bond strength. At the same time, it is essential to carefully consider the risk of electrical short circuits between adjacent bumps and potential damage to the substrate.
