JPS6057221B2 - semiconductor equipment - Google Patents

Abstract

PURPOSE:To improve bonding by mounting a semiconductor element, an upper surface thereof has an Al electrode, to an element disposed base material coated with a Ni or Ni alloy layer, and connecting the Al electrode and the base material by a wire made of Al or an Al alloy. CONSTITUTION:The surface of the lead frame 101 is coated with the Ni or Ni alloy layer 102, the semiconductor element, the upper surface thereof has the Al electrodes 111a, 111b, is mounted to an island section 103 of the lead frame 101, and the lead sections 104a, 104b of the lead frame 101 and the Al electrodes 111a, 111b are connected by the wires 112a, 112b consisting of Al or the Al alloy. Accordingly, both pellet bonding and post bonding can be improved, and the semiconductor device having high reliability can be obtained at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and more particularly to a semiconductor device having an improved element mounting base material on which a semiconductor element is mounted and wires connected to electrodes of the element are bonded.

Generally, semiconductor devices having structures shown in FIGS. 1 and 2 are known. That is, FIG. 1 is a perspective view showing a state in which a silicon semiconductor element (for example, a bipolar semiconductor element) is mounted on an element mounting base material (for example, a lead frame) and further wire bonded, and FIG.
This is a cross-sectional view showing the state after cutting, and numeral 1 in the figure is a lead frame having an island portion 2 on which a semiconductor element is mounted and lead portions 3a and 3b to which wires are bonded. A silver layer 4 is coated around the island portion 2 of the lead frame 1 and the bonding portions of the lead portions 3a and 3b. Further, a silicon semiconductor element 6 having base and emitter river electrodes 5a and 5b on its upper surface is mounted on the island portion 2 via a layer 7 mainly composed of gold. Al electrode 5a of this semiconductor element 6,
Gold wires Ba and 8b are connected to 5b, respectively, and the other ends of these gold wires Ba and 8b are post-bonded to internal leads 3a and 3b functioning as base and emitter electrodes, respectively. Further, reference numeral 9 in the figure denotes a gold wire B of the island portion 2 containing the semiconductor element 6 and the lead portions 3a and 3b.
a, 8b A resin sealing layer covering the vicinity of the connection portion. Note that the leads (not shown) of the island portion exposed from the resin sealing layer 9 and the lead portions 3a and 3b are covered with a solder layer 10. Further, a semiconductor device having a hermetically sealed structure is known in which a stem is used as an element mounting base material instead of a lead frame, as shown in FIG.

That is, 11 in FIG. 3 is a stem body made of copper whose periphery is coated with a silver layer 12. This main body 11 is provided with two through holes 13a, (13b), and these through holes 13a,
(13b) has a wide head portion 14a at the upper end, (14b)
) Copper lead wires 15a, (15b) are supported through glass insulators 16a, (16b). Note that the head portion 14a of the lead wires 15a, (15b)
, (14b) are also coated with the silver layer 12. A bipolar semiconductor element 18 is mounted on the silver layer 12 of the stem body 11 via a bonding layer 17 mainly composed of gold, and on the upper surface of the semiconductor element 18 there are electrodes 19a for the base and emitter. (19b) is provided. Gold wires 2 are attached to these Al electrodes 19a, (19b).
One end of these gold wires 20a, (20b) is connected to the head portions 14a, (14b) of the lead wires 15a, (15b) which function as the base and emitter electrodes. It is bonded to the silver layer 12. Further, the side of the stem body 11 on which the semiconductor element 18 is mounted is covered with a cap 21 for airtightly sealing the element 18. Note that 22 in the figure is a lead wire whose one end is connected to the stem body 11 and functions as a collector electrode. However, the second
In the semiconductor devices shown in Figs. and 3, the electrodes on the top surface of the three-piece semiconductor element to which the gold wires are connected are made of aluminum, and the element mounting base material (lead parts, etc.) is coated with a silver layer. Although gold wire can be post-bonded well to the lead part of the layer, when gold wire is pellet-bonded to the A1 electrode, purple play is likely to occur, and an intermetallic compound of gold and aluminum is formed, resulting in poor bonding between them. The drawback was that cracks occurred on the surface, significantly reducing the reliability of pellet bonding.

