Semiconductor device mounted on a substrate

Abstract: A semiconductor device comprises a semiconductor chip; a resin package body (11) for accommodating the semiconductor chip; a plurality of interconnection leads (14) provided on the resin package body along a lower edge of the package body such that the interconnection leads project outward from the lower edge; and a heat dissipation lead (31) held on the resin package body for dissipating heat generated by the semiconductor chip. The heat dissipation lead (31) comprises a plate of a heat conducting material having a stage part and a heat sink part, wherein the stage part is held inside the resin package body and supporting the semiconductor chip thereon, while the heat sink part projects outward from the resin package body and including a part that extends in a downward direction. The heat sink part has a lower edge (31a) that is formed at a level substantially flush with the outer lead part of the interconnection leads such that the semiconductor device is held upright, when placed on the substrate, by the outer lead part of the interconnection leads and by the lower edge of the heat sink part of the heat dissipation lead.

Description: The present invention relates to a semiconductor device and a substrate for mounting the same according to the preamble of claim 1. From DE-A-3 421 539 a semiconductor device and a substrate for mounting the same is known, comprising: a semiconductor chip; a resin package; interconnection leads having inner and outer parts; a heat dissipation lead having a stage part and a heat sink part extending in a direction perpendicular to a circuit board on which the device is to be mounted. The heat sink part has a lower edge that is flush with the outer lead parts. From the document JP-A-62-263667 a semiconductor device is known which is formed so as to be mounted in a space saving manner on a substrate. This known semiconductor device comprises a resin package accommodating a chip on a stage, wherein connection terminals project from one side of the package to a substrate supporting the package. Furthermore in order to improve the efficiency for mounting semiconductor devices on a support substrate such as a printed circuit board, a package structure designed for the surface mounting technology (SMT) is used extensively. By using the surface mounting technology, the semiconductor device can be mounted on the circuit board without providing holes for inserting leads of the device. The soldering of the leads is achieved by merely placing the device on the circuit board and passing through a heating furnace for causing a reflowing of the solder alloy. Thereby, the efficiency of the mounting process is improved significantly and the fabrication cost of electronic apparatuses that use the semiconductor devices is significantly reduced. In order to mount the semiconductor devices as many as possible on a single support substrate, a so-called single in-line package (SIP) is proposed. In the single in-line package, the leads are provided along a single edge of a flat package body to extend perpendicularly with respect to the edge, and the package body is held upright on the substrate by inserting leads into the corresponding holes of the substrate. As the package body is held vertically on the substrate, one can increase the number of the packages that are mounted on the single substrate. Further, such a structure is advantageous for cooling the device. In order to combine the advantageous feature of the single in-line package with the advantageous feature of the surface mounting technoloy, a package structure shown in FIG. 1 is proposed in the United States Patent 4,975,763. Referring to FIG. 1, the package designated by a numeral 1 includes a flat resin package body 2 that accommodates therein a semiconductor chip 3. At an edge 2a of the flat package body 2, there are provided a number of leads each having an inner lead part 4a connected to a bonding pad of the chip 3 and an outer lead part 4b extending outward from the edge 2a. Further, the outer lead part 4b of the leads 4 is bent laterally with respect to the extending direction of the leads 4. In order to support the package body 2 on the substrate at the time of mounting, there is provided a pair of study 5a each including a stop portion 6 and a cylindrical clip portion 7 of a reduced diameter for inserting into a corresponding hole provided on the substrate. FIG. 2 shows the mounting of the package 1 on a substrate 8, wherein the substrate 8 is formed with a hole 8a for holding the clip portion 7 of the stud 5. There, the portion 7 is inserted into the hole 8a as shown in FIG. 2 and the package body 2 is held upright on the substrate 8. The substrate 8 carries thereon a conductor pattern 8b for wiring, and the lead 4 is contacted with the conductor pattern 8b when the package 1 is held on the substrate 8. By passing the substrate 8 together with the package 1 in the state