JP2007100136A - Copper alloy for lead frame excellent in uniform plating property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper alloy for a lead frame excellent in uniform plating property. <P>SOLUTION: In the copper alloy of Ni-Si based copper alloy, Cr-Zr based copper alloy, Sn-P based copper alloy, etc., the copper alloy for lead frame excellent in the uniform plating property satisfies the following relations, as regards the size D of inclusion present in the depth L from the uppermost layer: in the case of 0.1μm≤L, D≤0.1μm; in the case of 0.1μm<L≤5μm, D<L; and in the case of 5μm<L≤10μm, D≤5μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lead frame material for a semiconductor package and an electronic component using the same.

  In recent years, electronic devices such as mobile phones and personal computers have been mounted with high density, and accordingly, electronic parts used in these electronic devices have been reduced in size and thickness. A semiconductor package that is the core of an electronic component is excellent in economy and mass productivity. Therefore, a plastic package in which circuit components such as a semiconductor, a resistor, and a capacitor are molded together with a lead frame with a thermosetting resin is often used. A copper alloy is widely used for the lead frame for energization used in this semiconductor package in order to cope with heat radiation and high-speed signal transmission.

In the lead frame manufacturing process described above, there is a process in which a copper alloy material is formed by etching or pressing, followed by a plating process entirely or partially. In the semiconductor assembly process, the lead frame undergoes a die bonding process for bonding the semiconductor element to the lead frame and a wire bonding process for bonding the semiconductor element to the lead frame Au wire. After plating, Ag plating is performed.
Ag plating of copper alloy for lead frames is required to be smooth in order to prevent poor bonding between the semiconductor element and the Au lead frame. Conventionally, however, the Ag deposition state becomes non-uniform, and Ag plating There was a problem of protrusions. As a method for preventing this, Patent Document 1 discloses a technique for preventing non-uniform precipitation by controlling the contents of specific components, for example, Mg, Al, and Ca, in a copper alloy.
Further, Patent Document 2 discloses a technique for defining the size and density of precipitates in a material so as not to deteriorate the plating properties of the lead frame material.

Japanese Patent No. 3056394 Japanese Patent No. 2501275

However, the adjustment of the components may prevent the occurrence of Ag plating protrusions to some extent, but cannot completely prevent them.
Moreover, the generation | occurrence | production of the protrusion of Ag plating cannot be prevented only by prescribing the size of inclusions and precipitates.
The problem to be solved by the present invention is to provide a copper alloy for lead frames capable of uniform and smooth Ag plating.

  The present inventors conducted extensive investigations on the portion where the Ag plating protrusion was generated, and found that inclusions exist in the parent phase (copper alloy) of the protrusion generation portion. Further, when the existence state of these inclusions was investigated in detail, a correlation was found between the position where these inclusions exist, that is, the depth from the surface of the base material and its size, and the presence or absence of protrusions of Ag plating. In addition, regarding the size of inclusions involved in the generation of protrusions in Ag plating, it has also been found that when the size is less than 0.1 μm, the generation of protrusions is not affected.

The reason for the occurrence of Ag plating protrusions due to the presence of inclusions and precipitates is not clear, but the inclusions and precipitates have different electrical conductivities from the parent phase (copper alloy). It is presumed that the density distribution is affected and that nonuniform electrodeposition is caused.
Here, the “inclusion” is a generic name including inclusions generated during heat treatment such as crystallization generated during casting and aging.

That is, it is as follows.
(1) With respect to the size of inclusions (hereinafter referred to as “D”) existing in the depth from the outermost layer (hereinafter referred to as “L”), the following relationship is satisfied. Excellent copper alloy for lead frame,
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm.

(2) Ni: 1.0 to 4.8% by mass, Si: 0.2 to 1.4% by mass as basic components, and Mg, Zn, Sn, Fe, Ti, Zr, Cr, Al, One or more of P, Mn, Ag, or Be is contained in a total amount of 0.005 to 2% by mass, the balance is substantially Cu, and precipitates such as Ni ₂ Si, Cu—S, and Mg—S The lead frame copper alloy having excellent uniform plating properties, characterized in that the oxide of the component composition satisfies the following relationship with respect to the depth (L) from the outermost layer and the size (D) of the precipitates:
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm.

