JPH09199654A - Machining method of lead frame and lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform precious metal plating to an inner led part with a photosensitive resist as a plating mask and to improve down set machining. SOLUTION: A method for machining a lead frame where precious metal plating is made, at least, to an inner lead part and a die pad part is subjected to down set machining has a process (A) for covering the surface of a lead frame 110 which is subjected to outer shape machining with a photosensitive resist and performing exposure and development treatment for exposing only a specific region, a process (B) for performing precious metal plating treatment to the exposed specific region, and a process (C) for performing the down set machining to the die pad part. Also, at least no down set machining part of a tab suspension bar part for supporting the die pad part is allowed to enter a specific exposed region where the above precious metal plating treatment is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a lead frame in which the inner lead portion is plated with a noble metal using a photosensitive resist as a plating mask and is downset, and a method for manufacturing the same. Related lead frame.

[0002]

2. Description of the Related Art Conventionally, a (single-layer) lead frame used as an assembly member of a resin-encapsulated semiconductor device is formed by a pressing method or an etching method. Generally, as shown in FIG. A die pad 612 for mounting a semiconductor element, and an inner lead 613 for connecting to a semiconductor element provided around the die pad 612
And an outer lead 614 for connecting the inner lead 613 to an external circuit, a dam bar 615 serving as a dam for resin sealing, a frame (frame) portion 616 for supporting the entire lead frame 610, and the like. Have.
Then, a lead frame (single-layer lead frame) 610
Is usually made of a metal having excellent conductivity such as Kovar, 42 alloy (42% nickel-iron alloy), and copper alloy.
As shown in FIG. 6B, the semiconductor element 620 is mounted on the die pad 612, and terminals (pads) of the semiconductor element 620 are provided.
The semiconductor device 600 is manufactured by connecting the wire 621 and the tip of the inner lead 613 with a wire 630 such as gold and then sealing with a resin 640. As described above, since the terminal (pad) 621 of the semiconductor element 620 and the tip of the inner lead 613 are connected with the wire 630 such as gold, silver plating having excellent conductivity and strong bonding force with the wire is applied. In general, partial silver plating is applied to the tip of the inner lead on the semiconductor element mounting side.

Conventionally, this partial silver plating treatment uses a plating apparatus 700 as shown in FIG.
A sparger-type jig plating method has been mainly performed in which the area other than the area 10 to be plated is covered with a masking jig 720 and pressed, and the plating solution 780 sprayed from the nozzle 740 is applied to the area to be plated. . In this jig plating method, a jig is required for each type of lead frame, and it takes a long time to manufacture the jig, and wear and fatigue occur as it is used, so replacement is necessary, and productivity is improved. It was also a problem in terms of cost and cost. In addition, when considering the quality of plating, the positioning is performed by the positioning pins, and the plating is performed after holding the single lead frame between the upper and lower jigs, so that the plating quality such as plating position accuracy and plating thickness uniformity can be improved. It is easily affected by the accuracy of the manufactured jig and the accuracy of mounting. Further, there is a problem that plating is likely to be deposited on the side surface and the back surface of the lead frame, which originally does not require plating, and requires a highly empirical technique for adjustment. Furthermore, the dimensional accuracy of the plated part has become more severe due to the increase in the number of input / output terminals of the semiconductor element due to the progress of the semiconductor process and the narrowing of the inner lead part due to the miniaturization of the package size. The response has become difficult.

