JPH0565602A - High strength lead frame material and its production - Google Patents

Abstract

PURPOSE:To stably produce a high strength lead frame material by forming the structure into dual phase without deteriorating the solderability and plating suitability as the principal characteristics of a lead frame and also relaxing the dependence of strength upon the final annealing temp. CONSTITUTION:This lead frame material has a composition containing, by weight, 0.5-22% Co, 22-32.5% Ni [where Ni is 27 to 32.5% when Co is <12% and also (Ni+Co) is 60 to 74% when Co is >=12%], <=0.5% Si, and <=1.0% Mn, also containing, besides the above-mentioned basic additive elements, 0.1-3.0%, in total, of one or >=2 elements among Nb, Ti, Zr, Mo, V, W, and Be, and having the balance essentially Fe except impurities (where 0.5-3% of Ni can be substituted by equivalent Cu), or containing 0.0001-0.03%, in total, of one or >=2 elements among B, Mg, and Ca and also has a structure consisting of >=50% of inversely transformed or further retained austenite and the balance martensite or ferrite.

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 devices and the reduction in thickness of packages, the lead frame tends to have more pins and thinner plates. For this reason,
There is a demand for lead frame materials with higher strength than ever before. Fe-42Ni and Fe-29Ni-17Co (Kovar) are conventionally known as Fe-based lead frame materials for these multiple pins. Proposals for these Fe-Ni-based and Fe-Ni-Co-based improved materials include JP-A-55-131155 and high-strength Fe-Ni-based alloys containing various strengthening elements.
Further, regarding an improved Fe-Ni-Co alloy, JP-A-55-12
8565, JP-A-57-82455, JP-A-61-6251, JP-B-1
-817, Japanese Patent Publication No. 1-15562, and Japanese Patent Laid-Open No. 1-61042 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 Fe
-29Ni-17Co thin plate multi-pin lead frame is liable to cause lead variations such as warping and bending during package assembly, transportation and mounting 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, an attempt to strengthen it by adding Si, Mn, and Cr (JP-A-55)
-131155), or other strengthening elements to improve strength, and related to thermal expansion of Fe-Ni-Co alloys {(a) JP-A-55-128565, (B) JP-A-57-57- No. 82455,
(C) Japanese Patent Laid-Open No. 61-6251, (D) Japanese Patent Publication No. 1-817, (E) Japanese Patent Publication
1-15562, (f) JP-A-1-61042)), but the former contains a strengthening element in addition to the main element in an excessive amount, so that surface oxidation is likely to occur, which is a main characteristic of the lead frame solder. However, none of the latter except (a) positively improves the strength of the lead frame. In addition, the above
The type (a) is different from the material of the present invention in the strengthening mechanism.

Therefore, the present inventor has conducted various experiments on the composition and manufacturing conditions focusing on the Fe-Ni-Co type alloy in which the austenite phase is unstable at room temperature. By precipitating the reverse transformation austenite phase by site transformation and subsequent annealing to make it more than the specified amount, and by making the other structure a structure consisting of martensite or ferrite phase, various characteristics of the lead frame, especially solderability, plating property The inventors have found that the strength can be increased without impairing the above-mentioned characteristics, and have made the invention that forms the basis of the present invention (Japanese Patent Application No. 1-163595, etc.). That is, the most important point of the lead frame material of the basic invention is the conventional Fe-N.
Whereas the i-Co alloy has a strengthened austenite single phase by the addition of a strengthening element, the austenite phase and martensite phase or ferrite phase can be structurally formed without adding a strengthening element that impairs solderability and plating property. It is a point that it was a composite organization. FIG. 2 shows typical microstructure photographs (a) and (b) of the material of the present invention in contrast with that of Kovar which is a conventional material (c). From this photograph, while the conventional Kovar alloy (c) has an austenite single phase structure, the alloys of the present invention (a) and (b) have
γ ″ (reverse transformation austenite) or further γR (retained austenite) and α ″
It has been found that the alloy has a composite structure composed of (martensite) or α (ferrite), and the alloy of the present invention has a high strength.

