JPH0788529B2 - Manufacturing method of ferritic stainless steel for lead frame - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Purpose of Invention" (Field of Industrial Application) A method for producing a ferritic stainless steel for lead frames, which is excellent in repeated bending properties.

(Prior art) As an IC lead frame material that requires high reliability (excluding some ceramic packages that require airtightness in particular), it has high strength, good bending characteristics, and thermal softening temperature. 42Ni alloy, which is high and has excellent corrosion resistance and heat resistance and good Au or Ag plating property, has been widely used in the past.

By the way, in recent years, stainless steel, which has excellent corrosion resistance and heat resistance, has a high thermal softening temperature, and is cheaper than 42Ni, has been attracting attention for this lead frame material because of the demand for further cost reduction. However, this material has a drawback that the plating property is not preferable because a dense oxide film is formed on the surface. Therefore, recently, for example, JP-A-56-4374
7, JP-A-59-200795, 201455, 219195, JP-A-60-196
As in 962, 4259 and JP-A-52-1865, surface treatment techniques have advanced, and many materials have been developed in which the surface of stainless steel is coated with a pure metal or an alloy thereof to improve the plating property.

In addition, for example, as disclosed in JP-A-60-91659 and 130848, a lead frame having a required strength and a good bending characteristic has been developed. That is, in JP-A-60-91659, after cold rolling, it is annealed at a temperature at which a substantially ferrite single-phase structure is formed.
Then, final finishing rolling is performed at a rolling reduction of 50% or less, and in JP-A-60-130849, the final finishing cold rolling is 400
It is annealed at a temperature of ~ 800 ° C.

(Problems to be Solved by the Invention) However, in the related art as described above,
It is difficult to properly respond to such factors as thinning and punching characteristics associated with higher density mounting of ICs. That is, it is strongly desired that the lead frame material itself is made thinner as the IC becomes more dense and mounted, and thus when the material is made thinner, a corrugation phenomenon of the material occurs at the time of passing through the high-speed press punching line, and the die This makes it difficult to perform the press work because of being caught inside, and the pattern accuracy at the time of internal drawing deteriorates.

In order to solve such a problem, it is necessary to further increase the rigidity of the material from the present condition. To increase the rigidity, a method of increasing the pressure regulation rate (final secondary cold rolling rate) is adopted. As described in the invention of KAISHO No. 60-91659, the elongation required for securing the bending property is lowered. Therefore, it is extremely difficult to manufacture a thin lead frame original plate which has a bending characteristic and rigidity by the conventional technique.

"Structure of the Invention" (Means for Solving Problems) The present invention was devised through repeated studies to solve the problems of the conventional ones described above, and has excellent rigidity and repeated bending characteristics. It has succeeded in providing a ferritic stainless steel original plate for lead frames, which has good spot plating properties and can be made thinner than before. (1) C: 0.05 wt% or less, Mn: 1.0 wt % Or less, Cr: 8 to 13 wt
%, S: 0.003 wt% or less, Al: 0.01 wt% or less, O: 0.006 wt%
Below, stainless steel containing Si: 0.1-0.5 wt% and the balance substantially consisting of Fe is hot rolled at a finishing temperature of 800 ° C or higher, and a steel strip wound at 650 ° C or higher is subjected to intermediate annealing. The primary cold rolling rate (CR ₁ %) was used for obtaining the original coil by performing primary cold rolling and secondary cold rolling, followed by secondary cold rolling, softening annealing, temper rolling, and stress relief annealing. ) And the secondary cold rolling rate (CR ₂ %) satisfy the relations of the following formulas I to III.

40 ≦ CR ₁ ≦ 75% …… I 40 ≦ CR ₂ ≦ 75% …… II CR ₁ + CR ₂ ≦ 130% …… III (Action) wt% (hereinafter simply referred to as%) and contains 8 to 13% Cr For ferritic stainless steels, the Cr content is 8% or more to ensure the corrosion resistance required for lead frame materials. On the other hand, if the content exceeds 13%, the dense oxide film formed on the surface impairs the spot plating property and, in some cases, the plating property when the entire surface is plated, so the above-mentioned upper and lower limits are defined. .

