JP2521417B2 - Electroforming method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroforming method for obtaining a precision electroformed body such as a lead frame for fixing semiconductor chips such as IC and LSI. 2. Description of the Related Art In recent years, electronic parts, etc.
As the device becomes thinner, a precise shape has been required. For example, semiconductor devices such as IC and LIS tend to have many pins,
In the lead frame that constitutes this, the pitch between the leads is narrowed, the width of the leads themselves is also narrowed, and moreover, accuracy is required. A conventional electroformed body manufacturing method will be described by taking a lead frame, which requires the most precision, as an example. This lead frame is formed by punching a thin metal plate with a press, etching or the like. Figure 1
As shown in FIG. 3, tab leads 3 for pointing the short tabs 2 to which the semiconductor chip 1 is attached at four corners thereof, a plurality of fingers 4 having inner ends facing the periphery of the tabs 2, and these fingers 4 and the tab leads 3 are provided. Frame part 5 supporting the outer end
And sprocket holes 6 provided at regular intervals along both side edges of the frame portion 5. In order to assemble a semiconductor device using such a lead frame 10, first, the semiconductor chip 1 is mounted on the tab 2 and then the electrodes of the semiconductor chip 1 and the inner ends of the fingers 4 corresponding thereto are wired. Alternatively, direct connection is made without using wires, then the inner region of the rectangular frame 5 is molded with synthetic resin to cover the semiconductor chip 1, and then the frame 5 is cut off to obtain a flat lead or in-line type semiconductor device. is there. By the way, in the above-mentioned semiconductor device, it is extremely difficult to connect the fingers 4 of the lead frame 10 to the electrodes of the semiconductor chip 1. When the number of pins of the semiconductor device, that is, the number of fingers 4 of the lead frame 10 has increased, and the gap between adjacent fingers 4 has become small due to the miniaturization, and the width of each finger 4 itself has become narrower, connection work has been done recently. The efficiency and certainty of the product cost cannot be ignored for the product cost. Therefore, as shown in FIG. 14, the aluminum electrode 8 formed on the silicon 7 is thinner than the protective film 9 formed on the silicon surface and is formed inside the semiconductor chip 1. Conventionally, a bump 4a is provided at the tip of the finger 4 connected to the electrode 8 to ensure reliable contact. However, in recent years, when a semiconductor device having a large number of pins is required, the width of the finger is unavoidably narrower, and it becomes difficult to form the bump. As a method of eliminating these drawbacks, facilitating manufacturing, and molding a fine portion, a lead frame using an electroforming technique has been recently developed. 15 to 21 are process drawings for explaining a method of manufacturing a lead frame using an electroforming technique. First, as shown in FIG. 15, polyimide,
Base material 11 in which a conductive metal film of aluminum, copper, stainless steel or the like is formed on the surface of a resin material such as polyester
The first resist layer 12 is applied to the surface of the metal film. When applying the resist layer 12, the base material 1
The coated surface of No. 1 has been previously subjected to a peeling process. Next, as shown in FIG. 16, the resist layer 1
A bump forming mask 13 is set (that is, masking) on the surface of No. 2, and in this state, exposure is performed from above the mask 13. In the mask 13, only the portions where the bumps are desired to be formed are made non-transparent, and the other portions are made transparent. Also,
The resist layer 12 is made of a material that cures when exposed to ultraviolet rays or electron beams. Therefore, the exposure hardens the resist layer portion immediately below the transparent portion 13a of the mask 13, and leaves the resist layer portion immediately below the light shielding portion 13b uncured. Next, as shown in FIG. 17, the resist layer 1
The uncured portion 2 is removed, the surface of the base material 11 exposed from this portion is etched to form a concave portion, and the etched portion is plated with gold. Then, the resist layer 12 left on the surface of the base material 11 is removed. The gold plating formed on the etched portion becomes the bump 14. Next, as shown in FIG. 18, the base material 11
Of the second sheet-like resist layer 15 on the formation surface of the bump 14 of
Cover with. Next, as shown in FIG. 19, a mask 16 for forming the lead portion is mounted. Only the lead forming portion of the mask 16 is made non-translucent and the other portions are made transparent. In this state, when exposed to ultraviolet light as in the case of FIG. 16, the resist layer 15 immediately below the transparent portion of the mask 16 is hardened, and the resist layer portion immediately below the non-light-transmitting portion is uncured. This uncured portion is removed from the surface of the base material 11, leaving only the resist layer 15 in the cured portion. Next, as shown in FIG. 20, the resist layer 1
Lead parts 17 made of a copper material are electroformed on the surfaces of the base material 11 and the bumps 14 other than 5. By this electroforming, bump 1
4 is connected to the lead portion 17. The height of the bump 4a (the step between the lower surface of the thin portion 4c and the lower surface of the bump 4a in FIG. 14) is generally about 12 to 30 μm. Further, as shown in FIG. 21, the lead portion 17 with bumps, that is, the inner lead is formed into the base material 11.