For this reason, a jig is not required, and it is possible to cope with an increase in the number of terminals of a semiconductor element and a reduction in an inner lead portion. As shown in the figure, a silver plating method for a lead frame is used in which a photosensitive electrodeposition resist having a resistance to a plating solution is used, and only a predetermined area of the lead frame is masked and plated so as to be exposed to the plating solution. It has come to be. This partial silver plating method will be briefly described with reference to FIG. FIG. 4 is a sectional view of a part (characteristic part) of the lead frame, that is, in order to easily understand the partial silver plating method using the above electrodeposition resist.
3 shows a portion corresponding to a cross section taken along line A1-A2 shown in FIG. First, the entire lead frame 410 is electrolytically degreased, pickled and chemically polished (see FIG. 4).
(A)), copper strike plating 420 as base plating is applied to the entire surface of the lead frame 410 (see FIG. 4).
(B)) After that, the electrodeposition resist 430 is formed on the entire surface. (FIG. 4C) Next, using a predetermined photomask 440, predetermined portions (tip portions of the die pad 412 and the inner leads 413).
Is exposed to ultraviolet rays (exposure light) 450 to cure only the exposed portion (FIG. 4D), and then development processing is performed to remove the electrodeposition resist 430 in the unexposed portion and expose the plated portion 460. (Fig. 4 (e)). The region where the electrodeposition resist 430 is developed and removed is a part of the tab suspension bar 412A, the entire die pad 412 and the tip of the inner lead 413. In addition, the plating unit 460 performs a process of removing the resist residue when it is present. Next, after the exposed plating part 460 is subjected to acid cleaning, the entire lead frame is immersed in a silver plating solution, and plating is performed at a predetermined current density and time while stirring, and the plating part 460 is subjected to the desired plating. A silver plating (film) 470 having a film thickness is obtained. (Fig. 4 (f))
After that, the electrodeposition resist 430 is stripped with a stripping solution (see FIG.
(G)), down-set processing is performed, and lead frame 410 having silver plating (coating) 470 only in a predetermined region.
Get A. (FIG. 4 (f)) FIG. 5 (a) shows a plan view of the lead frame 410A processed by the processing method shown in FIG. Incidentally, FIG. 5 (b)
Shows a cross section taken along line B1-B2 of FIG. However, in 5 (a), the copper strike plated portion is not shown in the figure for the sake of clarity. As a pretreatment for the plating treatment, in addition to acid cleaning, alkali cleaning or the like is performed as necessary to the extent that the electrodeposition resist is not damaged. Further, when the lead frame material is a copper alloy, copper strike plating is a thin copper plating as a base metal for silver plating because it contains impurities such as Sn and Ni, but it is not always necessary. do not do. In some cases, the lead frame material is directly plated with silver. In this case, the silver plating base metal is a lead frame material.

Recently, instead of silver plating, palladium or a palladium-based alloy as a noble metal has been formed on the lead frame by a plating method. In this case as well, the entire surface of the lead frame can be plated. Since it is relatively expensive, plating is applied only to the necessary areas, and as in the case of silver plating, in addition to the masking method using a jig, a photosensitive material that is resistant to the plating solution is used. A masking method using a positive electrodeposition resist has come to be adopted.

[0006]

In the masking method using the photosensitive electrodeposition resist shown in FIG. 4, as described above,
When the inner lead tip and the die pad are plated with a noble metal, the positional accuracy during exposure of the lead frame using the photomask 440 can be relatively rough. Therefore, the pattern of the photomask 440 is as shown in FIG.
A square light-shielding pattern 440A including a die pad portion and an inner lead portion as shown in (b) is provided, and the photosensitive electrodeposition resist is collectively exposed to expose this portion. In FIG. 3B, 440B is an exposure light (ultraviolet) transmitting region. However, in the masking plating method using a photosensitive electrodeposition resist using such a pattern, the tab suspension bar portion supporting the die pad portion is also plated with noble metal, but all the tabs supporting the die pad portion It is difficult to uniformly control the amount of plating applied to the hanging bar portion, and the amount of applied plating varies between the tab hanging bar portions. For this reason, when performing downset processing after precious metal plating, even if the machine accuracy for improving downset accuracy is increased, the amount of plating adhered between the tab suspension bars is different, which causes the decrease in downset accuracy. Next, the correspondence was demanded. The present invention
Under these circumstances, the accuracy of downset processing can be improved in the lead frame processing method in which the inner lead portion is plated with a noble metal using a photosensitive resist as a plating mask and the downset processing is performed. It is intended to provide a method. At the same time, it is intended to provide a lead frame with improved downset processing accuracy.