For this reason, wires are formed from aluminum, and the aluminum wires are used to connect the aluminum electrodes on the top surface of the semiconductor element and the silver layer coated on the leads, etc. of the element mounting base material. There is.

however,. In such a structure, pellet bonding between the electrode and the wire is good, but when the aluminum wire is bonded to the silver layer, local batteries occur between the aluminum and silver due to moisture adhesion, causing corrosion and significantly reducing post-bonding properties. be damaged. Furthermore,
In both the semiconductor devices shown in FIGS. 3 and 4 and the improved wire bonding means described above, a silver layer is coated on a wire post-bonded element mounting base material, and therefore, there are various problems listed below. occurs.

1 Since a silver layer is coated on the lead part (post bonding part) of the element mounting base material by plating, the manufacturing process of the element mounting base material increases, and the cost of the lead frame increases because silver itself is expensive. invites change.

The silver layer on the two-element substrate will sulfurize if left in the air, and is difficult to remove by simple treatment, resulting in poor bonding properties even when the wire is made of gold/7).

For this reason, extreme care must be taken during storage after plating the silver layer on the element-arranged substrate. If the thickness of the silver layer on the three-element substrate is thin, the underlying metal will oxidize, causing blistering and peeling of the silver layer. Especially when the temperature is high and humid, the blistering and peeling become even more likely to occur. Wire bonding properties are significantly reduced.

If the lead parts of the 4-element mounting base material are coated with a silver layer, if a hydrogen torch hits the silver layer on the lead part when bonding gold or gold alloy wire to the electrode on the top surface of the semiconductor element. Not only is the silver layer oxidized, but the underlying metal is also oxidized, impairing the bonding properties of the wire.

5 When a semiconductor device with a structure in which gold wires are post-bonded to the silver layer on the lead parts of the element-arranged base material is operated in a high-temperature atmosphere for a long time, water droplets may form on the electrodes (lead parts) of the element-arranged base material. A so-called migration phenomenon occurs in which silver adheres and dissolves from this lead portion, and silver is deposited on the other lead portion, causing a short circuit between the two leads, significantly impairing reliability. 6 When automating the manufacturing process from thin metal sheets to products, it is difficult to automate the process because a silver plating process is required.

7 In order to reduce the amount of silver used and reduce costs, if a silver layer is partially coated on the lead portions of the element-arranged substrate by partial plating, directionality occurs in the element-arranged substrate.

8. When manufacturing an element mounting base material from a thin metal plate using a press or the like, defects in the plating of the silver layer are inspected and removed during the press, which reduces the movability of the press.

The present invention has been made to solve the above various problems all at once, and uses an element mounting base material whose main surface is coated with a nickel or nickel alloy layer, and a semiconductor device having electrodes on the base material. By mounting the element and connecting the N electrode and the nickel or nickel alloy layer on the main surface of the base material with a wire made of aluminum or its alloy, a highly reliable semiconductor device with good pellet bonding and post bonding can be obtained. There is something we are trying to offer.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 4 and 5.

Figure 4 is a perspective view showing, for example, a bipolar semiconductor device mounted on a lead frame and wire bonded, and Figure 5 shows the semiconductor device after resin sealing and cutting. be.

In the figure, 101 is a lead frame made of iron material whose main surface is coated with a nickel layer 102.
1 has an island portion 103 on which a semiconductor element is mounted;
and the lead parts 104a and 10 to be wire bonded.
4b is formed. 105 in the figure is a vanadium layer 1 with a thickness of about 600A on the mounting surface as shown in FIG.
06, nickel layer 107 with a thickness of about 2000A, thickness 1.
0μm gold/germanium (Ge) 2wt% alloy layer 1
This is a bipolar silicon semiconductor device in which a gold layer 109 with a thickness of 1000 A and 0.08 mm is sequentially laminated, and as shown in FIG. Mounted by heating and pressing in a reducing atmosphere (for example, Yama-N2 forming gas). That is, the semiconductor element 105 is mounted on the island portion 103 via the bonding layer 110 that is made of an all-solid solution of Au-e-Ni that does not contain silicon. Also,
The upper surface of the semiconductor element 105 has a base and an emitter A.
1 electrodes 111a, 111b are provided, and these A1 electrodes 111a, 111b are provided with, for example, A1 wires 112a, 1
One end of each of the electrodes 12b is bonded in a reducing atmosphere (for example, H2-N2 forming gas). The other end of these A1 wires 112a and 112b is a lead portion 104a that functions as the base and emitter electrode of the lead frame 101 covered with the nickel layer 102.
, 104b in a reducing atmosphere (for example, H2-N2 forming gas). In other words,
The other ends of the AI wires 112a and 112b are the lead portions 104
It is joined to the nickel layer 102 of a and 104b by an Au-Ni binary alloy layer. Furthermore, the island portion 103 and lead portions 104a, 104bCf) of the lead frame 101 including the semiconductor element 105) Al wires 112a, 11
The vicinity of the connection 2b is covered with a resin sealing layer 113. Furthermore, the leads (not shown) in the island portion exposed from the resin sealing layer 113 and the lead portions 104a and 104b are covered with a solder layer 114. Note that the above-described semiconductor device can be manufactured, for example, by the method shown below.