shown in FIG. 2, the soldering alloy provided on the conductor pattern 8b causes a reflow and the lead 4 is soldered firmly upon the conductor pattern 8. In the conventional package structure, there is a problem in that one has to provide the hole 8a on the substrate 8 in correspondence to the stud 5 for holding the package body 2 on the substrate 8. As each lead 4 has to engage with corresponding pattern 8b when the package is mounted, it is necessary that the hole 8a be formed with high precision. This requirement ist particularly acute in the recent semiconductor devices that have a large number of leads on the package body. Obviously, such a formation of the hole and the insertion of the stud into the hole undermine the advantageous feature of the surface mounting technology, and the efficiency of mounting is inevitably deteriorated. Meanwhile, there are various semiconductor devices that generate heat upon operation. Thus, there are needs for a semiconductor package that facilitates efficient cooling of the device. The conventional package of FIG. 1 has a drawback with respect to this point in that the package lacks a cooling fin. Thus, the dissipation of the heat has to be achieved via the resin package body. As will be easily understood, such a process of heat dissipation is inefficient and the package structure of FIG. 1 can be used only for those devices that produce little heat. The process for mounting a cooling fin on the resin package body complicates the fabrication process of the device. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved useful semiconductor device and a substrate for mounting the same, wherein the problems of the prior art devices are eliminated, and in particular to provide a semiconductor device which has a single in-line package of the surface mounting type with an improved efficiency of heat dissipation and with an decreased space occupied by the semiconductor device. This object is solved by a semiconductor device and a substrate for mounting the same by the features of the characterizing part of claim 1. Advantageous embodiments are defined in the dependent claims. According to an embodiment of the present invention, one can provide a semiconductor device that can be held upright on the substrate such as a printed circuit board while maintaining an excellent efficiency of heat dissipation. It should be noted that the device is held upright on the substrate by the outer lead part of the interconnection leads and the heat dissipation lead. As the outer lead part of the interconnection leads are bent laterally so as to extend substantially in parallel to the mounting surface of the substrate and for engagement with said substrate. Such a semiconductor device is particularly suitable for mounting on the substrate by the surface mounting technology. Thereby, the heat dissipation lead is used simultaneously as a heat sink and a mechanical support. Other objects and further features of the present invention will become apparent form the following detailed description when read in conjunction with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a diagram showing a conventional semiconductor package for surface mounting; FIG.2 is a diagram showing the mounting of the semiconductor device on a substrate; FIG.3 is a diagram showing a semiconductor device having a package according to a first embodiment of the present invention in a plan view; FIG.4 is a diagram showing the semiconductor device in a side view in the state that the device is mounted on a substrate; FIG.5 is a diagram showing the semiconductor device of FIG.3 in an elevational cross section; FIG.6 is a diagram showing a modification of the device of FIG.3; FIG.7 is a diagram showing the mounting of the semiconductor device of FIG.6 on a substrate; FIG.8 is a diagram showing a modification of the device of FIG.6; FIG.9 is a diagram showing another modification of the device of FIG.6; FIG.10 is a diagram showing the construction of a composite heat dissipation lead used in the package of the present invention; FIG.11 is a diagram showing various combinations of the materials used for the heat dissipation lead of FIG. 10; FIGS.12(A) - 12(C) are diagrams showing the structure of other composite heat dissipation leads; and FIGS.13(A) - 13(F) are diagrams showing various examples of the stress relaxation structure used in the package of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the description will be made on a semiconductor device 10 according to a first embodiment of the present invention with reference to FIGS.3 - 5, wherein FIG.3 shows the device 10 in a perspective view while FIG.4 shows the device 10 in a side view. Further, FIG.5 shows the device 10 in an elevational cross section. Referring to the drawings, the semiconductor device 10 includes a package body 11 of an epoxy resin in which a semiconductor chip 15 is embedded as shown in FIG.5 by a transfer molding process. The package body 