JPH06287715A - High strength lead frame material and its production - Google Patents

Abstract

PURPOSE:To obtain a material minimal in anisotropy, having superior laminar shape, and excellent in solderability and plating suitability by subjecting an alloy having respectively specified Co, Ni, Mn, Si, and Fe contents to cold rolling and annealing under respectively prescribed conditions and regulating inversely transformed austenite phase to >=30%. CONSTITUTION:An alloy having a composition consisting of, by weight, 0.5-22% Co, 15-27% Ni, <=1% Mn, <=0.5% Si, and the balance Fe is refined. Cold rolling is applied at <=80% to the alloy in the course of or after cooling after solid solution heat treatment at a temp. not lower than the austenitizing finishing temp., by which >=50% martensite phase is formed. Then, annealing is done at a temp. not higher than the austenitizing finishing temp. to regulate inversely transformed austenite phase to >=30%. By this method, the material whose principal structure is composed of at least two structures of martensite phase and austenite phase and which has minimal material anisotropy and superior shape can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame material for semiconductor devices, which has higher strength than conventional ones.

[0002]

2. Description of the Related Art In recent years, with the increase in capacity and integration of semiconductor devices such as logic and the reduction in thickness of packages, the package tends to have a large number of pins and a thin plate. For this reason, there is a demand for lead frame materials with higher strength than ever before. As these Fe-based lead frame materials for multiple pins,
Conventionally, Fe-42Ni and Fe-29Ni-17Co (Kovar) are known. JP-A-55-131155 and JP-A-3-39446 have been proposed for these Fe-Ni-based improvers, and JP-A-55-12856 for the Fe-Ni-Co-based improvers.
5, JP 57-82455, JP 61-6251, JP-B 1-81
7, JP-B-1-5562, JP-A-3-39447 and JP-A-3-166340 previously proposed by the applicant of the present invention.

[0003]

The multi-pin lead frame is mainly manufactured by a photo-etching method which enables fine processing. However, these finely processed Fe-42Ni or F
The e-29Ni-17Co thin plate multi-pin lead frame is susceptible to lead variations such as warpage and bending during package assembly, transportation, mounting, etc. due to insufficient lead strength.
Further, there are various problems such as buckling due to impact during use.

In order to improve the Fe-Ni-based or Fe-Ni-Co-based alloy, it is attempted to strengthen it by adding Si, Mn, and Cr ((a) JP-A-55-131155) or other strengthening elements. Proposal of high strength ((b) JP-A-3-39446,
(c) JP-A-3-39447), related to thermal expansion of Fe-Ni-Co alloys ((A) JP-A-55-128565, (B) JP-A-57-82455, (C)) JP-A-61-6251, (D) Japanese Patent Publication 1-817
No. 1, (e) Japanese Patent Publication No. 1-5562, (f) Japanese Patent Laid-Open No. 1-61042), and the two-phase structure strengthening proposed by the applicant ((A) Japanese Patent Laid-Open No. 3-166340). However, since (a) ~ (c) contains a strengthening element in addition to the main element, there is a problem that surface oxidation is likely to occur and the solderability and plating properties which are the main characteristics of the lead frame are significantly deteriorated. None of (a) to (f) except (a) intends to positively improve the strength of the lead frame. In addition, the above (a) is
Reinforcement mechanism is high C (about 0.2 to 0.35%) or even Hf, N
One or more kinds of b, V, Zr, Ta, W, and Al are added, and they are different. Further, (A) is mainly focused on increasing the strength by work-induced martensite and reverse transformation austenite precipitation, and therefore requires cold working sufficient to obtain high-strength characteristics, and accordingly, This will be improved in this respect, because it gives harmful material anisotropy (difference between various characteristics in the rolling direction and the sheet width direction) and shape (material width warp, undulation, etc. due to strong rolling) to the multi-pin and thin lead frame. It turns out that there are parts that should be done.