[0007]

A method of processing a lead frame according to the present invention is a method of processing a lead frame in which at least an inner lead portion is plated with a noble metal and a die pad portion is downset. , (A) In order to perform plating of the noble metal on the inner lead portion or die pad portion, the outer surface of the lead frame is coated with a photosensitive resist having resistance to the plating solution, and exposed and developed. And (B) performing a noble metal plating process on the exposed predetermined region, and (C) downsetting the die pad portion, and the noble metal plating At least the downset processing part of the tab suspension bar part that supports the die pad part should not enter the exposed predetermined area where the processing is performed. It is an feature. And
The above-mentioned photosensitive resist is an electrodeposition resist. Further, the above noble metal plating treatment is characterized by including at least one treatment of silver plating treatment, palladium plating treatment, and palladium alloy.

In the lead frame processing method of the present invention, as the lead frame material, 42 alloy (42
% Nickel-iron alloy), Kovar, and various copper alloys can be used, and an etching method or a stamping method is adopted as the external processing of the lead frame. The photosensitive resist has resistance to plating and may be either a positive type or a negative type, and an electrodeposition resist is preferable. The electrodeposition resist may be either anion precipitation type or cation precipitation type, and the electrodeposition resist is deposited by applying a predetermined voltage and current, and heat treated to form an insulating film without pinholes or the like. You can The patterning of the photosensitive resist is performed by exposing and developing using a pattern for exposure having a predetermined shape to expose the metal part (base metal part) of the plated region. The exposure is performed according to the type of resist used, and is performed using an ultraviolet lamp having an emission spectrum in the exposure sensitivity region of the resist film. Further, the development is performed under a developing solution and developing conditions suitable for the resist to dissolve and remove the resist film in the plated region. As the noble metal plating, silver plating, palladium plating, palladium alloy plating or palladium composite plating can be used. As each plating solution, a commercially available one can be used, and the plating method and plating conditions are the methods and conditions suitable for the plating solution. Although the resist is peeled off after the plating film is formed, it is removed under a peeling solution and peeling conditions suitable for the resist used, and further degreased and washed if necessary.

The lead frame of the present invention is characterized by being processed by the method of processing a lead frame of the present invention.

[0010]

The method of processing a lead frame according to the present invention is capable of improving the accuracy of downset processing performed after the noble metal plating processing by adopting such a configuration. Further, since the photosensitive resist is used as the plating mask, there is no unnecessary deposition of the noble metal on the side surface and the back surface of the lead frame, and it is possible to process the lead frame with low cost and high reliability. More specifically, at least in order (A) to apply noble metal plating to the inner lead portion or the die pad portion, a photosensitive resist having resistance to the plating solution is coated on the surface of the lead frame that has been externally processed, and exposure, A developing process to expose only a predetermined region; (B) a noble metal plating process to the exposed predetermined region; and (C) a downset process of the die pad portion, and The tab suspension bar portion is down-set without being subjected to the precious metal plating treatment because at least the down-set processing portion of the tab suspension bar portion supporting the die pad portion does not enter the exposed predetermined area where the precious metal plating treatment is performed. Is processed. Therefore, it is possible to prevent a decrease in precision of downset processing due to a difference in the amount of plating adhered between the tab suspension bars, which occurs when the tab suspension bars are conventionally subjected to the noble metal plating process. Further, since the resist is an electrodeposition resist, the surface of the lead frame can be easily coated with the resist relatively uniformly, and the lead frame can be miniaturized. The lead frame of the present invention is manufactured by the above-described lead frame processing method, and it is possible to provide a lead frame in which unnecessary side surface and back surface plating is not adhered and down-set processing accuracy is improved. There is.

[0011]

