JPH04176844A - High strength lead frame material and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a lead frame material improving strength by making the specific composition of Fe-Ni-Co series material the specific two-phase structure with a final cold-working and a final annealing. CONSTITUTION:An allay composed of, by wt.%, of <=0.05 C, 0.5-22 Co, 22-32.5 Ni, <=1.0 Mn, <=0.5 Si, 0.0001-0.05 B and/or Mg, and in the case of <12 Co, 27-32.5 Ni and in the case of >=12 Co, under satisfying the relation of 66<=2Ni+Co<=74, and further, 0.1-5.0 one or more kinds of Nb, Ti, Zr, Mo, V, W and Be and the balance Fe with impurities, is prepared. Solution treatment is executed to this alloy at austenitizing completing temp. or higher and successively, a part of the austenitic phase is transformed to strain induced martensite with 40-90% cold-working and further, the finish annealing 18 executed at the austenitizing completing temp. or lower to precipitate inverse transformation austenitic phase. This material is composed of two phase of the inverse transformation austenitic phase and the martenstic phase and the austenitic phase is made to be <=50% in the structure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to lead frame materials for semiconductor devices that have higher strength than conventional materials.

[Conventional technology]

In recent years, as semiconductor devices such as logic devices have become higher in capacity and higher in integration, and packages have become thinner, there has been a tendency for lead frames to have more bins and become thinner. For this reason, higher strength lead frame materials are required than ever before.

Conventionally, Fe-42Ni and Fe-29Ni-17Co (Kovar) are known as Fe-based lead frame materials for multiple bins. Proposals for improved materials for these Fe-Ni and Fe-Ni-Co systems were made in Japanese Patent Application Laid-Open No. 55
．． -1.31155 or a high-strength Fe-Ni thread alloy with the addition of various reinforcing elements, and Fe-N1
- Regarding improved Co-based alloys, please refer to JP-A-55-1285.
No. 65, JP-A-57-82455, JP-A-61-62
51, Japanese Patent Publication No. 1-817, Japanese Patent Publication No. 1-15562, and Japanese Patent Application Publication No. 1-6104, which was previously proposed by the applicant of the present invention.
There is number 2.

[Problem to be solved by the invention]

Multi-bin lead frames are mainly manufactured using a photo-etching method that allows fine processing. However, these finely processed Fe-42N i or Fe-29N 1-17
CO's thin plate multi-bin lead frame is prone to warping, bending, and other variations in the leads during package assembly, transportation, and mounting due to lack of lead strength, and various problems such as buckling due to impact during use. was there.

Regarding the improvement of Fe-Ni-based or Fe-Ni-Co-based alloys, attempts have been made to strengthen them by incorporating Si, Mn, and Cr (Japanese Patent Application Laid-Open No. 131155/1983), or proposals to increase strength by using other strengthening elements. , relating to thermal expansion of Fe-N1-Cc alloys ((a) JP-A-1983-1
'28565, (b) JP-A-57-82455, (
c) 4! Kaisho No. 6176251, (d) Special Publication No. 1-81
No. 7, (e) Japanese Patent Publication No. 1-15562, (f) Japanese Patent Publication No. 1-15562.
-61042), but since the former contains an excessive amount of reinforcing elements in addition to the main elements, surface oxidation is likely to occur and there is a problem that the solderability and plating properties, which are the main characteristics of lead frames, are significantly deteriorated. Moreover, among the latter, none of the methods other than (a) are intended to actively improve the strength of the lead frame. Note that the material of (a) above has a reinforcing mechanism different from that of the material of the present invention.

[Means to solve the problem]

Therefore, the present inventors focused on Fe-N1-Co alloys whose austenite phase is unstable at room temperature, and conducted various experiments regarding the composition and manufacturing conditions. It was discovered that by precipitating the reversely transformed austenite phase during subsequent annealing to form a two-phase structure at a specific ratio, it was possible to increase the strength of the lead frame without impairing its various properties, especially its solderability and plating properties. .

However, since the reverse transformation from the martensitic phase to the austenite phase is sensitive to temperature, the strength is highly dependent on the annealing temperature, which causes many problems in terms of stable production. Therefore, the present inventors have developed an annealing temperature-dependent method that utilizes the reverse transformation from martensitic phase to austenite phase, as well as solid solution hardening or precipitation strengthening. It was discovered that it is possible to reduce the properties and increase the strength.

On the other hand, in the Fe-Ni-Co yarn alloy targeted by the present invention, it has been found that adding one or both of B and Mg in total has a great effect in order to improve high-temperature ductility. In other words, by adding a small amount of one or both of B and Mg in total, even large steel ingots can be easily hot worked, and thin materials such as lead frame materials, which is the object of the present invention, can be easily worked. Materials can be obtained with good yield.

Specifically, in terms of weight percent, the present invention contains G 0.05% or less, Co 0.5-22%, Ni 22-32.5%M
n1.0% or less, Si 0.5% or less, and one or two of B and Mg in total of 0. (Contains 100,L, -0,03%, the content of Ni and Co is 27-32.5% for Co less than 12%, 6 for Co more than 12%)
Satisfies the relationship of 6%≦ZNi+Co≦74%, and further N
b.