C is an element that enhances the strength and is advantageous for strengthening the material, but if it exceeds 0.05%, the degree of deterioration of the repeated bending property increases, so 0.05% is the upper limit and this repeated bending property can be obtained. Although the lower limit is not particularly defined, it is preferably 0.006% or more from the economical aspect of melting.

Si is an element effective for strengthening, and is also used as a deoxidizing agent in lead frame materials because it dislikes alumina inclusions. That is, since Al is not used in this alloy, it is basically necessary to perform deoxidation with Si, so 0.1% or more, and if it is less than this, deoxidation is insufficient and inclusions increase, and the plating property deteriorates. So the lower limit should be 0.1%.
However, if this Si exceeds 0.5%, it becomes unfavorable because it forms a Si oxide film that is harmful to spot plating property during annealing, and the amount of Si-based inclusions increases, which adversely affects the repeated bending properties. We will avoid these disadvantages by giving this 0.5% as an upper limit.

Mn is also an effective element for strengthening, and is preferably 0.1% or more to strengthen the material and suppress the emissivity during hot working. However, when the content exceeds 1.0%, the structure becomes non-uniform due to segregation in the material, the spot plating property deteriorates and the dispersion of mechanical properties increases, and an oxide film that is harmful to the spot plating property is formed during annealing. Therefore, the upper limit of this 1% is avoided.

S, Al, and O form inclusions in the steel and deteriorate repeated bending properties, so it is necessary to reduce any of them.
It is also reduced in order to improve the spot plating property.

That is, when S is 0.0030% or more, MnS in the steel is increased, the adhesion of the plating is deteriorated, and blisters are likely to occur during die bonding, so the upper limit is 0.003%. Al is 0.0
If it exceeds 10%, the amount of Al ₂ O ₃ in the steel will increase, which will deteriorate the adhesion and cause blistering, so the upper limit is 0.010%, and O will combine with Al and Si to form oxides during steelmaking. However, since there are many inclusions in the steel and the plating properties deteriorate, 0.0060%
By setting the upper limit to, the lead frame material free from these disadvantages can be obtained.

Next, the inventors of the present invention examined the cold-rolled annealing conditions that affect the repeated bending characteristics using the test materials having the above-described compositional ranges, and particularly the intermediate-rolled cold rolling before the final cold rolling for hardening. It has been found that the cold-rolling is performed twice by sandwiching, and when the cold-rolling rate of the two times satisfies a specific condition, the cyclic bending property is improved.

That is, in Fig. 1, the hot rolling finishing temperature is 870 ° C and the winding temperature is 7
Each of the test materials made of C steel in Table 1 described below, which was set to 00 ° C, was cold-rolled once (cold rolling 88%) and cold-rolled twice (primary cold rolling 70
%, Secondary cold rolling rate 60%, intermediate annealing 750 ° C) to 0.23 mm sheet thickness, 750 ° C softening annealing, then 36% cold rolling to final sheet thickness (0.15 mm) And then 0 for the rolling direction of the test material that was subjected to stress relief annealing at 450 ° C.
Taking the angles of °, 45 ° and 90 °, as shown in Fig. 2, punch out a pin-shaped sample with the width of the base 1 being 1.5 mm and the width of the tip 2 being 0.5 mm, and repeating according to MIL STANDARD. The results of the bending test are shown, and the in-plane anisotropy of the tensile strength of each sample is also shown.

That is, L and C corresponding to the punching direction of the REIT BRAME pin
When viewed in the direction, it is clear that the bending characteristics of the double cold-rolled material are significantly superior to those of the single cold-rolled material equivalent to the conventional material, and in particular, the repeated bending is 17 times or more in the L direction, It is clear that the same strength material of 42 alloy is superior even when compared with 10 times in this repeated bending. In terms of strength, the in-plane anisotropy of the double cold rolled material is considerably smaller than that of the single cold rolled material, and the strength level is as high as 70 kg f / mm ² or more.

