As is generally well-known, carrier tapes are commonly used to transport miniature or subminiature components or products from one station to another station in connection with or during production and assembly operations. Such carrier tapes are typically formed of a base strip of plastic, paper or the like and a cover strip. The base strip is formed with a plurality of cavities or pockets for holding the components and the cover strip is secured to the base strip so as to avoid accidental discharge of the components from the cavities. Heretofore, the cover strip was most commonly held in place by means of an adhesive, heat bonded or spaced snap-type fasteners. Typical examples of these types of prior art carrier tapes are disclosed in U.S. Pat. Nos. 3,465,874; 3,650,430; 3,700,019; 3,894,896; 3,910,410; and 4,298,120.
In addition to the above patents, there are various prior art carrier tapes which utilize a continuous mechanical interlock for securing the base strip and the cover strip together. For example, in U.S. Pat. No. 4,733,778 to Hugo Boeckmann et al. issued on Mar. 1, 1988, and entitled "Reusable Carrier Tape," there is disclosed a carrier tape construction in which the base and cover strips are uniformly and consistently secured to each other. At least one of the strips is provided with an integrally formed, longitudinally extending continuous profile which cooperates with the surfaces of the other strip so as to secure the two strips together in a locking arrangement. In addition, in U.S. Pat. No. 4,708,245 to Hugo Boeckmann et al. issued on Nov. 24, 1987, and entitled "Carrier Tape," there is disclosed a carrier tape which includes an elongated base strip, an elongated cover strip, and at least one elongated profile strip bonded to one of the other strips, preferably the base strip. The profile strip is provided with a longitudinally extending, continuous, integrally formed profile which cooperates with the surfaces of the cover strip so as to secure the base and cover strips together in a locking engagement.
Furthermore, in U.S. Pat. No. 4,842,135 to Herbert A. Borst issued on Jun. 27, 1989, and entitled "Improved Carrier Tape and Cover Applying and Removal Devices For Same," there is disclosed an improved carrier tape comprising an elongated base strip and an elongated cover strip both formed of a plastic film material. The base strip is provided with longitudinally spaced cavities for housing components to be transported therein as well as a series of spaced, longitudinally extending sprocket drive holes for engaging suitable sprocket drive means for advancing the tape through an associated assembly machine. The cover strip has sidewalls extending downwardly and terminating in inwardly directed barbs or profiles. The spacing between the sidewalls is substantially equal to the width of the base strip. A raised, longitudinally extending hump is provided so as to project upwardly from the top surface of the cover strip. When the hump is depressed, the sidewalls of the cover strip move laterally outwardly so as to clear the edges of the base strip and thus permit removal of the cover strip therefrom. On the other hand, when the hump is released, the sidewalls return to their relaxed positions securely interlocking the cover strip with the base strip edges.
Furthermore, in U.S. Pat. No. 4,958,053 to Hugo Boeckmann et al. and entitled "Carrier Tape and Method of Manufacturing the Same," there is disclosed a carrier tape having a cover strip and a base strip formed of a plastic material and designed to mechanically interlock with each other. The cover strip includes a top surface from which sidewalls extend downwardly. At least one of the sidewalls includes a segment extending outwardly away from the other sidewall so as to define a camming surface to which a force may conveniently be applied so as to urge the sidewalls apart, thereby facilitating removal of the cover strip from the base strip. The cover strip may further also be provided with a hump having a dovetail configuration.
Finally, in U.S. Pat. No. 4,897,074 to Richard K. Knight and entitled "Mechanism For Joining a Carrier Tape Cover to a Base Strip," there is disclosed a carrier tape system which includes an elongated base strip and an elongated cover strip both formed of a plastic film material. The cover strip is substantially coextensive in length with the base strip. The cover strip has a top surface and opposed sidewalls extending downwardly from the top surface. The opposed sidewalls are spaced apart from each other a distance substantially equal to the width of the base strip. The cover strip further includes a hump projecting upwardly from the top surface and extending longitudinally in a parallel relationship with respect to the sidewalls. Each of the sidewalls has an inwardly extending hooked portion formed integrally therewith. The hooked portion has its top surface disposed beneath the edge of the base strip so as to form a U-shaped recess so as to secure the cover strip to the base strip. All of the aforementioned U.S. Pat. Nos. 4,733,778; 4,708,245; 4,842,135; 4,958,053; and 4,897,074 are assigned to the same assignee as the present invention and are hereby incorporated by reference.
In use, the prior art carrier tapes are usually wound around a storage reel for shipping and handling. While the base strip is provided with cavities which are often contoured so as to hold the components in place, it has however been encountered heretofore that the components may still be moveable out of the cavities, especially when the components are small thin fragile parts, so as to be susceptible to physical and electrostatic discharge (ESD) damage as the carrier tape is wrapped onto the storage reel. As a result, the small thin parts tend to shift or move between the base and cover strips during the winding process, thereby causing them to prematurely fall out of the cavities. All of the various prior art methods of securing the base strip and the cover strip together previously discussed (both the adhesion technique and the mechanical interlock type) fail to effectively hold the small thin parts within the cavities of the base strip during the assembly operation.