JP5565084B2 - Lead frame manufacturing method - Google Patents

Description

The present invention relates to a method for fabricating a lead frame for use in semiconductor devices, to a structure of the inner lead portions to particularly reduce the improvements and wire length of the wire bonding of the inner leads.

  In general, semiconductor elements such as LSIs and ICs manufactured by a wafer process have a thickness of 1 mm or less and a size as small as a few centimeters or less, and a minute size for supplying and outputting electric signals by supplying power. In some cases, the number of terminals is several tens to thousands.

  Therefore, these semiconductor elements have terminals on one side having substantially the same pitch as the terminals formed on the semiconductor element, and on the other side a terminal having a pitch expanded to the extent that it can be easily and firmly connected to an external device. Mounted on a simple board for use. Electrical connection with the outside is made through terminals having an enlarged pitch. Examples of the special substrate include a BGA substrate (resin type, ceramic type), a TBGA substrate, a PBGA substrate, a lead frame, and the like.

  In particular, the lead frame is not suitable for mounting multi-terminal semiconductor elements having thousands of terminals, but for semiconductor elements of about several hundreds or less, plate-like iron-nickel alloy thin plates, copper alloys, etc. Since the metal material for a lead frame made of a thin plate can be manufactured by photo-etching using an etchant such as ferric chloride or by punching using a mold, it can be obtained at a very low cost.

  An example of the wiring pattern constituting the lead frame 1 is shown in FIG. The central square portion is an island 15 where a semiconductor element (not shown) is mounted with the terminal portion facing upward. The island 15 is fixed to the center of the lead frame 1 by connecting the suspension leads 16 extending outward from the four corners to the side rails 19 on the outer peripheral portion.

  The connecting inner lead 10 for extending the pitch is formed so as to surround the periphery of the island 15 with the side rail 19 as a starting point and the tip portion directed toward the island. Normally, the inner lead itself maintains its shape after etching or punching due to the rigidity of the inner lead, but depending on the case, the tip of the inner lead is temporarily connected to the island 15 or the tip of the inner lead. In some cases, the inner leads may be temporarily connected to each other by the connecting piece 17 so that the inner leads that are being manufactured are not separated. In obtaining the lead frame, the inner leads are individually separated by removing the connecting portion between the inner lead and the island 15 or removing the connecting piece 17.

  The front end portion of the inner lead 10 and the upper surface connection terminal of the semiconductor element are connected to each other by wire bonding with a metal wire so as to be electrically connected. After mounting the semiconductor element and performing the wire bonding process, the inner lead portion including the semiconductor element and the metal wire is covered with a mold resin. Thereafter, even if it is necessary for processing such as side rails, a part that is not necessary for electrical connection is cut and removed, and if necessary, a semiconductor package that can be handled can be obtained by covering with a case.

By the way, at present, the pitch between the inner leads at the tip is about 130 μm, but in order to facilitate wire bonding, a silver plating layer 18 is formed on the bonding surface to which the wire is bonded, and the portion indicated by the broken line in the figure From the bonding surface side (upper side in the figure), a polyimide tape is applied to fix the inner lead 10 (for example, see Patent Documents 1 and 2).
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Hereinafter, in this specification, the upper surface of the tip portion of the inner lead used for the wire bonding is particularly referred to as a bonding surface, and the back surface of the portion is referred to as a bonding surface back surface.

JP 04-42564 A Japanese Patent Application Laid-Open No. 08-204111 Japanese Patent Laid-Open No. 08-139266

  In recent years, semiconductor devices have been increased in speed and density, and the number of terminals for connection has increased, and the number of inner leads required for a lead frame tends to increase. In order to maintain the pitch between the leads of the inner lead tips at about 130 μm, it is necessary to install the bonding surface away from the central island, assuming that the island size is the same. In this case, the length of the metal wire (typically, gold wire) becomes long and the semiconductor device becomes large. In addition, the length of the wire becomes long, so that the wires are likely to come into contact with each other.

