A THERMOFORMED CARRIER TAPE REEL AND METHOD OF MANUFACTURING THEREOF FIELD OF THE INVENTION

The present invention relates to a carrier tape reel assembly, and in particular it relates to the manufacturing of a thermoformed carrier tape reel. BACKGROUND OF THE INVENTION

In general, carrier tape reels are used to store and for transporting semiconductor devices and such electronic components. A known way to provide a continuous supply of electronic components to a desired location is to use a carrier tape. These carrier tapes are generally manufactured in one location, wound round a carrier tape reel to be transported to a second location where the tape is unwound and continuously feed into a machine for automatic loading of electronic components on to the tape.

Thereafter the loaded tape is then wound round another carrier tape reel to be transported and fed on to the robotic placement machines that remove the components from the tape on to the circuit boards. Carrier tape reels have to be specifically designed for the purpose of holding and accommodating the carrier tapes both when they are empty and when they are carrying a plurality of electronic components on to an automatic assembly line. In prior art, typically, a carrier tape reel assembly comprises a flange portion consisting of two surfaces which are distanced from each other by a tape width and provided in parallel with and opposed to each other and are connected to a hub portion provided between the two surfaces.

Carrier tape reels are generally made from plastic materials with an injection molding process. The molded plastic is either an integral one piece structure having a central hub and a pair of circular side members, where the central hubs of adjacent plastic reels are heat sealed together to form a unitary carrier tape reel or a reel assembly having interlocked hubs of reel sections, wherein the reel sections may be nested together to provide a compact structure.

Such prior art devices are described in US Pat. No 4,726,534, which further discloses a two-piece reel structure in which two halves of the reel can be assembled to one another through easy alignment and engagement of ears and locking lips portions on a first half with corresponding receiving ears and locking lips on a second half to form a complete reel assembly. US Pat. No. 5,524,850, US Pat. No. 6,343,765, and US Pat. No. 6,425,550 also relate to Carrier Tape Reel Assemblies and disclose various improved methods for easily joining the two reel halves together to form a complete reel assembly. US Pat. No. 6,451,623 discloses a plurality of recess areas to hold moisture absorbing desiccant pouches wherein a varying number of such pouches, corresponding to the electrical requirements of the components, can be added to the tape reel assembly without affecting the overall volume of the entire packaged reel assembly.

Due to the mechanical forces present in automation equipment, the rigidity required to pass packaged shock & vibration testing, the various intricate designs and close tolerances that are required to meet their specific purposes, carrier tape reels are generally formed through an injection molding process using either thermoplastic or thermosetting materials. However, thermoforming process using thermoplastic materials, with all its attendant advantages, may also be applied in the manufacture of carrier tape reels as has been anticipated in US. Pat. No. 4,726,534 provided the technical difficulties of design, tooling, forming, trimming and fabrication of the assembly, which still exist until today, can be overcome.

Thermoforming is a method of manufacturing custom plastic enclosures by preheating a flat sheet of plastic and bringing it into contact with a mold whose shape it takes. This can be done by vacuum, pressure and/or direct mechanical force. Thermoforming is generally preferred over injection molding because of shorter tool development lead-time, lower tooling cost, faster tooling set-up, higher production capacity, and greater flexibility for low-

volume / high-mix production. Thin-film thermoforming generally relates to raw material sheet thicknesses of 1.5mm or less, whereas heavy gauge or thick- film thermoforming generally utilizes raw material sheet thicknesses greater than 1.5mm. It is generally accepted that the cost of the raw material required for injection moulding or thermo formed parts is the major contributor to the final cost of the plastic part. There is also a need to reduce the amount of raw material required from an environmental standpoint. Finally, reducing the part weight can result in significant transportation savings, especially if the parts are shipped by airplane. By utilizing thin-film thermoforming for the manufacture of plastic parts it is possible to significantly reduce the amount of raw material required and therefore reduce the part cost, environmental impact, and freight cost provided that the technical difficulties of achieving equivalent structural performance can be circumvented. A thin-film thermoformed carrier tape reel will typically weigh 50% less than an equivalent thick-film thermoformed part or injection molded part.