[0005]

Therefore, the present inventors
Focusing on the phase transformation mechanism of the e-Ni-Co alloy, various experiments were conducted on the composition and manufacturing conditions. As a result, the reverse transformation austenite phase was precipitated by the martensitic transformation and final annealing during annealing and cold working. By forming at least two phases, various characteristics of the lead frame, especially solderability,
It has been found that there are areas where the problems of anisotropy and plate shape can be solved by maintaining the characteristics of the previous proposal that strength can be increased without impairing the plating property, and by further reducing the cold working rate. , Which was previously proposed in Japanese Patent Application No. 4-65859.

That is, the proposal (Japanese Patent Application No. 4-65859)
In the above-mentioned JP-A-3-166340, Fe-
While the precipitation-strengthening is carried out by the work-induced martensitic transformation by cold working of Ni-Co alloy and the subsequent reverse transformation austenite phase, the cooling process after solid solution treatment is achieved by reducing Ni compositionally. , Or further thereafter, cold working with a relatively low working degree is performed to obtain a martensite phase, which is further annealed to precipitate a reverse transformation austenite phase and strengthen, and not only high strength,
It is intended to obtain a lead frame material suitable for multi-pinning in terms of shape and anisotropy. Further, the proposed material is cheaper than the one disclosed in JP-A-3-166340.

However, it was found that the reverse transformation from the martensite phase to the austenite phase in the proposed material is temperature-sensitive, so that the strength greatly depends on the annealing temperature and there are many problems in stable production. Therefore, the present inventors alleviate this annealing temperature dependency by utilizing solid solution hardening other than the reverse transformation from the martensite phase to the austenite phase, thereby improving the solderability, plating property, and thermal expansion characteristics without impairing it. It was found that it can be strengthened.

The material of the present invention is characterized by its structure control and solid solution strengthening or precipitation strengthening by a specific element. The material of the present invention is also deoxidized in the process of evaluating solderability and plating property. Mn, S added as an agent and remaining
Regarding i, and impurities of carbon, sulfur, oxygen, and nitrogen, if soldering is regulated to a specific value or less, solderability and plating properties are further improved, and practical properties required other than strength and thermal expansion properties are improved. all right. Furthermore, the present inventors have studied the influence of the additional element on the crevice corrosion resistance, and have found that the addition of the specific element can improve this characteristic. That is, the material of the present invention is a completely novel material in the combination of the alloy composition and its structure control, and is a solid solution or a precipitate with respect to the newly proposed invention which is a lead frame material excellent in strength and thermal expansion characteristics. Utilizing strengthening, the material whose temperature dependence of strength is relaxed, and / or the above-mentioned impurities are regulated to a specific value or less, or a material to which a specific element is added to further improve solderability and plating property, or It is a material with improved crevice corrosion resistance.

Specifically, in the first invention of the present application, Co 0.5 to 22%, Ni 15 to 27%, Mn 1.0% or less, Si
0.5% or less, the content of Ni and Co is less than 12% Co Ni
20% -less than 27%, Co12% or more 52% ≤ (2Ni + C
o) High strength lead satisfying the relation of <66%, consisting of balance Fe and unavoidable impurities, and having a main structure of at least two-phase structure of martensite phase and austenite phase and said austenite phase being 30% or more. In the frame material, among the unavoidable impurities, C is 0.020% or less, S is 0.015% or less, O is 150 ppm or less, N is 100 ppm, preferably C is 0.010% or less, S is 0.008% or less, and O is 80 ppm.
Hereinafter, a high-strength lead frame material, characterized in that N is 50 ppm or less,

