Advantages of a Floating Annular Ring in Three-Layer Tab Assembly

A mechanically formed unsupported annular ring in three-layer tape automated bonding (TAB) material offers a number of advantages to the user. Leads are stabilized in x, y, and z axes so as to be in precise alignment for inner lead bonding to integrated circuits. Narrower leads may be designed, increasing packaging density, because they do not have to be self-supporting. Longer cantilever lengths can be used than when a supporting ring is absent. The adhesive holding the leads to the support ring acts as a secondary dielectric, providing high moisture resistance and excellent electrical properties. The adhesive is chemically resistant to processing solutions and, as a thermoset, resists any reflow during soldering or thermode bonding. The floating annular ring is suitable for inclusion in the final package. The unsupported ring has two specific advantages over corner-supported rings heretofore available. Outer lead excise tooling needs only pierce copper, and may be of simple square design. In addition, the entire periphery of the floating annulus may be used for lead layout, whereas supported rings require certain areas (usually corners) to be free of leads.