JPH061798B2 - Lead frame - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lead frame of a semiconductor utilization device such as an IC or a transistor (hereinafter simply referred to as a semiconductor device), and in particular, an Au wire can be easily bonded to the lead frame. The present invention relates to a lead frame that can be obtained economically.

[Prior Art] A lead frame of a semiconductor device is generally formed of a Cu alloy, and an Au wire is used as a wire material for electrically connecting the lead frames to each other and the lead frame and the semiconductor. When joining the Au wire to the lead frame, ultrasonic heating, thermocompression bonding or the like is adopted.

By the way, when the Au wire is directly bonded to the lead frame where the Cu alloy is exposed as it is, it is difficult to obtain sufficient bonding strength because the adhesion of the Au wire to the surface of the lead frame is poor, and moreover, it is difficult to obtain a sufficient bonding strength at the bonding interface. A junction portion is generated, which adversely affects the electrical characteristics of the semiconductor device.

Therefore, when joining the Au wire to the lead frame, Ag plating is applied to the entire surface of the lead frame to improve thermal conductivity and the like, and the Au wire is adhered to the Ag plated surface to improve the joining strength and the joining interface. The method of preventing the peeling of is adopted and it has achieved some results. However, since the cost required for Ag plating is quite high, the above method is not always desirable from the viewpoint of reducing the manufacturing cost of semiconductor devices. Therefore, consideration was added to reduce the manufacturing cost of semiconductor devices,
As the surface treatment method of the lead frame, (1) a method of limiting the Ag plating treatment part, or (2) a method of reducing the Ag plating thickness, etc. have been submitted, but these methods have sufficient cost reduction effects. Can't get Further, as the recently developed method, (3) directly Au wire to the lead frame surface plating is N ₂ or an inert gas or N _2, such as Ar, without applying any in a reducing gas atmosphere plus of H ₂ Although a method of joining is proposed, this method is not sufficient in terms of joining strength and interfacial peeling resistance.

[Problems to be Solved by the Invention] Shimadzu Inventor Shima Under such circumstances, a technique for reliably bonding an Au wire to a Cu alloy lead frame without applying Ag plating or the like is expected. We have been conducting research for some time, and have developed the following technologies as part of such research and have already applied for patents. That is, the method is a method of forming an oxide film having a film thickness of 80 Å or less and a surface grain size of R _{max of} 0.25 μm or less on the surface of a Cu alloy lead frame, and by forming such an oxide film. The Au wire can be reliably joined.

By the way, in order to form such an ultra-thin oxide film,
After the lead frame material manufactured by rolling is subjected to an oxide film removal treatment such as pickling, it must be washed with water, dried and stored under vacuum. Examples of means for obtaining the above-described surface roughness include (1) mechanical polishing such as buffing, (2) rolling with a mirror surface roll, (3) chemical polishing or electrolytic polishing, and the like. In order to obtain a high level of surface roughness, not only strict process control and great effort are required, but also surface defects often occur in the slitter process and winding process, resulting in low yield and low manufacturing cost. Very high.

Moreover, in the case of a semiconductor device using a Cu alloy containing many additive alloy components as a lead frame material, (a) heat at the time of assembling the semiconductor device (die bonding, wire bonding, molding) (b) when mounting on a circuit of a semiconductor product Heat during soldering (c) When heat effects such as the heat of the operating environment and the heat generated by the semiconductor device itself are added, the additive components and impurities of the Cu alloy diffuse and segregate at the joint interface, resulting in a decrease in joint strength. There are also problems such as breakage of wires and changes in electrical characteristics.

The present invention has been completed as a result of further research based on such knowledge, and its purpose is to manufacture a Cu alloy capable of securely and firmly bonding Au wires without causing the above problems. It is intended to provide a lead frame.

[Means for Solving Problems] The lead frame according to the present invention has a Vickers hardness (Hv) of 50 to 50 on the surface of the CU alloy lead frame.
Cu with 100 kg / mm ² and maximum surface roughness of 1 μm or less
The gist is that the plated layer is formed with a thickness of 0.5 to 5 μm.

[Operation] In the present invention, since the hardness of the Cu plating formed on the surface of the Cu alloy lead frame, the maximum surface roughness, and the thickness thereof are specified is the most characteristic, the reasons for setting them will be clarified below. To

<Specification of hardness of Hv 50 to 100 kg / mm ² > When the Au wire is directly bonded to the surface of the lead frame,
The surface hardness has a great influence on the bonding strength. The hardness of Au wire used for normal wire joining is Hv50-6.
The surface hardness of the lead frame is H because it is 0 kg / mm ^2.
If it is less than 50kg / mm ^2, Au due to the pressure at the time of joining
Since the wire deformation is small, the adhesion is insufficient and a satisfactory joint strength cannot be obtained. On the other hand, 100 kg /
When it exceeds mm ² , only the Au wire is excessively deformed at the joint surface, which causes rather insufficient adhesion, so that a satisfactory joint strength cannot be obtained. The more preferable hardness range of the Cu plating layer is Hv 70 to 80 kg / mm ² .

<Surface Roughness _Rmax 1 μm or Less> When the surface roughness of the Cu plating layer is too large, the adhesion of the Au wire is carried out only on the edge portion of the unevenness on the Cu plating surface, and thus the surface roughness is substantially increased. However, in the present invention, R _max is set to 1 μm or less as a requirement for ensuring the minimum bonding strength that meets the purpose, but a more preferable surface roughness is required. The degree is R _max 0.5 μm or less.