11 has a flat shape defined by a pair of opposing flat major surfaces. At the bottom edge of the package 11, a plurality of interconnection leads 14 are provided to extend in a downward direction, while there is provided a heat dissipation lead 12 to extend in an upward direction from the top edge of the package body 11. The heat dissipation lead 12 thus extending in the upward direction is then bent twice successively, each time by an angle of about 90 degrees, and extends in the downward direction along the flat major surface of the package body 11. Thereby, the part of the heat dissipation lead 12 that is located outside the package body 11 forms a heat sink part 12b that is ended at a lower edge part 12a. On the other hand, the heat dissipation lead 12 has a stage part 12c that is embedded in the package body 11 such that the stage part 12c supports the semiconductor chip 15 thereon. See the cross sectional view of FIG.5. Referring to FIG.5, it should be noted that each lead 14 is formed of an outer lead part 14a projecting outward from the package body 11 and an inner lead part 14b held inside the package body 11. The inner lead part 14b is connected to the semiconductor chip 15 by a bonding wire 14c. There, the outer lead part 14a is bent laterally by an angle of about 90 degrees as shown in FIG.4 for the engagement with a substrate 19 such as a printed circuit board. It should be noted that the substrate 19 carries thereon conductor patterns forming a circuit with a solder 18 provided thereon. Further, the heat dissipation lead 12 is formed such that the lower edge part 12a is formed at a level substantially flush with the level of the laterally-bent outer lead part 14a of the interconnection leads 14. By constructing the device as such, the device is held upright on the substrate 19 by the interconnection lead 14 and the heat dissipation lead 12. Thus, by passing the device together with the substrate 19 through a heating fixture, a reflowing of the solder 18 occurs and the device is mounted firmly upon the substrate 19 as indicated in FIG.4. Thereby, the device of the present embodiment can be mounted on the substrate by the surface mounting technology and the efficiency of production of electronic apparatuses is improved significantly. Further, the package structure as disclosed in the present embodiment is applicable to the devices wherein the semiconductor chip 15 generates substantial heat. The heat is transferred from the chip 15 to the heat sink part 12b along the heat dissipation lead 12 and radiated into the space. In the embodiment of FIG.4, it can be seen that the heat sink part 12b of the heat dissipation lead 12 is fixed upon the flat major surface of the package body 11 by a heat-conductive adhesive 13. Thereby, the efficiency of heat dissipation from the semiconductor chip 15 to the heat sink part 12b and further to the space is even more improved. FIG.6 shows a semiconductor device 30 according to a modification of the semiconductor device 10 of FIG.3. In the device of FIG.6, a heat dissipation lead 31 substantially identical with the heat dissipation lead 12 is used, wherein the heat dissipation lead 31 is different from the heat dissipation lead 12 in one point that the heat dissipation lead 31 has a lower edge part 31a that is formed into a comb-shape and is bent laterally for improved mechanical stability of the device. By bending the part 31a laterally, the area for soldering the lead 31 on the substrate is increased. See FIG.7. Preferably, the teeth of the lower edge part 31a are provided in correspondence to the gap formed between the adjacent interconnection leads 14 for avoiding possible short circuit connection. Further, the comb-shape construction of the lower edge part 31a facilitates the bending process. FIG.8 shows a semiconductor device 40 according to a modification of the device 30 of FIG.6, wherein the device has a heat dissipation lead 41 similar to the heat dissipation lead 31 except that the heat dissipation lead 41 has a lower edge part 41a that is bent in two, opposite lateral directions. There, each tooth of the comb-shaped part 41a is bent laterally and alternately in two opposing directions for improved mechanical stability on the substrate. Alternatively, the teeth of the comb-shaped part 31a is bent in either of the two opposing directions to avoid any obstacles provided on the substrate. FIG.9 shows a semiconductor device 50 according to a modification of the device 30 of FIG.7, wherein the device 50 has interconnection leads 50 corresponding to the interconnection leads 14 except that each lead has an outer lead part that is bent laterally at the lower edge of the package body 11 where the lead projects outward from the package body. Thereby, the length of the lead 50 is reduced and the delay in the signal transmission through the lead is minimized. Further, such a reduction in the length of the lead 50 minimizes the chance that external noises