However, thin-film carrier tape reels may not be rigid enough to support the weight of the components they carry. Additionally, thin-film carrier tape reels may not be rigid enough to withstand the requirements of shock and vibration testing. Furthermore, these thin-film reels may not be strong enough to resist the mechanical forces present in typical automation equipment utilized for carrier tape reels without failure, particularly with the interfaces associated with the mechanisms used to drive and rotate the reels as specified in industry standard ANSI/EIA-418-C and other similar industry standards and equivalent. Accordingly, there is a need for a carrier tape reel made from thermoforming thin-film materials and yet meets the requirements of stringent industry standards to support the weight of components they carry and rigid enough to withstand the forces of typical present day manufacturing processes, especially against shock and vibration that occurs during shipping and handling.

Because of these factors and despite the obvious advantages as have been enumerated thermoformed carrier tape reels, especially with thin-film parts, have been found to be difficult to design and manufacture and until now have not been really suitable for use as opposed to injection molded carrier tape reels with their thicker walled parts. Objects and advantages of this invention will become apparent from the following descriptions taken in conjunction with the accompanying drawings, wherein, are set forth, by way of illustration and example, certain embodiments of this invention. SUMMARY OF THE INVENTION The present invention relates to a carrier tape reel assembly made by thermoforming thin-film material having a pair of reel sections, that are interconnected together with a central cylindrical body, wherein the reel section has an outer rim joined to radially inwardly directed spokes which are integral with a central cylindrical hub that comprises an outer arcuate hub wall and flat hub base at the center of which is a cone-shaped boss provided with an opening for accommodating a support, such as a shaft or splined shaft for the reel assembly. The opening in the boss is precisely trimmed according to the dimensions and tolerances specified in industry standard ANSI/EIA-481-C and other similar standards, and with the surrounding rib structures provides reinforcement against the mechanical forces of the drive shaft utilized to control the rotation of the tape reel in typical automation equipment.

In the tape reel spoke surface, as well as in the hub base surface, there are preferably a plurality of additional openings for engaging the reel structure and controlling rotation of the reel assembly. Each of these openings has a surrounding rib structure which provides reinforcement against the mechanical forces of the drive mechanism of the automation equipment, and also aid in the thermoforming process to maintain the flatness of the spoke structure.

In the spoke structure, there are additional arcuate openings which provide access for inserting the leading end of the carrier tape into a slot in the

hub wall. Each of these arcuate openings has a surrounding rib structure which provides mechanical reinforcement against the weight of components contained in the carrier tape, and further provides rigidity to the spoke structure for shock and vibration testing, and also aids in the vacuum forming process to maintain the flatness of the spoke structure during thermoforming. The said rib structure extends into the outer wall of the hub in order to rigidly maintain the orientation of the spoke with the outer wall of the hub.

In the spoke structure, there are pluralities of flat surfaces, between the arcuate openings, which are often utilized to affix identification labels to the reel assembly. There are reinforcing rib structures on these flat surfaces that help to strengthen them against the weight of the components contained in the tape reel, and further provide rigidity to the spoke structure for shock and vibration testing, and still further to help maintain the flatness of the spoke structure during thermoforming. There is also a peripheral reinforcing rib structure, located close to the outer edge of the rim section, for providing reinforcement against the mechanical forces of the weight of the product, and further to provide rigidity to the rim structure for shock and vibration testing, and still further to maintain the flatness of the rim structure during thermoforming. The base of the hub has a plurality of rib structures that extend radially from the central boss outward toward the outer wall of the hub. These radial rib structures help to reinforce the base against the mechanical forces of the automation equipment, and further help to maintain the flatness of the base during thermoforming. All these reinforcing rib structures are designed to reinforce the reel sections against the mechanical forces of the various drive shafts used to rotate the thermoformed carrier tape reel assembly in typical automation equipment, and to maintain the flatness and rigidity of the thin-film reel sections, especially against shock and vibration that occurs during shipping and handling.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. FIG. 1 illustrates typical mechanism used to rotate tape reels and typical drop test set-up;

FIG. 2 is a perspective view of the carrier tape reel assembly of the present invention;

FIG. 3 is a side view of the present invention; FIG. 4 is a plan view of the present invention;