Looking at the in-plane anisotropy of bending properties, D
Whereas the direction (45 ° direction) shows the highest inverted V shape,
It is clear that the double cold rolled material shows a V shape having the highest L direction, and that a preferable product can be obtained by following a conventional method of obtaining a lead frame parallel to the rolling direction.

However, the inventors of the present invention have repeatedly investigated the cause of the in-plane anisotropy of the repeated bending characteristics being different depending on the cold rolling conditions as described above. That is, the (100) pole figure of each sample of the above-mentioned C steel 1 time cold rolled material and 2 time cold rolled material is shown in FIG.
As shown in (B), in any case, {111} <11
>, {112} <10>, but the major difference is that {100} <011> is stronger in the single cold-rolled material, and the bending property difference between the two materials is the texture. It is thought that the difference between is largely controlled. Further, regarding the steels A and B in Table 1 in the composition range of the present invention, the similar texture tendency as in FIG. 3 was recognized. That is, as a result of such studies, the present inventors have found that it is necessary to control the texture, that is, to weaken the {100} <011> component in order to improve the bending characteristics in the L and C directions. confirmed.

The cold rolling conditions for further improving the bending characteristics by the double cold rolling method using a hot rolled sheet made of steel (B steel in Table 1) in the composition range of the present invention The cold rolling rate was changed and examined. After the first cold rolling, the annealing after the second cold rolling was 750 in each case.
℃ and secondary cold rolling-36% cold rolling after annealing,
Second from the L direction of the test material subjected to stress relief annealing at 450 ° C
The pin-shaped sample as shown in the figure is punched out and the repeated bending test is conducted. The result is shown in FIG. That is, according to the results of Fig. 4, both the primary cold rolling rate (CR ₁ ) and the secondary cold rolling rate (CR ₂ ) are 40 to 75%, and CR ₁ and CR ₂
It has been found that when the sum of the above is less than 130% (the lower limit is 80%), excellent characteristics of 15 times or more can be obtained in the repeated bending property. Primary cold rolling rate (CR ₁ ) Secondary cold rolling rate (C
If both R ₂ ) are less than 40%, it is recognized that the annealed structure becomes coarse and the grains are mixed, and the bending property in the L direction is inferior also in terms of the texture. Even lower.

Further, in the steel having the above-described composition range of the present invention, when the cold rolling rate becomes higher, {100} <011> becomes stronger as the cold rolling texture, and it is considered that it is succeeded even after recrystallization. Therefore, the effects of CR ₁ and CR ₂ are additive, and if at least _one of CR ₁ and CR ₂ exceeds 75%, or if the sum of CR ₁ and CR ₂ exceeds 130%, {100} <100> becomes stronger,
As shown in FIG. 4, the bending property in the L direction is deteriorated and the repeated bending property becomes 12 to 13 times or less.

