Lead frame and semiconductor package

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a lead frame for semiconductor package and a semiconductor package in which the semiconductor device is mounted on a lead frame and the outside thereof, particularly, the top surface of semiconductor device is encapsulated with molding compound.

[0003] 2. Description of the Related Art

[0004] In recent years, it has been required to miniaturize and shape semiconductor product mounted on a substrate thinner, as packaging of semiconductor is made denser. It has been severely required for LSI to reduce the number of chips by improving integration level and to miniaturize and make a package lighter. The popularization of so-called CSP (Chip Size Package) is rapidly advancing. Particularly, in the development of thin semiconductor product with lead frame, the semiconductor package of single side encapsulation type has been developed in which a semiconductor device is mounted on a lead frame and the surface of semiconductor device mounted on a lead frame is encapsulated with molding compound.

[0005]
FIG. 1 is a sectional view of one example of semiconductor package. FIG. 2 is a plan view thereof seen through molding compound. The semiconductor package shown in FIGS. 1 and 2 is comprised of a lead frame 1, a semiconductor device 4 mounted on die-pad 3 supported with suspending leads 2 of lead frame 1, metallic thin wires 6 electrically connecting electrodes provided on the top face of the semiconductor device 4 with terminals 5 of lead frame 1, respectively and molding compound 7 for encapsulating the outside region of semiconductor device 4 including the upper side of semiconductor device 4 and the lower side of die-pad 3. The semiconductor package is of so-called non-lead type of semiconductor package in which outer leads are not projected from the semiconductor package and the two of inner leads and outer leads are integrated into terminals 5, wherein in used lead flame 1, suspending leads 2 are directed upward in such a manner that die-pad 3 is positioned higher than terminals 5. Since such a step is provided between die-pads 3 and terminals 5, molding compound 7 can be inserted into the lower side of die-pad 3.

[0006] Since semiconductor device is miniature, a matrix type frame is mainly used for the above-mentioned non-lead type of semiconductor package of non-lead type, in which plural semiconductor devices are arranged in a direction of a width of the matrix type frame. Further, recently, from a demand for cost down, it is thought to switch over a frame of individually molding type shown in FIG. 3 to a frame of collectively molding type shown in FIG.4.

[0007] In the frame of individually molding type, as shown in FIG. 3(A), individual molding cavities C of small size are provided separately within a frame F. After molding, individual semiconductor packages are stamped out so that semiconductor packages S shown in FIG. 3(B) are obtained. Namely, semiconductor devices are mounted on die-pads of lead frames through silver paste and others, and wire bonding is carried out. Thereafter, respective semiconductor devices are individually molded with molding compound and the molded semiconductor devices are stamped out to form individual semiconductor packages.

[0008] In the frame of collectively molding type, as shown in FIG. 4(A), some molding cavities C of large size are provided within a frame F. Multiple semiconductor devices are arranged in matrix within each molding cavity C, respectively and collectively molded with molding compound. Thereafter, the collectively molded semiconductor devices are cut at grid-leads L by means of dicing saw so that a semiconductor package S shown in FIG. 4(B) is obtained. Namely, semiconductor devices are mounted on die-pads of lead frames through silver pastes and others and wire bonding is carried out. Thereafter, plural semiconductor devices arranged are collectively molded with molding compound to a given cavity size, and then the collectively molded semiconductor devices are cut to form individual semiconductor packages by dicing.

[0009] Generally, in the above-mentioned semiconductor package, in order to facilitate wire bonding in the process of forming the semiconductor package, noble metal plating such as silver plating is previously given to parts of terminals of lead frame to be wire-bonded. As to the areas of noble plating, in a semiconductor package of such a type that outer leads are projected from the semiconductor package, there are many standards that the plating areas of noble metal are restricted between a point 0.3 mm away from ends of inner leads and the inside of dam bar. According to the standards, judgment on whether the plating areas of noble metal are good or defective can be easily made by visual observation. On the other hand, in case of the above-mentioned non-lead type of semiconductor package, plating areas are small, wherein the accuracy of plating areas is assured with values measured in the random sampling. Therefore, the labor costs are required for measurement of size of plating areas, which was a factor of increase in cost.

[0010] Further, non lead type of semiconductor packages are separated from each other by punching or dicing, wherein there was a problem that peeling is produced between molding compound and terminals of lead frame, since stress is applied to terminals of lead frame in separating non-lead type of semiconductor packages from each other. Further, there was a problem that the reliability of assembly after mounting semiconductor package on a printed circuit board is low.

[0011] Further, in case of giving noble metal plating to parts of terminals to be wire-bonded according to a method of plating using masking means, there was a problem that leakage of the least amount of plating solution through a mask of the masking means occurs no matter what.

SUMMARY OF THE INVENTION

[0012] In order to achieve the above-mentioned problems, a lead frame of the present invention is a lead frame used for the production of semiconductor package characterized in that each of terminals to be wire-bonded to electrodes provided on the top surface of semiconductor device mounted on a die-pad has one or two groove(s) for limiting plating area of noble metal for wire-bonding.

[0013] Further, a semiconductor package of the present invention is a non-lead type of semiconductor package comprising a semiconductor device mounted on a die-pad supported by suspending leads of lead frame, wires electrically connecting electrodes provided on the top surface of the semiconductor device and terminals of the lead frame and molding compound for encapsulating the outside region of semiconductor device including wires such that the lower surface and sides of the terminals are exposed characterized in that each of the terminals of lead frame has one or two groove(s) for limiting a plating area of noble metal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]
FIG. 1 is a sectional view of one example of a conventional semiconductor package.

[0015]
FIG. 2 is a plan view of the semiconductor package shown in FIG. 1, showing a state thereof seeing through molding compound.

