We usually see an IC or other components soldered directly to a PCB. However, sometimes it is necessary to use those components with another PCB. In such a case, there are not many solutions. PCB wire bonding is a solution that can be vital and beneficial in such situations. Although it is very beneficial, it is not that common.

So, here we will be elaborating on everything you need to know about this technique of using different components across different PCBs.

What is PCB wire bonding?

Many electronics use more than one PCB for their complete functionality. So, connecting those two PCBs is an important part of the whole manufacturing process. Printed Circuit Board Wire Bonding is the method where we use thin metallic wires and bond them to metal pads present in either of the PCBs.

Then those wires connect the two (inner and outer) PCBs. This way, connecting specific components of a PCB or connecting 2 whole PCBs becomes possible. One may think of designing a new PCB with space for all the components. However, there are several restrictions where this flexible way of connecting two PCBs is necessary.

Why do we still use the wire bonding technique today?

Wire bonding technology is a rather old technology for connecting 2 PCBs because newer technologies like flip-chip seem more beneficial these days. However, we still use wire bonding technology because it has specific benefits for devices where bandwidth is not an issue. It brings material cost, packaging cost, and several other benefits that we will discuss below.

Benefits of PCB Wire Bonding

PCB wire bonding technique brings many benefits to the manufacturing unit and the designers. Below are some amazing benefits of the PCB wire bonding technique.

• Allows testing

The first benefit of using PCB wire bonding is that it allows for testing. Testing things like BGA chips and other complete circuits is not easy. However, PCB bonding with wire makes two separate components work together. With the help of a proper schematic, you can note the signals going through the wires.

So, testing becomes possible and easy. If you convert that circuit into a single circuit with more complex IC chips, then testing may not be that simple and easy.

• Flexibility

Some applications of a PCB only need one straight chip. A common example is laptops and computers, where one PCB does the job. However, it is sometimes impossible to fit a whole straight PCB into the device. It is where the size is small or different PCBs connect with different sensors across the device.

In that case, PCB needs flexibility, and PCB Wire Bonding provides that flexibility. With the help of thin metal wires connecting the PCBs, you can achieve flexibility for devices with moving or folding parts.

• Very reliable method

Wire bonding PCBs is very reliable whether we consider complex circuits or simpler ones. The bonds need a specific force, and they only break under shear pressure. So, this type of bonding between 2 PCBs can be a reliable option for many different applications. It is a preferable choice for applications with chances of putting excessive pressure on PCB and joints between them.

• Repairability

Repairability is something that we are lacking with devices getting more powerful and compact. These days the best solution for a repair job is replacing the whole thing. Why? It is because repairing is not efficient in terms of time, effort, and cost savings. However, with wire bond PCB, the repairability options increase.

Individual thin wires help track the issue between 2 components or PCBs. Thus, it allows for better repairability options.

• Saves space

PCB wire bonding is famous for its space-saving benefits in different ways. Things start with simply dealing with complex circuits. So, wire bonding saves space that complex circuits will otherwise use. The flexibility benefit of this bonding technique provides space-saving for both packing time and deployment time.

So, the wire bonding technique for different PCBs allows you to save space in your product and when packing and installing the PCB.

• Budget-friendly

PCB wire bond technique is budget-friendly on so many levels. First of all, it saves prices by reducing the overall packaging cost. The wire bond technique between PCBs saves packing space. So, the cost of packing and shipping can be less than usual. Secondly, it is not unrepairable like other PCB types and components. Here you get the chance to track down the issue and repair the malfunctioning part.

Lastly, the overall production process cost can be significantly lower with the help of wire bonding. It is because you can use different materials for production according to the circuit’s requirements.

Different types of wire bonding

Various types of wire bonding are available that are differentiated based on the bonding method, the material used, and its shape. Here are a few you need to know.

• Different types of wire bonding according to the bonding method

3 main bonding methods differentiate the wire bonding technique. Below are the details about each one of them.

• Thermocompression

For the system to work, semiconductor chips are electrically connected with the other components. The bonding is heated at 200 to 300 Celsius, and then high pressure is applied to create the bond between the chip and surface.

• Ultrasonic

It is a type of bonding in which two metals that are supposed to be bonded are polished together, applying high energy, so the pollutants on the surface are removed, and molecules of metals are close enough to create a bond.

• Thermosonic

Silicon IC is electrically utilized in this bonding process. Ultrasonic power, heat and mechanical force are utilized to create a bond between gold or aluminum on a surface substrate and gold wire.

• Different types of wire bonding according to the material used

Wire bonding can be done with metal wires of different types. The most common ones are Gold, Copper, and Aluminum wires. Here is how each one of them is different.

• Gold

It is a type of bonding in which two nodes are connected with gold wire in a single assembly that ensures electrical conductivity. Mechanical force, heat and Ultrasonic power are utilized to create a connection.

• Copper

Copper wire bonding is similar to gold wore bonding, but the only difference is that we use Copper wire which is not restricted to the diameter, which can be between 15µm to 50µm. It is more beneficial than gold wire in heat and electric conductivity.

• Aluminum

The aluminum wire bonding requires a conductive connection, but no heat treatment is required. Only mechanical force and Ultrasonic power are enough to create the bond.

• Different types of wire bonding according to shape

Different shapes differentiate the wire bonding. It is usually about the shape of the pads and the bonding shape with those pads. Below are the 3 different types of bonding shapes.

• Ball

The bonding is similar to a cycle in which pads bond with silicon die and a lead frame or substrate that utilizes fine diameter wires. It involves three steps which are 1st bond shaping, 2nd bond shaping and wire loop.

• Wedge

A capillary tube works for squeezing a wire stub into the bond pad with the Ultrasonic energy that creates a bond within the wire and bond pad. The process is repeated to create a 2nd bond to ensure strength.

• Fine-pitch

A 35 µm pitch ball commonly combines with a 15 µm wire for bonding within the diameter of 27 µm. In this process, higher wire bonder aptitude is necessary for better control.

How to choose the right bonding type?

A confusing thing about selecting a wire bond type is selecting the one that will be right for your requirements. It is usually about the shape. So, considering physical requirements like temperature and size with no physical restrictions is important. In this way, the bond can be more durable and reliable according to application and usage.

How to remove the wire bond?

It is a rare thing for many because we hardly need to remove PCB wire bonding. However, whenever there is a need to remove the bond, the most common methods fail to work. People commonly try the soldering method for removing this bond which fails. So, the right way to remove this wire bond is by shearing. You can know the bond of the padding present on the PCB.

A pair of plastic tweezers can easily provide the necessary sideways shear force. You only need to put a little sideways pressure on the bond, and it will go away. Using the flat side of a scalpel blade may help remove this bond.

Conclusion

There are many applications in the world where the PCB wire bonding technique is still applicable. It is not only applicable, but it saves a lot of resources and costs. Here we discussed the amazing benefits it brings along with the different types of wire bonding we use today. Even though it is a pretty old technique and newer techniques bring major benefits, it is still the perfect choice for many PCBs.