Resin-encapsulated electronic device

Abstract: A resin sealed electronic device has an electronic element (30), a first external lead (10) with an element placement pad (11) having a thickness t of less than 0.1 mm, and a second external lead (20), which is disposed at a distance from the element placement pad (11), the first external lead (10) being bent into an S shape, the bending depth d thereof being made at least the thickness t of the first external lead (10), and the thickness T of the sealing resin on the non-element side of the element placement pad (11) being made smaller than the bending depth d. The electronic element (30), part of the first external lead (10), and part of the second external lead (20) are sealed by a sealing resin(40). This structure provides a compact electronic device, the vertical, horizontal, and height dimensions of which are all under 1 mm.

Description: The present invention relates to a method for producing an electronic device according to the preamble of claim 1. US-A-5,508,557 describes a surface mounting type diode to be mounted on a circuit board comprising a diode chip, a pair of plate-like leads, each of the leads including an inner end and an outer end, a first bend closer to the inner end, a second bend closer to the outer end and an intermediate portion between the first and second bends, a single resin package enclosing the diode chip together with part of the respective leads. The resin package is realized by introducing fluid resin in the molding cavity through a runner located on an upper mold member and directed towards the top of the electronic device. JP-A-4 206 764 shows a lead frame for a semiconductor element. The sealing resin is injected into a cavity for forming the sealing resin package through a port with the longitudinal direction of the first and second leads being in parallel with the injection direction. With reductions in the size of electronic equipment, there has been an increase in the use of surface mount semiconductor devices, such as diodes and transistors, and the size of these devices also is being reduced. Fig. 2 shows the general construction of a surface mount diode of the past, Fig. 2 (A) being a plan view thereof, and Fig. 2 (B) being a cross-section view as seen from the direction indicated by the arrows along the line II-II in Fig. 2 (A). The electronic device 100 of Fig. 2 has a first lead 110, which has a electronic element placement pad (die pad) 111 for placement of an electronic element, and a second lead 120, which is disposed at a distance from the element placement pad 111. A semiconductor element 130 is placed on the element placement pad 111. A bonding wire 150 makes a connection between an external connection terminal of the semiconductor element 130 and the second lead 120. The semiconductor element 130, the electronic element placement pad 111, the inner lead part of the first lead 110, the inner lead part of the second lead 120, and the bonding wire 150 are sealed by a sealing resin 140. As shown in this drawing, the first lead 110 and the second lead 120 are bent in an S shape, with one end of the leads 110 and 120 exposed to the outside of the sealing resin 140, so as to form outer lead parts. The lower surfaces of the outer leads extend in a direction that is substantially parallel to the bottom surface 141 of the sealing resin 140, and are substantially on the same plane as the bottom surface141 of the sealing resin 140. The above-noted electronic device is manufactured by first punching out and bending a thin metal sheet to the appropriate shape to form a lead frame, onto which the semiconductor device is placed. Then, after making the prescribed connections, the device is sealed using sealing resin. The sealing with the sealing resin 140 is done within a die of the prescribed shape, so as to include the electronic element placement pad 111, the inner lead part of the first lead 110, and the inner lead part of the second lead 120, resin being injected via a resin injection port 190, indicated by the double-dot-dash line, on one of the shorter sides of the device. The dimensions of a usual resin sealed electronic device of the past were approximately a vertical dimension (X-axis dimension L X in Fig. 2) of 1.3 mm, a horizontal dimension (Y-axis dimension L Y in Fig. 2) of 0.8 mm, and a height (Z-axis dimension H in Fig. 2) of 0.7 mm. Because the thickness of the lead frame used in an electronic device of the past was 0.1 mm or greater, however, it was difficult to achieve a surface mount electronic device with a resin package having all of the vertical, horizontal, and height dimensions smaller than approximately 1 mm, including resin-sealed semiconductor devices making use of a semiconductor substrate. Because the thickness of the lead frame is 0.1 mm or greater, the spacing between the element placement pad 111 of the first lead 110 and the second lead 120 grows to over 0.2 mm by the formation of the lead. Because of the relationship between such parameters as the lead bending depth, the associated thickness of the resin at the bottom of the element placement pad 111 that is required therefor, the lead length required for bending, and the establishment of a flat surface for placement of an element, in the case of diodes in particular, it was not possible to achieve a vertical length of less than 1.0 mm. As electronic devices became smaller, because of the delicate bending shape of the bent parts 112 and 122 near the bottom surface of the sealing resin of first and second leads, there was a tendency toward such problems as insufficiencies in the adhesion and filling in of sealing resin, the strength of the lead itself, and the adhesive strength between the lead and the sealing