The basic invention is specifically, in terms of weight percent,
Co 0.5-22%, Ni 22-32.5%, Mn 1.0% or less, Si 0.5%
The following are contained, and the contents of Ni and Co satisfy Ni27 to 32.5% when Co is less than 12% and 66% ≦ 2Ni + Co ≦ 74% when Co is more than 12%, and the balance is substantially Fe except for impurities. Consisting of a reverse transformation austenite phase, or further consisting of a single or composite phase of an austenite phase and a martensite phase or a ferrite phase consisting of a retained austenite phase, and a total of the reverse transformation austenite phase alone or a retained austenite phase. Of 50% or more, or a high strength leadframe material of the above tissues in which 0.5 to 3% of Ni of the above composition is replaced by an equal amount of Cu, and further B, Mg , Ca
At least one of the above-mentioned high-strength leadframe materials and alloys of the above-mentioned compositions are subjected to solution treatment at a temperature above the austenitizing end temperature, and then 40 to 90% cold. A part or all of the austenite phase is transformed into a work-induced martensite by working, and further, final annealing is performed at a temperature lower than the austenitization end temperature to precipitate a reverse transformed austenite phase, and the structure according to any of the above claims is obtained. And a method for producing a high-strength lead frame material. Further, in the material of the present invention, Mn, Si and carbon, sulfur, oxygen, which are added as deoxidizing agents and remain in the process of evaluating solderability and etching property,
Regarding nitrogen impurities, if you regulate below a certain value,
It was found that the soldering property and the plating property were further improved, and the practical properties required in addition to the strength and the thermal expansion property were improved.

However, in the basic invention, it has been found that the reverse transformation from the martensite phase to the austenite phase is temperature-sensitive, so that the strength largely depends on the annealing temperature and there are many problems in stable production. Therefore, it is an object of the present invention to provide a high-strength lead frame material that alleviates the annealing temperature dependency of the strength and a method for manufacturing the same. The present invention utilizes the reverse transformation from the martensite phase to the austenite phase and utilizes the solid solution hardening or the precipitation hardening, so that the solderability, plating property, and thermal expansion characteristics are not impaired, and the strength depends on the annealing temperature. This is based on the finding that a high-strength lead frame material with relaxed properties can be obtained.

[0007]

That is, according to the present invention, in addition to the additive alloy elements of the basic invention, Nb, Ti, Zr, Mo,
Any one or more of V, W, and Be 0.1 to 0.1 in total
The main content is 3.0% and the balance is substantially Fe except for impurities.

[0008]

First, the reasons for limiting the numerical values of the present invention will be described. The Co content is optimal for minimizing the thermal expansion coefficient at about 17% and about 5%, and when it is less than 0.5% or exceeds 22%, the thermal expansion coefficient becomes large, and it becomes Deteriorates the thermal expansion consistency. Therefore, the Co content is 0.5
Limited to ~ 22%. The Ni content is determined in relation to the Co content. Is less than 12% Co and less than 27% Ni,
When the content of Co is 12% or more and (2Ni + Co) is less than 66%, the martensite transformation start temperature is high and the austenite becomes unstable, causing martensite transformation in the cooling process during the solution treatment and obtaining a sufficient amount of austenite. I can't. Also,
If Co is less than 12%, Ni exceeds 32.5%, or if Co is 12% or more ((2
When Ni + Co) exceeds 74%, the austenite phase becomes too stable at room temperature, and it becomes difficult for work-induced transformation to occur. Therefore, if Co is less than 12%, Ni 27 to 32.5%, Co 12%
As described above, Ni is limited so as to satisfy the relationship of 66% ≦ 2Ni + Co ≦ 74%. Further, it is important to adjust the Ni and Co contents so that the optimum composition has a martensite starting temperature of 0 ° C or lower.

Mn acts as a deoxidizing agent, but if it exceeds 1.0%, it increases the thermal expansion coefficient and deteriorates the solderability and plating property, so it is limited to 1.0% or less. Si is added as a deoxidizer, and it is desirable that Si does not remain in the material.
Up to 0.5% does not cause an extreme increase in the coefficient of thermal expansion or extreme deterioration in solderability and plating properties, and is therefore acceptable. B, M
g and Ca are added as necessary to improve hot workability,
If the total addition amount of one or two kinds is less than 0.0001%, its effect is small, and if it exceeds 0.03%, the ductility during cold working is decreased and the material etching property is deteriorated.
Limited to ~ 0.03%. It is more preferably 0.01% or less.