First, a thin iron plate coated with a nickel layer is pressed to produce a lead frame coated with a nickel layer.

Next, on the mounting surface of the silicon substrate on which a plurality of Npn bipolar transistors were formed, a vanadium layer with a thickness of about 600A, a nickel layer with a thickness of about 2000A, and a nickel layer with a thickness of 1.
After successively vacuum-depositing and laminating a 0μm gold/germanium (Gel2wt%) alloy layer and a 1000A thick gold layer, the silicon substrate is diamond scribed or blade dicer scribed from its upper surface (the surface opposite to the mounting surface). The semiconductor element 105 shown in FIG.
Create. Note that these semiconductor elements are stored covered with vinyl chloride or the like. Next, while the lead frame is heated to 370 to 4000 C in an inert gas atmosphere, preferably a H2-N2 forming gas (reducing atmosphere), the semiconductor element is vibrated on the island portion of the lead frame. Mount it by pressing with a load of 50 to 80 y. After that, one end of the A1 wire was bonded to the Al electrode of the mounted semiconductor element in the above-mentioned forming gas atmosphere, and the other end of the N wire was bonded to the lead part of the lead frame coated with a nickel layer in a reducing atmosphere for 30 to 30 minutes. After post-bonding and resin sealing at 350° C., the extended leads and the like are immersed in a solder bath and soldered to produce the semiconductor device shown in FIG. According to the present invention, the A1 wire 11-2a
, 112b, and one end thereof is pellet-bonded to the Al electrodes 111a, 111b on the upper surface of the semiconductor element 105 using conventional Al'Ri. A good connection can be made without producing purple brags or intermetallic compounds of Al and Au, as in the case of A1 wire bonding.

In addition, the other ends of the AI wires 112a and 112b are post-bonded to the lead parts 104a and 104b of the lead frame 101 coated with the nickel layer 102, respectively, via the AI-Ni binary alloy layer, so that The A1 wire can be connected very well without causing local batteries or corrosion due to moisture adhesion, unlike bonding with a silver layer. Therefore, since the A1 wire makes both pellet bonding and post bonding good, it is possible to obtain a semiconductor device that is significantly cheaper and more reliable than when gold wire is used. Further, since wires can be bonded well without coating the lead parts 104a and 104b of the lead frame 101 with a silver layer, two various effects listed below can be achieved.

(1) Since it is not necessary to cover the lead frame with a silver layer, the process can be shortened by omitting the silver plating process, and the lead frame can be manufactured at low cost.
3 (2) Since there is no need to cover the silver layer, it is possible to eliminate the disadvantages of silver, such as the decrease in bonding strength of the wire due to silver flow and the oxidation of the base under the silver layer, making it easier to store and mount the lead frame. 3. Carefully insert the wire into the lead section of the lead frame.
Creates a strong bond. (3) Since the wire bonding part of the lead frame is not coated with a silver layer, even if the semiconductor device is operated for a long time in a high-temperature atmosphere, the shortening between the electrode lead parts due to the silver migration phenomenon cannot be eliminated. , reliability can be significantly improved.

(4) Even if the hydrogen torch hits the lead part of the lead frame when bonding the N wire to the electrode on the top surface of the semiconductor element, the lead part is not covered with a silver layer, so the silver layer will not cover it. Wires can be bonded well without causing oxidation or deterioration of the lead portion due to oxidation or deterioration.