resin, and poor adhesion and filling in of solder used for mounting, and it was difficult to achieve an electronic component that provided improvements in these deficiencies. Accordingly, it is an object of the present invention to provide a method for producing an electronic device that solves the problems of the limitation in size reduction of surface mount resin sealed electronic devices in the past, and to enable the achievement of an electronic device having a resin package with vertical, horizontal, and height dimensions that are all below 1 mm. It is another object of the present invention to provide a method for producing a resin sealed surface mount electronic device that, even with a reduction in size of the electronic device, provides good filling in of sealing resin to the bent parts near the bottom surface of the sealing resin of first and second leads, good adhesion strength between the leads and the sealing resin, and good strength in the leads themselves, and further providing good adhesion and filling in of solder when the device is mounted. To achieve the above-noted object, the present invention is characterized in, that the sealing resin is injected from a side position on a longer side of the resin die, said position being offset from the center towards one shorter side thereof with the first direction being perpendicular to the direction of the injection of the sealing resin. By the above invention, it is possible to limit the height of the electronic device, and to achieve the flat area required in the element placement pad. Additionally, because the spacing between the element placement pad and the second lead can be made short, it is possible to reduce the dimension in the vertical direction. Furthermore, the injected resin extends well into the package die, without a tendency toward the formation of eddies and/or accumulations, thereby preventing problems with insufficient sealing resin filling. In the configuration of the above-noted first aspect of the present invention, it is preferable that the spacing between the element placement pad and the second lead be made no greater than 0.12 mm. Using this preferable configuration, it is possible to make a further reduction in the vertical-direction dimension of the electronic device. In the above-noted configuration, it is preferable that the outer vertical, horizontal, and height dimensions of the sealing resin package all be no greater than 1.0 mm. Using this preferable configuration, it is possible to achieve a compact electronic device that was not possible to achieve in the past, thereby contributing to the reduction in size of electronic equipment. According to the present invention, it is preferable that the width of the inner lead parts of the first and second leads within the sealing resin package be of a substantially uniform width and not broaden beyond the exposed part. Using this preferable configuration, it is possible to obtain a compact electronic device having a width (Y-direction dimension) that does not become large. The effect of reducing the package size is particularly significant in the case in of an electronic device having three or more terminals. In the above-noted configuration, it is preferable that the thickness of the electronic element be substantially the same as the thickness t of the first lead. Using this preferable configuration, it is possible to make the height of the bonding wire the same as that of the chip. According to the present invention, it is preferable that near the bottom surface of said sealing resin surface the bending radius R of outer surface of the bent part of the first lead opposite to the surface on which said electronic element is placed is at least 0.05 mm, and is not greater than the lead thickness t. Using this preferable configuration, it is possible not only to prevent both constriction of material and lead bending during lead formation, but also to achieve flexibility of the frame with respect to stress that is applied in downstream processes. According to the present invention, it is preferable that the sealing resin includes filler that has a particle diameter that is no greater than half the bending depth d of the lead. This preferred configuration facilitates the filling in of sealing resin and filler at the lower surface of the bent lead, thereby maintaining sufficient formation strength. Fig. 1 is a drawing that shows the general construction of an electronic device as made by the method according to the present invention, (A) being a plan view thereof, and (B) being a cross-section view thereof, as seen from the direction indicated by the arrows along the line I-I shown in (A). Fig. 2 is a drawing which shows the general construction of an example of a electronic device of the past, (A) being a plan view thereof, and (B) being a cross-section view thereof, as seen from the direction indicated by the arrows along the line II-II shown in (A). Fig. 1 shows the general construction of an electronic device produced according to the present invention, (A) being a plan view thereof, and (B) being a cross-section view thereof, in the direction indicated by the arrows along the line I-I shown in (A). As shown in this drawing, the electronic device 1 has a first lead 10, which has an element placement pad (die pad) 11, and a second lead 20, which is disposed at a distance from the element placement pad 11. A semiconductor electronic element 30 is mounted to the element placement pad 11 by means of die bonding or the like. Bonding wires 50 make a connection between an external connection terminal of the electronic element 30 and the second lead 20. The semiconductor electronic element 30, the element placement pad 11, the inner lead part of the