Contains 0.1 to 3.0% of one or more of Ti, Zr, Mo, V, W, and Be, with the remainder consisting essentially of Fe excluding impurities, and the structure is A high-strength lead frame material comprising two phases: a reversely transformed austenite phase (accompanied by a retained austenite phase) and a martensite phase, the austenite phase accounting for 50% or more, and an alloy having the above composition. is solution-treated at a temperature above the austenitization finish temperature, then a part of the austenite phase is transformed into strain-induced martensite by 40 to 90% cold working, and then final annealed at a temperature below the austenitization finish temperature. This is a method for producing a high-strength lead frame material, which is characterized by precipitating a reversely transformed austenite phase.

[Effect]

Next, the reason 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 around 17% and around 5%, and when it is less than 0.5% or over 22%, the coefficient of thermal expansion increases and silicon Degrades thermal expansion compatibility with the chip. Therefore, the Co content is limited to a range of 0.5 to 22%.

The Ni content is determined in relation to the Co content.

Co less than 12% and Ni less than 27% or 001
21 or more and (2Ni + Co) is less than 66%, the martensitic transformation start temperature is high, austenite becomes unstable, martensitic transformation occurs during the cooling process during solution treatment, and a sufficient amount of austenite is not obtained. I can't. Also, if Co is less than 12% and Ni is more than 32.5%,
When CO exceeds 12% and (2Ni+Co) exceeds 74%, the austenite phase becomes too stable at room temperature, making deformation-induced transformation difficult to occur. For this reason, Co 12%
Ni was titrated so that the relationship of 66%≦2Ni+Co≦74% was titrated when N'i was less than 27-32.5% and Co was 12% or more. Further, it is important to adjust the Ni and Co contents so that the martensite starting temperature becomes O''C or lower as for the optimum composition.

Nb, 'ri, Zr, Mo, V, W, and Be are important elements that strengthen 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 the precipitation of reversely transformed austenite phase during final annealing, but from the viewpoint of thermal expansion characteristics, it is desirable to have a large amount of austenite.
For this purpose, the final annealing temperature must be as high as possible. However, as shown by the solid line in Figure 1, Fe-N
In the i-Co system, the mechanical properties decrease rapidly as the annealing temperature increases. Therefore, from the viewpoint of production stability, it is desirable to reduce the dependence of mechanical properties on annealing temperature.

By adding these solid solution strengthening or precipitation strengthening elements, the present invention can alleviate the dependence of mechanical properties on annealing temperature, as shown by the dotted line in Figure 1, and further improve the properties on the high temperature side. This is because I discovered what I could do.

If the amount of these reinforcing elements added is less than 0.1%, there is no stabilizing effect, and if it exceeds 3%, surface oxidation is promoted and the solderability and plating properties are significantly impaired. In addition, these elements act on the austenite formation side, so if the amount added increases, the austenite in the matrix becomes too stable.
%.

Mn acts as a deoxidizing agent, but if it exceeds 1.0%, it increases the coefficient of thermal expansion and also deteriorates solderability and plating properties, so it is limited to 1.0% or less.

Si is added as a deoxidizing agent, and it is preferable that it not remain in the material, but Si up to 0.5% is acceptable because it does not cause an extreme increase in the coefficient of thermal expansion or extreme deterioration of solderability and plating performance.

B and Mg are added to improve hot workability, and if the amount of one or both added amounts is less than 0.0001%, the effect will be small, and if it exceeds 0.03%, the effect will be reduced during cold working. 0.0 to lower ductility and deteriorate material etching properties.
0001-0.03%. More preferably 0.
01% or less.

C is an impurity, and if it exceeds 0.05%, the etching properties of the material will deteriorate significantly, so it is limited to 0.05% or less. A more desirable range of C is 0.015% or less.

In addition, the final structure is determined by the retained austenite phase during solution treatment, the deformation-induced martensite phase, and the reversely transformed austenite phase that precipitates during final annealing, but if the residual and reversely transformed austenite is less than 50%, thermal expansion The coefficient becomes large and the thermal expansion matching with the silicon chip deteriorates. Also, the austenite phase becomes 100%.
Since this significantly reduces the strength of the matrix, the structure consists of two phases: an austenite phase consisting of retained austenite and reverse transformed austenite, and a martensite phase, and the total amount of the austenite phase is limited to 50% or more.

In addition, the amount (%) of austenite phase in the present invention is
The value is determined from the X-ray diffraction intensity, which will be explained in Examples below.

Next, in the method for producing the material of the present invention, if the solution treatment before cold working is performed at a temperature below the austenitization end temperature, the austenite phase will not be in sufficient amount, so the solution treatment temperature is set at a temperature equal to or higher than the austenitization end temperature. . However, since it is necessary to refine the crystal grains in the next step, the solution treatment temperature is preferably 950° C. or lower.

The cold working rate is limited to 40-90% because if it is less than 40%, a sufficient amount of deformation-induced martensitic transformation will not occur, and if it exceeds 90%, the anisotropy of the material will become strong.

