The present invention relates to apparatus for continuously patterning a photosensitive tape by projection printing, comprising the steps of translating the photosensitive tape between a tape-feeding source and a tape-receiving source; and optically coupling an optical system between a predetermined pattern to be projected and the tape. The step of translating the tape between the source and receiver, and the step of optically coupling are both described in U.S. Patent 3,562,005. The latter, however, only discloses continuous contact printing, and discontinuous projection printing.
GB patent 1,339,550 discloses a projection printing system for duplicating commercial type documents. It discloses continuous scanning and printing using two drums rotating at the same speed and provides the degree of accuracy required for such a printing system. Such a system can not however, provide the degree of accuracy required in high precision printing.
Continuous projection printing is also known from Schaffert "Electrophotography" published by Focal Press, 1965 (Pages 135-6 and Fig. 79).
Up to a few years ago, wire-bonding was the most commonly used method for making external connections to an integrated circuit (IC) chip. An alternative to wire-bonding consists of using a tape carrier, similar to a movie film, having lead frames formed along its surface. In this tape carried approach, usually a polyimide film carries a copper lead pattern that repeats itself along the length of the film. The finger-like leads of an individual site on the film are bonded simultaneously to the pads of an IC chip, as for example, described in U.S. Patents No. 3,689,991 and 3,968,563.
These processes make use of a thin strip of a continuous electrically insulating tape having a plurality of prepunched apertures at regularly spaced intervals. A thin foil-like strip or layer of electrically conducting material is secured to the tape. By photolithographic masking and etching, portions of the layer are removed to form a plurality of sets of metallic finger-like leads. This subtractive technique, used to form the finger-like leads, is described in an article by S. E. Grossman entitled "Film-Carrier Technique Automates the Packaging of IC Chips" in Electronics, May 16, 1974, pages 89--95. According to this article, the technique consists in first bonding a 1-ounce copper foil to a polyimide film by means of an adhesive. Photoresist techniques form the image of the desired lead frame in a step-and-repeat fashion along the film-mounted copper laminate. This step-and-repeat projection requires indexing, settling and alignment, all of which are time-consuming and expensive operations. Moreover, such a projection technique is difficult if long lengths of tapes are needed since accelerations associated with high speed indexing are damaging to the fragile tape. Furthermore, the high cost of the polyimide carrier increases the cost per site of such a tape especially when small quantities of custom tapes are needed.
German patent No. 758,260 discloses a continuous projection printing system for duplicating film for the motion picture industry. In that specification, negative film to be duplicated is fed by a sprocket drive system continuously past an object position, and copy film is fed by another sprocket drive system continuously past an image position. The two sprockets are mechanically linked together and facilitate duplication with a degree of precision commensurate with the requirements of the motion picture industry. A conventional projection lens system is located between the object and image positions and necessitates a significant spacing between the object and image positions.
It is an object of the present invention to provide a highly accurate system for projection printing.
According to the present invention there is provided apparatus for continuously patterning a photo-sensitive tape by projection printing, comprising driving means for continuously translating the photosensitive tape in a predetermined direction at a predetermined speed past one particular location a cylindrical transparent body having its longitudinal axis perpendicular to the said predetermined direction and a cylindrical surface thereof spaced from but adjacent to the said particular location and adapted to have defined thereon a predetermined pattern to be projected, means for coupling the driving means and the cylindrical body such that the pattern continuously rotates at said predetermined speed, and an optical projection system for projecting an image of the pattern onto one side of the tape at said one particular location, characterised in that the coupling means is provided solely by electrical drive circuitry synchronously locking the driving means and the cylindrical body, in that the resolution of the optical system is less than the minimum dimensions of the pattern, and in that the electrical drive circuitry is designed to ensure that any deviation from synchronism between the movement of the pattern and the tape is less than the resolution of the optical system.
One advantage of the embodiments is to achieve a highly accurate method and apparatus for continuously patterning a photo- sensitive tape or foil. Another advantage is to achieve a high-speed continuous patterning process of a tape or foil by means of projection exposure techniques.
Another advantage is to realize a projection exposure system having a very long mask life.
Under tensions on the tape or foil are prevented during the patterning process. The embodiments provide a simple, flexible and high-speed projection exposure system for photosensitive tapes or foils.
A photosensitive tape or foil is continuously patterned and the tape or foil is prevented from breaking, thereby achieving an economically attractive projecting process.
Reference is now made to the accompanying drawings in which
- Fig. 1 shows apparatus made according to an embodiment of the present invention;
- Fig. 2 is an enlarged view of a portion of the apparatus shown in Fig. 1 including its optical system;
- Fig. 3 shows a circuit diagram of the phase- locking system of the apparatus shown in Fig. 1;
- Figs. 4 and 5, respectively, illustrate a front and side view of another embodiment of the apparatus;
- Fig. 6 shows a further embodiment of the apparatus; and
- Fig. 7 is an enlarged view of a portion of the apparatus shown in Fig. 6 including its optical system.
