JPH083134B2 - Lead frame material for Au-Si eutectic bonding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lead frame material for bare bonding, and more particularly to a lead to a semiconductor element even if bare bonding using an Au—Si eutectic alloy method is performed. The present invention relates to a lead frame material for bare bonding in which the constituent elements of the frame material are not adversely affected.

[Prior Art] The semiconductor assembly process includes a die bonding process for joining a device (semiconductor chip) and a lead frame, a wire bonding process for connecting the device wiring and the lead frame with a wire of Au or Al, and sealing with a resin. It consists of steps. Since the lead frame is heated in these steps,
The lead frame material used is required not to be softened by such heating, that is, to have heat resistance.

On the other hand, copper alloys, which have excellent thermal conductivity and electrical conductivity, have been used as lead frame materials mainly for applications requiring good heat dissipation, such as transistors.

These copper-based lead frame materials are copper alloys containing various additive elements in order to satisfy the properties required as a lead frame material such as the above heat resistance and mechanical strength.

In the die bonding step of the above assembling steps, the element and the lead frame are usually joined by three types of methods. That is, the Au-Si eutectic alloy bonding method, the solder bonding method, and the conductive resin bonding method. Among these methods, the Au-Si eutectic alloy method is 420 to 440 ° C, which is 50 to 70 ° C higher than the eutectic temperature of 370 ° C.
Bonding is performed by heating the element and the lead frame to the temperature of tens of seconds for several tens of seconds.

By the way, there is a strong demand for cost reduction in semiconductor devices, and as one means therefor, a technique called bare bonding, in which plating on a lead frame is omitted to perform die bonding or wire bonding, is spreading mainly in transistors. . In this bare bonding, when die bonding was carried out by the above Au-Si eutectic alloy method, it was found that the characteristics of the semiconductor element were changed.

[Problems to be Solved by the Invention] The present invention does not change the characteristics of a semiconductor element even if bare bonding is performed using an Au-Si eutectic alloy bonding method, and the heat resistance and mechanical properties are not changed. An object is to provide a lead frame material for bare bonding which is also excellent in strength.

[Means for Solving the Problems] The feature of the lead frame material for Au-Si eutectic bonding according to the present invention is that Fe: 0.5 to 3.0 wt%, Si: 0.005 to 0.25 wt%, Zn: 0.05 to 1.0wt
%, And the elements belonging to the IIIb group and the Vb group as impurities are regulated to 0.002% or less, and the balance substantially consists of Cu.

[Operation] The operation of the present invention will be described below together with the findings obtained in the present invention and the reasons for limiting the components.

The present inventor first clarified the cause of changes in the characteristics of semiconductor elements when bare bonding was performed using the Au-Si eutectic alloy bonding method.

As a result, the following was revealed. That is, 400 to 440
The constituent elements in the copper alloy lead frame that are in contact with the molten Au-Si layer while being heated to ℃ for several tens of seconds pass through the Au-Si layer and diffuse into the Si element.

Among the elements diffusing into Si, B, Al, Ga, In belonging to the IIIb group of the periodic table and N, P, As, Sb belonging to the Vb group act as acceptors and donors on the Si semiconductor, and are P-type. And forming an N-type semiconductor. When the device is a transistor, the bottom surface of the Si device, which is usually joined to the lead frame, is the collector.
It was found that elements belonging to Group V or Vb enter from the lead frame and form an impurity semiconductor, which adversely affects the electrical characteristics of the transistor. That is, the conventional copper alloy contains various additive elements in order to enhance heat resistance and mechanical strength, but these additive elements cause deterioration of the electrical characteristics of the semiconductor element.

When the Au-Si eutectic alloy bonding method is applied to bare bonding, if the copper-based lead frame material used contains a constituent element belonging to Group IIIb or Vb, it adversely affects the Si element as described above. The problem arises. Therefore, in such a case, a copper alloy having high heat resistance, conductivity, and mechanical strength,
There is a demand for an inexpensive lead frame material that does not contain a component element belonging to the Vb group.

Therefore, the present inventor does not contain elements belonging to the IIIb group and the Vb group that adversely affect the Si element as component elements, and has high conductivity and required strength, and is inexpensive and has excellent heat resistance. We explored lead frame materials.

As a result, it was found that a lead frame having excellent heat resistance and mechanical strength can be obtained by limiting the basic components to a predetermined range without containing an additive element, and the present invention was accomplished. It is a thing.

First, the contained components and component ratios of the bare bonding lead frame material according to the present invention will be described.

(Fe) Fe is an element that contributes to the improvement of strength and heat resistance by finely precipitating in Cu. Fe content of 0.5wt%
If it is less than 3.0 wt%, its effect is small, and if it exceeds 3.0 wt%, the strength and heat resistance are improved, but it becomes Fe rich, resulting in poor hot workability. Further, crystallized Fe is likely to be generated, which causes a problem during plating. In addition, it takes time for Fe to burn through during melting, resulting in an increase in cost. Therefore, the Fe content is 0.5 wt% to 3.0 wt%.