FIG. 5 is an enlarged perspective view of a portion of the hub of the present invention;

FIG. 6 is an enlarged perspective view of a portion of the hub of the present invention, engaged with a typical drive mechanism used to rotate tape reels;

FIG. 7 is a process flow diagram for the present invention;

FIG. 8 is a perspective view of the present invention in a closely nested stack;

FIG. 9 is table showing the percent weight savings, and associated air freight savings, between typical injection molded tape reels and the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As required, a detailed embodiment of the present invention is disclosed herein, however, it is to be understood that the disclosed embodiment, is merely exemplary of the invention, which may be embodied in various forms. Therefore specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

Referring to FIG. Ia, there is shown a simple illustration of a typical machine which may be used to load or unload objects such as electronic components into or from a flexible carrier tape film which is unwound from a supply tape reel, and then rewound onto a take-up tape reel. Referring to FIG. Ib and FIG. Ic, the take-up reel is mechanically rotated by means of a central drive shaft which has a thin spline that engages with a corresponding opening in the take-up reel. The center drive shaft may be attached to a drive arm which has a secondary shaft radially spaced some distance away for added leverage in rotating the take-up reel. The center drive shaft and spline, and secondary shaft apply considerable torque and mechanical forces to the take-up reel, especially at the openings for these shafts or like supports. The structural design of the take-up reel is critical to ensure proper and continuous function of the take-up reel in such typical machinery.

Referring to FIG. Id, there is a shown a tape reel which has been wound with loaded carrier tape film, and packed inside a shipping carton. These packaged tape reels are typically required to withstand rigorous shock and vibration testing, to ensure the product can be shipped by common carrier and arrive undamaged. The structural design of the tape reel is critical to ensure that it can withstand the severe mechanical forces exerted upon it when it is dropped from a height of up to one meter or more onto a hard surface.

Referring to FIG. 2 to 4, there is shown the carrier tape reel assembly (1) of the present invention for accommodating flexible sheet material, such as film, tape, and like elongated ribbons. The sheet material can be laminated sheets enclosing objects, such as electronic components. The carrier tape reel assembly (1) is made by thermoforming thin- film material and has a pair of reel sections (2) that are interconnected together with a central cylindrical body (3).

Reel section (2) has a circular outer rim (4) joined to radially inwardly directed spokes (5). The outer rim (4) has an outwardly directed rim rib (6)

which helps to maintain the flatness and rigidity of the outer rim (2), especially against shock and vibration that occurs during shipping and handling. The rim rib (6) is generally peripheral to the outer rim (4).

The spokes (5) are integral with a central cylindrical hub (7). The hub (7) has an outer arcuate hub wall (8) which forms part of the central body (3) of reel (2). The spokes (5) are separate arcuate segments of a circle. Each spoke (5) is a generally flat segment having an outwardly directed spoke rib (9) which helps to maintain the flatness and rigidity of the spoke (5), especially against shock and vibration that occurs during shipping and handling. The spoke ribs (9) are generally peripheral to the spokes (5). Spokes (5) have spoke shaft cutouts (10) to accommodate a shaft or like support, which may be used to mechanically control the rotation of the carrier tape reel assembly (1) in typical automation equipment. The spoke shaft cutout (10) has an outwardly directed spoke shaft rib (11) which helps to reinforce the spoke shaft cutout (10) against the mechanical forces of the shaft or like support used to rotate the thermoformed carrier tape reel assembly (1). The reinforcing spoke shaft rib (11) is generally peripheral to the spoke shaft cutout (10). Without the reinforcing spoke shaft rib (11), the spoke shaft cutout (10) on a thin-film thermoformed carrier tape reel assembly (1) would likely tear or crack in repeated use.