The second invention of the present application is, in% by weight, Co 0.5 to
22%, Ni 15 to less than 27%, Mn 1.0% or less, Si 0.5% or less, and one or more of Nb, Ti, Zr, Mo, V, W and Be in total of 0.1 to 3%, When the content of Ni and Co is less than 12% of Co, the content of Ni is 20% to less than 27%, and when the content of Co is 12% or more, the relationship of 52% ≦ (2Ni + Co) <66% is satisfied, and the balance is Fe and inevitable impurities. A high-strength leadframe material, characterized in that the main structure is at least a two-phase structure of a martensite phase and an austenite phase, and the austenite phase is 30% or more, and the third invention of the present application satisfies the above impurity regulations. While having the same structure as the high-strength leadframe material having the strengthening element,

In a fourth invention of the present application, the alloy having the composition described in the first, second or third invention has a C content equivalent to 0.5 to 3% of Ni.
A high-strength lead frame material having a structure similar to that described above, which is substituted with u, and a fifth aspect of the present invention is the cooling process after the solution treatment at the austenitization end temperature or higher, or thereafter. 50% or more of martensite phase by cold rolling below 50%, and then annealed at a temperature not exceeding the austenitizing end temperature to make the reverse transformation austenite phase 30% or more, high strength lead It is a method of manufacturing a frame material.

[0012]

Next, the reasons for limiting the numerical values of the present invention will be described. The Co content is optimal for minimizing the coefficient of thermal expansion at about 17% and about 5%, and the coefficient of thermal expansion becomes large when the content is less than 0.5% or exceeds 22%. Deteriorates thermal expansion consistency. Therefore, the Co content is 0.5%
Limited to ~ 22%. The Ni content is determined in relation to the Co content. Co less than 12% and Ni less than 20% C
If the content of (2Ni + Co) is less than 52% in the range of 12% or more, the austenite becomes too unstable, and the reverse transformation austenite precipitated during the final annealing causes the martensite transformation in the cooling process to increase the thermal expansion coefficient. Also, less than 12% Co and 27% or more Ni, or more than 12% Co (2N
When i + Co) is 66% or more, the martensite transformation during the cooling process after solution treatment or during cold working becomes insufficient. Therefore, if Co is less than 12%, Ni is 20% to 27%.
Less than 12% and more than 12% Co, Ni is limited so as to satisfy the relationship of 52% ≦ (2Ni + Co) <66%.

Mn is used as a deoxidizing agent, but if it exceeds 1.0%, the coefficient of thermal expansion increases, and the solderability and plating property deteriorate, so it was limited to 1.0% or less. Si is added as a deoxidizer and it is desirable not to remain in the material, but 0.5%
Up to the above, there is no extreme increase in the coefficient of thermal expansion and no extreme deterioration in the solderability and the plating property, so it is acceptable. Next, the impurity element will be described. If C, which is an impurity, exceeds 0.020%, the etching property of the material is remarkably deteriorated, and the excessive precipitation of carbide deteriorates the solderability and plating property.
Limited to 0% or less. The desirable range of C is 0.010% or less. When S exceeds 0.015%, an excessive amount of MnS is formed, surface defects are likely to occur, and solid solution S reduces hot workability, so the content is limited to 0.015% or less. The desirable range of S is 0.008% or less.

When O exceeds 150 ppm, O forms an excess oxide with an element having a strong affinity with O, such as Si as a deoxidizer and Al, Mg which are inevitably mixed, which deteriorates the surface cleanliness. 150ppm or less to reduce solderability and plating property. The desirable range of O is 80 ppm or less. Since N has an austenite stabilizing effect, if it is contained in an amount exceeding 100 ppm, the austenite phase is excessively stabilized and the work-induced transformation is hard to occur. Further, the nitride is excessively deposited to deteriorate the solderability and the plating property, so the content is set to 100 ppm or less. The preferred amount of N is 50 ppm or less.

Nb, Ti, Zr, Mo, V, W and Be are important as elements for strengthening the matrix by solid solution strengthening or precipitation strengthening of the alloy of the present invention. The alloy of the present invention is strengthened by precipitation of the reverse transformation austenite phase at the time of final annealing, but it is desirable that the amount of austenite is large from the viewpoint of thermal expansion characteristics,
The final annealing temperature should be as high as possible. However, when these additive elements are not added, the mechanical properties sharply decrease as the annealing temperature rises. For this reason,
For stable production, it is desirable to stabilize the mechanical properties on the high temperature annealing side.

The present invention is based on the finding that the addition of these solid solution strengthening elements or precipitation strengthening elements can improve the hardness of the final annealing, especially on the high temperature side, that is, the deterioration of mechanical properties. The amount of addition of these elements
If it is less than 0.1%, there is no effect in improving the deterioration of mechanical properties, and 3%
If it exceeds, the surface oxidation is promoted and the solderability and plating property are significantly impaired. Further, since these elements act on the austenite generation side, if the addition amount increases, the austenite of the substrate becomes too stable, so the addition amount is limited to 0.1 to 3%.

Although Cu is not essential in the present invention, it is an element that improves the crevice corrosion resistance between the package resin and the lead frame, so it may be added if necessary. When Cu is added in an amount of less than 0.5%, it is not effective in improving crevice corrosion resistance. When it exceeds 3%, a brittle intermetallic compound of Cu and Sn is formed at the interface with the solder, and solder peeling easily occurs. Become. Further, since Cu is an austenite stabilizing element, if added in excess of 3%, the austenite phase becomes too stable and martensitic transformation is less likely to occur, so Cu is limited to 0.5% to 3%.

Further, the final main structure is a structure consisting of at least two phases consisting essentially of a martensite phase and an austenite phase (a part of retained austenite may be included), but if the austenite phase is 30% or less, it is sufficient. However, the austenite phase is
Limit to 30% or more. The amount (%) of the austenite phase in the present invention is a value obtained from the X-ray diffraction intensity described in Examples below.

Next, in the method for producing the material of the present invention, if the solution treatment temperature is lower than the austenitization end temperature, a cooling process to the room temperature or further after that, in order to promote the work-induced martensite transformation, it is inserted if necessary. Since the martensitic transformation does not occur in cold rolling, the solution treatment temperature is set to the austenitization completion temperature or higher. The austenitization finish temperature changes depending on the component system,
For the components of the present invention, 800 ° C or higher is a desirable range. Further, if the working rate of cold working after solution treatment exceeds 80%, the material anisotropy in the rolling direction and the sheet width direction becomes strong, and it is not preferable in terms of shape warpage, waviness, etc. The cold working rate is limited to 80% or less. Desirably, cold working is 6
By controlling the content to be 0% or less, and more preferably 50% or less, a better material shape can be obtained. Further, this cold working also has an effect of transforming the austenite phase remaining during the solution treatment into work-induced martensite.

Thus, the martensite phase obtained in the cooling process after the solution treatment or in the subsequent cold working is
Since it is not possible to obtain sufficient reverse transformation austenite precipitation strengthening in the subsequent step annealing is 50% or less, the amount of martensite before annealing is limited to 50% or more, 70% to obtain a more stable precipitation strengthening It is desirable to set it as above. Furthermore, when the annealing temperature after the solution treatment or cold working exceeds the austenite finish temperature, all the martensite phases are transformed into the austenite phase, and the structure cannot be composed of at least two phases. Since precipitation strengthening of is not obtained, the temperature is limited to the austenitization end temperature or lower.

[0021]

EXAMPLES The material of the present invention will be described with reference to examples. Alloys having the compositions shown in Table 1 were melted and cast in a vacuum melting furnace,
Forged at 50 ℃ and hot rolled to a thickness of 3mm, then 1000 ℃ × 1
After Hr solution treatment, cold rolling was performed to 0.25 mm. Of the sample Nos. In the table, A to N are the materials of the present invention. O to R each contain impurities C, S, O, and N in excess, S contains excess strengthening elements, U has Ni lower than the regulation of the present invention, and V has Ni is a comparative material that is higher than specified in the present invention. Z is a conventional Kovar alloy, and Ni and Co are higher than those specified in the present invention. Table 2
In addition, various characteristics of the material obtained by subjecting each of the above materials (0.25 mm thickness) to a solution treatment at 800 ° C., cold rolling to 0.125 mm (50%), and subsequently a series of treatments at 580 ° C. final annealing ( The measurement conditions are shown in the table).

The structural ratio I is the amount of martensite after the solution treatment cooling at 800 ° C., the amount II is the amount of martensite after 50% cold rolling, and the amount III is 580 to 600. The amount of austenite after annealing at ° C is shown in%, and the measurement is the value obtained by the following. Martensite phase (%) = {Iα / (Iα + Iγ)} × 100 Austenite phase (%) = 100-Martensite phase (%) Iα = Iα ₍₁₁₀₎ + Iα ₍₂₀₀₎ + Iα ₍₂₁₁₎ Iα ₍₁₁₀₎ X-ray diffraction intensity of martensite Iγ = Iγ ₍₁₁₁₎ + Iγ ₍₂₀₀₎ + Iγ ₍₂₂₀₎ + Iγ ₍₃₁₁₎ Iγ ₍₁₁₁₎ is the austenite X-ray diffraction intensity

[0023]

[Table 1]

[0024]

[Table 2]

From this table, the invention materials A to N and the comparative materials
O-S is a martensite amount after cold rolling is 50% or more, and the microstructure ratio III after final annealing is a mixed phase with martensite containing austenite of 30% or more, whereby U, V, As can be seen from the values of hardness and tensile strength with respect to Z, it can be seen that high mechanical properties are exhibited. Further, the inventive materials A to N are excellent in comparison with the comparative materials U and V. That is, U whose austenite became too unstable due to its composition had a martensite content of 100% after the solution treatment (I) and after cold rolling (II), but the reverse transformation austenite was precipitated in the final annealing. Since it does not have the desired strength, the coefficient of thermal expansion is also high, and V in which the austenite has become too stable from the composition does not cause martensitic transformation after solution treatment at a thickness of 0.25 mm (composition ratio). I is 0
%), And the work-induced martensitic transformation after cold working is 16
%, The reverse transformation austenite precipitation amount in the final annealing is as small as 98-84 = 14%, which shows that the strength is also small.

The alloys A to N of the present invention are C, which is an impurity,
It has less S, O, N and has superior solderability and plating properties compared to the comparative materials O to R. Since S contains an excessive amount of reinforcing elements, it has poor plating properties and soldering properties. Further, it can be seen that C, M and N with Cu added are superior in crevice corrosion resistance as compared with the other examples. Further, the materials D to N of the present invention added with one or more of Nb, Ti, Zr, Mo, V, W and Be have higher mechanical properties than those of A to C without addition thereof. ing.

1 and 2 show the material J of the present invention.
The relationship of hardness and coefficient of thermal expansion with respect to the final annealing temperature of B and B is shown. Among the materials of the present invention, the material J to which the strengthening element is added has a coefficient of thermal expansion substantially equal to that of the material of the present invention to which these elements are not added, and particularly at a temperature of 580 ° C. or higher,
Even after the final annealing, the high mechanical properties are still maintained, and therefore, it is possible to have both the properties of low thermal expansion and high strength. It is also advantageous from the standpoint of stable production in mass production. On the other hand, the material S in which these strengthening elements exceed 3%,
As described above, the plating properties and soldering properties are significantly reduced.