  In addition, the inner lead width becomes extremely narrow as well as manufacturing inner leads with a pitch of 130 μm by etching or pressing, so the tip of the lead with tape or a part closer to the side rail, not shown However, when the bonder capillaries come into contact with the bonding position, “lead rollover” or “lead shift” occurs, resulting in a reduction in bonding efficiency.

  When the bonding surface side of the inner lead tip portion is fixed using a tape, the metal wire straddles the tape, resulting in a problem that the wire length becomes long (Patent Document 2). If the vicinity of the side rail is fixed, there is a problem that the shape retention of the inner lead is inferior.

  Accordingly, there is a long-awaited need to obtain a lead frame having a structure that does not cause a bonding error by reducing the length of the metal wire used for wire bonding, and the object of the present invention meets this demand. That is.

The present invention is Ru der been made to meet the above requirements.

The invention according to claim 1 is a lead frame having an island and a plurality of inner leads extending radially from the periphery of the island, wherein the inner lead pitch is 130 μm or less, and the width of the bonding surface at the tip of the inner lead is set to the back surface of the bonding surface. A method of manufacturing a lead frame that is wider than the width of the inner lead, the back surface of the bonding surface at the tip of the inner lead is fixed with tape, and the tape is located directly under the bonding site,
A step of producing a lead frame in which the inner lead tips are fixed to each other by a connecting piece, a step of attaching a tape to the tip of the back side of the lead frame, a tape extending from the inner lead tip and the connecting piece are cut to form an inner Separating the lead and holding the tip of the inner lead with the remaining tape, and the cut is a cut in which the die and the bonding surface are brought into contact with each other and punched from the tape side,
It is obtained by the manufacturing method of the characteristics and to Brighter over lead frame to set the clearance of the punch and die to 5μm or less.

According to the lead frame manufactured by the manufacturing method of the present invention, wire bonding can be performed at the tip of the inner lead, and the bonding portion can be brought close to the island portion, so that the gold wire used for wire bonding can be Reduction is possible. Moreover, since the length of a wire can be shortened, it can prevent that wires contact.
In addition, since the bonding surface is fixed from the back side just below the bonding surface, “lead rolling” and “lead shifting” do not occur as compared with the conventional method.
Using a lead frame that will be produced by the method of the present invention, the size of the semiconductor package after assembly is not increased even by mounting a semiconductor element multiterminal.

  Furthermore, according to the manufacturing method of the present invention, the connecting piece for connecting the tips of the inner leads provided to prevent the variations of the tips of the inner leads is removed, and the cutting step for separating the inner leads is performed on the back side (tape Since the process is performed from the side of the affixing surface, it is possible to prevent the occurrence of defects such as cracks, chips, crushing, and burrs in the lead during cutting.

(A)-(c) is process drawing of the top view explaining the manufacturing process of the lead frame which becomes this invention. Figure viewed from the lead frame that will be produced by the production method of the present invention and (a) is a cross-sectional view of FIG. (B). The figure of the sectional view explaining the way of the wire bonding between the semiconductor element mounted in the inner lead and the island, and the position of the fixing tape. (A) The present invention, (b) Conventional invention. The figure of the sectional view explaining the shape of an inner lead. (A) 110 μm pitch, (b) 130 μm pitch.

The structural differences between the production methods prior to the lead frame that will be produced in the technology of the present invention in FIG. 3 (a), shown as (b). The essential difference is the position of the tape 11 for fixing the inner lead 10. Conventionally, as shown in FIG. 3 (b), the tape 11 has conventionally been attached on a silver plating layer 18 on the same side as the bonding surface or at a predetermined location in the base direction on the same side of the inner lead 10. In the lead frame manufactured by the manufacturing method of the present invention , as shown in FIG. 3A, the tape 11 is attached to the back side of the bonding surface immediately below the bonding position. By doing so, even if the pitch of the inner leads 10 is reduced to, for example, 110 μm, troubles associated with wire bonding can be avoided.