Hub wall (8) projects inwardly from the inner ends of spokes (5). The hub wall (8) comprises a plurality of convex wall sections. Adjacent convex wall sections are spaced from each other with recesses (12) located about hub (7). At least one of the spokes (5) has an enlarged spoke cutout (13) to provide access for manually inserting the end of the flexible sheet material into the recess (12). Each spoke cutout (13) has an outwardly directed cutout rib (14) which helps to maintain the flatness and rigidity of the spoke (5) after material has been removed to create the spoke cutout (13). The cutout ribs (14) are generally peripheral to the spoke cutout (13) and extend radially toward the hub

(7) and continue onto hub wall (8) in order to rigidly link and help to maintain the orientation of the spokes (5) with the hub wall (8). Without the reinforcing cutout ribs (14), the spokes (5) on a thin-film thermoformed carrier tape reel assembly (1) would not be rigid enough to withstand the forces on them during a packaged drop, resulting in severe damage to the product contained therein.

The hub (7) has a generally flat hub base (15) joined to hub wall (8). Hub base (15) is generally parallel to spokes (5). The central portion of hub base (15) has an outwardly directed cone-shaped boss (16).

Referring to FIG. 5, the center of the boss (16) has a circular boss cutout (17) with radial recesses to accommodate a spindle, spline shaft, or a like support, which is used to mechanically control the rotation of the thermoformed carrier tape reel assembly (1) in typical automation equipment. The boss cutout (17) has an outwardly directed boss rib (18) which helps to reinforce the boss cutout (17) against the mechanical forces of the drive shaft used to rotate the thermoformed carrier tape reel assembly (1). The reinforcing boss rib (18) is generally peripheral to the boss cutout (17). Further by referring to FIG. 6, it is shown that without the reinforcing boss rib (18), the boss cutout (17) on a thin-film thermoformed carrier tape reel assembly (1) would likely tear or crack or otherwise fail in repeated use. Referring again to FIG. 5, ANSI/EIA-481-C and other similar standards specify the dimensions and tolerances of such a circular shaft opening with radial recesses in typical tape reels. Injection molded tape reels are easily molded with these shaft openings; however thermoformed carrier tape reels must be precisely trimmed in a secondary operation, typically using a hardened matched-metal punch and die, to create the shaft opening. Furthermore, the trimmed edge of the boss cutout (17) on a thin-film thermoformed carrier tape reel assembly (1) must have a minimum offset from the reinforcing boss rib (18) to facilitate easy insertion of the splined drive shaft which is used to mechanically control the rotation of the thermoformed thin-film carrier tape

reel assembly (1) in typical automation equipment. The boss rib (18) is used during the secondary trim operation to precisely align the matched-metal punch and die to the untrimmed thermoformed part and thereby create the boss cutout (17) with a minimum offset. Referring again to FIG. 2 to 4, the hub base (15) has a plurality of outwardly directed hub ribs (19) which help to maintain the flatness and rigidity of the hub base (15). The flatness and rigidity of the hub base (15) is especially important for proper assembly of the reel sections (2). The reinforcing hub ribs (19) extend radially outward from the boss (16). The hub base (15) has a plurality of hub cutouts (20) to accommodate a secondary shaft or like support, which may be used in conjunction with the central drive shaft, to mechanically control the rotation of the carrier tape reel assembly (1) in typical automation equipment. Each hub cutout (20) has an outwardly directed hub cutout rib (21) which helps to reinforce the hub cutout (20) against the mechanical forces of the secondary drive shaft used to rotate the thermoformed carrier tape reel assembly (1). The reinforcing hub cutout rib (21) is generally peripheral to the hub cutout (20). Referring again to FIG. 6, it is shown that without the reinforcing hub cutout rib (21), the hub cutout (20) on a thin-film thermoformed carrier tape reel assembly (1) would likely tear or crack or otherwise fail in repeated use.

The entire reel section (2) is a one-piece plastic member. The plastic member is thermoformed from thin film plastic sheet. The aforementioned various reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) are critical to ensure that the thin-film thermoformed carrier tape reel assembly (1) of the present invention possesses the robust structure required to properly function when used in typical automation equipment and when subjected to typical shock and vibration testing of packaged products. The specific design of these reinforcing ribs (6), (9), (1 1), (14), (18), (19), and (21), and further more the specific design and fabrication of the tooling used to form these reinforcing ribs

(6), (9), (11), (14), (18), (19), and (21), and still further the specific thermoforming process parameters used to form the thin-film thermoformed carrier tape reel assembly of the present invention (1) are critical to ensure the various reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) have said robust structure.