(3) Cr: 0.04 to 0.4% by mass, Zr: 0.03 to 0.25% by mass as basic components, and further Mg, Zn, Fe, Al, P, Mn, Co and Ni One or more kinds selected from the county are contained in a total amount of 0.01 to 1.0%, the balance is substantially Cu, and precipitates such as Cr and Cu-Zr and oxides of component composition are from the outermost layer. A copper alloy for lead frames excellent in uniform plating property, characterized by satisfying the following relationship with respect to depth (L) and size (D) of precipitates:
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm.

(4) Sn: 3.5 to 11% by mass, P: 0.03 to 0.35% by mass, S: 0.001% by mass or less, the balance being made of Cu and its inevitable impurities, The lead frame copper alloy having excellent uniform plating properties, characterized in that the oxide of the component composition satisfies the following relationship with respect to the depth (L) from the outermost layer and the size (D) of the precipitates:
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm.

  In addition to the above copper alloys, inclusions and Ag plating can be used as long as they are copper alloys for lead frames containing at least one of Fe, P, Zn, Sn, Ni, Mg, and Al. A relationship similar to the above is observed between the presence or absence of protrusions.

  As described above, by defining the depth from the material surface layer where inclusions exist and the size thereof and controlling them within a certain range, a copper alloy for lead frames capable of uniform and smooth Ag plating can be provided.

The reason for limitation of the present invention will be described below.
(1) Relationship between the position and size of inclusions The present inventors conducted extensive investigations on the presence or absence of protrusions due to Ag plating and the protrusions of the materials used in the lead frame, resulting in the occurrence of protrusions. , There are inclusion particles in the base material of copper alloy, and as a result of organizing the relationship between the depth from the surface of the base material where the particles exist and the size of the particles, there is a strong correlation between them. I found out.

  Also, as a result of considering the relationship between this result and the generation of protrusions due to Ag plating, when particles having a conductivity different from that of the base material exist in the vicinity of the surface of the material, the current distribution of the material is affected, which is the cause. It is considered that the partial electrodeposition abnormality occurs, and the influence on the current distribution depends on the particle size and the position of the particle depending on the depth from the material surface. In addition, regarding the size of inclusions involved in the generation of protrusions in Ag plating, it has also been found that when the size is less than 0.1 μm, the generation of protrusions is not affected.

From the above, regarding the size of inclusions and the depth from the surface on which they exist, the conditions under which Ag plating protrusions do not occur are defined as follows.
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm.

  That is, when the inclusion is less than 0.1 μm, there is no effect on the generation of the protrusion, and when the inclusion is within 5 μm in depth from the material surface, the size of the inclusion is smaller than the existing depth, When the inclusion exists at a depth of 5 to 10 μm from the material surface, the size of the inclusion may be 5 μm or less. In addition, when the inclusion exists in the part exceeding the depth of 10 μm from the material surface, the projection of Ag plating does not occur regardless of the size.

(2) Types of copper alloys for lead frames Any copper alloy for lead frames can establish the relationship between the position and size of inclusions of the present invention, but is particularly effective for the copper alloys described below.
(A) Ni-Si-based chemical composition Ni and Si in the copper alloy, Ni and Si form the precipitated particles of the intermetallic compound mainly fine Ni 2 _Si to each other by performing the aging treatment, the alloy An alloy that significantly increases strength while maintaining high electrical conductivity. The Ni content is 1.0 to 4.8 mass%, and the Si content is 0.2 to 1.4 mass%.

  Mg, Zn, Sn, Fe, Ti, Zr, Cr, Al, P, Mn, Ag, or Be has an effect of improving the strength and heat resistance of the Ni—Si based copper alloy. Among these, Zn has an effect of improving the heat resistance of the solder joint portion, and Fe has an effect of refining the structure. Furthermore, Mg, Ti, Zr, Al, and Mn also have an effect of improving hot rollability. Therefore, the content thereof is set to 0.005 to 2.0 mass%.

