Lead frame assembly process

Abstract: A multi-layer lead frame (10) for a semiconductor device comprises a lead frame body (12) made from metal strip, a power supply plane (14) and a ground plane (16). The planes (14,16) are independent of the lead frame body (12), but laminated to the lead frame body (12) by means of adhesive films (18a,18b) which are coated directly on the planes (14,16) or the lead frame body (12), without using any insulative tape pieces. An insulative film (19) may also be provided between the lead frame body (12) and adjacent planes (14,16).

Description: This invention relates to a method of manufacture of a lead frame, more particularly to a multi-layer lead frame having at least one metal plate or plane, hereinafter referred to as "metal plane" which is used for a semiconductor device. A plastic package, whose speed and heat-radiation characteristics are as good as those of a ceramic package, has recently been developed. In addition, in place of a conventional single-layer lead frame, a multi-layer plastic lead frame for a semiconductor device has also been developed. Such a multi-layer lead frame comprises at least one metal plane connected via an insulative layer to the bottom surfaces of inner leads. Using such a multi-layer lead frame, it will be possible to mount a relatively power-consumable semiconductor chip on the metal plane, due to a good heat radiation capacity of the metal plane. Also, the metal plane can be used as a ground layer or a power supply layer to improve the electrical characteristics of the semiconductor device. Figure 9 shows a conventionally known multi-layer lead frame which comprises three layers, i.e., a signal layer (i.e., lead frame 12) and two metal planes, i.e., a power supplying metal plane 14 and a ground metal plane 16, which are laminated via insulative tape 17a and 17b made of heat-resistant material made of, such as a polyimide. Using such a multi-layer lead frame, it would be possible to prevent a so-called cross talk which might be generated between signal lines and also possible to reduce the capacitance between the lines or inductance. As shown in Fig. 9, in order to manufacture the above mentioned multi-layer lead frame, at the first stage, a lead frame 12, a power supplying metal plane 14, a ground metal plane 16, and insulative tape pieces 17a and 17b each having respective surfaces providing with adhesive layers must individually be made. Then, these individual pieces must be positioned by using a special positioning instrument (not shown), including an image reader or CCD array, and then heat-pressed to laminate and adhere them together. However, in the above mentioned manufacturing process, it has been so troublesome and laborious work to position and laminate the five layers including the insulative tape pieces 17a and 17b by using the positioning device. It also requires a lot of time and, therefore, an effective production would not be expected. In addition, after these pieces are gripped by the gripping means and laminated, when the pieces are released or disengaged from the gripping means, the laminated pieces might be moved slightly and, therefore, a precise laminated multi-layer lead frame might not be obtained. The multi-layer lead frame should originally have a good quality for multi-pin and, therefore, inner leads thereof are usually so dense. Thus, even a slight abberation might cause a disconnection between the terminals of the power supply plane 14 and ground plane 16 and the corresponding inner leads of the lead frame 10. In addition, an insulative sheet must be punched to form the insulative tape pieces 17a and 17b. Such a punching process requires a relatively laborious work. According to the present invention, a process of manufacturing a multi-layer lead frame body for a semiconductor device, the multi-layer lead frame body including a lead frame body, a first metal plane and a second metal plane, the process comprising the steps of: i. forming a lead frame strip comprising a plurality of lead frame bodies consecutively arranged and connected to each other; ii. forming a first metal plane strip comprising a plurality of first metal planes consecutively arranged and connected to each other; iii. coating a surface of the lead frame strip with one of a thermoset resin adhesive film or a liquid insulative resin film in accordance with a first predetermined adhesion pattern; iv. coating a first surface of the first metal plane strip with the other of said thermoset resin adhesive film and said liquid insulative resin film to that coated on the lead frame strip in accordance with the first predetermined adhesion pattern; v. drying the adhesive and insulative films and subsequently positioning the first metal plane strip adjacent to the lead frame strip, and adhering the first metal plane strip to the lead frame strip by heat pressing so that there is an insulation layer and an adhesive layer between the first metal plane strip and the lead frame strip, wherein said lead frame strip and said first metal plane strip have respective positioning means which are used for positioning said first metal plane strip with respect to said lead frame strip. Thus, in the present invention, the multi-layer lead