[0028]

As described above, the material of the present invention is the martensite transformation by solution treatment and cold working in the Fe-Ni-Co system specific composition of JP-A-4-65859 by the present inventors. In a high-strength lead frame material that is converted to reverse transformed austenite by subsequent annealing.
By adding one or more of b, Ti, Zr, Mo, V, W and Be, more stable low thermal expansion and high strength characteristics can be obtained. Further, by reducing the impurity elements of C, S, O and N, more excellent plating properties and soldering properties are obtained. Further, although the material of the present invention has a stable and low thermal expansion over a wide temperature range, high strength can be obtained, so that the package can be stably assembled without warping or bending of the leads. Further, the material of the present invention to which Cu is added can achieve a higher strength ratio and improve crevice corrosion resistance. According to the method of the present invention, due to the combined effect of the material composition, the heat treatment before and after the cold rolling is substantially at least 2 even though the cold rolling ratio is relatively low.
Since the structure can be composed of phases, it is possible to obtain a high-strength lead frame material having small anisotropy of material and excellent in shape.

[Brief description of drawings]

FIG. 1 is a diagram showing a final annealing temperature and mechanical hardness.

FIG. 2 is a diagram showing a relationship between a final annealing temperature and a thermal expansion coefficient α _RT-300 .

Claims (6)

[Claims] 1. Co 0.5 to 22% and Ni 15 to 27 in% by weight.
%, Mn 1.0% or less, Si 0.5% or less, and if the content of Ni and Co is less than Co 12%, Ni 20% to less than 27%, Co 12
% Or more, the relation of 52% ≦ (2Ni + Co) <66% is satisfied, the balance consists of Fe and unavoidable impurities, and the main structure is at least two-phase structure of martensite phase and austenite phase, and the austenite phase is In the high-strength lead frame alloy of 30% or more, C is 0.020% or less and S is 0.015% or less of the inevitable impurities.
Is 150ppm or less and N is 100ppm. A high strength leadframe material. 2. Co 0.5 to 22% and Ni 15 to 27% by weight.
%, Mn 1.0% or less, Si 0.5% or less, Nb, Ti,
Any one or more of Zr, Mo, V, W, and Be is 0.1 to 3% in total, and if the content of Ni and Co is less than Co 12%, Ni is 20% to less than 27% and Co is 12% or more. 52% ≤ (2
Ni + Co) <66%, the balance consists of Fe and inevitable impurities, and the main structure is at least two-phase structure of martensite phase and austenite phase,
A high-strength leadframe material, characterized in that the austenite phase is 30% or more. 3. Co 0.5 to 22% and Ni 15 to 27% by weight.
%, Mn 1.0% or less, Si 0.5% or less, Nb, Ti,
Any one or more of Zr, Mo, V, W, and Be is 0.1 to 3% in total, and if the content of Ni and Co is less than Co 12%, Ni is 20% to less than 27% and Co is 12% or more. 52% ≤ (2
Ni + Co) <66%, the balance consists of Fe and inevitable impurities, and C is 0.
020% or less, S 0.015% or less O 150ppm or less, N 100ppm
And a main structure is at least a two-phase structure of a martensite phase and an austenite phase, and the austenite phase is 30% or more. 4. An alloy having the composition of claim 1, 2 or 3, wherein 0.5 to 3% of Ni is replaced by an equal amount of Cu, and the main structure is at least 2 of a martensite phase and an austenite phase. A high-strength leadframe material having a phase structure, wherein the austenite phase is 30% or more. 5. The average coefficient of thermal expansion from room temperature to 300 ° C.
(3 to 9) × 10 -6 power / ° C, hardness is 260 or more at HV, and tensile strength is 80 kgf / mm ² (784.5 MPa) or more.
The high-strength leadframe material according to 3 or 4. 6. An alloy having the composition according to claim 1, 2, 3 or 4 is subjected to cold rolling at 80% or less in the cooling process after the solution treatment at a temperature above the austenitizing end temperature or further thereafter. According to the above, a martensite phase of 50% or more is obtained, and thereafter, it is annealed at a temperature not exceeding the austenitization end temperature to make the reverse transformation austenite phase (which may be accompanied by retained austenite) 30% or more. High strength lead frame material manufacturing method.