Referring to FIG. 7, the typical process flow begins with thin-film sheet material, which is uniformly heated in an oven, then formed to take the shape of the mold using pressure and/or vacuum, subsequently trimmed and then assembled to produce a thin-film thermoformed carrier tape reel assembly (1). Each of these process steps must be carefully engineered and tightly controlled to ensure the resulting thermoformed parts, and especially the various reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) are properly formed with rigid structures.

The effective strength of the reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) will be limited by any location which has thinner material thickness or is not sharply formed. These locations will be a weak point and the rib structure will likely fail at these locations under load or stress. Controlling the actual temperature of the thin-film material just prior to forming, and controlling the actual temperatures of the aluminum forming mold cavity and plug assist are most critical for minimizing these weak locations in the formed rib structures (6), (9), (11), (14), (18), (19), and (21).

The uniform heating of the thin-film material to an ideal target temperature, depending upon the resin type being used, is critical for allowing the thin-film material to easily flow and take the shape of the mold with uniform wall thickness. Typical thermoforming tries to control the temperature of the oven used to heat the thin-film material. However, by utilizing an infrared linescanning system, it is possible to accurately monitor and thereby precisely control the actual temperature of the heated thin-film material just prior to the forming step, and not just control the oven temperature.

Similarly, the consistent temperature control of the aluminum forming mold cavity and plug assist to an ideal target temperature, depending upon the resin type being used, is critical for allowing the thin-film material to easily flow and take the shape of the mold with uniform wall thickness. Typical thermo forming tries to control the temperature of the water flowing through the aluminum mold cavity and plug assist. However, by using individual internal thermocouples which are permanently inserted into the aluminum mold cavity and plug assist, it is possible to accurately monitor and thereby precisely control the actual temperatures of the aluminum mold cavity and plug assist, and not just the water flowing through them.

Furthermore, the specific machined profile of the ribs, and also the size and location of vacuum holes in the mold cavity, are critical for forming strong thin-film rib structures (6), (9), (11), (14), (18), (19), and (21). Through careful experimentation, the following design rules have been identified as key to ensuring such rigid structures: a. The side angle or draft of the reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) should be no more than 15 -degrees from vertical for robust structural design and uniform thin-film material flow; b. The height-to- width ratio of the reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) should be no less than 2-to-l and no more than 4-to-l in order to have optimum resulting material thickness and associated rigidity; c. The vacuum holes in the mold design should be 1.50 mm diameter and spaced no more than 12mm apart along the bottom edges on both sides of the reinforcing ribs (6), (9), (11), (14), (18), (19), and (21) to quickly evacuate air trapped between the heated thin-film sheet and the mold cavity, and to allow the thin-film sheet to completely and sharply conform to the mold profile before the thin-film sheet temperature has substantially decreased.

The reel sections (2) can be coated with electrical anti-static coating material. This eliminates electrical discharge which could damage electric components and collect dirt on the sheet material or tape. Small electrical components may adhere to the cover sheet of the tape due to electrostatic charge. This problem is eliminated with the use of an anti-static coating material applied to the surfaces of the reel sections (2).

Referring to FIG. 8, the reel sections (2) are stacked and nested together to minimize storage space and economize the shipment of reel sections (2) to a utilization location, where they are joined together to form the thermoformed carrier tape reel assembly (1). The thin-film thermoformed reel sections (2) of the present invention can be nested more closely than other typical injection- molded or heavy-gauge thermoformed reel sections, requiring proportionally less per-part storage space and transportation cost.

Referring to FIG. 9, the thin-film thermoformed carrier tape reel assembly (1) of the present invention requires much less raw material, and therefore is much lighter in weight than other typical injection-molded or heavy-gauge thermoformed reel sections. This reduction in raw material and associated weight savings not only are significant in terms of their environmental benefit, but they also result in significantly lower per-part cost and dramatically lower per-part shipping cost, especially for product shipped by air freight.

While there are shown and described several sizes of reel assemblies and reel sections of the invention, it is understood that changes in material, sizes, and shapes of the reel sections (2) may be made without departing from the invention. The invention is defined in the following claims :