TA.TEC Consulting
Ultrasonic-Drahtbonden
(Ultrasonic Wire Bonding)
Fundamentals, Bonding Technologies, Bonding Methods, Materials and Industrial Applications of Modern Wire Bonding
What Is Ultrasonic Wire Bonding?
Ultrasonic wire bonding is a solid-state interconnection process used for the electrical and mechanical connection of electronic components. During the bonding process, high-frequency ultrasonic vibrations are combined with a defined bond force and applied over a specified bond time to establish a permanent metallurgical bond between the bonding wire and the contact surface.
Unlike fusion welding processes, the joining partners are not melted during bond formation. The ultrasonic energy facilitates the removal of oxide layers and surface contaminants, promotes plastic deformation of the bonding materials, and increases the effective contact area. As a result, metallic microcontacts are formed, enabling atomic interactions and localized diffusion processes that contribute to the development of a durable metallurgical bond.
Owing to its reliability, cost-effectiveness, and suitability for automated manufacturing, wire bonding has become one of the most widely used interconnection technologies in microelectronics, power electronics, battery technology, and the automotive industry.
Benefits of Ultrasonic Wire Bonding
High process stability
Low electrical contact resistance
Minimal thermal stress on components
Excellent suitability for automated manufacturing
Modern wire bonding systems provide comprehensive process monitoring, full traceability, and high process repeatability.
Typical Applications
Microelectronics
Semiconductor packaging, integrated circuits (ICs), MEMS, sensors, RF modules, and optoelectronic devices.
Power Electronics
IGBT, MOSFET, and SiC power modules for inverters, battery chargers, DC/DC converters, and energy conversion systems.
Automotive Electronics
Traction inverters, onboard chargers (OBCs), battery management systems (BMS), cell-to-module interconnects, and battery modules.
High-Reliability Applications
Medical devices, aerospace and defense systems, radar technology, microwave systems, telecommunications infrastructure, and satellite applications.
How Can Wire Bonding Processes Be Classified?
Wire bonding encompasses a wide range of technologies, materials, and application areas. Terms such as ultrasonic wire bonding, thermosonic bonding, wedge-wedge bonding, ball-wedge bonding, fine wire bonding, and ribbon bonding describe different characteristics of a bonding process and should therefore not be used interchangeably.
A wire bonding process can be classified from several perspectives. The individual classifications complement one another and provide a clear technical description of a specific bonding process.
For a better understanding, wire bonding processes can be classified according to four fundamental characteristics:
Bonding technology
Bonding method
Wire geometry
Wire size category
These classifications complement each other and together provide a comprehensive description of a wire bonding process.
Overview of Wire Bonding Classification
Classification Level
Bonding Technology
Bonding Method
Wire Geometry
Wire Size Category
Material
Key Question
How is the metallurgical bond formed?
How is the bond geometrically created?
Which wire geometry is used?
Which wire cross-section is used?
Which wire or bonding material is used?
Examples
Thermocompression, Ultrasonic, or Thermosonic Wire Bonding
Wedge-Wedge Bonding or Ball-Wedge Bonding
Round Wire or Ribbon
Fine Wire, Fine Ribbon, Heavy Wire, or Heavy Ribbon
Aluminum, Copper, Gold, or Silver
Interaction of the Classification Categories
The individual classification categories are independent of one another and can be combined to describe a specific wire bonding process.
In practice, a wire bonding process is therefore defined by a combination of characteristics rather than by a single classification criterion.
Example: Microelectronics
Characteristics Classification
Bond Technology Thermosonic Wire Bonding
Bonding Method Ball-Wedge-Bonding
Drahtgeometrie Round Wire
Wire Size Category Fine-Wire
Material Gold
Typical Application
Semiconductor Packaging
Sensoric
RF-Modules
Mikroelektronics
Important Note on Wire Size Classification
The boundaries between Fine Wire, Heavy Wire, Fine Ribbon, and Heavy Ribbon are not internationally standardized. Classification may vary depending on the bonding process, material system, manufacturer, and specific application requirements.
Consequently, the size ranges commonly referenced in technical literature and industrial practice should be regarded as general engineering guidelines rather than fixed classification limits.
Bonding Technologies
The formation of a metallurgical bond during wire bonding can be achieved through different energy input mechanisms. In technical literature, wire bonding technologies are commonly classified according to the primary process energies used to create the bond.
Bond Technology Primary Energy Input
Thermocompression Bonding Heat + Bond Force
Ultrasonic Wire Bonding Ultrasonic Energy + Bond Force
Thermosonic Wire Bonding Heat + Ultrasonic Energy + Bond Force
Ultrasonic Wire Bonding
Ultrasonic wire bonding utilizes a combination of ultrasonic energy and bond force to establish a metallurgical bond between the bonding wire and the contact surface. The process is widely employed for aluminum, copper, and ribbon bonding applications and has become the dominant wire bonding technology in power electronics and automotive electronics.