When bonding this A1 wire, if a reducing gas (for example, a forming gas containing about 10% H2) is used, the hydrogen torch will not easily disappear, and the oxidation of the copper that makes up the lead part of the lead frame will be reduced, resulting in good bonding performance. Become. (5) Since the plating process for coating the lead frame with a silver layer can be omitted, reliability testing of the silver layer (
This eliminates the need for testing for silver layer blistering, peeling, plating thickness, and plating defects, making it easier to automate the manufacturing of semiconductor devices, simplifying cleaning after press processing, and reducing the need for silver layer coating. It is possible to obtain a high-precision lead frame with no directionality.

Additionally, oxidation due to local battery generation does not occur during cleaning of the lead frame. Furthermore, if a semiconductor element is used in which a barrier metal layer (vanadium or nickel layer), gold, or germanium alloy layer is sequentially laminated on the mounting surface, the semiconductor element can be attached to an island of a lead frame covered with a nickel layer (or nickel alloy layer). Since it can be mounted well on the body, various effects can be exhibited as listed below.

6) Since the minimum necessary gold/germanium alloy layer is mounted as a brazing material without using a gold preform, the positioning accuracy during mounting is good and the occurrence of wire bonding defects in the post-process is reduced.

7) Since no gold preform is used, a device for mounting the gold preform on a lead frame (element mounting base material) is not required, and the process can be shortened.

3) Since only the minimum amount of expensive gold is used in the gold/germanium alloy, it is possible to significantly reduce costs.

)) Since the barrier metal layer is interposed between the silicon semiconductor element and the gold/germanium alloy layer, the semiconductor element can be firmly mounted on the lead frame. A two-layer structure can significantly improve the adhesive strength between the semiconductor element and the gold/germanium alloy layer.

(10) The layer involved in bonding is made of a gold-germanium alloy, which has better cracking properties than the gold-silicon eutectic layer coated on the mounting surface of the conventional structure.・Do not cut from the silicon eutectic layer side! Cut the top surface of the silicon substrate (
The cutting can be performed along the dicing line (from the surface opposite to the mounting surface), making it possible to perform highly accurate cutting.

That is, gold-silicon eutectic (2.85 Wt% silico) and gold-germanium eutectic (12 Wt% germanium).
Comparing the cracking properties with gold, the density of each component is 1
9.3, silicon 2.42, germanium 5.46, the volume of silicon in the gold-silicon eutectic is 19%, and the volume of germanium in the gold-germanium eutectic is 33.
%, and in the 1 gold/germanium eutectic, the volume occupied by germanium is quite large, and the ratio occupied by gold is low.
Cracking is easier than with silicon eutectic, and the silicon substrate can be cut from the upper surface side as described above.

(11) Since the vapor pressures of gold and germanium are similar at around 10-1 Torr, gold-germanium alloys of a given composition can be made by vacuum evaporation without causing fractional evaporation like gold-silicon or gold-antimony. Can form layers.

(12) If the gold/germanium alloy layer is further coated with metal, it is possible to prevent the oxidation of the gold/germanium alloy layer 1' before mounting the semiconductor element, and the strength of the mount is extremely good, resulting in a highly reliable semiconductor. You can get the equipment.

(13) When mounting, the semiconductor element is coated with a nickel layer (or nickel alloy layer) at a heating temperature of 370 to 400°C.
A ternary alloy layer of Au-Ge-Cu can be formed by contacting the lead frame coated with light pressure without vibration, so there is less thermal influence on the semiconductor element, electrical identification is stable, and the mount is more stable. A semiconductor device can be obtained.

(14) Since there is no need to coat the lead frame with a silver layer, it eliminates the drawbacks of silver, such as the decrease in mount bonding strength due to silver sulfurization and the oxidation of the base under the silver layer. Semiconductor elements can be firmly bonded to lead frames without any precautions.

(15) The bonding layer formed by mounting the gold/germanium alloy layer and the lead frame contains gold, germanium,
A solid solution of copper that does not form an intermetallic compound.