Furthermore, as a result of research on manufacturing factors that improve the cyclic bending property, the present inventors have found that the finishing temperature of hot rolling is also an important control factor. That is, FIG. 5 shows the relationship between the hot rolling finishing temperature and the repeated bending properties in the L direction after final cold rolling and annealing. The test steel is the hot rolled sheet of the above-mentioned first B steel and C steel. Of primary cold rolling (70%)-annealing (750 ° C) -secondary cold rolling (60%)-annealing (750 ° C) -36% cold rolling-stress relief annealing (450 ° C) It has gone through the process.
The repetitive bending properties of all steels have a finishing temperature of 85.
It is excellent at 0 ° C or higher, but it tends to decrease at temperatures below that. In other words, in the present invention, the lower limit of the finishing temperature is set to 850 ° C. based on these results. The B steel is basically in the γ phase during hot rolling, but when the ferrite transformation occurs in the state where the austenite after hot rolling is recrystallized, the texture of the hot rolled sheet also becomes random. It is considered that the {100} <011> component can be weakened by setting the conditions within the range of the present invention, and 850 ° C. is estimated to be a critical temperature at which austenite is sufficiently recrystallized after finish rolling. On the other hand, most of C steel is austenite during hot rolling, and it is considered that the critical temperature at which this austenite is sufficiently recrystallized after hot rolling is 850 ° C. The upper limit of the finishing temperature was not specified, but raising the hot rolling heating temperature more than necessary leads to heat loss and is uneconomical. Further, the grain size of the recrystallized austenite after hot rolling finish becomes large, and the ferrite structure after transformation becomes coarse grain, which affects the mechanical properties after cold rolling annealing, and is therefore preferably 1000 ° C.
It is the following. If the coiling temperature is 650 ℃ or higher, austenite decomposes into ferrite + carbide after coiling.
If the temperature is lower than 0 ° C, the hot rolled coil is hardened due to the formation of martensite, and the mill load during the subsequent cold rolling becomes large, which is not preferable. In this case, softening can be achieved by annealing the hot-rolled sheet, but it is uneconomical due to the increase in the number of manufacturing processes and the cost of heat, and for these reasons, the lower limit of the coiling temperature is 650 ° C. I decided.

In the practice of the present invention, the annealing after primary and secondary cold rolling is intended for recrystallization softening, and the annealing temperature is
If it is increased to the ferrite + austenite region in the Fe-Cr-C phase diagram, depending on the cooling conditions, the load of the mill in the subsequent cold rolling will become high due to the formation of martensite, and the annealing temperature will be higher than necessary and the thermal economy will be increased. It is obvious that the annealing is performed in the temperature range of the ferrite single phase from the viewpoint of the manufacturing cost because the problem that the property deteriorates occurs.

Since the intention of the present invention is to improve the cyclic bending property by texture control, the annealing temperature itself may be a temperature sufficient for recrystallization, and such an annealing condition has the effect of the present invention. It does not hinder anything. Similarly, the temper rolling (final rolling) performed after the secondary cold-rolling annealing is usually adopted in order to harden the ferritic stainless steel in the sense that the rolling is performed according to the work hardening characteristics of the material. This is the method used.

From the viewpoint of texture control intended in the present invention, if the final cold rolling rate is less than 50%, the effect of the present invention is exhibited without any hindrance.

Although the cold-rolled material targeted in the present invention is a hot-rolled material, the improvement of the cyclic bending property intended in the present invention is achieved by texture control, so the cold-rolled material is limited to the hot-rolled material. Not only, the effect of the present invention is sufficient even through a step of producing a cold-rolled material by hot-rolling a steel strip cast by strip casting or a strip casting in which a cold-rolled material is immediately cast from molten steel. To be demonstrated. In this case, it goes without saying that the cold material is assumed to be a textured random material which is sufficiently recrystallized and transformed from austenite to ferrite in the manufacturing process.

Example (Example 1) Alloys of the present invention and alloys as comparative examples as shown in Table 2 below were melted in a vacuum furnace.

These alloys were subjected to slab-hot rolling (finishing temperature 880 ° C, coiling temperature 720 ° C) and surface-ground them into raw materials. The raw materials thus obtained were subjected to the double cold rolling method (primary cold rolling). Delay rate 70
%, Intermediate annealing 750 ° C, secondary cold rolling rate 60%) to a plate thickness of 0.23 mm, and after softening and annealing at 750 ° C, a final cold rolling of 36% is performed.
The final strip thickness of 0.15 mm was subjected to stress relief annealing at 450 ° C., and the repeated bending properties, tensile strength and silver plating properties of the obtained test material were investigated and the results are shown in Table 3 below. Is.

Repeated bending test is performed according to MIL STANDARD by punching out the pin shape shown in Fig. 2 from the rolling direction (L direction) and width direction (C direction) of the test material, and measuring the tensile strength in the L direction and silver plating. As for the property, the sample is deoxidized and washed, then pickled, strike-plated on the base, and a thickness of 3μ
m of silver was spot-plated, followed by heat treatment for 450 × 5 minutes and observation by observing the surface properties.

