JP5387374B2 - Lead frame manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a lead frame used in a semiconductor device, and is particularly called SON (Small Outline Non-Leaded Package) or QFN (Quad Flat Non-Leaded Package), and leads are exposed on the back surface of a resin package. The present invention relates to a method of manufacturing a lead frame used in a semiconductor device of a type that serves as an external connection terminal.

  2. Description of the Related Art In recent years, with high-density mounting on a substrate, the semiconductor device mounted on the substrate is required to be reduced in size and thickness, and the so-called CSP (Chip Size Package) is rapidly spreading. In particular, in a small semiconductor device using a lead frame, as shown in FIG. 3, the top surface of the lead frame on which the semiconductor element 7 is mounted is sealed with resin 9, and the leads 3 are formed from the back side of the sealed package. A semiconductor device 15 called a single-side sealing type SON or QFN whose bottom surface is exposed has been developed. Such a semiconductor device 15 often uses a lead frame having a form as shown in FIG. 4 with palladium plating on the entire surface.

  The SON or QFN type semiconductor device 15 has a structure in which the upper surface and side surface of the lead 3 are sealed with a resin 9 and the lower surface of the lead 3 is exposed from the resin 9 to serve as an external connection terminal. Adhesion is weak. For this reason, when the boundary portions that form the semiconductor devices 15 after being sealed with the resin 9 are cut by a dicing saw to form individual semiconductor devices 15, the leads 3 seal the upper surface and side surfaces of the leads 3. It has a defect that it is separated from the resin 9 and easily falls off.

  In general, the adhesion with the resin is poor in the order of copper, silver, palladium, and gold. In addition, it is known that the whole surface plating is worse than the partial plating. As described above, the SON or QFN type semiconductor device has a structure in which the upper surface and the side surface of the lead 3 are sealed with the resin 9. When the semiconductor device 15 is formed, not only the structural defect that the lead 3 and the resin 9 sealing the upper surface of the lead 3 are separated and easily fall off, but also the lead frame on which the entire surface is plated with palladium is in close contact with the resin. The nature is bad. In addition, when palladium plating is usually applied, palladium is plated on an underplating layer such as nickel, and gold is flash-plated on the palladium plating layer in order to improve reliability during wire bonding. It has a three-layer structure. Therefore, the adhesiveness with the resin is further poor.

  For example, Patent Documents 1 to 3 propose techniques for preventing such a semiconductor device lead from falling off.

  Patent Document 1 proposes a technique for preventing the lead from falling off by making the lead cross section into an inverted trapezoidal shape by press working.

  Patent Document 2 proposes a technique of roughening the lead surface by press working or plasma processing.

  Further, Patent Document 3 discloses a technique for partially plating palladium for the purpose of providing an inexpensive lead frame, which can reduce the area of the plating surface with poor adhesion to the resin, and has better adhesion than plating the entire surface. There are proposals for techniques to improve this.

Japanese Patent Laid-Open No. 11-260983 JP 2003-158234 A JP 2003-78097 A

  However, as in the technique described in Patent Document 1, when the lead frame is formed into an inverted trapezoidal shape or when press working is performed to roughen the surface of the lead frame, one side of the lead frame is processed. However, there is a problem that the lead frame is warped due to the influence of processing distortion and the quality is deteriorated.

  Further, as in the technique described in Patent Document 2, if a process for manufacturing a lead frame by plasma processing is newly added to roughen the surface of the lead frame, there is a problem that the manufacturing cost increases. In addition, even in the process of manufacturing the lead frame by etching to roughen the surface of the lead frame, it is necessary to newly add press processing to the process, which further increases the manufacturing cost.

  Further, in the lead frame in which palladium is plated on the entire surface of the lead frame or gold on the palladium as in the technique described in Patent Document 3, palladium, gold, and resin have poor adhesion in the first place. The lead frame having gold plated on palladium or palladium has poor adhesion to the resin. Therefore, when the anchor effect is obtained on the surface of the plating surface, if the surface is a rough plating surface, the adhesion with the resin is improved, but the wettability of the solder is deteriorated. On the other hand, when the plated surface is smooth, the wettability of the solder is improved, but the adhesion with the resin is poor. Therefore, there is a problem that a plated surface that satisfies both the adhesiveness to the resin and the wettability of the solder cannot be obtained.

  Therefore, the present invention has been made in view of the above-described problems of conventional methods. The aim is to improve the adhesion between the lead and the resin by improving the anchor effect of the plating surface without giving processing distortion to the lead frame and without increasing the manufacturing cost, It is an object of the present invention to provide a method for manufacturing a lead frame that prevents a lead from falling off from a resin.