Cu is an element that improves the crevice corrosion resistance between the package resin and the lead frame. When Cu is less than 0.5%, there is no effect in improving crevice corrosion resistance, and 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. Further, since Cu is an austenite stabilizing element, if it is added in an amount exceeding 3%, the austenite phase becomes too stable, and it becomes difficult for the work-induced transformation to occur, so it is limited to 0.5 to 3%.

Next, impurities will be described. The present invention does not cause any particular problem as long as it is an ordinary impurity. But,
By restricting C, S, O, and N in the following ranges, respectively, it becomes a particularly preferable material in terms of characteristics. C is
If it exceeds 0.02%, the etching piercing property is deteriorated, and further, excessive precipitation of carbide deteriorates the solderability and plating property, so that it is preferably 0.02% or less. A more desirable range of C is 0.015% or less. When S exceeds 0.015%,
Excessive MnS is formed, surface defects are likely to occur,
Further, since solid solution S deteriorates hot workability, it is desirable to limit it to 0.015% or less. A more desirable range of S is less than 0.010%. When O exceeds 150ppm, S as a deoxidizer
i and elements inevitably mixed with Al, Mg, etc., which have a strong affinity for O, and excessive oxides are formed, which deteriorates the surface cleanliness and deteriorates the solderability and the plating property, so it is set to 150 ppm or less. Is desirable. The more desirable range of O is 10
It is 0 ppm or less. Since N has an austenite stabilizing effect, if it is added in an amount exceeding 150 ppm, the austenite phase is excessively stabilized and the work-induced transformation is hard to occur. In addition, the nitride is excessively deposited to deteriorate the solderability and the plating property.
A preferable 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 during 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, as shown by the solid line in FIG. 1 described later, in the Fe-Ni-Co system, the mechanical characteristics rapidly decrease as the annealing temperature rises. Therefore, it is necessary to alleviate the annealing temperature dependence of mechanical properties from the viewpoint of production stability. In the present invention, by adding these solid solution strengthening elements and the like, the annealing temperature dependence of mechanical properties can be relaxed as shown by the dotted line in FIG. 1 (Example No. 7 in Table 1 below). This is due to the fact that the characteristics on the high temperature side can be significantly improved.
If the addition amount of these reinforcing elements is less than 0.1%, there is no effect on stabilization, and if it exceeds 3%, surface oxidation is promoted, solderability,
Plateability is 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 content is limited to 0.1 to 3%.

In the present invention, the final structure is determined by the retained austenite phase as it is during the solution treatment, the work-induced martensite phase, and the reverse transformation austenite phase precipitated in the final annealing. However, due to the above reasons, the reverse transformation austenite phase γ ″ (including some retained austenite γR) and martensite α ″ (including some ferrite α)
Various combinations are possible for the phase constitution of the metallographically. γ ″ + α ″: When all of γR is transformed into α ″ by cold working, and when part of α ″ is transformed into γ ″ in the final annealing γ ″ + γR + α ″: γR in cold working When a part of α ″ is transformed into α ″ by final annealing, and a part of α ″ is transformed into γ ″, γ ″ + γR + α ″ + α: A portion of γR is transformed into α ″ by cold working When a part of α ″ is transformed into γ ″ in the final annealing, and then the decomposition of the following formula 1 is involved

[0014]

[Equation 1]

