Click here to go to our page on chip-and-wire construction
Click here to learn about wirebond inductance, resistance and attenuation
Click here to learn about RF wirebonds
Click here to learn about wirebond compensation
Click here to learn about "V-bonds"
Bond, Wire Bond...
First, let's try to clear something up... which spelling is correct, "wirebond" or "wire-bond"? The answer... who cares? just pick one and stick with it when you write an article or report. If anyone has a better answer, let us know! For now we will stick with "wirebond".
History of wirebonding
The wirebonding industry grew out of the early days of the semiconductor industry. How do you attach a tiny wire to one of those new-fangled germanium transistors? Inventors Fred Kulicke and Al Soffa were the team that worked out the details at their small company that they formed in 1951. In 1956 Western Electric placed an order for K and S equipment, and the wirebond industry was off and running. Today's wirebonders are amazing examples of automation, with vision systems that allow bonds to be precisely placed 20 or more times per second, with controlled lengths and loop heights. Albert Soffa died in 2005 at the age of 84.
Wirebond materials
Wirebonds are almost always made using gold wire in microwave applications, although aluminum or copper wirebonds are also possible. Most silicon RFICs use aluminum top metal, and therefore are wirebonded with aluminum. Here's an article on Microwave Journal that will educate you on this topic.
Types of wirebonds
Ball bonding
Ballbonders are the most prevalent in the industry. A ball bonder feeds wire through a capillary, where the tip is heated enough to melt the wire. The molten wire forms a "ball" due to surface tension. The bonder sticks the ball onto the part (device or substrate) where it solidifies, then the capillary is lifted, pulling out more wire. The second bond is created when the capillary touches down on the second part to be connected, where it is joined though a combination of hear and thermosonic energy; this is called a wedge bond. The bonder tip then lifts and the wire is automatically melted off to form a new ball for the next bond.
Wedge bonding
Here's a short video on the difference between ball and wedge bonding.
Wirebond inductance and RF resistance
Now on a separate page!
Compensating for wirebonds
The inductance of wirebonds can generally be ignored up until you get to X-band or so. Then you have two choices... pull the wires tighter to reduce the inductance, or use established loop heights and wire lengths and compensate. The trick here is to add just a smidgen of shunt capacitance.
Click here to learn more about wirebond compensation.