Microbump Arrays

Pressure contacts Anisotropic conductive rubber Dimple contacts Microbump array Flex/rigid boards Flex/flex or rigid boards Flex/rigid parts (flex-flex) Flex/rigid boards and parts Facsimile Flat panel displays Inkjet printers Board testers... 

Microbump arrays (Housing) Special fixtures Suitable processes to build microbumps must be developed. 

FIGURE 64J2 Flat disk-shaped microbump array on flexible circuit fir area contacts. Contact metal is copper-nickle-gold at 0.5 mm pitch. (Source Asahi Fine Technology.)... 

Film Connectors. High height bumps built on the flexible substrates as shown in Fig. 64.23 enable various repeatable interconnections between flexible circuits and the other devices.. A flexible circuit with a microbump array makes made a connection thinner than 0.3 mm from the surface of the other circuits. Over 100 connections could be made in 5 mm square by a microbump array. The column-shaped microbumps work as the male parts of the connection. An appropriated design of the female parts of the flexible circuits enables over 1,000 repeated connections for the high-pin-count circuits. 

Figure 64.24 shows the concept of a film connector made with bumped flexible circuits.The column-shaped microbump array is built on both sides of a thin, flexible substrate, and it works as the film connector between two flexible circuits. The film connector could generally be used with standard designs because it manages high-pin-count connections of flexible circuits without special constructions. Many varieties for the constructions could be possible depending on the combinations of flexible circuits and other devices. 

High-density EGA for flip-chip 200 1 Microbump array (200 /um pitch)... 

Contact probe array 200 -1000 Microbump array hard gold plating on nickel... 

FIGURE 66.11 Microbump arrays on flexible circuits examples of bump shapes. 

The basic quality assurance concept for high-density flexible circuits is the same as for other circuit types. However, a difference for high-density flexible circuits is the acceptable defect size, which is one order smaller than that for traditional flexible circuits, necessitating higher inspection capabilities. Furthermore, new high-density flexible circuits contain additional structiues such as flying leads and microbump arrays that require additional inspection capabilities for reliable termination. Exact 3-D accuracy and uniform surface conditions are required. Dimensional allowances are smaller than 0.3 percent, and sometimes 2-ftm accuracy is required. 

This is true for trace pitches, but it is also true for Unewidths and spaces. Three-dimensional measurements are required to guarantee the quality of microbump arrays. Usually, it takes time to measure exact dimensions for each circuit, and this is one of the major costs of the circuits when the specification is very tight compared to the process capabUity. 

Both cosmetic inspections and dimensional measurements are required for microbump arrays. 

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