  In addition, the pitch of the inner leads 10 can be reduced from 130 μm to 110 μm. However, if the size of the bonding surface is reduced, the bonding property is lowered during wire bonding, so the width of the upper surface of the inner lead 10 is the same as when the pitch is 130 μm. Need to be maintained. Then, at the time of etching to the metal plate performed for manufacturing the lead frame, the etching depth from the bonding surface side becomes shallower than in the case of 130 μm. Naturally, if the etching depth from the back surface side is not increased, the leads will not be separated, but the width of the back surface side of the inner lead is reduced by that amount (see FIG. 4). Even on the back side, if the width is narrowed, the lead easily falls during wire bonding and the bonding performance deteriorates. Therefore, it is necessary to firmly fix the part with the tape 11 on the back side. This makes it possible to prevent the lead from falling even when the width of the back surface of the lead is narrow during wire bonding. Further, if the bonding surface side is fixed, wire bonding cannot be performed to the portion where the tape is applied, and the lead portion cannot be used for the width of the tape, and the metal wire 20 is applied so as to straddle the tape, which is disadvantageous.

  Hereinafter, the present invention will be described in detail based on embodiments with reference to the drawings.

  First, after preparing a roll-shaped metal material made of a copper alloy having a thickness of 125 μm and a width of 600 mm, and performing a cleaning process such as degreasing, a photoresist is applied to the surface of the metal material by screen printing. Dry to form a photoresist layer.

  Next, in order to form a metal pattern such as an island on which a semiconductor element is mounted, an inner lead, a connecting piece, a suspension lead that supports the island, and a peripheral side rail, a photoresist layer is formed through a photomask having a predetermined pattern. Next, the photoresist layer is subjected to a development process, and a hardening process is performed as necessary. As a result, a resist pattern is formed at a site corresponding to the aforementioned pattern, and the resist at other sites is removed, exposing the metal material from the resist.

  Similarly, a photoresist is applied to the back side of the metal material to form a photoresist layer. The aforementioned steps such as pattern exposure and development are repeated. Normally, the front and back photoresist patterns are plane-symmetrical on the front and back, but as described above, it is necessary that etching proceeds deeply from the back side.

  Therefore, first, a corrosion-resistant resin film is attached to the back surface of the metal material, and an etchant such as ferric chloride is used from the surface side of the plate-like metal material to the surface where the photoresist is not formed to a predetermined depth. Etching process (half etching process) is performed. Thereafter, washing treatment, drying treatment and the like are performed, and finally, a corrosion-resistant resin film is stuck on the surface.

  Next, the anti-corrosion resin film on the back surface is peeled off, and etching processing is performed from the back surface side of the plate-like metal material to the non-photoresist-formed portion on the back surface using an etchant such as ferric chloride solution to a predetermined depth. I do. Thereby, a penetration part is formed in the metal part in which the resist pattern corresponding to each of the front surface and the back surface is not formed, and becomes a top view opening part of the lead frame. This process is performed in a state where the lead frame is multifaceted. That is, the lead frame 1 as shown in FIG. 1A was formed by imposing a plurality of metal materials.

  The lead frame 1 has an island 15 supported at four corners by suspension leads 16 and a number of leads extending from the side rail 19 toward the island 15. The lead is formed with an inner lead 10 for wire bonding, an outer lead 12 extending from the inner lead 10 exposed to the outside after the casing, and a tie bar (not shown) for convenience during resin molding. Yes. As shown in FIG. 1, the tip of each inner lead is connected by a connecting piece 17 in order to prevent variations in the inner leads.

  In the above description, etching was performed on the metal material in two steps, but etching was performed simultaneously from both surfaces of the metal material by controlling the pressure of the etchant sprayed on each surface of the metal material, the liquid temperature of the etchant, and the like. The etching may be performed once.

  When the front and back widths of the inner lead portions were measured, the width of the bonding surface was 50 μm, and the width of the back surface was 20 μm. The cross-sectional shape is shallow on the bonding surface side and deep on the back side. The shallow bottom shape on one side (front side) and the deep pan bottom shape on the other side (back side) are formed by etching. The penetration part was formed so as to intersect at the bottom (FIG. 4A). The cross-sectional shape when the pitch is 130 μm is shown in FIG. 4 (b), but the etching on the back surface side was S-shaped for 130 μm.