Furthermore, the final annealing temperature is limited to below the austenitization end temperature because if it exceeds the austenitization end temperature, all the deformation-induced martensite phase will transform into reverse transformed austenite, and the desired precipitation strengthening due to the two-phase structure cannot be obtained. do.

In addition, αRT-s. . (Average coefficient of thermal expansion from room temperature to 300°C), hardness, and tensile strength were determined by considering the package assembly process and usage environment. is (3-9) X 10”/”C1 hardness Hv≧260,
It was judged that a tensile strength of 80 kgf/mm'' or more was sufficient to withstand use.

〔Example〕

The material of the present invention will be explained using examples. An alloy having the composition shown in Table 1 was melted and cast in a vacuum induction melting furnace, and
Forged at 150°C and hot rolled to a thickness of 3mm, and
After solution treatment at 950° C. for 1 hour (water cooling), cold rolling was performed to a tone of 0.35.

Table 2 shows each of the above materials at 0.35mm+j
Various properties of the material subjected to a series of treatments including solution treatment at 750° C. as in X, followed by cold rolling (71%) to 0.1 M and final annealing at 500 to 650° C. are shown. The alloy 30' is a material obtained by finishing the above-mentioned 0.35s No.30 material to a thickness of 0.1 stroke using the standard manufacturing process.

Note that the amount (%) of the austenite phase is a value determined as follows.

1 cho y: ITu++++Irt2oo++11tzzo+
+Iy(3+n+Iγ+222+ITf+++1, etc. is the XM diffraction intensity of austenite Ia=Iat++o++I
a(zoo)+Ia(2+++■α(1101 etc. is the X-ray diffraction intensity of martensite from the wood surface, materials 1 to 1 of the present invention
23 and Comparative Materials 24 to 29 have a mixed phase with the aforementioned martensite, unlike the conventional material 30 or 30', which is a single austenite phase (austenite content 100%), and as a result, they have significantly higher mechanical properties, That is, H
v≧260, tensile strength≧80 kgf/mm”.Also, as shown in Fig. 1, comparative material 24, which does not contain solid solution strengthening or precipitation strengthening elements, shows hardness when heated to 500°C or higher. In addition, alloys 1 to 1 of the present invention
Despite having high strength, 23 has good solderability, plating performance, and etching performance without any problems, and in comparison with comparative materials 28 and 29, the addition of B and Mg improves the properties during hot working. No more ear cracking, appropriate amount of B, M
It can be seen that productivity is improved by adding g. but,
It can be seen that addition of excessive B and Mg (comparative materials 25, 26, and 27) results in poor etching properties.

Figure 1 shows N among the solid solution strengthening or precipitation strengthening elements.
FIG. 3 is a diagram comparing changes in hardness with respect to final annealing temperature for cases with and without addition of b.

According to this, both have a hardness peak at the final annealing temperature of 500°C, and the Nb-free material has higher hardness than the non-additive material at the peak, but as the final annealing temperature increases, the hardness decreases sharply. , Yaki#i! It can be seen that the i temperature dependence is high. On the other hand, it can be seen that the 2.5% Nb additive material has low annealing temperature dependence, and has better mechanical properties than the non-additive material at temperatures higher than 520 to 530°C.

〔Effect of the invention〕

As described above, the material of the present invention combines deformation-induced martensitic transformation and precipitation of reverse transformed austenite through final cold working and final annealing in a specific composition of Fe-N1-C○ system, and further By stabilizing the strength on the high temperature side through solid solution strengthening, it is possible to obtain the high strength required for multi-bottle thin lead frames, reduce the dependence of the strength on annealing temperature, and improve hot workability. The industrial effect is extremely large.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1% by weight, C0.05% or less, Co0.5-22
%, Ni 22-32.5% Mn 1.0% or less, Si 0.
5% or less, one or two of B and Mg in total 0.00
01 to 0.03%, and the content of Ni and Co is C
When O is less than 12%, Ni is 27 to 32.5%, and when Co is 12% or more, it satisfies the relationship of 66%≦2Ni+Co≦74%,
Furthermore, it contains 0.1 to 3.0% of one or more of Nb, Ti, Zr, Mo, V, W, and Be, and the remainder consists essentially of Fe excluding impurities, and the structure is A high-strength lead frame material comprising two phases: a reversely transformed austenite phase (accompanied by a retained austenite phase) and a martensite phase, the austenite phase accounting for 50% or more. 2 The average coefficient of thermal expansion from room temperature to 300°C is (3 to 9)
The high-strength lead frame material according to claim 1, having a hardness of 260 or more in Hv and a tensile strength of 80 kgf/mm^2 or more. 3. The alloy having the composition of claim 1 is solution-treated at a temperature equal to or higher than the austenitization finish temperature, and then a portion of the austenite phase is transformed into deformation-induced martensite by 40 to 90% cold working, and further austenitization is performed. A method for producing a high-strength lead frame material, characterized by final annealing at a temperature not exceeding the final temperature to precipitate a reversely transformed austenite phase.