JPH04101426A - Formation of metal protrusion - Google Patents

Abstract

PURPOSE:To obtain a metal protrusion by a simple process at low cost by a method wherein multilayer-structured sheet metal material is punched with a punch and die into a small metal piece and the small metal piece is joined to a metal lead or an electrode formed on a substrate. CONSTITUTION:A metal lead 6 for a TAB film 5 is located on a heating stage 4. Multilayer-structured ribbon metal material 3 is fed into a press-working jig having a punch 1 and die 2. Then, the press-working jig is so positioned that the punch shaft may come to the top end of the metal lead 6. After that, specified pressure is applied to the punch 1 to allow the punch 1 to go down to punch the metal material 3 for forming a small metal piece. By repetition of elevation of the punch 1, the small metal piece is attached firmed onto the metal lead 6. Consequently, a metal protrusion is formed. At this time, a junction layer 32 between the metal lead 6 and the metal protrusion 8 shall be a solder alloy. Since grooves are made reticulately on the recessed head of the punch, the central part of the surface of the metal protrusion is formed into such a projected shape 16 as to fit into the shape of the punch head 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming metal protrusions, and particularly to a method for forming metal protrusions for mounting semiconductor elements.

[Conventional technology]

In recent years, the fields of application of semiconductor products such as LSI have been rapidly expanding, including various consumer devices and industrial devices. In order to expand the field of use of these devices, prices are being lowered and full versions are being developed. Therefore, in order to meet these demands, semiconductor products are also required to have high-density packaging, such as lower costs, lighter weight, thinner thickness, and smaller size in packaging and equipment integration processes.

Generally, the TAB method is known as a method suitable for high-density packaging of semiconductor elements, and efforts have been made to expand its practical use. For connection between a semiconductor element and a mounting wiring board using the TAB method, a metal lead made of Au or Cu plated with Sn and patterned to match the electrode arrangement of the semiconductor element is bonded to a polyimide film for holding the metal lead. A film carrier with a structure similar to the above is used. Here, in order to bond between the A1 electrode of the semiconductor element and the metal lead, it is necessary to make the bonding part convex, and a metal protrusion called a bump is provided on the AI electrode part or the metal lead. A thermocompression bonding method is usually used to bond the Al electrode and the metal relays 1 through the metal protrusions.

As a conventional method for forming metal protrusions, the so-called metal bump method has been widely used. FIG. 7 shows a general process for forming a plating bump. First, an adhesive layer 40 of Ti, Cr, etc., and a diffusion prevention layer 41 of Cu, Pt, etc. are laminated on the semiconductor element 30 by sputtering (FIG. 7(a)).
. In the figure, 35 is an A1 layer, 36 is a protective layer, and 37 is a silicon substrate. Next, after forming a resist layer 42 covering areas other than the A1 electrode part 31 by lithography, Au is applied to the electrode part 31.
A plating layer 43 of about 30 μm is formed (FIG. 7(b)).

After that, after removing the resistor layer 42, the AI electrode part 31
The diffusion prevention layer 41 and the adhesive layer 40 other than the At electrode portion 31 are removed by etching while being protected by a resist layer covering them (FIG. 7(C)). By performing the following steps, metal protrusions are formed on the A1 electrode by plating.

In addition to the plating bump method, the ball bump method, which uses Au wire hole bonding technology as shown in the process diagram of FIG. 8, has attracted attention and is being developed. Masu, capillary 5
The tip of the Au wire 51 exposed below 0 is melted by electric discharge using an electric torch 52 to form an Au ball 53 (FIG. 8(a)).

Next, after ultrasonically bonding the Au ball 53 to the AI electrode 8i31 using the capillary 50 (FIG. 8(b)), the capillary 50. Pull up the Au wire 51 and tear it off from the neck part of the AU ice ball 54 to remove the ball part 54.
8 (C)). This method has a simple process since it does not require a wet method, and it is suitable for producing a wide variety of products in small quantities because it is formed one point at a time on the electrode.

In addition, the transfer bump method is considered to be a promising method as it allows metal protrusions to be formed on the TAB film side. This method is A1
After forming Au protrusions on a plating substrate with conductor openings corresponding to the electrodes by electroplating, the Au protrusions are superimposed on the TAB metal leads and heated and pressed from the plating substrate onto the TAB metal leads. It is to be transcribed into.

[Problem to be solved by the invention]

The conventional method for forming metal protrusions described above has the following drawbacks. In other words, the plating bump method has a complicated process, requires high material costs and man-hours to apply a thick plating film, requires large capital investment, and is high in formation cost as it causes a decrease in device yield. There is a drawback.

In the case of the ball hump method, although it has the advantage of not being as easy as the wet method, there are variations in the size of the Au balls and variations in the height after tearing the wire, and since Au balls are used, the electrode pitch is about 100 μm. is the limit, and it is said that fine bonding below this limit is difficult. Furthermore, since mechanical stress is applied to the electrode portion not only when bonding the TAB film but also when forming bumps, reliability of the bonded portion becomes a problem. The transfer bump method does not affect the chip yield compared to the plating bump method because the plating is performed on the plating substrate, but it cannot eliminate the complexity of the process and
In order to transfer the u protrusions onto the TAB film without any problems, advanced management and know-how are required for the formation of the plating substrate, the plating process, etc.