Therefore, since no intermetallic compound is formed in the bonding layer, a highly reliable semiconductor device with low electrical resistance, chemical stability, and no deterioration in mechanical strength can be obtained. Furthermore, although the nickel layer (or nickel alloy layer) on the main surface of the lead frame is easily oxidized, the bonding layer becomes a precious metal through diffusion or melting of gold and becomes less likely to be oxidized. Furthermore, even when heated and oxidized in air, oxidation does not occur at the mount joint because the gold diffuses and the noble metal layer becomes wider. Note that the semiconductor device according to the present invention is not limited to the case where a lead frame made of iron material whose main surface is coated with a nickel layer as in the above embodiment is used, and the main surface layer is a nickel alloy layer such as copal. The material may be copper, copper alloy, cobalt, etc.

Further, the nickel layer or nickel alloy layer may be coated not only on the main surface but also on the entire surface of the lead frame material. Furthermore, the material of the lead frame is not limited to a single layer, and may have a laminated structure. The semiconductor device according to the present invention is not limited to using N wires as in the above embodiments, but may also use alloy wires such as A1-Cu.

As shown in the above embodiment, the semiconductor device according to the present invention uses a semiconductor element in which four metal layers of vanadium, nickel, gold/germanium, and gold are laminated on the mounting surface, and this element is connected to a lead coated with a nickel layer. The semiconductor element is not limited to the structure in which it is mounted on the island part of the frame, but may be mounted on an island part covered with a silver base or the like via a brazing material such as a gold preform or a gold eutectic alloy.

In other words, in the semiconductor device of the present invention, it is necessary that the main surface of the element mounting base material to which the gold or gold alloy wire is bonded is coated with a nickel layer or a nickel alloy layer, which is necessary for the mounting part of the semiconductor element. Depending on the situation, a group layer may be applied. The semiconductor device according to the present invention is not limited to the structure using a lead frame as the element mounting base material as in the above-mentioned embodiments, but can be similarly applied to the above-described structure with a fit seal shown in FIG.

In other words, the lead wire of the stem, which serves as the base and emitter extraction electrode, is coated with a nickel layer (or nickel alloy layer) on the top surface of the head, and this is covered with A1 or A.
A semiconductor device may be constructed by bonding L alloy wires. In this case, the main body surface of the stem may also be coated with a nickel layer (or nickel alloy layer), and a semiconductor element may be mounted on the stem body using a semiconductor element in which a barrier metal layer and a gold/germanium alloy layer are successively laminated on the mounting surface. good. As described in detail above, according to the present invention, an element mounting base material whose main surface is coated with a nickel or nickel alloy layer is used, and in this case, a semiconductor element having an N electrode is mounted, and the Al electrode and the By connecting the nickel or nickel alloy layer on the main surface of the base material with N or Al alloy wire, pellet bonding, post bonding, and ink are all good, and the various effects listed in (1) to (5) above can be achieved. Accordingly, it is possible to provide an inexpensive and highly reliable semiconductor device having the following characteristics.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing a state in which a silicon semiconductor element is mounted on a lead frame 2 and the element and the lead portion of the lead frame are connected with gold wire, and Figure 2 is a perspective view of the lead frame shown in Figure 1 sealed with resin. 3 is a sectional view showing a semiconductor device with a hermetically sealed structure; FIG. 4 is a sectional view showing a semiconductor device having a hermetically sealed structure; and FIG. Mount the same element and the lead part of the lead frame at A.
FIG. 5 is a cross-sectional view showing the semiconductor device after the lead frame shown in FIG. 4 has been sealed with resin and cut, and FIG. 6 is a cross-sectional view showing the semiconductor device shown in FIG. 4. FIG. 3 is a sectional view showing a state before mounting. 101...Lead frame, 102...Nickel layer, 103...Island part, 104a,
104b... Lead portion, 105... Bipolar silicon semiconductor element, 110... Bonding layer, 111a, 111b... Base, emitter A1 electrode, 112a, 112b...A1 wire,
113...Resin sealing layer.

Claims (1)

[Claims] 1. An element mounting base material made of a metal material whose main surface is coated with a layer of nickel or nickel alloy, a semiconductor element having an electrode on the upper surface, and a metal, gold, germanium alloy layer, nickel layer, and vanadium layer. Using a four-layered brazing material laminated in sequence, the semiconductor element is interposed on the base material such that the gold layer is on the base material side and the vanadium layer is on the semiconductor element side. 1. A semiconductor device, wherein the semiconductor device is mounted in a reducing atmosphere, and the element mounting substrate and the electrode of the semiconductor element are connected with a wire made of aluminum or an alloy thereof in a reducing atmosphere.