penetrate into the circuit from the exposed part of the interconnection lead 50. In correspondence to the reduced length of the interconnection lead 50, the heat dissipation lead 31 is formed with a reduced length such that the lower edge 31a is formed with a flush relationship with the outer lead part of the interconnection lead 50. FIG.10 is a diagram showing the cross section of a lead frame from which the heat dissipation lead 12 and the interconnection leads 14 of the semiconductor device of FIG.3 are formed. It should be noted, however, that the description given hereinafter with respect to the structure of the lead frame is applicable also to the heat dissipation leads and the interconnection leads of other embodiments. Referring to FIG.10, it will be seen that the heat dissipation lead 12 includes a plate 20c of a copper alloy (MF202 - a trade name, an alloy of Cu-Sn-Zn), and clad layers 20a and 20b, both of a Fe-Ni alloy, cover the first and second, mutually opposing major surfaces of the plate 20c, respectively. The clad layers 20a and 20b may be provided for example by a thermal bonding process. By using such a composite structure for the heat dissipation frames 12 as well as for the interconnection leads 14, it is possible to impart various preferable features to these parts such as a high electrical conductivity, a high mechanical strength and a high thermal conductivity. In order to obtain the desirable property as set forth above, it is preferable to set the thicknesses t 1 and t 2 of the clad layers 20a and 20b with respect to the thickness T of the copper alloy plate 20c to satisfy a relationship 0.3 ≤ (t/T) ≤ 2, where t represents the total thickness of the clad layers 20a and 20b (t = t 1 + t 2 ). Designating the total thickness of the heat dissipation lead 12 by a parameter W as indicated in FIG.10, it is also preferable to set the ratio t/W to fall in the range 0.4 ≤ (t/W) ≤ 0.7. Within the range where the foregoing two conditions (1) and (2) are met, one can set the thickness of the layers 20a, 20b and 20c as desired. FIG.11 shows a few examples of the combination that satisfy the foregoing requirements, under a constraint that the thickness t 1 is set equal to the thickness t 2 and that the total thickness W is set to about 150 µm. Further, it should be noted that, as long as the foregoing conditions (1) and (2) are met, one may modify the construction of the lead frame as shown in FIGS.12(A) - 12(C), where FIG.12(A) shows acase that clad layers 20e and 20f of the copper alloy are used to cover a core layer 20d of the Fe-Ni alloy, whereas FIG.12(B) shows a structure wherein a single clad layer 20g of the Fe-Ni alloy covers a core layer 20h of the copper alloy. Further, FIG.12(C) shows a structure similar to the structure of FIG.10 except that the thickness of both clad layers 20j and 20k, provided at both sides of a core layer 20i of the copper alloy in correspondence to the clad layers 20a and 20b, is made non-uniform. Even in the case of FIGS.12(A) - 12(C), one can obtain a lead frame member that has a sufficient electric and thermal conductivity as well as a sufficient mechanical rigidity, as long as the foregoing conditions (1) and (2) are met. FIGS.13(A) - 13(F) are diagrams showing the construction of the stage part 12c of the device shown in FIG.5. Referring to the drawings, the stage part 12c is provided with one or more apertures or openings such as an aperture 21a shown in FIG.13(A) for absorbing a mechanical stress that occurs in the stage part 12c at the time when the reflowing of the solder alloy is achieved. It should be noted that, without such apertures provided on the stage part 12c, there is a substantial risk that the semiconductor chip 15 comes off from the stage part 12c due to the mechanical deformation caused by the difference in the thermal expansion between the lead frame and the chip 15. The aperture 21a of FIG.13(A) extends laterally through the stage part 12c, while FIG.13(B) shows four apertures 21b that are disposed laterally and vertically to form a cross-shaped pattern. FIG.13(C), on the other hand, shows apertures 21c that includes a cross-shaped opening at the center of the stage part 12c and four elongated openings that extend obliquely to surround the central cross-shaped pattern. FIG.13(D) shows an aperture pattern 21d that includes a pair of T-shaped openings disposed to oppose with each other vertically and a pair of E-shaped openings that are disposed to oppose with each other laterally. FIG.13(E) shows an aperture pattern 21e that includes four elongated openings disposed radially. Further, FIG.13(F) shows four elongated apertures 21f that are disposed parallel with each other to extend laterally. Any of these apertures are effective in avoiding the concentration of the thermal stress particularly at the time of the reflowing of the solder alloy. Further, the present invention is not limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.