In the illustrative embodiment of the invention, shown in Fig. 1, an apparatus for continuously patterning a photosensitive tape 1 comprises a tape-feeding reel 2, a tape-receiving reel 3, and a tape-translating drum 4 for translating the tape 1 at a predetermined speed between reels 2 and 3. The tape 1 can be of any form as described in the art, and the photo- sensitive region is applied to the tape in accordance with tape processing requirements. The drum 4 is mechanically coupled to a driving mechanism 5 comprising, for example, an electric motor having its shaft directly driving the drum 4. However, other translating mechanisms may be substituted for drum 4, as will be explained in connection with another illustrative embodiment of the invention. A cylindrical transparent body 6 is positioned with its longitudinal axis perpendicular to the direction of translation of tape 1 on the drum 4. In other words, in the embodiment of Fig. 1, the axes of body 6 and drum 4 are parallel. Transparent cylindrical body 6 carries on a surface 7 thereof a predetermined pattern or mask 8 to be projected on the photosensitive tape 1.
The pattern 8 may be directly on the outer surface 7 and may be formed by first coating the surface with a thin metal film and then selectively removing portions thereof by thermal machining of the film. Another alternative for depositing pattern 8 onto the cylindrical surface 7 consists in first producing a predetermined pattern on a 16 mm or 35 mm filmstrip by means of conventional techniques. The filmstrip comprising a plurality of individual frames or patterns could be wrapped around the cylindrical body 6 and held by vacuum against the surface 7. Both ends of the filmstrip would be butted to produce a contiguous set of patterns on the cylindrical surface 7. The cylindrical body 6 is mechanically coupled to a driving mechanism 9 comprising, for example, a motor having its shaft directly driving the body 6.
The cylindrical transparent body 6 and the drum 4 are synchronously coupled electrically by means of a coupling circuit 10 responsive to a reference frequency signal to. The coupling circuit 10 may comprise a pair of phase-locked loops arranged such that the cylindrical transparent body 6 is the "slave". Thus, both cylinder 4 and 6 rotate at precisely the same rate but in opposite directions as shown by the arrows in Fig. 1. In effect, an electrical link exists between drum 4 and cylinder 6 resulting in locking of both cylinders to each other. The apparatus further comprises an optical system 11 positioned between cylindrical body 6 and drum 4 for projecting an image of the pattern 8 onto the tape 1. The optical system 11 may be positioned as shown in Fig. 1 between body 6 and drum 4, with the axis of the optical system at 90░ to the axis of the body and drum, or may be rotated by a 90░ angle such that its axis is parallel to the axes of the body and the drum, in which case the object and image have the same orientation in the direction of the width of tape 1, but have opposite orientation in the longitudinal direction of tape 1. Also, object and image would be offset in the latter direction.
Shown in Fig. 2 is an enlarged portion of the illustrative embodiment of Fig. 1 including the structural details of the optical system 11. By way of background, a known one-to-one imaging optical system is described in an article by J. Dyson entitled "Unit Magnification Optical System without Seidel Aberrations," published in Journal of the Optical Society of America, volume 49, No. 7, July 1959, pages 713-716. This known Dyson system consists of two components, namely, a concave spherical mirror of radius R, and a thick piano-convex lens of radius r, refractive index n and thickness equal to r. The centers of curvature of both spherical surfaces are substantially coincident, and r is chosen so that parallel rays incident on the piano surface are focused on the mirror surface, i.e.,
In this known system, object and image surfaces lie on or close to the plane face of the lens, and object and image are of opposite directions.
In this embodiment, the optical system 11 of Fig. 2 is a modified Dyson-type system comprising a piano-convex lens 111 of radius r and refractive index n and a spherical concave mirror 112 of radius R having substantially coincident centers of curvature. The plane face of the piano-convex lens 111 is cemented to two right-angle prisms 113 and 114 in order to bring object and image to usable positions. The pattern 8 to be imaged on the tape 1 is preferably placed or formed on the outer surface of the cylindrical transparent body 6 which is made, for example, of quartz. A narrow strip of this pattern 8 is imaged by the system onto the photosensitive resist coated tape which is held in the proper focal plane by the lower drum 4. If the two drums 4 and 6 rotate in synchronism, the pattern 8 is continuosly transferred to the resist coated tape 1. The optical system 11 can image the full tape width, and utilizes a very small field size or strip in the scan direction. The narrow strip object and image derived by a manner not shown lie close to the optical axis thus obviating the need for a beamsplitter. This permits an optical system design completely made of fused silica with its attendant high transmission in the ultraviolet range. The optical system 11 is telecentric and hence insensitive to first-order distortions due to focal plane shifts. Since the design is completely symmetrical, distortion, coma, and lateral color are zero. Resolution is nearly diffraction limited over a 2 mmx 16 mm field at F/2.5 and still has acceptable resolution at a 2x22 mm field at F/4. Resolution in all cases is better than 5 Ám which is adequate for lead patterns whose narrowest feature would be larger than 50 ,am. Over the range of 3000-4400 Angstroms the optical system is nearly achromatic.