<Point where the Cu plating thickness is set to 0.5 to 5 μm> If the thickness of the Cu plating layer is less than 0.5 μm, the leveling effect of the plating layer itself is insufficient, so the surface roughness after Cu plating is R _max 1 μm or less. The surface roughness of the lead frame material that is to be suppressed must be preliminarily adjusted, and not only the number of steps for the pretreatment is weighted, but also the elements contained in the lead frame material (for example, Sn, Zn, S
Segregation due to thermal diffusion of (i, P, etc.) can be sufficiently suppressed, and the bonding strength of the Au wire becomes insufficient. Note that the greater the thickness of the Cu plating layer, the greater the effect of suppressing the segregation described above. However, considering economic efficiency, it should be suppressed to 5 μm or less. The more preferable thickness of the Cu plating layer is 2 to 3 μm.

As described above, the hardness, surface roughness and wall thickness of the Cu plating layer are A
Although it has a significant effect on the bondability with u-wire, this has a close interaction with the bondability, and even if any one of them deviates from the above range, sufficient bondability can be obtained. I can't.

As a method for forming the Cu plating layer, an electroplating method using a copper sulfate bath or a copper borofluoride bath or an electroless plating method is exemplified as a preferable method, but the plating method itself is, of course, these methods. It is not limited to. However, when considering the plating effect, economical efficiency, pollution prevention, etc. comprehensively, the electroplating method using a copper sulfate bath can be said to be the most general.

In the present invention, as the means for joining the Au wire to the Cu alloy lead frame, the ultrasonic combined thermocompression bonding method, which is commonly used in the art, is generally adopted, but the method is not limited to this and is not limited to this. A pressure bonding method, an ultrasonic heating method, a laser heating method, or the like can also be adopted. In joining Au wires, it is recommended to seal the joint with an inert gas such as N ₂ or Ar, or a reducing gas obtained by mixing N ₂ with H ₂ .

The type of Cu alloy that constitutes the lead frame according to the present invention is not particularly limited, but the most common one is Cu-Fe.
-P, Cu-Ni-Si-Zn, Cu-Sn-Fe-
P, Cu-Sn-P, Cu-Ni-Sn, Cu-Fe-
P-Zn, Cu-Fe-Co-Sn-P alloy, etc.

[Example] A Cu-3.2% Ni-0.7% Si-0.3% Zn alloy lead frame was subjected to Cu plating with various plating conditions of a copper sulfate bath or a copper borofluoride bath, washed with water and dried to obtain Using each of the samples, a bonding test with an Au wire was performed by the following method. For comparison, a similar test was conducted on a lead frame without Cu plating.

<Joining method> After mounting the lead frame on the frame holder of the thermocompression bonding wire bonder combined with ultrasonic waves and shielding the holder with N ₂ gas, the stage temperature of the holder is 200 ° C, ultrasonic output is 0.2 W, ultrasonic oscillation time is 35 ms, Under the conditions of an extrusion load of 30 g, bonding is performed using an Au wire having a diameter of 30 μm and setting a bond distance to 1 mm.

When the joint strength and the interfacial peeling enhancement were examined for each of the obtained joints, the results shown in Table 1 were obtained.

In Table 1, Nos. 1 to 7 are all examples satisfying all the requirements defined by the present invention, and all have high bonding strength and no interfacial peeling is observed. On the other hand, No.
In Nos. 8 and 9, the hardness of the Cu plating layer is out of the specified range, and in No. 10, the surface roughness of the Cu plating exceeds the specified range. Therefore, in either case, the bonding strength is poor and the interfacial peeling rate is high. Nos. 12 and 13 are conventional examples. No. 12 has no Cu plating, but has sufficient surface polishing treatment to adjust the surface roughness to R _max 0.1 μm, so that good bonding is achieved. Strength and interfacial peel resistance are obtained. However, No. 13 has a large surface roughness and thus has a low bonding strength and an interfacial peeling rate of 100%.

No. 4 of the above test materials (example of the present invention: surface roughness R _max 1.
0 μm) and No. 12 (conventional example: surface roughness suppressed to R _max 0.1 μm) were examined with a scanning electron micrograph for the adhesion state with the Au wire, and both were intimately adhered. It was confirmed.

[Advantages of the Invention] The present invention is configured as described above, and by forming a Cu plating layer having a specified hardness, surface accuracy and thickness on the surface of a Cu alloy lead frame, It has become possible to reliably perform joining with a simple operation.
In particular, according to the present invention, it is not necessary to further reduce the surface roughness particularly at the preliminary adjustment stage when manufacturing the lead frame material, and the material manufactured through the normal process can be used as it is. Therefore, the process control is significantly simplified. Even when a Cu alloy lead frame material containing many additive elements is used, the presence of the Cu plating layer can prevent diffusion and segregation at the bonding interface. It is possible to join and it is possible to satisfy both economical efficiency and quality.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-183758 (JP, A) JP-A-53-141577 (JP, A) JP-A-58-136794 (JP, A) JP-B 1- 60948 (JP, B2)

Claims (1)

[Claims] 1. A lead frame made of Cu alloy prepared so that an Au wire can be directly bonded to a lead frame of a semiconductor device without interposing an Ag plating layer, the surface of which has a Vickers hardness (Hv). 50-100kg / mm ² ,
0.5 ~ CU plating layer with a maximum surface roughness of 1 μm or less
A Cu alloy lead frame, which is formed with a thickness of 5 μm.