Alloys No. 1 to No. 8 are alloys in which the amounts of C, Si, Mn, S, Al, and O are within the scope of the present invention, and both hot rolling conditions, cold rolling and annealing conditions are within the scope of the present invention. The tensile strength is 70 kg f / mm ² or more, which is high strength, and the repeated bending property is 17 times or more in the L direction and 15 times or more in the C direction, which are excellent as compared with the comparative example. Further, even after heating after silver plating, no discoloration or blistering was observed, and the plateability was good.

Alloys No. 9 and No. 10 have Si, Mn, S, Al, and O in the respective ranges of the present invention, and C exceeds the present invention range. The annealing conditions are adopted, the tensile strength is high at 70 kg f / mm ² or more, and the plating property is good, but the cyclic bending property is inferior in the L and C directions as compared with the invention examples.

Alloy No.11, No.12 and No.13 are O,
The amount of S and Al exceeds the requirements of the present invention, and the other components are alloys within the scope of the present invention. Both hot rolling conditions, cold rolling and annealing conditions are within the present invention range, and tensile strength is 70 kg f / Although the strength is as high as mm ² , the cyclic bending property is in the L direction as compared with the examples of the present invention,
It is also inferior to the C direction, and blisters are generated even after heating after silver plating, and the silver plating property is deteriorated.

Alloy No. 14 is an alloy in which the amounts of C, Mn, S, and Al are within the range of the present invention, but the amount of Si is less than the lower limit specified in the present invention, and the amount of O also exceeds the amount of the present invention. , Hot rolling conditions, cold rolling
Both the annealing conditions are within the scope of the present invention, and the tensile strength is 69 kg f / m.
The strength is slightly lower than m ² and other alloys, and the cyclic bending property is inferior in both the L direction and the C direction as compared with the examples of the present invention, and blistering occurs even after heating after silver plating, and silver plating Inferior in sex.

Alloy No. 15 is an alloy in which the respective amounts of C, Si, S, Al, and O are within the range of the present invention, but Mn exceeds the upper limit value specified in the present invention, and hot rolling conditions, cold rolling and annealing conditions are used. Both are within the scope of the present invention,
The tensile strength is as high as 70 kgf / mm ² or more, but the cyclic bending property is at the same level in the L direction but inferior in the C direction as compared with the examples of the present invention. Moreover, a lot of blisters are generated even after heating after silver plating, and the silver plating property is poor.

Alloy No. 16 is an alloy in which the amounts of C, Mn, S, Al, and O are in the range of the present invention, but Si exceeds the upper limit specified in the present invention, and the hot rolling conditions, cold rolling and annealing are performed. Although the conditions are within the scope of the present invention and the tensile strength is as high as 70 kg f / mm ² or more, the repeated bending properties are inferior in the L direction and the C direction as compared with the examples of the present invention, and heating after silver plating is performed. However, it is clear that blistering occurs a lot and the silver plating property is inferior.

As described above, ferritic light stainless steel having high strength, excellent repeated bending characteristics, and good plating property has hot rolling conditions and cold rolling annealing conditions within the scope of the present invention, and C, Si, Mn, S, Al,
It is understood that this is achieved only when the respective amounts of O are controlled within the range of the components of the present invention.

(Example 2) The lump slabs of the alloys of the present invention of Nos. 1 to 3 shown in Table 2 above were finished at the hot rolling finishing temperature shown in Table 4 below and wound at 730 ° C. The materials were subjected to surface grinding to form materials, and these materials were subjected to the same cold rolling and annealing conditions as shown in Table 4 and having a final plate thickness of 0.18 mm. The results are shown on the right side of Table 4.

That is, each of the reference numerals 1 to 6 has a hot rolling finish temperature within the range of the present invention, and the primary and secondary cold rolling ratios are within the range of the present invention both independently and in total, and the cyclic bending property is L. In the direction
16 times or more, 14 times or more in the C direction, which is superior to the comparative example, and tensile strength is 70 kg f / mm ² or more, which is high strength.