Illumination is provided, for example, by a 1 kW water-cooled mercury capillary arc 12. However, alternative light sources may be used. Water cooling filters out most of the infrared radiation beyond 1 Ám and assures cool operation. A combination of lenses and mirrors schematically shown in Fig. 2, is coupled to the arc for directing the arc's rays onto the cylindrical surface 7. The operation of the optical system is such that an object 13 that is part of the pattern 8, when illuminated by light source 12, is projected onto an image plane corresponding to the tape 1. The incoming object rays 15 are first reflected by right-angle prism 113 and directed through lens 111 and mirror 112. The rays from mirror 112, after reflection by right-angle prism 114, are directed to the tape 1 to form the image thereon. As shown in Fig. 2, object 13 and image have the same orientation in the direction of the tape 1. However, in a direction corresponding to the width of the tape, i.e., in a plane perpendicular to the page in Fig. 2, there is an Inversion between object and image. Furthermore, as the pattern 8 rotates, the movement of the image 14 is in the same direction as the movement of the tape 1, thus enabling a continuous projection patterning of the tape.
Since in the present case, scanning of the pattem takes place in the direction of movement of the tape 1, there is no inversion in the scanning direction and no need to invert the image.
As described above, the tape-carrying drum 4 and the cylindrical transparent body 6 are synchronously coupled by means of coupling circuit 10. The latter is schematically illustrated in Fig. 3 wherein the drum 4 and the cylindrical body 6 are mechanically driven by electric motors 5 and 9, respectively. The drum 4 and the body 6, rotate at precisely the same rate, namely synchronously, but in opposite rotational directions. Moreover, the drum 4 and the body 6 are locked to each other within the lens resolution of the optical system on the circumference, i.e., within less than 5 ,um. This corresponds to a rotational tolerance of approximately 20 arc seconds. By using precision optical encoders 31 and 32 and phase-locked loop techniques, the body 6 can move with respect to the tape-carrying drum 4 with a speed accuracy of 0.001%. In this illustrative embodiment, the drum 4 is locked to a predetermined speed by means of a reference frequency signal f. coupled to one input terminal of phase detector 33. The other input terminal of the phase detector 33 is coupled to the output terminal of optical encoder 31. A low-pass filter 35 has its input terminal coupled to the phase detector 33 output terminal, and its output terminal coupled to one input terminal of operational amplifier 37. The other input terminal of operational amplifier 37 is coupled to the output terminal of optical encoder 31 via a frequency-to-amplitude converter 39. The output terminal of amplifier 37 is coupled to the driving motor 5 of the tape-carrying drum 4. The upper half of the coupling circuit 10 coupled to the cylindrical transparent body 6 and its driving motor 9 is identical to the lower half of the loop 10, i.e. it comprises a phase detector 34, a low-pass filter 36, an operational amplifier 38 and a frequency-to-amplitude converter 40.
In this illustrative embodiment of the coupling circuit, the motion of tape-carrying drum 4 serves as the "master". The output of the optical encoder 31 serves as the reference frequency to which the cylindrical transparent body 6 is the "slave". Thus, low frequency torque disturbances on the drum 4 are tracked by the body 6, and high frequencies are damped by the inertia of the loop and motors. The system comprising the drum 4, the body 6, the motors 5 and 9, and the coupling circuit 10 is stiff enough so that torque disturbances in the tape disturb the tape position by less than the image resolution. In the illustrative embodiment of the coupling circuit 10, the reference frequency signal fo is, for example, a 1000 Hz signal and the optical encoders 31 and 32 are 16-bit encoders generating 2" or 65,536 pulses/revolution. The phase detectors 33 and 34, the filters 35 and 36, the amplifiers 37 and 38, and the converters 39 and 40 may be selected from conventional and commercially available components.
The tape-carrying drum 4 and the cylindrical transparent body 6 can both be the "slaves" of the reference frequency signal fo. This is achieved by coupling the reference signal fo to phase detectors 33 and 34, and by connecting the optical encoder 31 output signal only to the other input terminal of phase detector 33. Thus, instead of having a "master-slave" arrangement as shown in Fig. 3, the drum and the body would be "slaves" and locked to fo.