Peel from. In the description of FIG. 21, the manufacturing process of the pair of leads has been described, but as shown in FIG.
A large number of semiconductor chips 1 are simultaneously formed corresponding to the number of electrodes. The lead frame manufactured in this way can accommodate a large number of electrodes. However, when the sheet-like resist layer 15 is arranged in the state shown in FIG. 18, the recesses in the bumps 14 are closed as shown in FIG. 22, so that air remains in the recesses. However, this air expands due to the force applied when the resist layer 15 is bonded and the ambient temperature, and lifts up and impairs the adhesion. As a result, it becomes difficult to produce a precise electroformed body due to hardening blurring or electroforming of the electroformed article. In order to solve this, for example, in the above-mentioned conventional lead frame manufacturing method, it is conceivable to apply gold plating until the recess is at the same level as the base material 11 to eliminate the recess, but the gold plating of the bump exists on the surface. Since it is enough, filling the entire recess with gold is wasteful. When the sheet-like resist layer 15 is covered in a vacuum state, the surface of the resist layer 15 is dented according to the amount of dents, the thickness of the electroformed body changes, or the dents face toward the dents. The electroformed body grows in an overhanging state and the accuracy is impaired. Such a recess is a recess groove for the bump.
As described above, the air expansion phenomenon occurs remarkably in the case of a relatively large size, but the higher the precision of the electroformed body is, the more the depression of the surface itself of the base material influences. The purpose of the present invention is to
It is made on the surface of the base material.
Smooth the dents and use electroforming that is not easily affected by these dents.
To provide a highly accurate electroformed body that can be
It SUMMARY OF THE INVENTION The present invention provides a conductive surface.
A base member on having fills the recess of the base material surface
And a resist for a base having a continuous resist surface on the surface
Formed on the strike layer and the underlying resist layer, and electroformed
Resist layer for securing thickness of electroformed body for securing body thickness
Is laminated, and a predetermined pattern of uncured is formed on the laminated resist layer.
Forming a cured portion and a cured portion, and removing the uncured portion
After that, electroforming is performed. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a lead frame of a semiconductor device according to an embodiment of the electroforming method of the present invention. The lead frame 20 is composed of a lead portion 20a and a chamfered bump 20b formed on the tip of the lead portion 20a so as to be orthogonal to the length direction of the lead portion 20a and formed over the entire width thereof. The bump 20b is formed as shown in FIG. 11 through a process using a resist and an electroforming process. 2 to 11 are process drawings for explaining the manufacturing process of the lead frame according to the present invention. First, as shown in FIG. 2, the first metal film is formed on the surface of the base material 21 in which a conductive metal film of aluminum, copper, stainless steel or the like is formed on the surface of a resin material such as polyimide or polyester. Resist layer 22 is applied. When applying the resist layer 22, the base material 2
The coated surface of No. 1 has been previously subjected to a peeling process. Next, as shown in FIG. 3, a resist layer 22 is formed.
A mask 23 for bump formation is set (that is, masking) on the surface of, and in this state, exposure is performed from above the mask 23. As shown in FIG. 12, the mask 23 has a ring-shaped light-shielding portion 23a in which only portions where bumps are desired to be formed are made non-translucent.
And a transparent portion 23b whose other portion is made transparent. Further, the resist layer 22 is made of a material which is cured by being irradiated with ultraviolet rays. Therefore, the exposure cures the resist layer portion immediately below the transparent portion 23a of the mask 23, and leaves the resist layer portion immediately below the light shielding portion 23b uncured. Next, as shown in FIG. 4, a resist layer 22 is formed.
The uncured portion is removed and the surface of the base material 21 exposed from this portion is etched to form the recessed groove 24. Next, as shown in FIG. 6, a second resist layer 25 is formed on the surface of the base material 21. This resist layer 2
5 consists of two layers, an underlying resist layer 25a of the recess groove 24 is set embedded, painful thickness conductive to ensure the thickness of the lead portion
Formed by laminating a securing resist layer 25b, underlying resist layer 25a by way soft enough to familiar, embedding settings and depressions on the surface of the base material 21, in this embodiment, a solution form resist. As shown in the figure,
Resist layer 25a for use has a continuous resist surface on the surface.