In addition to the photo etching method as described above, the lead frame 1 can be applied by a pressing method using a mold.However, if the metal portion includes a portion having a different thickness, or includes a fine pattern, the etching depth of the front and back surfaces is increased. In the case where they are different, the photo etching method is suitable.

  Next, after covering the back surface with a protective film (not shown), a silver plating treatment is applied to the wire bonding portion of the inner lead 10 in order to improve the connectivity when physically connecting the inner lead and the semiconductor element. Thus, a silver plating layer 18 having a thickness of 4 to 8 μm was formed (FIG. 1B).

  The plating on the bonding area may be gold plating or palladium plating instead of silver plating. Further, prior to performing silver plating, gold plating, or palladium plating on the surface of the electrical connection area, a base plating such as Ni (nickel) plating having excellent heat resistance diffusibility may be performed.

  Next, a lead fixing tape 11 with an adhesive was attached to the back surface of the inner lead 10 directly below the bonding area using a tape applicator. The tape was a polyimide-based thermosetting material with low outgas and high migration resistance (R-1000, R-970A, UH1S: manufactured by Yodogawa Seisakusho).

  Finally, an unnecessary portion (for example, the connecting piece 17) inside the fixing tape was cut at the tip of the inner lead. Thereby, the connection between the tip portions of the inner leads is released. In the cutting, it was first investigated whether there was no problem by cutting the laminated portion of the tape and the inner lead, or whether only the inner lead portion of the non-laminated portion should be cut. When the laminated portion was cut regardless of the cutting direction and clearance, the inner lead was crushed. Therefore, the tape 11 is attached with a distance of about 0.15 mm from the tip of the inner lead 10.

  Next, it was investigated whether the clearance between the die and the punch and the cutting direction should be the front or back side. A lead frame base material connected to a plurality of lead frames was placed on the die, and the periphery of the cut line was fixed with a clamp, and then a predetermined portion was punched with a punch. The clearance between the die and the punch was set to three levels of 15, 10, and 5 μm, and the cutting direction was set to two levels on the front and back sides. At the time of cutting, it was examined whether or not the cut portion of the inner lead tip was cracked, chipped, crushed, or whether the lead tip was drawn into the clearance to cause burrs. The results are shown in Table 1.

In the table, ○ indicates that no cracks, chips, crushing, burrs or other defects were observed. The clearance was 5 μm or less, and no defects occurred in the lead frame base material cut from the back surface direction (tape application direction). Therefore, this is a preferable cut mode.
In this way, the lead frame shown in FIG. 2 could be obtained.

  As described above, by setting the inner lead pitch to 110 μm, an inner lead of about 0.95 mm could be extended inward for a 256-pin semiconductor element. As a result, the wire bondin distance is shortened by 0.9 mm, so that the gold wire can be saved by about 23 cm in total. In addition to this, since the gold wire can be saved by the tape width (for example, 3 mm) as compared with the conventional method, the effect is enormous.

1. Lead frame 10, inner lead 11, lead fixing tape 12, outer lead 13, lead (outer lead and inner lead)
15, island 16, suspension lead 17, connection piece 18, plating layer 19, side rail 20, gold wire 21, semiconductor element 22, semiconductor element connection terminal

Claims (1)

A lead frame having an island and a plurality of inner leads extending radially from the periphery of the island, wherein the inner lead pitch is 130 μm or less, and the width of the bonding surface of the inner lead tip is wider than the width of the back surface of the bonding surface. A method of manufacturing a lead frame in which the back surface of the bonding surface is fixed with a tape and the tape is directly under the bonding site,
A step of producing a lead frame in which the inner lead tips are fixed to each other by a connecting piece, a step of attaching a tape to the tip of the back side of the lead frame, a tape extending from the inner lead tip and the connecting piece are cut to form an inner Separating the lead and holding the tip of the inner lead with the remaining tape, and the cut is a cut in which the die and the bonding surface are brought into contact with each other and punched from the tape side,
Features and to Brighter over de production method of the frame to set the clearance of the punch and die to 5μm or less.

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