Γ ″ + γR + α: When a part of γR is transformed into α ″ by cold working, and when all of α ″ is accompanied by decomposition of number 1 in the final annealing, γ ″ + α: By cold working Transform all of γR into α ″,
Furthermore, when all of α ″ is decomposed into the number 1 in the final annealing, γ ″ + α ″ + α: All of γR is transformed into α ″ by cold working, and further all of α ″ is converted in final annealing. When it is transformed into γ ″ and then accompanied by decomposition of number 1, in any case, if the reverse transformation or residual austenite is less than 50%, the coefficient of thermal expansion becomes large and the thermal expansion matching with the silicon chip deteriorates. Let Further, the strength of the substrate is significantly reduced when the austenite phase becomes 100%, the structure is composed of a composite phase of retained austenite phase and reverse transformation austenite phase and ferrite phase or martensite phase, the total of the austenite phase is 50% or more. Limited to. In addition, 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,
When the solution treatment before cold working is at or below the austenite finish temperature, the austenite phase does not have a sufficient amount,
The solution treatment temperature is set to the austenitization end temperature or higher. However, preferably, the solution treatment temperature is more preferably 950 ° C. or lower because it is necessary to refine the crystal grains in the next step. If the cold working ratio is less than 40%, a sufficient amount of work-induced martensitic transformation does not occur,
Also, if this exceeds 90%, the material anisotropy becomes strong, so it is limited to 40-90%. Furthermore, when the final annealing temperature exceeds the austenitizing end temperature, all work-induced martensite phases are transformed into reverse transformation austenite,
Since the desired precipitation strengthening by the composite structure cannot be obtained, the temperature is limited to below the austenitizing end temperature. Regarding α ₃₀₀ (average coefficient of thermal expansion from room temperature to 300 °), hardness, and tensile strength, as a result of examining the package assembly process and usage environment, α ₃₀₀ is (3 to 9) × 10 minus 6 / ℃, hardness is 2 in Hv
A tensile strength of 60 or more and a tensile strength of 80 kgf / mm ² or more were judged to be sufficiently durable for use.

[0017]

EXAMPLES The material of the present invention will be described with reference to examples. Alloys having the compositions shown in Table 1 and Table 2 were melted and cast in a vacuum induction melting furnace, forged at 1100 to 1150 ° C., and hot rolled to a thickness of 3 mm,
Furthermore, after solution treatment at 1000 ° C. for 1 hour (water cooling), cold rolling was performed to 0.35 mm. Tables 3 and 4 show various kinds of materials obtained by subjecting each of the above materials having a thickness of 0.35 mm to a solution treatment at 750 ° C, cold rolling to 71 mm (71%), and final annealing at 530 ° C. Show the characteristics. 34 'is the 0.35 mm 34
This shows a material that has been finished to a thickness of 0.1 mm by the conventional Kovar standard manufacturing process. In addition, the amount (%) of the austenite phase is a value obtained by Equation 2. Platability is evaluated by solvent degreasing-electrolytic degreasing-acid treatment, and then thickness 0.5
Cu strike plating of μm is applied, and Ag of 3 μm is applied on it.
After plating, it was heated in the air at 450 ° C. for 5 minutes to observe blisters. All were good without blister (A). Regarding the soldering property, a solder weather resistance test (holding in the air at 150 ° C x 1000hr, bending at 90 °,
The presence or absence of peeling of the solder interface was observed. In all cases, there was no peeling and it was good (A). For crevice corrosion resistance, 65 ℃, 1
% NaCl solution, number of corrosion between resin / lead (piece / c
m) was counted.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Equation 2]

The materials Nos. 1 to 32 shown in Tables 1 and 2 are all materials of the present invention, and are different from the conventional material 34 or 34 'which is an austenite single phase (austenite amount 100%) as shown in FIG. As shown in (a) and (b), it is understood that it is a mixed phase of an austenite phase and a ferrite phase or a martensite phase, and exhibits higher mechanical properties than this. FIG. 1 shows the change in hardness with respect to the final annealing temperature for the material of the present invention containing 0.9% Nb as a strengthening element and the comparative material containing no strengthening element (No. 7 and No. 33 in Tables 1 and 2). The results of the examination are shown. According to this, it is clear that the addition of the strengthening element (Nb) greatly relaxes the final annealing temperature dependency of hardness. Further, as shown in Tables 3 and 4, various properties of Nos. 2, 4, 6, 21 to 32 to which B, Mg, and Ca were appropriately added were confirmed to have an effect of improving hot workability without deteriorating various characteristics. It was It can be seen that No. 4,5, No. 14 to 20 and No. 27 to 32, to which Cu is added, have high strength and excellent crevice corrosion resistance.