[0016] FIGS. 3(A) and (B) are explanatory views of an individually molding type of semiconductor package, FIG. (A) being a partly plan view of a frame with mold cavities and FIG. (B) being a side view of each semiconductor package.

[0017] FIGS. 4(A) and (B) are explanatory views of a collectively molding type of semiconductor package, FIG. 4(A) being a frame with mold cavities and FIG. 4(B) being a side view of each semiconductor package.

[0018]
FIG. 5 is a plan view of one example of an individually molding type of semiconductor of the present invention.

[0019]
FIG. 6 is a sectional view taken on line X-X of FIG. 5.

[0020] FIG.7 is a sectional view of a semiconductor package produced using a lead frame shown in FIGS. 5 and 6.

[0021]
FIG. 8 is a plan view of alteration of lead frame shown in FIG. 6.

[0022]
FIG. 9 is a sectional view of alteration of semiconductor package shown in FIG. 7.

PREFERRED EMBODIMENT OF THE INVENTION

[0023] Then, referring to figures, embodiments of the present invention are explained.

[0024] Lead frame 1 shown in FIGS. 5 and 6 is used for the production of an individually molding type of semiconductor, wherein a die-pad 3 is supported by four suspending leads 2 and four terminals 5 are projected from each of four peripheral sides of lead frame toward the die-pad 3, respectively. Each of terminals 5 has a groove 8 formed by half-etching the front side of terminals 5 at a given distance from the inside of each terminal 5. Further, in the lead frame shown in FIGS. 5 and 6, the backside of die-pad 3 is half-etched so that a thin die-pad is formed.

[0025] The lead frame 1 is made of cupper sheet with thickness of 0.2 mm, in case of almost illustrations. From a view point of the strength of terminals 5, grooves 8 formed by half-etching have a width of about 0.05 mm to 0.15 mm and a depth of about 25 to 75 per cent of the thickness of terminals 5, wherein a groove having a depth of about 0.1 mm is given as a preferable example. In case of individually molding type of semiconductor package, the lead frames are arranged in a frame in a certain order shown in FIG. 3(A).

[0026] Plating of noble metal such as silver for wire-bonding is given to terminals 5 of lead frame 1, wherein grove(s) 8 formed in each terminal 5 are utilized for limiting an area of the plating of noble metal. Namely, plating of noble metal is given inward from groove 8. In this case, an outside edge “a” of groove 8 limits a maximum area and inside edge “b” limits a minimum area. In the inspection of plating area of noble metal, if the edge of area of plating area of noble metal is positioned in groove 8, the plating area of noble metal passes in inspection. The inspection can be made easily by the visual observation. The plating area is to be positioned at about 0.3 mm to 0.6 mm from the forward end of terminal 5.

[0027] As a method of plating terminals 5 with noble metal given are a method comprising the steps of applying masking material of resist on the surface of terminal except an area to be plated and thereafter plating the area to be plated with noble metal and a method comprising the steps of plating the whole surface of terminals and thereafter electrolytically removing the formed plating film except an area to be bonded through the masking means, wherein in the latter method, leakage of plating solution can be also prevented by forming the inside of groove 8 into an area able to plated.

[0028] The process for producing a semiconductor package using the lead frame 1 after terminals are plated with noble metal is as follows. First, semiconductor device is mounted on a die-pad 3 supported by suspending leads 2 of lead frame 1 through silver paste. Wire bonding between an electrode provided on the top surface of semiconductor device and parts plated with noble metal through gold wire is carried out. Thereafter, lead frames 1 are set in molds so that semiconductor devices with lead frames are individually molded and then semiconductor packages are stamped out individually.

[0029]
FIG. 7 shows a sectional view of semiconductor package produced in the above-mentioned process. Each of terminals 5 is formed with groove 8 for limiting a plating area of noble metal. Since molding compound 7 is inserted in the groove 8, the adhesion of terminal 5 to molding compound 7 is improved. Since the backside of semiconductor device 4 is covered with molding compound 7 as shown in FIG.7, dendrite is prevented from being generated between the backside of semiconductor device and wires on the printed circuit board under die-pad 3, when mounting semiconductor device on the printed circuit board. Further, die-pad 3 does not come off molding compound 7.

[0030] In the above-mentioned example, grooves 8 are formed such that the grooves cross terminals 5. However, grooves 5 may be formed into such a shape that not etched parts exist so as to form banks at both ends of groove 5 seeing in the crosswise direction of terminal 5. The groove 8 having banks has the improved strength against bending of terminal 5 as compared with groove 8 with no bank shown in FIG. 5.

[0031] In the above description, an individually molding type of semiconductor package of the present invention is explained. However, a collectively type of semiconductor can be explained in the same manner.

[0032] Industrial Applicability

[0033] Since a lead frame according to the present invention is characterized in that each terminal of lead frame is formed with groove(s), the accuracy of plating area can be easily checked by visual observation. Accordingly, the cut of inspection cost can be carried out.

[0034] Further, the grooves absorb stress applied to terminals when molded semiconductor packages are separated individually from each other by means of punching or dicing. Accordingly, coming off of molding compound from terminals is prevented. Further, since the grooves absorb stress applied to terminals by vibration after mounting a semiconductor device on the printed circuit board, the reliability of assembly is improved.

[0035] Further since molding compound is inserted into the grooves of terminals, the adhesion of terminals to molding compound is improved so that moisture is difficult to be absorbed between terminals and molding compound. Accordingly, the reliability of semiconductor is improved.

[0036] Further, when a method comprising the steps of plating the whole surface and thereafter electrolytically removing plating film except an area to be bonded through the masking means is employed as a method of plating terminals, leakage of plating solution can be also prevented by forming the inside of groove so as to be able to plated so that plating with a high accuracy is become possible.

Lead frame and semiconductor package

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