It Depression amount of the bump recess groove 24 (12 to 30)
It intended Finer μ approximately), in addition to the liquid resist, may be a soft resist that can set embedded fine dents. As the thickness adjusting resist layer 25b, a sheet resist which can easily secure the thickness of the resist layer is used. In this manner, the surface of the underlying resist layer 25a is smoothed, and the sheet-shaped resist layer 25b is set on the surface of the underlying resist layer 25a and pressed or heat-bonded to bring them into close contact. Next, as shown in FIG. 7, using the mask 26 shown in FIG. 13 in which the portion corresponding to the finger 4 is a light-shielding portion, it is exposed to ultraviolet rays as in the case of FIG. As a result, the resist layer 25 immediately below the transparent portion of the mask 26 is formed.
Is hardened, and the resist layer 25 immediately below the light shielding part is uncured. Next, as shown in FIG. 8, the uncured portion is removed from the surface of the base material 21, leaving only the resist layer 25 in the cured portion. Next, as shown in FIG. 9, a bump tip 27 is formed on at least the bottom of the concave groove 24 by electroforming of gold, and the upper portion of the bump tip 27 and the resist layer 25 are formed.
The removed portion is subjected to electroforming of copper to form the lead portion 28.
By this step, the bump and the lead portion are formed. Further, as shown in FIG. 11, the lead portion 28 with bumps, that is, the inner lead is formed into the base material 21.
Peel from. Although the manufacturing process of the pair of leads has been described in the description of FIG. 11, as shown in FIG. 13, a large number of electrodes are simultaneously formed corresponding to the number of electrodes of the semiconductor chip 1. Since the assembly of the inner leads manufactured by FIGS. 2 to 11 is the same as that described in FIG. 13, the description thereof will be omitted. The obtained inner lead is shown in Fig. 1.
Since the line contact is made as compared with the conventional point contact, the connection to the electrode 8 is surely made, and
It does not cause connection failure due to bump crushing. As described above, according to the present invention, the concave portion of the surface of the base material is formed on the base material having the conductive surface.
Underneath, which fills the area and has a continuous resist surface on the surface
Formed on the ground resist layer and the underlying resist layer
Te, electroforming body hurts thickness securing resist layer conductive to ensure the thickness and lamination, to form a uncured portion and the curing portion of the predetermined pattern on the laminated resist layer, removing the uncured portions after, since by performing electroforming, turned into a flat smooth surface depression of the base material, affected by the recess poorly electroforming can be performed, it is possible to obtain a high accuracy of electroformed member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the structure of an inner lead made according to an embodiment of the present invention. FIG. 2 shows a coating state of a first resist on a base material in the manufacturing process of the lead frame shown in FIG. FIG. 3 shows an exposure state with a mask in the same manufacturing process. FIG. 4 shows a recess groove formation state in the same manufacturing process. FIG. 5 shows the first resist layer removed state in the same manufacturing process. FIG. 6 shows a second resist layer forming state in the same manufacturing process. FIG. 7 shows an exposure state with a mask in the same manufacturing process. FIG. 8 shows a cured state of the resist layer in the same manufacturing process. FIG. 9 shows a gold electroformed state of an exposed portion in the same manufacturing process. FIG. 10 shows an electroformed state of a lead portion in the same manufacturing process. FIG. 11 shows a peeled state of a lead portion in the same manufacturing process. 12 is a perspective view of a mask used in the process of FIG. FIG. 13 is a plan view showing a general lead frame shape. FIG. 14 is a cross-sectional view showing the relationship between bumps and electrodes of a semiconductor chip. FIG. 15 shows a coating state of a first resist on a base material in a conventional lead frame manufacturing process. FIG. 16 shows an exposure state with a mask in the same manufacturing process. FIG. 17 shows an electroformed state of bumps in the same manufacturing process. FIG. 18 shows a second resist layer formation state in the same manufacturing process. FIG. 19 shows an exposure state with a mask in the same manufacturing process. FIG. 20 shows an electroformed state of a lead portion in the same manufacturing process. FIG. 21 shows a lead portion peeled state in the same manufacturing process. 22 is an explanatory diagram showing a problem at the time of forming the resist layer in FIG. [Description of Reference Signs] 1 semiconductor chip 25 laminated resist layer 25a underlying resist layer 25b electroformed body thickness adjusting resist layer

Claims (1)

(57) [Claims] 1. On the base material that has conductivity on the surface, fill the recesses on the surface of the base material and continue to the surface
The underlayer resist layer having a resist surface and the underlayer resist layer
Formed on the gist layer to ensure the thickness of the electroformed body
The electroformed body thickness ensuring resist layer is laminated, and an uncured portion and a cured portion having a predetermined pattern are formed in the laminated resist layer, and after the uncured portion is removed, electroforming is performed. Method.