(Si) Si is an element that acts as a deoxidizer during ingot formation, reduces oxygen in the molten metal, eliminates defects generated inside the ingot, and creates a good ingot. If the content is less than 0.005 wt%, the effect is small, and if it exceeds 0.25 wt%, there is a deoxidizing effect.
Cold workability and hot workability are reduced. Further, the peeling resistance of the solder deteriorates and the conductivity decreases. Therefore
The Si content is 0.005-0.25 wt%.

(Zn) Zn is an element that improves the peeling resistance of the solder. If the content is less than 0.05 wt%, its effect is small, and if it exceeds 1 wt%, its effect is saturated, but the conductivity is descend. Therefore, the Zn content is 0.05 to 1 wt%.

None of the above component elements belong to the IIIb group or the Vb group. Therefore, the plating of the lead frame material according to the present invention is omitted, and even if die bonding is performed by the Au-Si eutectic alloy method, these elements do not diffuse into the Si element and do not adversely affect the characteristics of the Si element. .

On the other hand, elements such as B, Al, Ga, In, N, P, As, and Sb belonging to the IIIb group and the Vb group are contained in the raw material as impurities, and enter the manufactured copper alloy. Therefore, by controlling the content in the raw material, the invasion into the intended copper alloy is prevented. As is clear from the above description, it is preferable that the content of these impurities is small, and although it depends on the semiconductor used, the content of each is preferably 0.002% or less.

[Examples] The leadframe material for bare bonding according to the present invention will be described by examples.

Using the Cryptor furnace, the alloys with the ingredients and proportions shown in Table 1 are melted in the atmosphere under charcoal coating,
A 45 mmt × 75 mmw × 200 mml ingot was cast using a cast iron book mold. In Comparative Example No. 7, a defect due to insufficient deoxidation occurred inside the ingot, so the subsequent sample adjustment was abandoned. Next, after the front and back surfaces of this ingot are chamfered by 2.5 mm each, at a temperature of 850 °
It was hot-rolled to 15 mmt and water-cooled from a temperature of 700 ° C or higher at a rate of 30 ° C / sec.

Furthermore, after cold rolling to a plate thickness of 0.5 mm, 580 ℃
After annealing at the temperature of 2 hours, when reaching 500 ° C. during cooling, annealing was further performed for 4 hours.

 Then, cold rolling was performed to obtain a plate material of 0.3 mmt.

The following tests were performed on these samples. The test results are shown in Table 2.

 The test method is as described below.

(1) Conductivity was calculated from the value of electric resistance measured by a double bridge using a test piece of 15 mmw × 300 ml.

(2) Hardness is 50 with a micro Vickers hardness tester
It was measured at 0 gr.

(3) The heat resistance was evaluated by measuring the hardness after heating for 5 minutes at each temperature using a nitrite furnace and measuring the temperature at which the hardness after heating was 80% of the hardness before heating.

(4) The peel resistance of solder is 60Sn for a test piece of 20mmw x 50mml.
After immersing -40Pb solder in a weakly active flux at 230 ° C for 5 seconds and soldering, after heating at 150 ° C for 1000 hours, bend back 180 ° at 2mmR and check for peeling. did.

As is clear from Table 2, the alloys No. 1 to No. 4 of the present invention are
It has good conductivity of 70% IACS or more, Vickers hardness of Hv110 or more, and heat resistance of 400 ° C or more.

 Further, the effect of Zn also provides good resistance to peeling of solder.

On the other hand, Comparative Example No. 5 has excellent conductivity but poor hardness, and has low heat resistance of 380 ° C. No. 6 has good hardness, heat resistant conductivity, and solder peeling resistance, but Fe
Is contained in an amount of more than 3.0 wt%, it takes time for Fe to burn through during melting, resulting in an increase in cost. No. 8 has a Si content of 0.
It exceeds 2wt%, and No. 9 has a Zn content of 0.05wt.
%, The peeling of the solder occurs. No.10 is Z
Since the n content exceeds 1.0 wt%, the conductivity is reduced.

[Advantages of the Invention] As described above, since the bare-bonding lead frame material according to the present invention has the above-mentioned constitution, it has excellent conductivity, strength, and heat resistance, and is inexpensive. Even if die bonding is carried out by the Au-Si eutectic bonding method without plating, the element is not adversely affected.

Claims (1)

[Claims] 1. Fe: 0.5 to 3.0 wt%, Si: 0.005 to 0.25 wt%, Zn:
0.05b-1.0wt%, and IIIb as an impurity
A lead frame material for Au-Si eutectic bonding, characterized in that the elements belonging to Group V and Group Vb are regulated to 0.002% or less and the balance substantially consists of Cu.