Thermosonic Wire Bonding
In thermosonic wire bonding, ultrasonic energy is supplemented by an elevated process temperature. The applied temperature acts as activation energy, reducing the bond force and ultrasonic energy required to establish a reliable metallurgical bond. The process is predominantly used for fine wire applications in microelectronics and semiconductor packaging.
Thermocompression Bonding
In thermocompression bonding, bond formation is achieved exclusively through the application of heat and bond force. Unlike ultrasonic and thermosonic bonding processes, no ultrasonic energy is applied. As one of the foundational interconnection technologies in wire bonding, thermocompression bonding has played a significant role in the development of modern bonding processes and is today primarily employed in selected specialized applications.
Bonding Methods
Wedge-Wedge Wire Bonding
In wedge-wedge bonding, both the first bond and the second bond are formed using a wedge bonding tool.
The geometry of the bonding tool determines wire guidance, bond geometry, and energy transfer during the bonding process. The resulting interconnection consists of the bond foot, loop, and bond tail. Wedge-wedge bonding is suitable for fine wire, heavy wire, and ribbon bonding applications.
Internal Links:
Fine-Wire Wedges | Heavy-Wire Wedges
Ball-Wedge Wire Bonding
In ball-wedge bonding, a free air ball (FAB) is first generated using an electronic flame-off (EFO) process. The first bond is formed as a ball bond, while the second bond is created as a stitch bond. This bonding method is particularly well suited for fine-pitch applications and highly integrated semiconductor devices.
Internal Links:
iBOND5000ball | iBOND5000dual
Bonding Materials
Aluminum (Al):
The industry-standard material for numerous ultrasonic wedge bonding processes in power electronics applications.
Copper (Cu):
Offers high electrical and thermal conductivity, excellent mechanical strength, and cost advantages for high-volume manufacturing.
Gold (Au):
Provides excellent corrosion resistance, stable process performance, and remains the preferred material for thermosonic fine wire bonding applications.
Silver (Ag):
Features exceptionally high electrical conductivity and represents an attractive alternative for selected bonding applications.
Classification by Wire Geometry and Wire Size
In addition to the bonding material, bonding wires are commonly classified according to their geometry and cross-sectional dimensions. The selection influences current-carrying capability, electrical performance, bond pad design, packaging density, and overall bond process configuration.
In industrial practice, a distinction is commonly made between fine wire/fine ribbon applications and heavy wire/heavy ribbon applications.
However, the boundaries between these categories are not internationally standardized and may vary depending on the bonding process, material system, manufacturer, and application requirements. The size ranges presented below reflect typical industry practice and should be regarded as general guidelines rather than fixed classification limits.
Fine Wire (Round Wire)
Typical Wire Diameters:
Approx. 12.5 µm to 75 µm
Typical Materials:
Gold (Au)
Copper (Cu)
Silver (Ag)
Typical Applications:
Semiconductor Packaging
MEMS
RF Modules
Sensors
Optoelectronics
Fine Ribbon
Typical Ribbon Dimensions:
Widths typically ranging from approximately 25 µm to 300 µm
Thicknesses typically ranging from approximately 25 µm to 50 µm
Typical Materials:
Gold (Au)
Typical Applications:
Microwave Technology
High-Frequency Applications
RF Modules
Heavy Wire
(Round Wire)
Typical Wire Diameters:
Approx. 100 µm to 600 µm
Typical Materials:
Aluminum (Al)
Copper (Cu)
Typical Applications:
Power Electronics
Battery Technology
SiC Power Modules
Heavy Ribbon
Typical Ribbon Dimensions:
Widths from approximately 0.3 mm to several millimeters
Thicknesses from approximately 50 µm to more than 300 µm
Typical Materials:
Aluminum (Al)
Copper (Cu)
Typical Applications:
Power Electronics
EV Battery Systems
High-Current Interconnects
Key Process Parameters
The ultrasonic wire bonding process is primarily governed by the interaction of bond force, ultrasonic power, bond time, process temperature, and bonding tool geometry.
These parameters determine the frictional energy at the bonding interface and, consequently, the formation of the metallurgical bond between the bonding wire and the bond pad. Optimal process parameter selection depends on factors such as the bonding technology, wire material and diameter, bond pad metallization, as well as the requirements for process capability, reliability, and product lifetime.
Internal Links:
Common Failure Modes
Failure modes in ultrasonic wire bonding are often caused by inappropriate process parameters, material incompatibilities, or surface contamination.
Typical bond defects include Non-Stick-On-Pad (NSOP), Lift-Off, Heel Crack, Wire Break, Cratering, Wire Nick, and Overbonding.
These defects can compromise the mechanical strength and electrical integrity of the bond connection and may negatively impact the long-term reliability of electronic assemblies.
Systematic process monitoring and failure analysis are therefore essential for ensuring stable, robust, and reproducible bonding processes.
Internal Links: