JPH0684533B2 - Lead frame and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a lead frame and a manufacturing method thereof,
More specifically, the present invention relates to a consumer product such as a semiconductor device lead frame and a method for manufacturing the same.

[Technical Background of the Invention and Problems Thereof] Consumer products such as semiconductor devices are required to have high output and multiple functions, and along with that, they may be manufactured with high productivity and at low cost. is necessary.

Although various manufacturing methods have been developed to meet this demand, the resin molding method is a very useful method among them.

However, this method has the following problems, and its solution is demanded.

That is, the above method includes a mounting step and a bonding step between the semiconductor element and the lead wire as indispensable steps, but the problem is related to the lead frame which is an important component.

Generally, lead frames have low surface oxidation, high tensile strength, sufficient ductility and excellent bending workability, high temperature characteristics, such as excellent mechanical strength at temperatures of 250 ° C or higher, wetting with solder. Manufacture; price and products, satisfying the conditions such as sufficient heat resistance and weatherability, good etching property, and excellent workability such as press punching property and press bendability. It is extremely advantageous in terms of characteristics.

Since it satisfies these various characteristics relatively well, 42Ni-Fe has been used as a conventional lead frame material.
Alloys were widely used.

However, in recent years, the lead frame has been increased in number of pins as seen in a flat package. For this reason,
The lead frame requires precise and fine etching. In addition, lead frames that have been subjected to bending with high curvature have also appeared in some products. However, the above-mentioned conventional 42Ni-Fe alloy cannot meet the above requirements due to the increase in the number of pins.

For this reason, copper alloys, which are soft and have good etching properties, are beginning to be used frequently as lead frame materials.However, this material does not match the thermal expansion coefficient of silicon chips and is too soft. It has the drawback of being easy to do.

Thus, the material of the lead frame, especially the material for the lead frame of the flat package, has excellent etching property, is appropriately soft and has excellent workability at the time of press working, and causes work hardening to cause deformation after working. The fact that there are few and that it has low thermal expansion has emerged as major problems in terms of properties to be solved.

[Object of the Invention] An object of the present invention is to provide a lead frame made of a Ni-Fe alloy in which the above-mentioned characteristic items (1) to (3) required for a lead frame are improved, and a manufacturing method thereof.

[Summary of the Invention] In the process of earnestly researching to achieve the above-mentioned object, the present inventors made a study on the improvement of the above-mentioned characteristics, particularly the etching property. First, it is judged that the etching property is poor because the portion formed at the time of etching has irregular small and large irregularities in the inner wall, and becomes an irregular inner wall. Therefore, fine etching finish required by the design standard cannot be applied to a material having poor etching property.

This means that the type and homogeneity of the metallographic structure of the material,
It is considered that the problems are caused by the size of the crystal grain size, the aggregation of the crystal orientations, and the like. Therefore, the present inventors have made various studies on the influence of each of the above factors on the characteristics required for the lead frame. At the same time, the search for a suitable condition for the item (1) and the item (2) was clearly considered as an object of investigation, and the lead frame and the manufacturing method thereof according to the present invention were developed.

That is, the lead frame of the present invention has Ni of 25 to 45% by weight, Cr of 0.3 to 10% by weight, and the balance of F.
Consisting of an alloy consisting of e and inevitable impurities, JIS-G0551
It is characterized in that the crystal grain size defined by is 6-12.
The present invention also provides a lead frame in which a part of Cr of the lead frame is replaced by Mn, and further, 7 wt% of Co.
Up to the amount of lead frame contained. In addition, a method of manufacturing such a lead frame is based on a method of producing 25-45 wt% Ni.
A step of melting 0.3 to 10% by weight of Cr and Fe into an alloy ingot (first step); the alloy ingot is subjected to multiple rolling-annealing treatments, and finally cold rolled at a rolling rate of 40% or more. Process (second process); cold-rolled product annealed at a temperature of 500 to 1200 ° C (third process); and annealed product adjusted rolling at a rolling rate of 30% or less. The step of applying (fourth step);

In the lead frame of the present invention, the grain size of the alloy is 6
If less than, the grain size is too coarse, the etching removal during etching does not proceed sufficiently, eventually resulting in a portion that does not open, and if the crystal grain size exceeds 12, the grain size is A lot of irregular chips are formed on the inner wall of the hole that is too fine and opened during etching.
It is easy to form irregular inner walls. Practically, it is preferably 8 to 12, and particularly preferably 9 to 11.

This crystal grain size is largely defined by the temperature conditions of the above-mentioned second step and third step, especially the third step.

Regarding the etching property, when the metal structure of the lead frame is in a state where each structure such as ferrite, martensite, and austenite is mixed, the etching rate of each structure is different, so that the etching proceeds smoothly. That is, there is a possibility that a phenomenon such as clogging may occur. Therefore, it is generally preferable that the tissue is a single tissue,
However, when it is difficult to do so, there is practically no inconvenience as long as the structure has austenite content of 80% or more.

Further, in the lead frame of the present invention, it is desirable that the crystal orientations of the alloy are aggregated in (100). that is,
This is because, when the material is etched, the inner wall surface of the formed hole becomes very smooth and smooth as in the conventional case, and is suitable for fine etching. Generally, the degree of aggregation to (100) is preferably 40% or more. The aggregation in this crystal orientation can be adjusted by the rolling rate in the above-mentioned second step.

In the alloy of the present invention, Ni is set in the range of 25 to 45% by weight. When the amount of Ni is out of the above range, the thermal expansion coefficient of the alloy becomes large and the thermal expansion is low, specifically, the thermal expansion coefficient is 100 × 1.
The object of the present invention of 0 ^-7 / ° C or less cannot be achieved. In addition, the amount of Ni increases. Specifically, if it exceeds 50% by weight,
The 0.2 yield strength of the material increases and its workability decreases significantly. Furthermore, when the amount of Ni increases, irregular inner walls frequently occur during etching, making fine etching difficult,
Alternatively, the amount of Ni dissolved from the material in the etching solution increases, and the etching solution is modified, resulting in a phenomenon that the etching rate decreases. It is preferably 35 to 45% by weight.

Cr is a component that contributes to improving the workability of the material.It is important when the material is etched to form a lead frame with multiple legs, and then heat treatment during bonding or heat treatment for curing the epoxy resin for sealing. Exerts various effects. Its content is set in the range of 0.3 to 10% by weight.

That is, generally, when Cr is added to the Fe-Ni alloy and only strong rolling treatment is not performed and annealing is performed, the alloy is stored at room temperature.
Although 0.2% proof stress is increased and its strength is improved,
However, it remains a material in which it is difficult to maintain the lead processing curvature of the lead frame during processing, that is, a material whose workability is not improved. However, as described below,
When this material is annealed as described below, Cr-free
The 0.2% proof stress of Fe-Ni alloy is significantly reduced and the workability is improved.

For example, 0.2% relative to the annealing temperature of a Ni-Fe alloy (A) containing 6 wt% of Cr and a 42Ni-Fe alloy containing no Cr (B).
The change in yield strength is shown in the figure. As is clear from the figure, alloy A
The 0.2% proof stress of (the material of the lead frame of the present invention) is large at room temperature, but decreases at the annealing temperature of 300 ° C. in reverse to that of alloy B (conventional material). That is, the workability is improved by annealing.

However, if the Cr addition amount is less than 0.3% by weight, the above effect is not exhibited, and conversely if the Cr addition amount is more than 10% by weight, the coefficient of thermal expansion becomes 100 × 10 ^-7 / ° C or more and the above characteristics are satisfied. It will not be done. Because of this, and also etchability,
Considering low chromium content and low thermal expansion in the waste liquid,
The Cr amount is preferably 1 to 4% by weight.

Mn is a component that exhibits the same action and effect as Cr. Therefore, in the material of the present invention, a part of the above Cr is
It may be replaced with Mn, and the total content of Cr and Mn should be 0.3 to 10% by weight. Rice cake, Mn alone is effective. Usually, the substitution amount is 0.3-
It is 7% by weight, and if Mn exceeds 7% by weight, the coefficient of thermal expansion becomes large.

Furthermore, when Co is added, the effects such as the improvement of the etching property and the reduction of the thermal expansion coefficient appear, which is useful. At that time, the addition amount of Co is at most 7% by weight,
It is preferably 1.0 to 6.0% by weight. If this Co content becomes too large, the 0.2% proof stress increases and the workability deteriorates.

The lead frame of the present invention can be manufactured by a manufacturing method including the following steps.

The first step is a step of melting a predetermined amount of each of the above-mentioned components and preparing an alloy ingot having a predetermined composition from the melt. This may be carried out by applying a conventional vacuum melting method, or may be an electroslag melting method.

The second step is a step of rolling the obtained alloy ingot. What is important in this step is that the final rolling is cold rolling, and the rolling rate during cold rolling is 40% or more. In this step, the degree of aggregation of crystal orientations on the (100) plane is basically adjusted. When the rolling ratio is less than 40%, it is difficult to orient the crystal orientation in the ingot to the (100) plane because the processing energy input is small, and further, the annealing treatment of the next stage (3rd In the process), the recrystallized grains growing do not have a desired size, and the crystal grain size becomes small. However, when working at an extremely high rolling rate, a phenomenon such as a crack occurs in the working process due to the accumulation of added working strain. It is preferably 80% or more.

The third step is a step of subjecting the cold-rolled material obtained in the second step to an annealing treatment so that the grain size becomes a predetermined grain size and at the same time, a 0.2% proof stress reduction is achieved.

The annealing temperature is 500 to 1200 ° C. If the temperature is lower than 500 ° C, the above-mentioned annealing effect is not sufficiently exhibited, and if the temperature exceeds 1200 ° C, the crystal grain size becomes large and the etching property deteriorates. It is preferably 750 to 1100 ° C.

In the fourth step, since the annealed material obtained in the third step is usually thermally deformed, it is a rolling step of correcting this thermal deformation and adjusting it into a flat plate. The rolling rate at this time is controlled to 30% or less.

This is because when the rolling rate is higher than 30%, the already formed aggregate state of the crystal orientation on the (100) plane is destroyed. It is preferably 20% or less.

In addition, in this process, processing strain during rolling is accumulated in the plate material, and this strain may cause problems such as dimensional deformation in various steps of the lead frame manufacturing in the subsequent stage. Temperature below ℃, preferably 200-500 ℃
It is effective to apply the annealing treatment at.

EXAMPLES OF THE INVENTION Example 1 41% by weight of Ni, 4% by weight of Cr, C as an incidental component
0.005 wt%, Si 0.01 wt%, P and S 0.001 each
An alloy ingot was prepared by a vacuum melting method, the alloy ingot being composed of wt% and the balance being Fe.

This ingot was repeatedly hot-rolled, then pickled and the primary and secondary
Next cold rolled. The rolling ratio during this cold rolling was 80%.

Then, the rolled material was placed in an annealing furnace, annealed at 1 × 10 ⁻⁴ Torr and 800 ° C., and then adjusted and rolled at a rolling rate of 100%. Finally 500
It was annealed at ℃ to correct the thermal deformation.

This plate material has a grain size of 7 according to the method specified in JIS-G0551, a degree of aggregation of crystal orientation to the (100) plane of 60%, an austenite structure existence ratio of 95%, and a thermal expansion coefficient of 6 × 10 ^-7 / ° C.
(20-100 ° C).

Photoresist is applied to both surfaces of the obtained plate material, dried, and then a film with a standard frame pattern is brought into close contact with it, and the photoresist is exposed and developed to dissolve and remove the photoresist in the unexposed area. did. After burning and curing the remaining photoresist,
A lead frame was manufactured by etching with a 20% ferric chloride solution and then removing the remaining resist with hot alkali. The width of each lead was 1 mm, and the distance between each lead was 0.5 mm. When the side surface of each lead was observed under a microscope, there was no irregular inner wall.

This lead frame was plated with 1000Å of copper, and then the entire surface was plated with 2 μm of silver. Then, using a silver paste, die-bond the silicon chip, and
After bonding the gold wire at a temperature of 150-300 ℃,
The whole was sealed with an epoxy resin and cured at 150 ° C. Finally, when each lead was bent with a predetermined pressing machine, all the leads were processed according to the design standard, and further, no deformation was observed after the processing, and the press workability was good.

Example 2 The alloy ingot has a composition of 36 wt% Ni, 3 wt% Cr, 0.05 wt% C, 0.02 wt% Si, and P and S are all
A plate material was prepared in the same manner as in Example 1 except that 0.001% by weight and the balance were Fe.

The grain size of this plate was 10, the degree of crystal orientation on the (100) plane was 45%, the austenite structure was 85%, and the thermal expansion coefficient was 32 × 10 ^-7 / ℃ (20 to 100 ℃).

Using this plate material, a lead frame was manufactured in the same procedure as in Example 1. No springback was observed on each lead.