frame can be effectively and precisely manufactured, since the positioning of the lead frame strip and the metal plane strip can be easily conducted. Also, coating these planes with an adhesive material and/or an insulative resin can be easily and precisely conducted, by using masking, for example. Therefore, the positions of the metal plane with respect to the lead frame and the patterns of the adhesive material and/or the insulative resin can be precisely defined and controlled. Particular embodiments of lead frames and their assembly in accordance with this invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a schematic view illustrating a manufacturing process of the multi-layer lead frame; Figure 2 is a plan view of a lead frame strip; Figure 3 is a plan view of a power supply plane strip; Figure 4 is a plan view of a ground plane strip; Figures 5 and 6 are schematic cross-sectional views of heat pressing devices; Figure 7 is a schematic cross-sectional view of an embodiment of a multi-layer lead frame according to the present invention; Figures 8(a), 8(b), and 8(c) are schematic cross-sectional views of the lead frame strip, the power supply plane strip, and the ground plane strip, respectively; and, Figure 9 is an exploded view of a conventional multi-layer lead frame known in the prior art. Fig. 7 shows a multi-layer lead frame 10 having a lead frame 12, a power supply plane 14, and a ground plane 16. According to the invention, the respective planes are adhered to each other by means of two insulative layers comprising an adhesive film 18 made of a thermosetting resin and another insulative resin film 19, which is an insulative liquid resin coated and dried. Since the two insulative layers 18 and 19 are served to keep a predetermined thickness between the respective planes, an insulation efficiency can still be improved. It should not be understood that the adhesive film 18 and the insulative resin film 19 are limited to be provided between the lead frame 12 and the power supply plane 14, and between the power supply plane 14 and the ground plane 16. A method of manufacturing a multi-layer lead frame 10 is described below with reference to Fig. 1, wherein A is a line of process for manufacturing a lead frame strip 20, B is a line of process for manufacturing a power supply plane strip 22, and C is a line of process for manufacturing a ground plane strip 24. The process line B intersects perpendicularly at Al with the process line A and, at the downstream of the intersection Al, the process line C intersects perpendicularly at A2 with the process line A. In the process line A, a metal strip is forwardly fed through several metal moulds (not shown). Along these moulds the metal strip is formed in a conventionally known manner. Thus, as schematically shown in Fig. 2, obtained is a lead frame strip 20 comprising a support frame 25 and a plurality of lead frames 12 longitudinally and continuously arranged and connected to each other by means of connecting portions. The support frame 25 is provided with a plurality of regularly arranged guide holes 26 which cooperate with guide means (not shown) for feeding this lead frame strip 20 forwardly through the metal moulds. One face of the lead frame strip 20 is coated with an insulator or adhesive. In the process line B, another metal strip is first intermittently coated with an adhesive made of thermosetting resin or an insulator on one face in accordance with a predetermined adhesion pattern defined between the lead frame 12 and the power supply plane 14, and an adhesive or insulator on the other face. The metal strip is then fed to a low-temperature dryer (not shown), where the coated adhesive is dried and becomes to be a coated film 18a. Then, the metal strip is fed forwardly through the metal moulds. In these metal moulds, the metal strip is formed as schematically shown in Fig. 3, and obtained is a power supply plane strip 22 comprising a plurality of power supply planes 14 longitudinally and continuously arranged and connected to each other by means of connecting portions 27. The connecting portions 27 are provided with regularly arranged positioning guide holes 28. A reference numeral 29 indicates terminals protruded from the power supply plane 14. A reference numeral 18 indicates a pattern of the adhesive film. In the same manner as the above, in the process line C, a still another metal strip is first intermittently coated with an adhesive made of thermosetting resin or an insulator in accordance with a predetermined adhesive pattern defined between the power supply plane 14 and the ground plane 16. The metal strip is then dried, so that the adhesive becomes to be a coated film 18b. Then, the metal strip is fed forwardly through the metal moulds. In these metal moulds, the metal strip is formed as schematically shown in Fig. 5 and obtained is a ground plane strip 24 comprising a plurality of ground planes 16 longitudinally and continuously arranged and connected to each other by means of connecting portions 30. The ground plane strip 24 is also provided with positioning guide holes 31 and terminals 32. Fig. 8 shows an embodiment for manufacturing a multi-layer lead frame according to this invention. Fig. 8(a) shows a ground