Another illustrative embodiment of the present invention for patterning both sides of a photoresist coated tape is shown in Figs. 4 and 5. The apparatus for projecting an image onto the continuous tape 1 comprises the first cylindrical transparent body or drum 6 having on its cylindrical surface 7 the predetermined pattern 8 to be projected. A first optical system 11 is positioned between the drum 6 and the tape 1 as described in connection with the embodiment shown in Fig. 1. In order to achieve projection printing onto the other side of photo- sensitive tape 1, a second cylindrical transparent drum 6' is positioned with its longitudinal axis parallel to the axis of drum 6. A second predetermined pattern 8' is formed on cylindrical surface 7' of drum 6'. A second optical system 11' identical to the optical system 11, is positioned between the drum 6' and the tape 1. Photosensitive tape 1 is translated at a constant and predetermined speed by means of guiding rolls 41 and 42 between a tape-feeding reel and a tape-receiving reel (not shown). The motion of guiding rolls 41 and 42 serves as the "master" reference frequency in the phase-locked loops of Fig. 3. Both drums 6 and 6', rotating in opposite directions, are locked to the guiding rolls 41 and 42 and are, therefore, the "slaves" in the coupling circuit 10 of Fig. 3.
As shown in Fig. 5, in order to achieve simultaneous and continuous projection of patterns 8 and 8' onto both sides of the tape 1, double-sided illumination of the tape is required. This may be realized by using a single light source 12, such as a 1 kW water-cooled mercury capillary arc, coupled to a pair of mirrors 51 and 52 for directing the radiations from source 12 toward the patterns 8 and 8' on drums 6 and 6'. The foregoing is achieved by interposing a condenser 53 and a mirror 57 between mirror 51 and pattern 8. Also, another condenser 54 and a second mirror 58 are interposed between mirror 52 and pattern 8' of drum 6'. Condensers 53 and 54 may, for example, comprise all reflecting optical components such as a spherical concave mirror for receiving the radiations reflected by mirrors 51 or 52, and a spherical convex mirror for reflecting the incoming radiations from the concave mirror and directing them to the mirrors 57 or 58. However, other types of condensers may alternatively be used. Both mirrors 57 and 58 are positioned within the transparent drums 6 and 6' in order to reflect the incoming radiations from source 12 by a 90-degree angle. With the arrangement shown in Fig. 5, illumination for tape exposure from both sides is available from the same source 12. Both drums 6 and 6' are preferably made of quartz ground and polished to high accuracy. The quartz drums 6 and 6' have, for example, a 381 mm circumference which is a convenient multiple of standard tape pitches. As explained in connection with the embodiment of Fig. 1, the patterns 8 and 8' may be formed, for example, directly on surfaces 7 and 7' by thermal machining. Alternatively, patterns 8 and 8' may be formed on a filmstrip wrapped around the drums 6 and 6' and held by vacuum against surfaces 7 and 7'. However, other means of forming a pattern onto a cylindrical surface can alternatively be used.
Referring now to Figs. 6 and 7, wherein double-sided patterning of photosensitive tape 1 is shown, identical numerals corresponding to the numerals of the previous figures are utilized to illustrate the similarities of the illustrative embodiments. In this illustrative embodiment, topside exposure of photosensitive tape 1 is obtained by projection printing from the drum 6 of pattern 8 as explained in connection with the previously described embodiments. The back or other side of tape 1 is patterned by means of contact printing of a pattern 60 onto the tape. The pattern 60 on drum 6' and pattern 8 on drum 6 may be identical. However, different patterns may be used when it is desirable to project on both sides of the tape a different beam lead pattern. Contact printing consists of first forming a mask 60 according to conventional mask producing techniques, and wrapping the mask around the cylindrical surface 7' of drum 6'. In this illustrative embodiment, as in the embodiment of Fig. 1, both drums 6 and 6' are synchronously coupled and locked to each other by means of coupling circuit 10. Condensers, shown in Fig. 6, each comprise all reflecting optical components. It should be noted that other types of optical components can alternatively be employed.
Double-sided exposure either through projection printing as shown in Fig. 4, or through projection printing on one side and contact printing on the other as shown in Fig. 6, is required for etching with negative photoresists. Contact printing requires changing of the mask 60 after a predetermined number of runs. Projection printing, instead, offers the advantage of avoiding contact between the mask and the resist coated tape. The apparatus of Figs. 6 and 7 enables the combination of these two patterning techniques for double-sided patterning by using only one optical system 11.
In all of the above illustrative embodiments of the present invention, the photosensitive tape 1 may be a photoresist coated copper tape or a photoresist coated continuous metal-composite tape. Either negative photoresists or positive photoresists may be employed. After patterning the photosensitive copper tape by using any of the above-described method and apparatus, the copper is etched where exposed (if positive resist is used) leaving a set of thin copper leads suitable for simultaneous bonding to a chip.