Wire Bonding PCB Components – A Comprehensive Guide

Wire bonding PCB components like chips is the most prevalent connection method today. Various reasons explain why, as you will learn below. The topics we will cover include defining the technology and its types. We will also explain the process and discuss its testing and applications.

What is Wire Bonding in PCB?

It means using micro-welds and fine wires to connect chip contacts to their carriers or PCB substrates. Sometimes, manufacturers use the technology for PCB-to-PCB connections.

The wire diameter can be as small as 10 microns or as large as a few hundred micrometers wide. It mainly depends on the application, with high-power circuits requiring thicker wires.  

The wires create low-resistance paths that allow signal exchange and transmission. The connections also help transfer and dissipate heat, allowing packages to run cooler.

Wire bonding is inexpensive, which partly explains its widespread use. It accounts for over 70% of the chip and other micro-connections in today’s PCB and semiconductor industries.

Types of PCB Bond Wires

Wire bonds for PCB applications can be of various types, such as balls, wedges, and ribbons. Here’s more about them, including their structure and other attributes or features.

Ball Bonds

The wires melt into a spherical ball at either end. Ball bonding uses heat and ultrasonic energy, forming sturdy, dependable connections. They also suit fine-pitch connections.

Wedge Bonds

These involve creating wedge shapes between the bonding wire and pad. Wedge bonding suits larger-sized connections, unlike ball types. The technique is best for power circuits, owing to their size and excellent stability.

Ribbon Bond

These are thin, flat wires. They replace round types, allowing higher-density connections and other benefits, such as reduced parasitic capacitance in higher-frequency applications.

PCB Wire Bonding Materials

PCB makers use various materials for the process. Each material has specific characteristics that make it suit some uses. The material options include gold, silver, copper, and aluminum.

Gold Wires – gold offers better corrosion resistance and has good conductivity. It creates good bonds, making it a dependable choice despite its higher costs.

Silver Wires – silver has good electrical and thermal conductivity. On the downside, it produces less reliable bonds.  

Copper Wires – Cu has a higher electrical conductivity, making smaller diameters possible without sacrificing performance. However, it’s prone to oxidation and challenging to use.

Aluminum Wires – the AL is either pure or alloyed types. Alloyed aluminum offers better characteristics, such as higher strength. The increased strength means you can stretch the wires to finer sizes.

What is the Process of Wire Bonding in PCB Electronics?

The process’s equipment includes the bonding tool, work holder, and automated vision devices. Others are ultrasonic sources and controls. The process uses the following steps:

• Cleaning the package to rid it of contaminants.
• Applying a thin adhesive layer for package attachment
• Placing and aligning the chip with the bonding pads
• Positioning the bonding wires
• Bonding the connections using balls or wedges
• Cutting the connections to achieve the required length
• Encapsulating the package as needed

Optimizing the wire bonding process produces better results. The engineer must correctly design the die pads. They must also properly size the connection materials.

PCB Wire Bonding Techniques

The PCB manufacturer uses one of these methods to make the wire connections: thermo-sonic, ultrasonic, and thermo-compression bonding. Let’s see how each works, including their benefits and downsides.  

Thermo-sonic Bonding

This method uses low mechanical force and moderate heat to attach the wires to the pads. The heat range is typically 100-150 degrees Celsius. It also mainly suits gold wires.

Ultrasonic Bonding

The ultrasonic method relies on mechanical force and ultrasonic energy to create the bonds. The pressure and temperatures are relatively low, with the heat reaching approximately 25 degrees Celsius.  It typically works with Au and Al wires.

Thermo-compression Bonding

This technique only uses heat and pressure to weld the wire ends. It requires no ultrasonic energy but requires more pressure than other methods. The heat ranges from 300-500 degrees Celsius. It mainly works with Au wires.

Wire Bonding PCB Quality Control and Inspections

Bonding wires are susceptible to defects. Quality control measures, including inspections, help to catch these flaws. The following are measures manufacturers employ to ensure perfect connections.

Quality Inspections

Inspections include checking the wires for sagging, stretches, and sweep or lateral movement. The methods include visual inspection, automated optics, and X-ray imaging for hidden defects. Inspections check the following.

• Bond quality and placement by examining their positions and orientation
• Wire quality by checking their height, shape, and position

Control Tests  

The engineer ensures critical connection parameters during the process. They include setting correct values for the bonding pressure and process duration. It also includes conducting the pull and shear tests.

• The pull test measures the force required to break the wire free from the bond.
• The shear test determines the bonding strength by measuring the force to tear the connection from the pad. It provides better results when testing ball bonds than the pull test.

Wire Bonding PCB Benefits and Limitations

Like other chip technologies, using fine wires to make connections has good and bad sides. These determine its application suitability, depending on the specific device. Let’s start with the benefits.

Benefits

• Cost-Effective – the technology is relatively inexpensive, reducing PCB costs without affecting reliability.
• Versatile – manufacturers can use it in many applications as it supports different chip sizes and connection needs.
• Turnaround Times – the technique offers increased manufacturability, enabling PCB makers to reduce assembly times.
• Flexibility – wires allow changes, including reworks, making the connection method more flexible.

Limitations

• Chip Size Limits – it mainly works with larger chips as it requires bond pads
• Longer Interconnects –  it produces longer connections that can reduce electrical performance
• Reduced I/O Density –  it supports fewer connections compared to other methods, reducing high-density capabilities

Wire Bonding PCB Applications

Wire-bonded PCB boards are cost-effective options. The technology also creates robust electrical connections.  These attributes make wired connections common in these applications.

Integrated Circuits, ICs – many integrated chips attach to their packages using wires. These connections allow them to communicate with external circuits, making them usable in various industries.

Optoelectronics – these are PCBs combining electrical and optical circuits, such as lasers. They use the technique for signal transmission and device attachment, allowing micro-connections.

Memory Components – some memory chips use the technology for their electrical inputs and outputs. It reduces costs and allows design flexibility.

Chip-on-Board LEDs – COB devices benefit from technology by enabling compact LEDs with better electrical transmission and heat dissipation properties.

Sensor Technology – sensors connect to their application circuits using various technologies, including wires. These can be pressure, temperature, and other sensing devices.

Power Electronics – power semiconductor devices, such as MOSFETS, use wires to create electrical connections. These have uses in automotive, renewable energy, and similar systems where voltage and current levels are high.  

Conclusion

Wire bonding is a popular chip and PCB technology. It offers flexibility and reduces board production costs, among other benefits like faster fabrication. Venture provides unique wire bonding solutions for your product or other projects. Get in touch today for more, including technical advice and costing.