plane strip 24 which is formed on the process line C (Fig. 1). Fig. 8(b) shows a power supply plane strip 22 which is formed on the process line B (Fig. 1). Fig. 8(c) shows a lead frame plane 20 which is formed on the process line A (Fig. 1), in the same manner as mentioned above. The ground plane 16 is provided on its surface facing to the power supply plane 14 with an insulative resin film 19 and also provided on the opposite surface with an adhesive film 18 of thermosetting resin. Also, the power supply plane 14 is provided on its surface facing to the lead frame 12 with an insulative resin film 19 and provided on the opposite surface with an adhesive film 18 of thermosetting resin. The lead frame 12 and the respective planes 14 and 16 are then laminated and heat-pressed together. Thus, the adhesive film 18 is thermoset to obtain a laminated multi-layer lead frame. In this laminating process, the power supply plane strip 22 and the ground plane strip 24 may be first positioned and then cut into individual planes to be laminated. Fig. 5 shows an example of the heat-press apparatus which comprises a cutting punch 35, a die 36, and a heater block 37. When the power supply plane strip 22 is positioned by means of the above-mentioned positioning guide holes 28 on a predetermined position above the lead frame 12 and fed to a position between the cutting punch 35 and the die 36, the cutting punch 35 is lowered to cut the connecting portions 27, so that the power supply plane strip 22 is cut into the individual power supply plane 14, which is then heat-pressed against the lead frame 12 provisionally heated by the heater block 37. The heat-pressing in this process is sufficient to soften the adhesive film 18a, but not to completely harden the adhesive film 18a. The pressing surface of the cutting punch 35 is provided with some suction holes (not shown) communicated to any vacuum means (not shown) for sucking to hold the power supply plane 14 and simultaneously to press the same against the lead frame 12. Thus, the power supply plane 14 is stably held against the lead frame 12 of the lead frame strip 20. The lead frame strip 20, to which the power supply plane 14 is adhered, is further fed forwardly and, at the intersection A2 of the process line C, the ground plane 16 is then provisionally adhered to the power supply plane 14 by means of the adhesion film 18b in the same manner as mentioned above. That is to say, when the lead frame strip 20 and the ground plane strip 24 are positioned to each other by means of the respective guide holes 26 and 31 and fed forwardly to the intersection A2 of the process line C, the cutting punch (not shown) is lowered to cut into the individual ground plane 16, which is then heat-pressed against the power supply plane 14 on the lead frame 12 provisionally heated by the heater block to soften to provisionally adhere the ground plane 16 against the power supply plane 14. Thus, the lead frame strip 20, to which the power supply plane 14 and the ground plane strip 16 are laminated, is further fed forwardly along the process line A. The lead frame strip 20 is further heated and pressed by upper and lower heater blocks 40a and 40b and thus the adhesive films or layers 18a and 18b are suitably thermoset to obtain a multi-layer lead frame 10. The respective terminals 29 and 32 of the power supply plane 14 and the ground plane strip 16 are connected to the corresponding leads of the lead frame 10 by a spot welding or the like. Although, in the above-mentioned embodiment, the adhesive film 18a for adhering the power supply plane 14 to the lead frame 12 is provided on the power supply plane 14, such an adhesive film 18a may be provided on the lead frame strip 20. Otherwise, the power supply plane 14 may be provided on its respective surfaces with adhesive films for adhering the same to the lead frame 12, as well as to the ground plane 16. Alternatively, as shown in Fig. 6, the power supply plane strip 22 and the ground plane strip 24 need not cut into individual planes, but may themselves be positioned with respect to each other by any positioning means, such as, pilot pins and superimposed onto the lead frame strip 20, so that they are heat-pressed together by means of upper and lower heater blocks 41 and 41 to thermoset the adhesive films 18. The connecting portions 27 and 30 of the power supply plane strip 22 and the ground plane strip 24 are thereafter cut into individual planes. These connecting portions 27 and 30 may be provided at the base thereof with V-shaped notches or the like extending to the direction of thickness so as to easily cut these connecting portions. Although, in the above mentioned embodiments, the multi-layer lead frame comprises three layers, i.e., the lead frame 12, the power supply plane 14 and the ground plane 16, this invention can also be applied to the other multi-layer lead frame comprising, such as, two layers, i.e., a lead frame and a single metal plane. In this case, the metal plane may be a power supply plane, a ground plane or a radiation/stage plane which is not electrically connected to the lead frame. A multi-layer lead frame manufactured according to the present invention may, of course, be comprised of four or more layers.