In order to achieve the above object, the lead frame manufacturing method of the present invention uses a resist on both sides of a metal plate to form a mask that exposes portions to be plated, and after plating, leads are etched. a manufacturing method of forming a frame shape, the anode in the plating bath for the upper surface of the metal plate for applying rough plating of the surface on the upper surface of the metal plate is installed only on the side of the upper surface of the metal plate on the upper surface of the metallic plate the plating, by plating on the lower surface of the anode at the lower surface for plating bath of a metal plate for applying a smooth plating surface to the lower surface of the metal plate is installed only on the side of the lower surface of the metal plate metallic plate, Plating layers having different surface roughnesses are formed on the upper surface and the lower surface of the metal plate, respectively.

In addition, in order to achieve the above object, the lead frame manufacturing method of the present invention forms a mask that exposes a portion to be plated using a resist on both surfaces of a metal plate, and has a rough surface on the upper surface of the metal plate. In the nickel plating bath for the upper surface for plating, the anode is installed only on the upper surface side of the metal plate, the upper surface of the metal plate is plated , and the lower surface of the metal plate is used for smooth plating of the lower surface of the metal plate After forming the nickel plating layers with different surface roughness on the upper and lower surfaces of the metal plate by plating the lower surface of the metal plate by installing the anode only on the lower surface side of the metal plate in the nickel plating tank for It is characterized in that a palladium plating layer is formed on both surfaces of the metal plate at the same time, and then a gold plating layer is formed.

A method of manufacturing a lead frame of the present invention, the step of forming a nickel plating layer having different surface roughness on the upper surface and the lower surface of the metal plate, it is preferable to use a nickel plating bath having different compositions.

  According to the lead frame manufacturing method of the present invention, adhesion to the resin can be improved without giving processing distortion to the lead frame and without increasing the manufacturing cost.

  In addition, since the lead frame manufactured by the manufacturing method of the present invention can be a partial plating for plating only a necessary portion of the lead frame, the plating surface has poor adhesion to the resin even if palladium plating is performed. Can be minimized. In addition, since the wire bonding portion, which is the upper surface of the lead, can be formed into a rough plating layer having a rough surface that can be bonded and improves the adhesion to the resin, the lead can be obtained by doing so. It will be possible to prevent omission. In addition, the external connection terminal portion, which is the lower surface of the lead, can be a smooth surface plating layer having a smooth surface with good solder wettability. You can do it.

(A) is sectional drawing of the lead frame which concerns on Example 1 of this invention, (b) is an expanded sectional view of a lead. (A)-(l) is process drawing which shows the manufacturing method of the lead frame which concerns on Example 1 of this invention. (A) is sectional drawing of a semiconductor device, (b) is sectional drawing of the semiconductor device which plated to the circumference | surroundings of a pad as a bonding part for grounds. (A) is a top view of a lead frame, (b) is a top view which shows a unit lead frame.

First, the manufacturing procedure of the lead frame of the present invention will be described with reference to FIG.
As shown in FIG. 2 (a), the present invention uses a metal plate 12, and as a pretreatment, as shown in FIG. 2 (b), a dry film resist 13 is provided on both surfaces of the metal plate 12, and FIG. As shown in c), the dry film resist 13 is peeled off from the upper and lower surfaces of the metal plate 12 where plating is necessary.

  After the pretreatment for plating, as shown in FIG. 2D, nickel plating is performed only on the upper surface of the metal plate 12 in the first nickel plating tank. Next, as shown in FIG. 2E, nickel plating is performed only on the lower surface of the metal plate 12 in another nickel plating tank. Here, as in the lead frame manufacturing method according to the present invention, in the first nickel plating tank, if the anode is installed only on one surface side of the metal plate and plating is performed, only the surface side of the metal plate with the anode is provided. A plating layer is formed on the substrate. In this case, the plating layer is not formed on the other surface side of the metal plate with the metal plate as a boundary. Next, in another nickel plating tank, if an anode is installed only on the other side of the metal plate and plating is performed, a plating layer is formed only on the other side of the metal plate. Thus, according to the lead frame manufacturing method of the present invention, both surfaces of the metal plate 12 can be made independent and the plating layers can be formed separately.

  In these two platings, the plating bath is set so that a plating layer having a desired surface roughness can be obtained. For example, in order to apply rough nickel plating as shown in FIG. 1 (b), the chlorine concentration of the Watt bath is adjusted to at least twice the normal concentration, and smooth nickel plating as shown in FIG. 1 (b) is applied. 1, a nickel plating layer having a rough surface shown in FIG. 1B is formed on one surface side of the metal plate 12 by using a nickel sulfamate plating bath, and FIG. 1 is formed on the other surface side of the metal plate 12. It becomes possible to obtain the metal plate 12 on which the nickel plating layer having a smooth surface shown in (b) is formed.

  In these two platings, when plating only one surface of the metal plate 12, it is more effective to set and shield a vinyl chloride plate or the like.