(B) Chemical composition of Cr-Zr-based copper alloy Cr and Zr are aging after solution treatment, and Cr and Cu-Zr are precipitated in the Cu matrix, thereby significantly increasing the strength of the alloy. It is a copper alloy that maintains high conductivity. The Cr content is 0.05 to 1.0 mass%, and the Zr content is 0.03 to 0.25 mass%.

  Mg, Zn, Fe, Al, P, Mn, Co, or Ni has the effect of improving strength by being dissolved or precipitated in the copper matrix phase without greatly reducing the electrical conductivity. The total content of these elements is 0.01 to 1.0%.

(C) Chemical composition of Sn-P based copper alloy The Sn-P based copper alloy is a so-called solid solution strengthening other alloy, the Sn content is 3.5 to 11.0 mass%, and the P content is 0. 0.03 to 0.35% by mass. It was determined. In addition, when the S content is 0.001% by mass or less, the number of S-based inclusions generated is small. However, when this content exceeds 0.001% by mass, the S-based inclusions are increased and the plating property is lowered. The S content was 0.001% by mass or less.

(3) Evaluation of inclusions In the present invention, the size of inclusions in the material and the position of the inclusion from the material surface are defined. The presence state of these inclusions can be grasped by chemically polishing the material surface.
As a chemical polishing liquid used for chemical polishing, a general mixture of peroxide and acid is used. The peroxide has an action of liberating oxygen ions to oxidize copper as a base material, while the acid has an action of dissolving the oxide. Therefore, the surface layer of the copper alloy can be removed by coexistence of these. As the peroxide, hydrogen peroxide and persulfates such as ammonium persulfate are used. Moreover, as an acid, a thing with high solubility of copper is desirable, For example, a sulfuric acid, nitric acid, borohydrofluoric acid, etc. are used.

  In the present invention, the depth of inclusions refers to the thickness removed when the inclusions can be observed for the first time by chemical polishing. In addition, the size of the inclusion in the present invention refers to the diameter of the minimum circle including the inclusion when the inclusion is observed with an optical microscope or a scanning electron microscope.

(1) Example 1
Copper alloys having various compositions shown in Table 1 were melted in a high frequency melting furnace and cast into an ingot having a thickness of 20 mm. Next, this ingot was hot-rolled at a temperature described in Table 1 up to a thickness of 8 mm under various temperature conditions, and after chamfering was performed for removing scale on the surface, a 2 mm plate was formed by cold rolling. Then, after performing the solution treatment for 10 minutes at the temperature of 750 degreeC or more and less than 900 degreeC, it cold-rolled to 0.5 mm. Then, an aging treatment is performed at 400 to 600 ° C. for 5 hours, and then a sheet having a thickness of 0.15 mm is formed by cold rolling so as to obtain a higher strength, and finally at 500 to 550 ° C. for 30 seconds to 10 minutes. Strain relief annealing was applied as appropriate.

  The characteristics of each alloy thus obtained were evaluated. As for strength, tensile strength was measured by a tensile test. Electrical conductivity was evaluated by electrical conductivity (% IACS). The inclusions were obtained by chemically polishing the surface of the material, observing a 10 mm × 10 mm surface after polishing with an optical microscope, and measuring the size of the inclusions that became the maximum within the observation range. The plating property is “X” when the surface of the sample is subjected to silver plating with a thickness of 5 μm, and then the surface of the silver plating is observed, and a protrusion having a size of 10 μm or more is observed, and “○” when it is not observed. It was determined.

Invention Example No. 1 to 3, the chemical composition is within the scope of the present patent claim, and by controlling the hot rolling and aging conditions, the size of the inclusion is within the scope of the present patent claim, so that good silver plating properties can be obtained. ing.
On the other hand, Comparative Example No. 4 is the same chemical composition and aging conditions as in Examples 1 and 2, but because the heating temperature before hot rolling and the temperature after hot rolling are low, the coarse crystallized product and precipitation generated during casting Since the object remained without being dissolved in the heating and hot rolling before hot rolling, the inclusion size was outside the scope of the present invention at a depth of 3 μm or more from the surface. Generation of protrusions is observed.

