A New Technique for Wirebonding Using Indium Spheres 

by Kimberley A. Olver 

ARL-TR-5240 July 2010 

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Army Research Laboratory 

Adelphi, MD 20783-1197 

ARL-TR-5240 July 2010 

A New Technique for Wirebonding Using Indium Spheres 

Kimberley A. Olver 

Sensors and Electron Devices Directorate, ARL 

Approved for public release; distribution unlimited. 
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July 2010 

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A New Technique for Wirebonding Using Indium Spheres 

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6. AUTHOR(S) 

Kimberley A. Olver 

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U.S. Army Research Laboratory 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

A new technique has been developed for wirebonding mercury cadmium telluride (MCT) devices using indium spheres. 

Indium powder with a mesh size of 170/200 is made up of indium spheres. These spheres are used as solder between the gold 

pad on the MCT device and the gold ball of the wirebond. This novel technique eliminates damage that typically occurs to the 

MCT material under gold wirebonding pads due to force and ultrasonic power needed in wirebonding. 

15. SUBJECT TERMS

Wirebonding indium, Mercury Cadmium Telluride, MCT 

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14 

19a. NAME OF RESPONSIBLE PERSON 

Kimberley A. Olver 

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iii 

Contents 

List of Figures iv

Acknowledgments v

1. Introduction 1

2. Procedure and Results 2

4. Conclusion 4

5. References 5

Distribution List 6 
iv 

List of Figures 

Figure 1. Indium spheres placed on the device package. ................................................................1

Figure 2. A scanning electron microscope (SEM) image of indium spheres. ................................1

Figure 3. Indium balls placed on the package in close proximity to the devices being 

wirebonded. ................................................................................................................................2

Figure 4. Indium ball statically held onto the gold ball at the end of the capillary. .......................3

Figure 5. Capillary brought over to the device bonding area. ........................................................3

Figure 6. Indium makes contact with the device pad and the first bond is completed. ..................3

Figure 7. Capillary is brought over to the package bonding pad and the second bond is 

completed. ..................................................................................................................................4

Figure 8. Completed indium sphere wirebonds on an MCT device. ..............................................4
v 

Acknowledgments 

The author would like to thank Dr. Wendy Sarney of the Electro-optic (EO) Materials and 

Devices branch for helping with the scanning electron microscope (SEM) image of the indium 

spheres. 
vi 

INTENTIONALLY LEFT BLANK. 
1 

1. Introduction 

A novel technique for gold wirebonding of delicate mercury cadmium telluride (MCT) devices 

has been developed. Gold ball wirebonding to MCT devices is challenging. The act of applying 

force and ultrasonic power to MCT very easily creates damage under the device bond pads, 

damage that sometimes goes unnoticed until testing the device’s integrity at a later date. Indium 

spheres placed between the gold wirebond ball and the gold bonding pad on the MCT material 

allows one to use less force and ultrasonic power to attach the wire and acts as a soft solder in the 

process. In this study, an indium powder of a mesh size of 170/200 is used as a cushion between 

the free air gold ball and the device pad being wirebonded. Indium powder is made up of small 

(70–90 microns diameter) indium spheres (figures 1 and 2). The properties of indium make it a 

good choice in this technique. Indium is malleable and thermally and electrically conductive, and 

has a low oxide formation level. These qualities make it an ideal cold-welding material. 

Figure 1. Indium spheres placed on the device package. 

Figure 2. A scanning electron microscope (SEM) 

image of indium spheres. 
2 

2. Procedure and Results 

For this technique, the equipment used was a Marpet Enterprise, Inc. (MEI), 1204B Hybrid Ball 

Wirebonder (1) threaded with Kulicke & Soffa AW14 0.7-mil gold wire. The ceramic capillary 

tool make and size was a Gaiser Tool Company #1513-12-375 GM-20D (2). The indium spheres 

were purchased from Indium Corporation of America and the mesh size of the indium (powder) 

was 170/200 (3). 

Conventional ultrasonic ball wirebonding (4) consists of several steps: welding the wire to the 

contact pad on the device (known as the first bond); forming the wire loop as the capillary is 

moved to the second bond position; creating the second bond (also called the crescent or stitch 

bond), which connects the wire to the device package; and firing the electric flame off (EFO), 

which forms the next ball at the bottom of the capillary tool. This new technique follows the 

traditional steps of ball wirebonding with the addition of placing an indium sphere in between 

the gold wirebond ball and the device bond pad on the first bond. 

Indium spheres were placed onto the package such that they were in close proximity to the 

devices being bonded (figure 3). The ultrasonic power and the firing time on the transducer unit 

of the wirebonder were turned to near zero for the first bond. Normal settings for power and time 

(based on the individual wire bonder equipment) were used for the second bond. At the first 

bond position the capillary is brought over to an indium sphere, the capillary is lowered just to 

the point that the gold ball on the end of the capillary makes contact with the indium (figure 4). 

Pressure is not applied to the indium; instead, static electricity holds the indium sphere to the 

gold ball. The capillary is then brought up slightly and the indium ball is positioned directly over 

the pad that will be accepting the first bond (figure 5). The capillary is brought down to the bond 

pad and slight pressure is applied. The indium flattens, adhering to the metal bond pad, and the 

gold ball adheres to the indium on the pad (figure 6). The capillary then rises to the loop height 

position, and the wire is brought over to the second bond position. The second bond is formed, 

the wire disconnects, the EFO fires, and the cycle is complete (figure 7). Figure 8 shows the 

completed wirebonds. When the indium sphere wirebonding has been completed, the unused 

indium spheres are simply put back into the container by a gentle tapping on the back of the 

package over the container. 

Figure 3. Indium balls placed on the package in close 

proximity to the devices being wirebonded. 
3 

Figure 4. Indium ball statically held onto the gold ball 

at the end of the capillary. 

Figure 5. Capillary brought over to the device bonding 

area. 

Figure 6. Indium makes contact with the device pad and 

the first bond is completed. 
4 

Figure 7. Capillary is brought over to the package bonding 

pad and the second bond is completed. 

 

Figure 8. Completed indium sphere wirebonds on an MCT device.

4. Conclusion 

This new technique of wirebonding works very well for wirebonding the delicate MCT material 

devices. It reduces or eliminates the damage caused by traditional wirebonding processes by 

allowing one to perform wirebonding without using the ultrasonic power and force that damages 

the device material. This method has also been used successfully for wirebonding devices when 

there has been an issue with metallization liftoff of the bond pads. 

There is one limitation to this technique, This technique is not suitable for wirebonding devices 

that will experience an operating temperature of 157 °C or higher―the melting temperature of 

indium. 

a b
5 

5. References 

1. MEI 1204B Hybrid Ball Bonder Operations Manual, Marpet Enterprises, Inc., Danvers, MA 

01923. 

2. Gaiser Tool Company Semiconductor and Hybrid Microelectronics Wirebonding Tools 

Catalog, Gaiser Tool Company, Ventura, CA 93003. www.gaisertool.com (accessed March, 

2010). 

3. Indium Corporation of America, Utica, NY 13502. www.indium.com (accessed March 

2010). 

4. Harman, G. Wirebonding in Microelectronics Materials, Processes, Reliability, and Yield, 

2nd ed., McGraw-Hill, 1997. 
6 

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