[Means for Solving the Problems] The method for forming a metal protrusion of the present invention includes a punching step of punching out a plate-shaped metal material having a multilayer structure by a press method using a punch and a die to form a small metal piece; and a step of joining the metal piece to a metal lead or an electrode on the substrate. The small metal piece can be crimped onto the metal lead wire or the electrode on the substrate by using a punch that punches out a plate-shaped metal material having a multilayer structure by continuously moving the punch. Attach four parts to the tip of the punch to insert metal leads or substrates.
It is effective to pressure-bond the metal piece to two electrodes and form a convex portion on the surface of the metal piece.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing the steps of an embodiment of the present invention. First, the metal lead 6 of the TAB film 5 is placed on the heating stage 4, and a press processing jig having a punch 1 and a die 2 into which the metal material 3 having a ribbon-like multilayer structure is fed is placed so that the punch shaft is attached to the metal lead 6. Align it so that it is at the tip (Figure 1(a)). Next, the bonder 1 is lowered by applying a predetermined pressure in the direction of the arrow to punch out the metal material 3 to form a small metal piece, and the bonder 1 is continuously lowered to press the small metal piece onto the metal lead 6 (first Figure 1 (b
)). When the press jig is removed, the process of forming the first metal protrusion 8 is completed (FIG. 1(C)). In this way, a plurality of metal pieces are sequentially pressed onto the TAB leads, thereby forming metal protrusions corresponding to the series of A1 electrodes of the semiconductor element. Here, since the metal protrusion 8 is simply punched out of the metal material 3 and crimped onto the lead as it is, it has a multilayer structure corresponding to the structure of the metal material. In addition,
The machined hole of the die 2 can be formed by precision electrical discharge machining. The outer shape of the punch 1 can be made by grinding. Dice 2
, Suitable materials for the punch 1 include high-speed steel, cemented carbide, and die steel.

Since the shape and height of the metal protrusion formed by the above method can be controlled by the thickness of the metal material and the shape of the punch tip, the precision is good and the reliability of subsequent bonding with the semiconductor element electrode is also high. Unlike the ball bump method for making Au holes, the present invention can also be applied to TABs with narrow pitch leads of 100 μm or less by reducing the punch diameter. In the above-mentioned example, the small metal piece was joined to the lead using a processing punch, but after the small metal piece is formed, the small metal piece may be crimped onto the lead using a dedicated jig for feeding the small metal piece using a guide mechanism. good.

FIG. 2.3 is a cross-sectional view illustrating an example of forming a metal protrusion in a multilayer structure suitable for bonding to a metal lead of a TAB film of an A1 electrode of a semiconductor device. FIG. 2 shows a metal protrusion 8d having a three-layer structure formed by punching out a three-layer structure plate metal material and pressing it onto the metal lead 6 using the method explained using FIG.
This is an example of forming a . When bonding the TAB Au plating lead 6 to the A1 electrode 31 of the semiconductor element 30, the bonding layer 32 with the lead and the bonding layer 33 with the A1 electrode are made of Au, which has a proven bonding experience, and the intermediate layer 34 is made of low-cost Au. It is better to use Cu. In case of 40 μm height metal protrusion, Au on both sides
Layers 31, 33 have a thickness of 5 μm to provide good bonding. Such a three-layer material can be easily formed by rolling or plating, and the material cost can be reduced compared to when a single-layer Au material is used. Although similar to the above, it is also effective to use a solder alloy for the bonding layer 32 with the metal lead 6. In this case, the pressure welding to the lead is performed lightly with low pressure, and the bonding strength can be obtained by thermally melting the solder. In addition, AU has conventionally been widely used as a plating material for TAB metal leads due to its bondability with Au, which is a metal protrusion material, but Pb
Another advantage is that low-cost materials such as -Sn-based hunters can be used. As described above, the present invention allows selection of metal protrusion configurations for various electrodes and metal leads, and has great effects on cost reduction and high reliability of bonding.

FIG. 3 shows a two-layer metal protrusion 8e attached to a semiconductor element 30.
An example is shown in which the metal lead 6 is formed on the A1 electrode 31 and then the metal lead 6 is bonded. In this case, the metal protrusion 8e may be formed in the same manner as when it is attached to the metal lead first. However, similar to the ball bump method, mechanical stress is applied to the AI electrode portion 31 of the semiconductor element 30 when forming the metal protrusion.

If mechanical stress is not to be applied again when bonding to the metal lead 6, it is preferable to configure the metal protrusion 8e as described below. In this embodiment, the layer 39 on the A1 electrode side is made of Au, and the layer 38 on the metal lead side is made of Au-8i solder. When thermocompression bonding the metal lead 6, the heat melting properties of the solder can be utilized, so it can be carried out with a small pressing force, and the reliability of the joint can be ensured. In this way, the present invention can be applied to various mounting methods.