On the other hand, each of the reference numerals 7 and 16 has a hot rolling finish temperature outside the scope of the present invention, and the others are within the scope of the present invention, and has a high tensile strength of 70 kg f / mm ² or more, The cyclic bending characteristics have not reached the invention examples in both the L direction and the C direction, and the materials 11 and 12 have hot rolling finish temperatures within the scope of the present invention, but only in the case of single cold rolling. The secondary cold rolling rate is far higher than the upper limit of 75% of the present invention, and the tensile strength is as high as 70 kg f / mm ² or more, and the cyclic bending property is extremely poor at 10 times or less.

Each of the reference numerals 9 and 15 is within the scope of the present invention for the hot rolling finishing temperature and the primary and secondary cold rolling rates alone, but the sum of the primary and secondary cold rolling rates is outside the scope of the present invention. In some cases, the tensile strength is high, but the cyclic bending properties are still poor. Reference numeral 8,
As for No. 13, when the primary cold rolling rate and the secondary cold rolling rate alone exceed the range of the present invention, the repeated bending properties are inferior, as described above. Further, each of the materials 10 and 14 is a case where the primary cold rolling rate and the secondary cold rolling rate alone under the manufacturing conditions of the present invention do not reach the scope of the present invention, and the tensile strength is still
It is over 70 kg f / mm ² , but the cyclic bending property is inferior.

That is, it was confirmed that satisfying the conditions of the present invention for all of the individual and secondary cold rolling ratios and the sum thereof had a great influence on the cyclic bending property.

"Effects of the Invention" According to the present invention as described above, it is possible to appropriately provide a ferritic stainless steel base plate for a lead frame, which is excellent in both rigidity and cyclic bending characteristics, and has good plating properties. Fully compatible with thinning, for example, lead frame materials for high density multi-pin high density packages such as flood packages, general IC packages such as dual in-line packages, and even lead frames for general devices such as diodes and transistors. This is an invention that can be thinned to reduce the material cost and has a great effect industrially.

[Brief description of drawings]

The drawings show the technical contents of the present invention. FIG. 1 is a diagram showing the effect of cold rolling conditions on cyclic bending properties and in-plane anisotropy of tensile strength, and FIG. 2 is cyclic bending. FIG. 3 is an explanatory view of the structure of the test piece, FIG. 3 is a (100) pole figure of the first cold rolled material and the second cold rolled material, and FIG. 4 is the primary cold rolling rate and the secondary cold rolling rate in the present invention. FIG. 5 is a chart summarizing the range, and FIG. 5 is a chart summarizing the relationship between cyclic bending characteristics and finishing temperature. In FIG. 2, 1 is a base portion and 2 is a tip portion.

Continuation of the front page (56) References JP 59-9149 (JP, A) JP 60-103158 (JP, A) JP 62-287045 (JP, A) JP 62-287048 (JP , A) Japanese Patent Publication Sho 61-54863 (JP, B2)

Claims (1)

[Claims] 1. C: 0.05 wt% or less, Mn: 1.0 wt% or less, Cr: 8 to
13wt%, S: 0.003wt% or less, Al: 0.01wt% or less, O: 0.006w
Stainless steel containing t% or less and Si: 0.1 to 0.5 wt% and the balance being substantially Fe is hot-rolled at a finishing temperature of 800 ° C or more, and a steel strip wound at 650 ° C or more is annealed intermediately. The first cold rolling rate (CR) is used to obtain the original coil by first and second cold rolling, followed by secondary cold rolling, softening and annealing, temper rolling, and stress relief annealing. ₁ %) and secondary cold rolling rate (CR ₂ %) satisfy the relations of the following formulas I to III. 40 ≦ CR ₁ ≦ 75% …… I 40 ≦ CR ₂ ≦ 75% …… II CR ₁ + CR ₂ ≦ 130% …… III