EXAMPLES A method for processing a lead frame of the present invention will be described based on examples. FIG. 1 is a process diagram for explaining a method for processing a lead frame of an embodiment, showing a cross section taken along line A1-A2 of a lead frame of the present invention produced by the processing method of this embodiment shown in FIG. Is. still,
In FIG. 1A, the copper strike plated portion is not shown for the sake of clarity. In FIG. 1, 110 is a lead frame after external processing, 112 is a die pad, 11
3 is inner lead, 120 is copper strike plating, 1
30 is an electrodeposition resist, 140 is a photomask, 150 is ultraviolet rays (exposure light), 160 is a plated portion, 170 is silver plating (coating), and 110A is a lead frame after downset processing. This example is a QF made of a copper-based alloy having a thickness of 0.15 mm, which has been externally processed by an etching method.
An inner lead portion and a die pad portion of a P (Quad Flat Package) type lead frame 110 are silver-plated and then downset. First, the lead frame 110 obtained by etching is electrolytically degreased, pickled and chemically polished (FIG. 1 (a)), and copper strike plating 120 as an undercoat is applied to the entire surface of the lead frame. (FIG. 1 (b)), the lead frame 110 is immersed in an electrodeposition resist bath and current is applied to deposit the resist, followed by hot-air drying to deposit the electrodeposition resist 130.
Was formed. (FIG. 1C) Next, ultraviolet light (exposure light) 150 was contact-exposed using a photomask 140 that shields only the plated portion to cure only the exposed portion. (FIG. 1D) The photomask 140 has a light-shielding pattern 140A having the shape shown in FIG. 3A. When exposure is performed using this photomask, the tab suspension bar is exposed, and the die pad 112 and the inner layer are exposed. Only the tip portions of the leads 113 are shielded from light, and after development, the entire die pad 112 and the inner leads 4
The electrodeposition resist 130 is removed only on the tip of 13.
In addition, 140B in FIG. 3A is an exposure light (ultraviolet) transmitting region. As the electrodeposition resist, a negative electrodeposition type negative electrodeposition resist (Product No. 2100, Shipley Co.) was used.
The resist film thickness is about 20 μm. Then, a development process was performed to remove the electrodeposition resist 130 in the unexposed portion and expose the plated portion. (FIG. 1 (e)) As the developing solution, product number 2005 (manufactured by Shipley) was used. At this stage, if the resist residue (organic thin film) remains in the plating part 160, ultraviolet rays are irradiated to the plating part in the air using a low pressure mercury lamp to decompose the resist residue (organic thin film). Perform processing such as removal. After this,
The entire lead frame was immersed in a silver plating solution and plated at a predetermined current density and for a period of time with stirring to obtain a silver plating (coating) 170 having a desired film thickness. (FIG. 1 (f)) The plating solution is potassium cyanide to which is added a phosphoric acid-based or boric acid-based PH buffer and a brightening agent of a compound containing selenium, sulfur, etc. or an organic compound. , The basic composition is the same as the plating solution used in the case of the sparger method (also called high-speed jet method) of spraying the plating solution using a mask jig, but the silver concentration is 50 g / l,
CN ^- concentration 1.0 g / l, liquid temperature 40 ° C, pH 8.0
The one of 8.3 was used here. In the sparger method, the electrodeposition resist is partially destroyed, and unnecessary deposition of silver occurs in that area. Therefore, the entire lead frame is immersed in the plating tank that is being stirred as described above, and the current is applied to perform plating. I went. Then, the electrodeposition resist 130 is peeled off with a peeling liquid product number 2007 (manufactured by Shipley Co., Ltd.) (see FIG.
(G)), lead frame 110 that has been subjected to downset processing and has silver plating (film) 160 only in a predetermined area
A was obtained. (Fig. 1 (h)

In the above embodiment, the electrodeposition resist 130 is used.
When the film thickness is 30 μm or more, it is possible to withstand physical damage due to spraying of a plating solution, and it is also possible to employ plating by a sparger system.

Next, an embodiment of the lead frame of the present invention will be described with reference to FIG. 2A is a plan view of the lead frame of this embodiment, and FIG. 2B is a plan view of FIG.
It is sectional drawing containing the tab suspension bar part in 1-A2.
In FIG. 2, 110A is a lead frame, 112 is a die pad, 112A is a tab suspension bar, 113 is an inner lead, 114 is an outer lead, 115 is a dam bar, 11
6 is a frame, and 170 is silver plating (coating). The lead frame of this example was manufactured by the method for processing the lead frame of the above example, and was 0.15
A copper alloy having a thickness of mm is used as a material, and silver plating for wire bonding is applied to the tips of the inner leads 113, and silver plating for die bonding is applied to the die pad portion. Then, as shown in FIG. 2A, in the lead frame 110A of this embodiment, the tab suspension bar 112A is not silver-plated, and as shown in FIG. The hanging bar 112A is downset.

