Thermosonic wire bonding

Ultrasonic aluminum wire bonding is easily accomplished with the nickel-plated DEC. It should be noted that ultrasonic wire bonding of aluminum wire to copper can be effected the resultant bond is not as reliable as with the nickel plating. Gold thermocompression or thermosonic wire bonding requires at least 50 pin. of gold plating. 

If the subsequent assembly process calls for thermocompression or thermosonic wire bonding, plated copper under the wire-bond sites should be avoided. This can be accomplished by selectively plating the copper. When the adhesion layer is Nichrome or titanium-tungsten, then precision-deposited thin-film resistors can be fabricated. 

Wire bonding is still the foremost method used. Aluminum or gold wire, generally 1-mil diameter, is used for most applications. High current power circuits require thicker wire up to 10-mil diameter. Die can be wire bonded at high speed with automatic thermocompression, thermosonic, or ultrasonic equipment. 

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. 

Wire bonds can be made with wire diameters as small as 0.8 mil. Thermosonic baU-wedge bonding of a gold wire, shown in Fig. 3.15(e), is performed in the following manner ... 

FIGURE 3.15 DCA interconnect methodologies (a) die bond/wire-bond module (b) TAB module (c) flip TAB module (d) flip-chip module (e) thermosonic gold wirebonding (f) TAB bonding (g) flip-chip bonding. 

Figure 11.12 illustrates aluminum ultrasonic bonding of heavy wire, whereas thermosonic bonding is illustrated in Fig. 11.9 and Fig. 11.10. 

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