[0024]

As described above, the material of the present invention is F
By combining precipitation-induced martensitic transformation and reverse transformation austenite in the final cold working and the final annealing in the specific composition of the e-Ni-Co system, respectively, it is possible to achieve the high required height for the lead frame for multi-pin thin type. In order to obtain strength, it is possible to secure stable production by relaxing the dependency of strength on final annealing temperature without deteriorating major specificity such as solderability and plating property. It's a big one.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between final annealing temperature and mechanical properties.

FIG. 2 Inventive materials (a) and (b) and conventional Kovar
It is a microscope metallographic photograph of (c) (magnification × 400).

Claims (12)

[Claims] 1. In weight%, Co 0.5 to 22%, Ni 22 to 3
Contains 2.5%, Mn 1.0% or less, Si 0.5% or less, Ni and Co
When the content of Co is less than 12%, Ni is 27-32.5%, and Co is 12%.
In the above, the relation of 66% ≦ 2Ni + Co ≦ 74% is satisfied, and 0.1 to 3.0% of any one or more of Nb, Ti, Zr, Mo, V, W and Be is contained, and the balance contains impurities. Except that the structure is substantially Fe, and the structure thereof is a reverse transformation austenite phase and a retained austenite phase and a martensite phase and a ferrite phase, and the total amount of both austenite phases is 50%.
A high-strength lead frame material characterized by the above. 2. The alloy according to claim 1, further comprising a reverse-transformed austenite phase, a retained austenite phase and a ferrite phase, wherein the total content of both austenite phases is 50% or more. Strength leadframe material. 3. A high-strength leadframe material comprising the alloy having the composition of claim 1, further comprising a reverse-transformed austenite phase and a ferrite phase, the austenite phase being 50% or more. 4. An alloy having the composition of claim 1, further comprising a reverse-transformed austenite phase and a martensite phase and a ferrite phase, the austenite phase being 50%.
A high-strength lead frame material characterized by the above. 5. The alloy according to claim 1, comprising 0.5 to 3% of Ni in the composition of claim 1 replaced by an equivalent amount of Cu, and having a structure according to any one of claims 1 to 4. High strength lead frame material characterized by. 6. In addition to the additive alloy element according to claim 1, B, M
One or two or more of g and Ca are contained in a total amount of 0.0001 to 0.03 wt%, the balance is substantially Fe except impurities, and the structure is as described in any one of claims 1 to 4. A high-strength leadframe material characterized by: 7. In addition to the additive alloy element of claim 5, B, M
One or two or more of g and Ca are contained in a total amount of 0.0001 to 0.03 wt%, the balance is substantially Fe except impurities, and the structure is that according to any one of claims 1 to 4. A high-strength leadframe material characterized in that 8. The alloy according to claim 5, further comprising a reverse transformation austenite phase (which may include a retained austenite phase) and a martensite phase, wherein the austenite phase is 50% or more. Characteristic high strength lead frame material. 9. In addition to the additive alloy element of claim 1, Ca is used alone or in combination with one or two of B and Mg to form (Ca
+ B + Mg) in an amount of 0.0001 to 0.03 wt%, the balance being substantially Fe except for impurities, and the structure is as described in claim 8. 10. In addition to the additive alloy element of claim 5, B,
0.001 to 0.03 wt% of one or more of Mg and Ca in total
A high-strength lead frame material, characterized in that it contains Fe and the balance is substantially Fe except impurities, and has a structure according to claim 8. 11. The average thermal expansion coefficient from room temperature to 300 ° C. is (3 to 9) × 10 -6 powers / ° C., the hardness is 260 or more in Hv, and the tensile strength is 80 kgf / mm ² or more. The high-strength leadframe material according to any one of claims 1 to 10. 12. The method for producing a high-strength lead frame material according to claim 1, wherein the alloys having the respective compositions are subjected to solution treatment at a temperature equal to or higher than the austenitization end temperature, and then 40 to 90%. During cold working, part of the austenite phase is transformed into work-induced martensite, and further final annealing is performed at a temperature not exceeding the austenitization end temperature to precipitate the reverse transformation austenite phase, and finally the reverse transformation austenite phase or A method for producing a high-strength lead frame material, which has a structure comprising an austenite phase formed of a retained austenite phase and at least one of a ferrite phase and a martensite phase.