first lead 10, the inner lead part of the second lead 20, and the bonding wire 50 are sealed by a sealing resin 40 package. As shown in Fig. 1, the first lead 10 and the second lead 20 are bent in an S shape (substantially a step shape), with one end of the leads 10 and 20 exposed to the outside of the sealing resin 40 package, extending in a direction that is substantially parallel to the bottom surface of the sealing resin 40 package so as to form outer lead parts respectively. In this case, the thickness t of the first lead 10 is less than 0.1 mm. If this thickness t is larger than this, it is not possible to achieve a compact electronic device. In a case in which the thickness of the inner lead part within the sealing resin package and the thickness of the outer lead part differ (for example, in the case in which the outer lead part is plated with solder), the thickness t refers to the thickness of the inner lead part. If the bending depth of the first lead 10 shown in Fig. 1 is d, it is necessary that the thickness t of the lead satisfy the condition d t. If the thickness of the sealing resin package on the non-element side of the element placement pad 11 is T, it is necessary that the condition T<d be satisfied. By satisfying these relational conditions, it is possible to make the vertical-direction (X-axis direction) dimension L X and the height-direction (Z-axis direction) dimension H small. In the above-noted embodiment of an electronic device produced according to this embodiment, it is preferable that the widths of the inner lead parts of the first lead and second leads within the sealing resin package be of substantially uniform width and not broaden beyond the widths of the exposed (outer) lead parts. In the past, because thick leads were bent within the resin, externally applied stress caused by cutting of the lead frame or common connection parts during the manufacturing process risked pulled-out leads and damage to the sealing resin package. To prevent these problems, therefore, the lead ends of the first and second leads within the sealing resin package were widened (refer to Fig. 2 (A)). With this embodiment of the present invention, however, by making the thickness of the leads less than 0.1 mm, it is possible to establish a mechanical balance, thereby enabling the shape (width) of the first and second leads to be made substantially uniform, without widening in its inner lead part. By doing this, it is possible to reduce the horizontal-direction (Y-axis direction) dimension L Y . To achieve a balance in strength within the sealed package, it is preferable that the inner lead part thickness t be made substantially the same as the semiconductor element 30 thickness. The position of the sealing resin injection port 90 as shown by the double-dot-dash line in Fig. 1, is preferably on a longer side of the package, offset from the center thereof forward one of the shorter sides, avoiding the bonding wires 50, with sealing resin being injected therethrough in the direction shown by the arrow, in order to prevent the bonding wires 50 from toppling by injection pressure of the sealing resin acting on the side surfaces of the bonding wires 50 directly. By making the resin package small, it would be difficult as done in the past to provide a resin injection port on a shorter side of the package. Additionally, because the spacing between the inner wall of the resin die and the inner lead becomes narrow, it would be difficult to cause resin to sufficiently fill in under the inner lead. For this reason, by injecting sealing resin, as noted above, from a longer side at a position that is offset forward one of the shorter sides of the package, the resin fills into the die smoothly, thereby preventing problems with insufficient resin filling. It is preferable that the bending radii R at the outer surfaces of the bent part of the inner lead part of the first lead 10 near the bottom surface of the sealing resin be at least 0.05 mm and no greater than the thickness t of the lead. Specifically, in Fig. 1 (B), it is preferable that the bending radii R 11 and R 12 of the outer surfaces of the bent part 12 of the first lead 10 in the region of the bottom surface of the sealing resin package be at least 0.05 mm and no greater than the thickness t of the lead. Additionally, it is preferable that the bending radii R 13 and R 14 of the outer surfaces of the bent part near the element placement pad 11 of the inner lead part of the first lead 10 also satisfy the same type of condition. It is further preferable that the outer surface bending radii R 21 and R 22 of the bent part 22 of the second lead 20 near the bottom surface of the sealing resin package be at least 0.05mm and no greater than the thickness of the second lead. Additionally, it is preferable that the bending radii R 23 and R 24 of the outer surfaces of the bent part nearer to the wire bonding end of the inner lead part of the second lead 20 satisfy the above-noted type of condition. If these conditions are satisfied, it is possible to prevent constriction of material and bending of leads when the leads are formed, as well as to achieve flexibility of the frame with respect to stress that is applied in downstream processes. A more specific form of the above-noted embodiment is described below. Using a lead frame having a thickness t of 0.08 mm, with a bending depth d of the first lead 10 of 0.12 mm and a resin thickness T of 0.11 mm at the bottom of the element placement pad 11, it was possible to place an semiconductor element 30 having a chip size of 0.3 mm square, the spacing L 1 between the element placement pad 11 and the second lead 20 being 0.1 mm. All the bending radii R 11 , R 12 , R 13 , R 14 , R 21 , R 22 , R 23 , and R 