Claims: A semiconductor device mounted vertically on a substrate, comprising: a semiconductor chip (15); a resin package body (11) accommodating therein said semiconductor chip, said resin package body having first and second, mutually opposing major surfaces connected with each other by a circumferential wall that surrounds said resin package body, said circumferential wall including a substantially straight bottom edge facing the mounting surface of said substrate and a top edge opposing said bottom edge; and a plurality of interconnection leads (14) provided on said resin package body along said bottom edge such that said interconnection leads project outward from said bottom edge, each of said interconnection leads including: an inner lead part (14b) held inside said resin package body and connected electrically to said semiconductor chip; and an outer lead part (14a) located outside said resin package body and contacting an external conductor pattern on said substrate; characterized in that said device further comprises: a heat dissipation lead (12) for dissipating heat generated by said semiconductor chip (15), said heat dissipation lead comprising a plate of heat conducting material having a stage part (12c) and a heat sink part (12b) continuous with said stage part, said stage part being held inside said resin package body and supporting said semiconductor chip thereon, said heat sink part projecting outwardly from said top edge of said resin package body and including a part that extends substantially parallel to said first and second major surfaces in a direction from said top edge to said bottom edge, said heat sink part having at least one portion with a free edge flush to said outer lead part of said interconnection leads when viewed in a direction perpendicular to said first and second major surfaces, said at least one portion (12a) of said heat sink part (12b) being separated from any of said first and second major surfaces; said at least one portion (12a) thereby forming at least one support leg (12a) supporting said resin package body upright on said substrate. A semiconductor device as claimed in claim 1, characterized in that the outer lead parts (14a) of said interconnection lead are bent laterally so as to extend substantially in parallel to the mounting surface of said substrate and for engagement with said substrate (19). A semiconductor device as claimed in claim 1, characterized in that respective outer lead parts of said interconnection lead (81) are bent laterally so as to extend substantially in parallel to the mounting surface of said substrate in one of two opposite directions. A semiconductor device as claimed in claim 3, characterized in that respective outer lead parts (81) are bent alternately in said two opposite directions. A semiconductor device as claimed in claim 1, characterized in that said heat sink part (12b) of said heat dissipation lead extends from said package body in an upward direction at said upper edge and is bent subsequently in the downward direction towards said mounting surface. A semiconductor device as claimed in claim 5, characterized in that said package body (11) has substantially flat major surfaces, and said heat sink part (12b) of said heat dissipation lead extends in the downward direction substantially orthogonally to said mounting surface of said substrate along one of said major surfaces. A semiconductor device as claimed in claim 6, characterized in that said heat sink part (12b) establishes an intimate contact with said side wall of said package body (11) by means of an adhesive layer (13). A semiconductor device as claimed in claim 6, characterized in that said lower edge (31a) of said heat sink part (31) is bent laterally so as to extend substantially in parallel to the mounting surface of said substrate for engagement with said substrate. A semiconductor device as claimed in claim 6, characterized in that said lower edge (31a) of said heat sink part (31) includes a plurality of teeth spaced from each other and projecting laterally substantially in parallel to said mounting surface of said substrate in correspondence to said lateral bending of said lower edge. A semiconductor device as claimed in claim 9, characterized in that each tooth (41a) of said teeth projects in one of two opposing directions. A semiconductor device as claimed in claim 9, characterized in that each tooth (31a, 41) of said teeth is formed in correspondence to a space formed between adjacent interconnection leads. A semiconductor device as claimed in claim 1, characterized in that each interconnection lead (51) has said outer lead part bent laterally substantially in parallel to said mounting surface of said substrate at a part where the interconnection lead emerges from the lower edge of the package body (11). A semiconductor device as claimed in claim 1, characterized in that said stage part (12c) includes an aperture (21a - 21f) for relieving a concentration of thermal stress in correspondence to where said stage part contacts with said semiconductor chip. A semiconductor device as claimed in claim 1, characterized in that said heat dissipation lead (12) comprises a composite plate comprising one or more of first alloy layers (20a, 20b, 20d, 20g, 20j, 20k) containing iron and one or more of second alloy layers (20c, 20e, 20f, 20h, 20i) containing copper, said first alloy layers having a total thickness t and said second alloy layers having a total thickness T that satisfy a relationship 0.3 ≤ t/T ≤ 2. A semiconductor device as claimed in claim 1, characterized in that said heat dissipation lead (12) comprises a composite plate comprising one or more of first alloy layers (20a, 20b, 20d, 20g, 20j, 20k) containing iron and one or more of second alloy layers (20c, 20e, 20f, 20h, 20i) containing copper, said first alloy layers having a total thickness t and said composite plate having a thickness W that satisfy a relationship 0.4 ≤ t/W ≤ 0.7.

Inventors: KASAI JUNICHI, MITOBE KAZUHIKO, SAITO KOUJI, SONO MICHIO, YOSHIMOTO MASANORI, KASAI, JUNICHI, MITOBE, KAZUHIKO, SAITO, KOUJI, SONO, MICHIO, YOSHIMOTO, MASANORI, KASAI, JUNICHI, C/O FUJITSU LIMITED, Mitobe, Kazuhiko, c/o Fujitsu Limited, Saito, Kouji, c/o Fujitsu Limited, Sono, Michio, c/o Fujitsu Limited, Yoshimoto, Masanori, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: H01L23
IPC codes: H05K1, H01L23