Ball bonds

K. Atsiimi and co-workers, "Ball Bonding Technique for Copper Wire," 36th Proceedings of the IEEE Electronic Components Conference, Seattie, Wash., May 5-7, 1986, pp. 312-317. 

NTD wafers were produced by irradiating natural ultra pure Ge crystals by means of a flux of thermal neutrons (see Section 15.2.2). To realize the electrical contacts, both sides of the wafers (disks, 3 cm in diameter, 3 mm thick) were doped by implantation with B ions to a depth of 200nm. The implanted layers are doped to such a high concentration that the semiconductor becomes metallic. Then a layer of Pd (about 20 nm) and Au (about 400 nm) was sputtered onto the both sides of the wafers. Finally, the wafers were annealed at 200°C for 1 h. The wafers are cut to produce thermistors of length 3 mm between the metallized ends (3x3x1 mm3 typical size) the electrical contacts are made by ball bonding with Au wires. 

Figure 14.7. Left Solution-processed quantum dot structure of InP nanoparticles (black dots) in a Ti02 nanoparticle array (open circles). The QDs could sensitize an optical response similar to the dye in a Gratzel cell. Right A schematic of very small QDs (balls) bonded to a controlling surfactant that is bonded to a surface specific element, such as a TCO surface.

A substrate 10 of HgCdTe is provided with an upper surface region 11 formed by an annealing procedure, or as an epitaxial layer or evaporated film. A layer of insulating material 12 is formed in which windows are provided. The windows are partially filled with a thin layer of metal 13 which is deposited therein to form a metal-semiconductor diode with the upper surface region. The metal layer is deposited to a thickness on the order of 10-50 nm thick and is sufficiently thin to be semi-transparent to infrared radiation. A thick layer of metal 14 is deposited to form an expanded contact and an anti-reflection coating 15 is provided. External conductors in the form of jumper wires 16 are ball bonded to the contact 14. 

Bond failures that occur following encapsulation of IC s have been successfully Investigated using AES. For example Au ball bonds failed after thermal cycling and thallium was detected on the failed surfaces ( 40 ). The thallium contamination was traced to transfer from lead frames during processing. 

Thermosonic gold bonding is the most widely used bonding technique, primarily because it is faster than ultrasonic aluminum bonding. Once the ball bond is made on the device, the wire may be moved in any direction without stress on the wire, which greatly facilitates automatic wire bonding, as the movement need only be in the x and y directions. 

FIGURE 45.4 Cross-sectional micrograph of SAC EGA solder ball bonded to a silver surface finished PWB bond pad. Planar voids are clearly evident in the section and in the magnified inset. Voids in close adjacency above the intermetallic layer and the BGA ball can significantly detract from the solder-joint strength. (Courtesy of Hewlett-Packard). 

In many acute applications, microelectrodes are fixed to stationary electronics for use in anesthetized animals. For chronic use, Michigan probes have been connected to flexible polyimide interconnect cables through thermocompression gold ball bonding [48]. In this case, the polyimide cable links the microfabricated silicon probe and an external connector for long-term recording. 

SAM protects the copper bond pad surface until it is removed by the ultrasonic energy during wire bonding. The mechanism of formation of the ball bond involves the removal of the SAM by the ultrasonic energy in the first step and then the formation of welded interface in between the deformed ball and the bond pad. Liu and Hutt studied SAM of octadecanethiol as preservative to enable... 

Wires may be joined to surfaces using TC ball bonds or wire bonds, solder bonds, sonic bonding techniques, etc. The wires may then be pulled to evaluate adhesion. These bonding techniques duplicate the bonding techniques used in fabrication. A possible problem with these tests is that the bonding method (heat, pressure, etc.) can degrade the adhesion. 

TD. Hund, P.V. Plunkett, Improved thermosonic gold ball bond reliability. Transactions of lEEE/CHMT 8 (4) (1986) 446. 

Ball bond A wire bond to a film consisting of a ball formed on the tip of a wire that is bonded to the surface under heat and pressure (Thermocompression (TC) bonding) or under pressure and ultrasonic scrubbing (Ultrasonic bonding). See also Wire bond. 

Wire bond An electrical connection to a surface made by pressing a section of wire under heat and pressure (thermocompression bonding) or pressixre and ultrasonic scrubbing (ultrasonic bonding) against the surface. See also Ball bond. 

Finally, the wire is cut, leaving a length protruding to form the next ball, before the process continues making numerous ball bonds within a single device (Figure 13.3). 

FIGURE 13.2 Schemmatic of the ball bonding process, indicating the length (Le) of the heat affected zone (HAZ). 

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