Example 3 The composition of the alloy ingot is 36 wt% Ni, 8 wt% Cr, 0.05 wt% C, 0.02 wt% Si, and P and S are all
The balance was 0.001% by weight, and the balance was Fe. Melt as in Example 1, final rolling 90%, annealing 1000 ° C., preparatory rolling 5
%, And strain relief annealing was performed at 350 ° C.

The crystal grain size of this plate material was 9, the degree of aggregation of crystal orientation on the (100) plane was 80%, the austenite structure existence ratio was 90%, and the thermal expansion coefficient was 70 × 10 ⁻⁷ / ° C. (20 to 100 ° C.).

Using this plate material, a lead frame was manufactured in the same procedure as in Example 1. No springback was observed on each lead.

Example 4 The composition of the alloy ingot was Ni 30% by weight, Cr 2% by weight,
A plate material of the present invention was prepared in the same manner as in Example 1 except that Co was 5% by weight, C was 0.05% by weight, Si was 0.02% by weight, P and S were all 0.001% by weight, and the balance was Fe. .

The grain size of this plate was 9, the degree of crystal orientation on the (100) plane was 60, the austenite structure was 90%, and the thermal expansion coefficient was 25 × 10 ^-7 / ° C (20 to 100 ° C).

Using this plate material, a lead frame was manufactured in the same procedure as in Example 1. No springback was observed on each lead.

The plate material containing Co is a material having a low thermal expansion coefficient as indicated by the value of the thermal expansion coefficient. However, its 0.2% proof stress is generally higher by about 2 to 5 kg / mm ² than that in the case where Co is not added, and its workability deteriorates. Therefore, in the present invention, by adding Co and Cr at the same time, the 0.2% proof stress can be lowered without impairing the low thermal expansion property.

Example 5 The composition of the alloy ingot was as follows: Ni 36% by weight, Cr 1% by weight,
A plate material was prepared in the same manner as in Example 1 except that Mn was 1 wt%, C was 0.05 wt%, Si was 0.02 wt%, P and S were all 0.001 wt%, and the balance was Fe.

The grain size of this plate was 10, the degree of crystal orientation on the (100) plane was 65%, the austenite structure was 90%, and the thermal expansion coefficient was 25 × 10 ^-7 / ° C (20 to 100 ° C).

Using this plate material, a lead frame was manufactured in the same procedure as in Example 1. No springback was observed on each lead.

[Advantages of the Invention] As is clear from the above description, the lead frame of the present invention has a low thermal expansion coefficient of 120 × 10 ⁻⁷ / ° C. or less, and has a small thermal expansion difference with the silicon chip. Since it is a material, it has a good etching property and can be finely etched, has a small 0.2% proof stress, is rich in workability, and does not cause springback, so its industrial value is extremely large.

[Brief Description of Drawings] The figure shows the annealing temperature and 0.
It is a relationship diagram with 2% proof stress. A: material of the present invention, B: conventional material

Claims (7)

[Claims] Claims: 1. It is characterized by comprising 25 to 45% by weight of nickel, 0.3 to 10% by weight of chromium, and the balance being an alloy of iron and inevitable impurities, and having a grain size of 6 to 12 specified by JIS-G0551. And lead frame. 2. The lead frame according to claim 1, wherein the austenite structure is 80% or more and the crystal orientation is aggregated in (100). 3. A crystal grain size specified by JIS-G0551, which is composed of 25 to 45% by weight of nickel, 0.3 to 10% by weight of chromium partially substituted with manganese, and the balance of iron and inevitable impurities. Is a lead frame of 6 to 12. 4. An alloy comprising 25 to 45% by weight of nickel, 0.3 to 10% by weight of chromium, 7% by weight or less of cobalt, and the balance of iron and inevitable impurities, and has a grain size of 6 to 6 specified by JIS-G0551. Lead frame characterized by being 12. 5. A step of dissolving 25 to 45% by weight of nickel, 0.3 to 10% by weight of chromium and iron into an alloy ingot, and then subjecting the alloy ingot to multiple rolling-annealing treatments and then rolling. Final cold rolling treatment at a rate of 40% or more; cold rolling treatment at a temperature of 500 to 1200 ° C; and annealing treatment at a rolling reduction of 30% or less; A method for manufacturing a lead frame, comprising: 6. The method according to claim 5, wherein the rolling ratio in the final cold rolling treatment is 80% or more. 7. The method according to claim 5, wherein the adjusted rolling treatment is a treatment of performing strain relief annealing at a temperature of 800 ° C. or lower after the rolling treatment.