Claims: A process of manufacturing a multi-layer lead frame body (10) for a semiconductor device, the multi-layer lead frame body (10) including a lead frame body (12), a first metal plane (14) and a second metal plane (16), the process comprising the steps of: i. forming a lead frame strip (20) comprising a plurality of lead frame bodies (12) consecutively arranged and connected to each other; ii. forming a first metal plane strip (22) comprising a plurality of first metal planes (14) consecutively arranged and connected to each other; iii. coating a surface of the lead frame strip (20) with one of a thermoset resin adhesive film (18) or a liquid insulative resin film (19) in accordance with a first predetermined adhesion pattern; iv. coating a first surface of the first metal plane strip (22) with the other of said thermoset resin adhesive film (18) and said liquid insulative resin film (19) to that coated on the lead frame strip (20) in accordance with the first predetermined adhesion pattern; v. drying the adhesive and insulative films (18, 19) and subsequently positioning the first metal plane strip (22) adjacent to the lead frame strip (20), and adhering the first metal plane strip (22) to the lead frame strip (20) by heat pressing so that there is an insulation layer (19) and an adhesive layer (18) between the first metal plane strip (22) and the lead frame strip (20), wherein said lead frame strip and said metal plane strip have respective positioning means which are used for positioning said first metal plane strip with respect to said lead frame strip. A process according to claim 1, wherein said metal plane strip is punched to be cut into an individual metal plane (14,17), which is then adhered to said lead frame body (12) of said lead frame strip. A process according to any one of the preceding claims, wherein said insulative resin (19) is gel-like. A process according to any one of the preceding claims, wherein said positioning means comprise guide holes. A process according to any one of the preceding claims, comprising the additional steps of: in step ii additionally forming a second metal plane strip (24) comprising a plurality of second metal planes (16) consecutively arranged and connected to each other; in step iv additionally coating a second surface of the first metal plane strip (22) with one of a thermoset resin adhesive film (18) or a liquid insulative resin film (19) in accordance with a second predetermined adhesion pattern; coating a surface of the second metal plane strip (24) with the other of said thermoset resin adhesive film (18) and said liquid insulative resin film (19) to that coated on the second surface of the first metal plane strip (22) in accordance with the second predetermined adhesion pattern; in step v additionally positioning the first metal plane adjacent to the adhesive (18) or insulative (19) layers on the second metal plane strip (24); and adhering the first metal plane strip to the second metal plane strip (24), by heat pressing, so that there is an insulation layer (19) and an adhesive layer (18) between the first metal plane strip (22) and the second metal plane strip (24).

Inventors: SHIMIZU MITSUHARU, TAKEDA YOSHIKI, SHIMIZU, MITSUHARU, TAKEDA, YOSHIKI
Applicants: SHINKO ELECTRIC IND CO, SHINKO ELECTRIC INDUSTRIES CO. LTD.
Application year: 1991
Main classification: H01L23
IPC codes: H01L23, H01L21