The shape of the punched metal piece was good when the clearance between the punch and the die and the axis misalignment were 8% or less and 2 μm or less, respectively. 4.5 and 6 are cross-sectional views illustrating the shape of the tip of the punch and the shape of the metal protrusion formed on the metal lead. Figure 2 shows bond 1 at the tip or flat surface.
This is a case where . On the outer periphery of the upper surface of the metal protrusion, a gap 13 remains on the outer periphery of the upper surface of the metal lead 6 due to being crushed under the punch when crimped onto the metal lead 6, and the upper surface of the formed metal protrusion becomes concave. When it is necessary to strengthen the bond between the small metal piece and the lead 6 in advance, the pressing force of the punch is increased, so the size of the pin 13 increases. At this time,
When crimping the semiconductor element with the A1 electrode after forming the protrusions,
It is difficult to apply pressure to the center of the electrode, and the bonding strength with the A1 electrode decreases.

On the other hand, FIG. 5 shows the case when the punch tip is concave, and FIG. 6 shows the case when the punch tip has a mesh-like groove. For the same reason as mentioned above, a protrusion 13 is formed on the outer periphery of the metal protrusion, but a convex portion 16 corresponding to the shape of the punch tip 15 is formed in the central portion. In this case, even if there is a paris on the outer periphery, since there is a convex portion in the center, pressure is easily applied to the center of the electrode when it is crimped with the A1 electrode of the semiconductor element, thereby increasing the reliability of the bonding. The strength of the bond with the lead is determined by crimping it with the A1 electrode of the semiconductor element using a normal thermocompression bonding process.This crimping process also strengthens the bond between the metal lead and the metal protrusion, so it will not come off during handling. It is fine as long as it is moderate.

If the punch pressure is small and pressed against the lead after punching, the amount of crushing of the small metal piece during crimping will be small, and variations in the size of the punch and the height of the center part can be reduced.

〔Effect of the invention〕

The method for forming metal protrusions of the present invention is not as wet as 1, and 1
The process is simple because a single press machine can form a small metal piece and bond it onto a lead or substrate electrode.
This method has the advantage of being able to form metal protrusions at low cost, such as requiring less material costs and equipment investment. In addition, since the shape and height of the metal protrusion can be controlled by the thickness of the metal material and the shape of the punch tip, it is possible to form metal protrusions with high precision, making the bond highly reliable, and also having the advantage of being able to support narrow pitch bonding. There is. Furthermore, there is an advantage that the structure of the metal protrusion can be selected according to the mounting configuration, resulting in lower cost and higher reliability.

[Brief explanation of drawings]

1(a) to 1(c) are cross-sectional views showing an example of the present invention in the order of steps, FIGS. FIG. 6 is a cross-sectional view illustrating the shape of the tip of the punch and the shape of the formed metal protrusion according to the embodiment of the present invention. FIG. 4 shows the tip of the punch when the tip is flat, and FIG. Figure 6 shows the case where the punch has a groove on the tip surface, Figure 7 is a sectional view showing the process order of the conventional method of forming metal protrusions, and Figure 8 shows the conventional method. FIG. 7 is a cross-sectional view illustrating the ball bump method, which is another method for forming metal protrusions, in order of steps. 1.1b, IC...punch, 2...dice, 3...
・Metal material, 4... Stage, 5... TAB film, 6... Metal lead, 7... Polyimide film, 8.8
b, 8C18d, 8e...Metal protrusion, 9...Punching remaining part, 10...Die hole part, 13...Paris, 1
4... Punch operation, 15... Punch tip surface, 16.
...Top surface of metal protrusion, 30...Semiconductor element, 31...
・AI electrode part, 32.33.34.38.39... Layer inside metal projection, 35... A1 layer, 36... Protective layer, 37... Silicon substrate, 40... Adhesion layer, 41・
...Diffusion prevention layer, 42...Resist layer, 43...A
U plating layer, 50... Capillary, 5]... Au wire, 52... Electric torch, 3... Au ball, - Au ball part.

Claims (1)

[Claims] 1. A punching step of forming a small metal piece by punching out a plate-shaped metal material having a multilayer structure by a press method using a punch and a die, and bonding the small metal piece to a metal lead or an electrode on a substrate. A method for forming a metal protrusion, comprising the steps of: 2. A punch that punches out a plate-shaped metal material having a multilayer structure in cooperation with a die continues to move to press the small metal piece to a metal lead or an electrode on a substrate positioned below the die. A method for forming metal protrusions. 3. The method for forming metal protrusions according to claim 1 or 2, wherein at least one layer of the multilayer structure is one selected from gold, copper, and a solder alloy. 4. The method of forming a metal protrusion according to claim 1, 2 or 3, wherein a concave portion is provided at the tip of the punch to form a convex portion on the surface of the metal piece crimped onto the metal lead or the electrode on the substrate. 5. The method of forming a metal protrusion according to claim 4, wherein the recessed portion is a plurality of grooves and the convex portion is a plurality of protruding stripes. 6. Metal lead or electrode on substrate The method of forming a metal protrusion according to claim 1, 2, 3, 4 or 5, wherein the metal protrusion is a metal lead of a TAB type film carrier or an electrode of a semiconductor element.