  Next, as shown in FIG. 2 (f), a palladium plating layer is simultaneously formed on the nickel plating layers formed on both surfaces of the metal plate 12, and a gold plating layer is further formed thereon. Thereby, plating layers 5 and 6 having a three-layer structure with different surface roughnesses shown in FIG. 1B of the present invention are obtained on both surfaces of the metal plate 12, respectively.

  Next, as shown in FIG. 2G, the dry film resist 13 is peeled from the metal plate 12 on which the plating layers 5 and 6 are formed. Next, as shown in FIG. 2 (h), the dry film resist 13 is again provided on the entire surface of the metal plate 12 on which the plating layers 5 and 6 are formed. Next, as shown in FIG. 2 (i), an etching pattern is formed and an etching process is performed to form a predetermined lead frame shape as shown in FIG. 2 (j). Next, as shown in FIG. 2 (k), the dry film resist 13 is peeled off. Thereby, the lead frame is completed.

  For example, the plating layers 5 and 6 are formed of a nickel plating layer having a thickness of about 1 μm, a palladium plating layer having a thickness of about 0.1 μm, and a gold plating layer having a thickness of about 0.05 μm, respectively.

  The surface roughness of the plated surface of the formed three-layered plating layer is determined by controlling the surface roughness of the plated surface of the thick nickel plated layer as a base. Moreover, the roughness of the surface of the plating layer formed is controllable by controlling the bath composition of the nickel plating tank at the time of performing nickel plating.

  Table 1 shows the evaluation results of solder wettability, resin adhesion, and bondability with respect to the surface roughness of the plating surface of the plating layer formed as described above.

Table 1

  In Table 1, the wettability of the solder is measured by a meniscograph method using a solder checker. A sample piece is immersed in a crucible containing H63S eutectic solder melted at 230 ° C., and the zero cross time (ZCT) at that time is measured. The measurement was performed and the sample piece was pulled up, and then evaluated by checking the wetness of the solder to see if there was any portion that was not wet with a microscope. In this evaluation, there is no portion that is not wet, and when ZCT is within 1 second, Δ is that there is no portion that is wet, and when ZCT is within 1 to 3 seconds, × is that there is no portion that is not wet, Each represents a case where ZCT is 3 seconds or more.

The adhesiveness with the resin was obtained by forming a 2 mm square pod on the plated surface at 175 ° C. for 90 seconds and then performing post mold curing for 4 hours. This molded resin piece was evaluated by measuring the strength when the resin was peeled from the plated surface by pressing it with a shear tool from the side. In this evaluation, ◯ represents an average of 10 kgf / 4 mm ² or more, Δ represents an average of 5 to 10 kgf / 4 mm ² , and x represents an average of 0 to 5 kgf / 4 mm ² .

  In addition, the bonding property is a so-called hook pull, in which wire bonding is performed at a heater block set temperature of 200 ° C. using a Φ30 μm gold wire, a hook is then placed under the bonded wire, and the wire is pulled up vertically from the bottom to the top. The pull strength was measured by a method and evaluated by measuring the strength when the wire was cut. In this evaluation, “◯” represents a case where the average pull strength is 5 gf or more, and “Δ” represents a case where the average is 5 gf or less.

  As shown in Table 1, the surface roughness (Ra) of the rough plating layer 5 on the bonding surface side in close contact with the resin 9 is preferably 0.20 μm or more and 0.70 μm or less. In the smooth plating layer 6 on the surface exposed from the back surface of the package and serving as the external connection terminal, the surface roughness (Ra) is preferably 0.10 μm or less.

  1 and 2 are explanatory views of a lead frame according to an embodiment of the present invention, FIG. 1 is a cross-sectional view of the lead frame, and FIGS. 2A to 2L show the steps of the lead frame manufacturing method. It is explanatory drawing.

  First, as shown in FIG. 2 (a), a copper alloy was used as the metal plate 12, and as shown in FIG. 2 (b), a dry film resist 13 was attached to both surfaces. Thereafter, as shown in FIG. 2 (c), a glass mask that shields a portion of the lead frame that requires the plating layer 5 shown in FIG. 1 as the upper surface and the plating layer 6 shown in FIG. 1 as the lower surface is required. In a state where a glass mask that shields the portion was aligned, it was placed on both sides of the copper alloy with the dry film resist 13 and exposed to ultraviolet light through the covered glass masks on both sides.

  After exposure, the glass mask is removed, and the copper alloy with the dry film resist 13 is dipped in a developing solution and developed, so that plating is performed on the portion where the ultraviolet light is shielded, that is, the pad portion, wire bonding portion, external connection terminal portion, etc. Only the necessary dry film resist 13 was removed.