24 on the outer surfaces of the bent parts of the inner lead parts were made 0.05 to 0.1 mm. Under these conditions, the resin package vertical dimension (X-axis direction length in Fig. 1) L X , horizontal dimension (Y-axis direction length in Fig. 1) L Y , and height (Z-axis direction length in Fig. 1) H were 1 mm, 0.5 mm, and 0.5 mm, respectively, this representing an extremely compact package. An example of a method for manufacturing the above-noted electronic device is described below. First, a flat lead frame having a thickness of 0.08 mm was punched out and formed with a 0.12 mm depth bend. An element placement pad was formed on the first lead, and a wire bonding region was formed on the second lead. Next, the element placement pad was placed on a heater, and die bonding of a semiconductor element was performed while applying heat thereto. Then, the external connection terminal of the semiconductor element was wired to one end of the external lead with bonding wire. After that, the element placement pad, the semiconductor element, and one end of the first and second leads were sealed using a sealing resin. The resin injection port used to do this was provided on one of the longer sides of the package, offset from the center toward a shorter side. The particle diameter of the filler that was included in the resin was selected as approximately 50 µm or smaller, which was not greater than half of the bending depth d of the leads, so as to improve the filling in of the sealing resin around the bottom parts of the first and second leads. With a lead thickness t of 0.08 mm, if the lead bending depth d was made shallower than the lead thickness t, it was found that the balance between the thickness of the resin that holds the lead at the bottom part of the lead and the lead strength is disturbed, resulting in a tendency for the package to crack. It was further discovered that, with a lead thickness t of 0.08 mm, if the lead bending depth d was made larger than 0.13 mm in an attempt to shorten the vertical-direction (X-axis direction) dimension L X , it was difficult to achieve a flat surface on the element placement pad for the purpose of die bonding, making it difficult to make an electronic device any smaller. Thus, it was found to be preferable to establish the depth d as no greater than 0.13 mm under above condition. Next, solder plating was done on the outer lead part of the first lead, having an element placement pad, and the outer lead part of the second lead. Although this can result in a case in which the lead thickness after solder plating exceeds 0.1 mm, this presents no problem. Finally, the lead frame was cut at a length of 0.2 mm from the outer edge of the resin package, thereby completing the device.

Claims: Method for producing an electronic device, said electronic device comprising: an electronic element (30); a first lead (10) with an element placement pad (11) having a thickness t of less than 0.1 mm on which said electronic element (30) is placed; and a second lead (20) that is disposed at a distance from said element placement pad (11), wherein said electronic element (30), element placement pad (11), part of said first lead (10) and part of said second lead (20) are placed in a resin die and sealed by injecting a sealing resin through a resin injection part in said resin die to form a rectangular sealing resin package (40) having shorter sealed parts of said and longer sides said first and second leads emerging from opposing shorter sides of said resin package and extending in a first direction parallel to said longer sides, said first and second leads (10) being bent in an S shape, when viewed from the longer sides of said resin package, a vertical distance d between the surface of the element placement pad (11) and the corresponding surface of the unsealed part of the first lead (10) being at least as large as the thickness t of said first lead (10), and the thickness T of said resin (40) on the side of said element placement pad (11) opposing said electronic element being smaller than said distance d, characterized in that the sealing resin is injected from a side position on a longer side of said resin die, said position being offset from the center towards one shorter side thereof with said first direction being perpendicular to the direction of the injection of the sealing resin. Method according to claim 1, characterized in that the spacing between said element placement pad (11) and said second lead (20) is no greater than 0.12 mm. Method according to claim 1, characterized in that the vertical horizontal, and height outer dimensions of said resin package (40) are each no greater than 1.0 mm. Method according to claim 1, characterized in that widths of inner lead parts of said first (10) and second leads (20) within said sealing resin package (40) are substantially uniform. Method according to claim 1, characterized in that the thickness of said electronic element is substantially the same as the thickness t of said first lead (10). Method according to claim 1, characterized in that near the bottom surface of said sealing resin package (40) the bending radius R on the surface of a bent part of said first lead (10) opposite to the surface on which said electronic element (30) is placed is at least 0.05 mm and is not greater than the lead thickness t. Method according to claim 1, characterized in that the sealing resin contains a filler, whose particle diameter is not greater than half the bending depth d of the said lead.

Inventors: FUKAZAWA HIDEKI, KOBAYASHI TAKESHI, UTSUNOMIYA SATOSHI, FUKAZAWA, HIDEKI, KOBAYASHI, TAKESHI, UTSUNOMIYA, SATOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1999
Main classification: H01L23
IPC codes: H01L23, H05K3