Ultrasonic / thermosonic bonding is a process used primarily for flip chip bonding to generate a mechanically and electrically stable connection.
In contrast to thermocompression bonding, ultrasonic / thermosonic bonding is a friction welding process where the component's bumps are slightly pressed on the corresponding pads and moved lateral to the working plane. Heat is generated exactly where it is needed, namely in the contact plane between bumps and pads. Consequently, there is lower thermal stress to component and substrate, so ultrasonic / thermosonic bonding is the process of choice in cases of thermally sensitive materials. Moreover, bonding force can be much lower compared to thermocompression bonding, resulting in less mechanical stress to substrate and component which is advantageous if materials are susceptible to deformation or cracking.
What are the Challenges?
Ultrasonic / Thermosonic bonding is a critical process with many influencing factors:
- If bonding causes high demand on the clamping devices for component and substrate. While the substrate will stay in place during the bonding process (without the slightest movement against its support), the component must follow the vibration of the die collet as close as possible. Therefore, advanced substrate clamping and customized tool design is necessary.
- Bottom heat and ultrasonic burst have to be applied in a synchronized manner and the burst time must be adjusted thoroughly: too short times lead to abortive joining whereas extensive bursts may cause "unbuttoning" on the substrate's contact layer.
- To get sufficient output power at the bonding joint, the oscillating system "ultrasonic transducer - die collet - component" has to be kept at resonance frequency all the time, independent from the die's mass and the contact's friction coefficient. To achieve this, the ultrasonic generator must use electronic circuits to compensate various degrees of damping.
- To bond the thinnest and most brittle materials, as well as large components with lots of bumps, the parameters burst time, power, temperature and force must be widely adjustable with finest resolution and kept stable even under changing environmental conditions.
The Finetech Solution
Principle of Thermosonic Bonding
To create a thermosonic joint, the substrate is first heated to temperatures between 100°C and 150°C. Then the component held by the die collet is pressed slightly on the substrate's target area. After that, a defined ultrasonic burst is triggered. The joint builds up by friction welding and can be burdened immediately.
- Process time: 0.1 s … 0.5 s
- Bottom Heating temperature: 100°C … 150ºC
- Bonding force: 0.03 N/bump … 0.7 N/bump
- Ultrasonic power: up to 20 W
FINEPLACER® Bonding Systems
Due to the modular design approach, FINEPLACER® bonding systems can be configured for virtually any application challenge.
The main distinguishing features between the machines are the
- degree of automation
- optical resolution and
- placement accuracy
Browse our product range or get in contact with your sales contact to figure out the best equipment solution for your specific application requirements.