Next, after pre-treatment with alkali or acid, as shown in FIG. 2 (d), a current density of 2 A / dm is applied by a watt bath using a plating tank in which an anode is installed only on the upper surface of the lead frame. ² for 2 minutes to form a rough nickel plating layer having a thickness of 1 μm as shown in FIG. Next, as shown in FIG. 2 (e), using a plating tank having an anode only on the lower surface of the lead frame, plating is performed at a current density of 2 A / dm ² for 2 minutes using a nickel sulfamate plating bath. A smooth nickel plating layer having a thickness of 1 μm as shown in FIG. 1B was formed.

  Next, as shown in FIG. 2 (f), a palladium plating layer having a thickness of 0.10 μm is simultaneously formed on the nickel plating layers formed on both sides of the copper alloy, and further, A gold plating layer having a thickness of 0.05 μm was formed. Thereby, plating layers 5 and 6 each having a three-layer structure with different surface roughnesses were obtained on both surfaces of the copper alloy. Next, as shown in FIG. 2G, the dry film resist 13 was peeled from the plated copper alloy with the dry film resist 13.

  Next, as shown in FIG. 2 (h), a dry film resist 13 serving as a photoresist was attached to the entire surface of both surfaces of the plated copper alloy. Next, the dry film resist 13 is plated in a state where the glass mask that shields light other than the shape of the lead frame as the upper surface of the lead frame and the glass mask that shields light other than the shape of the lead frame as the lower surface of the lead frame are aligned. The coated copper alloy was covered on both surfaces and exposed to ultraviolet light through the covered glass masks on both surfaces.

  After the exposure, the glass mask is removed, and the plated copper alloy with the dry film resist 13 is developed by immersing it in a developer to develop a portion where the ultraviolet light is shielded, that is, the portion other than the shape of the lead frame. The resist 13 was removed.

  Next, as shown in FIG. 2 (i), an etching process is performed by spraying an etching solution onto the both surfaces of the plated copper alloy with the dry film resist 13 by using a spray nozzle 14, and the result is shown in FIG. 2 (j). Thus, a predetermined lead frame shape was formed. Next, as shown in FIG. 2 (k), the dry film resist 13 was peeled off to produce a lead frame with a plating layer.

  The surface roughness (Ra) of the plating surface of the gold wire bonding portion, which is the upper surface of the lead frame thus fabricated, is 0.21 μm, and the surface roughness (Ra) of the plating surface of the external connection terminal portion, which is the lower surface, is 0.06 μm.

  The glass mask for etching was designed so that the upper surface of the lead 3 was wider than the lower surface, and the lead 3 of the lead frame was formed wider than the lower surface by etching.

  Next, a metal to be cut is cut so that a boundary between the individual semiconductor devices 15 is half-etched and sealed with a resin 9, and metal burrs can be reduced when cutting into individual semiconductor devices 15 by a subsequent dicing saw. I tried to reduce the number of parts.

DESCRIPTION OF SYMBOLS 1 Pad 2 Suspended lead 3 Lead 4 Dam bar 5 Rough plating layer 6 Smooth plating layer 7 Semiconductor element 8 Wire (gold wire)
9 Resin 10 Half etching 11 Unit lead frame 12 Metal plate 13 Dry film resist 14 Injection nozzle 15 Semiconductor

Claims (3)

A method of forming a lead frame shape by etching after forming a mask that exposes portions to be plated using resist on both sides of a metal plate, and performing plating, wherein the surface of the metal plate is formed on the upper surface of the metal plate. metal for applying rough plating anodes in the upper surface for plating bath of a metal plate for applying installed only on the side of the upper surface of the metal plate is plated on the upper surface of the metallic plate, a smooth plating surface to the lower surface of the metal plate by it the anode in the lower surface for plating bath of the plate is installed only on the side of the lower surface of the metal plate to the plating on the lower surface of the metallic plate, plating layers of different surface roughness, respectively on the upper and lower surfaces of the metal plate is formed A method for manufacturing a lead frame, characterized in that: Using a resist on both sides of the metal plate, a mask exposing the part to be plated is formed, and the anode is placed on the upper surface side of the metal plate in a nickel plating bath for the upper surface to apply rough plating to the upper surface of the metal plate. only by installing the plating on the upper surface of the metal plate, the anode on the lower surface for nickel plating bath of a metal plate for applying a smooth plating surface to the lower surface of the metal plate is installed only on the side of the lower surface of the metal plate metal plate by the lower surface plating, after forming a nickel plating layer having different surface roughness on the upper surface and the lower surface of the metal plate, both sides at the same time to form a palladium plating layer on the plating layer of both sides of the metal plate, the following Forming a gold plating layer on the lead frame. Forming a different surface roughness nickel plating layer on the upper surface and lower surface of the metal plate, the manufacturing method of lead frame according to claim 2, characterized by using a nickel plating bath having different compositions.

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