The lead frame of this embodiment and the one shown in FIG.
The results of comparing the accuracy of downset processing with the conventional lead frame are as follows. In addition, a hydraulic press type 5 ton press was used as a press machine for down set processing, and a 4-pillar die set manufactured with a specification of processing accuracy of ± 50 μm was used as a die. The variation in the tab location dimension of the conventional product was ± 100 μm, but in the present embodiment, the variation in the tab location dimension ± 50.
It became μm, which was significantly improved. As described above, the lead frame of this embodiment has greatly improved downset processing accuracy as compared with the conventional lead frame shown in FIG.

[0015]

The processing method of the lead frame of the present invention is
As described above, it is possible to provide a processing method capable of improving the accuracy of downset processing performed after the precious metal plating processing. At the same time, it is possible to provide a lead frame with improved downset processing accuracy. Further, in the lead frame processing method of the present invention, since the photosensitive resist is used as the plating mask, it is assumed that no noble metal is unnecessarily deposited on the side surface and the back surface of the lead frame. As a result, it is possible to prevent unnecessary precipitation of precious metals, particularly expensive silver, palladium, palladium-based alloys, etc., thereby enabling cost reduction. The lead frame of the present invention is manufactured by the lead frame processing method of the present invention, and it is possible to provide a lead frame with improved downset processing accuracy.

[Brief description of drawings]

FIG. 1 is a process schematic diagram of an embodiment of a method for processing a lead frame of the present invention.

FIG. 2 is a schematic view of an embodiment of a lead frame of the present invention.

FIG. 3 is a diagram for explaining a pattern shape of a photomask.

FIG. 4 is a diagram for explaining a conventional plating method using a photosensitive resist as a mask.

FIG. 5 is a diagram of a conventional lead frame.

FIG. 6 is a plan view of a lead frame (single layer lead frame) and a sectional view of a semiconductor device.

FIG. 7 is a schematic diagram for explaining a plating method.

[Explanation of symbols]

110, 410 Lead frame 110A, 410A (after external processing) Lead frame 112, 412 Die pad 112A, 412A Tab suspension bar 113, 413 Inner lead 114, 414 Outer lead 115 Dam bar 116 Frame (frame) 120, 420 Copper strike plating 130, 430 Electrodeposition resist 140, 440 Photo mask 140A, 440A Light-shielding pattern 140B, 440B Exposure light transmission region 150, 450 Ultraviolet (exposure light) 160, 460 Plating part 170, 470 Silver plating (film) 600 Semiconductor device 610 Lead frame 612 Die pad 613 Inner lead 614 Outer lead 615 Dam bar 616 Frame part 620 Semiconductor element 621 Terminal (pad) ) 630 wire 640 resin 700 plating device 710 lead frame 720 masking jig 730 press jig 730A press material 730B elastic material 740 nozzle 750 constant current source 760 anode electrode 770 cathode electrode

Claims (4)

[Claims] 1. A method of processing a lead frame in which at least an inner lead portion is plated with a noble metal, and a die pad portion is down-set, wherein (A) the inner lead portion or the die pad portion is at least in order. In order to perform plating, a step of coating a photosensitive resist having resistance to a plating solution on the surface of the lead frame subjected to the outer shape processing, performing exposure and development processing, and exposing only a predetermined region, (B) The method has a step of subjecting the exposed predetermined region to a precious metal plating treatment, and (C) a step of down-setting the die pad portion, and the exposed predetermined region to be subjected to the precious metal plating treatment has a die pad portion. A method of processing a lead frame, characterized in that at least the downset processing portion of the tab suspension bar portion supporting the lead frame is not inserted. 2. A method of processing a lead frame, wherein the photosensitive resist according to claim 1 is an electrodeposition resist. 3. A method for processing a lead frame, wherein the noble metal plating treatment according to claim 1 or 2 includes at least one treatment of silver plating treatment, palladium plating treatment, and palladium alloy. 4. A lead frame processed by the method for processing a lead frame according to claim 1.