Comparative Example No. In No. 5, the same chemical composition as in Example 1 and hot rolling conditions were used, but the temperature of the aging treatment was high, the time was longer, and the conditions were overaging, so the precipitates were coarsened. Further, since the size of inclusions deviates from the scope of the present invention at a depth of 1 μm or more from the surface, the generation of protrusions of 10 μm or more is observed in silver plating.
Comparative Example No. 6 is the same hot rolling and aging conditions as in Example 1, but the amount of Si component exceeds the scope of the present claim, and the coarse crystallization and precipitates in the casting process or in the aging process Due to the coarsening of the precipitate, the size of inclusions is outside the scope of the present invention at 1 μm or more from the surface, and protrusions of 10 μm or more are observed in silver plating.
(2) Example 2

  Copper alloys having various compositions shown in Table 2 were melted in a vacuum in a high-frequency melting furnace and cast into an ingot having a thickness of 30 mm. Next, the ingot is subjected to homogenization annealing at 900 ° C. or more for 300 minutes or more, then hot-rolled, and the solution is heated at a cooling rate of 0.5 to 10 ° C./second until the material temperature becomes 650 ° C. after the hot rolling. The sheet was processed in the steps of cold rolling, aging treatment, cold rolling, and strain relief annealing to obtain a plate having a thickness of 0.15 mm. Inclusions were controlled by hot rolling and aging conditions.

  The characteristics of each alloy thus obtained were evaluated. As for strength, tensile strength was measured by a tensile test. Electrical conductivity was evaluated by electrical conductivity (% IACS). The inclusions were obtained by chemically polishing the surface of the material, observing a 10 mm × 10 mm surface after polishing with an optical microscope, and measuring the size of the inclusions that became the maximum within the observation range. The plating property is “X” when the surface of the sample is subjected to silver plating with a thickness of 5 μm, and then the surface of the silver plating is observed, and a protrusion having a size of 10 μm or more is observed, and “○” when it is not observed. It was determined.

  Invention Example No. 7-10, the chemical composition is within the scope of the present claims, and by controlling the hot rolling conditions, the solution treatment conditions and the aging conditions, the size of the inclusions is within the scope of the present claims. Silver plating property is obtained.

  On the other hand, Comparative Example No. 11, Invention Example No. 8 has the same chemical composition, solution treatment conditions, and hot rolling conditions, but the temperature of the aging treatment is high, the time is longer, and the conditions are overaging, so the precipitates are coarsened. Since the size of the inclusion is outside the scope of the present invention at a depth of 1 μm from the surface, the generation of protrusions of 10 μm or more is observed in silver plating.

  Comparative Example No. 12, Invention Example No. 8 has the same chemical composition, hot rolling and aging conditions, but the cooling rate in the solution treatment is slow and the solution treatment is not sufficient, so that precipitated particles remain and the depth of inclusions is 1 μm from the surface layer. Is out of the scope of the present patent claims, the generation of protrusions of 10 μm or more is observed in silver plating.

  Comparative Example No. In Invention No. 13, Invention Example No. 9 is the same hot rolling, solution treatment conditions and aging conditions as in No. 9, but the Cr content exceeds the scope of the present claim, and the coarse crystallization and precipitates in the casting process or in the aging process Due to the coarsening of the precipitate, the size of inclusions is outside the scope of the present invention at 1 μm or more from the surface, and protrusions of 10 μm or more are observed in silver plating.

  Comparative Example No. 14, Invention Example No. 10 has the same chemical composition, solution treatment conditions, and hot rolling conditions, but the temperature of the aging conditions is high, the precipitate is re-dissolved, the strength is low, and the conductivity is greatly reduced. Since the precipitate is dissolved, the inclusions are small and the silver plating property is not a problem. However, since the strength is low and the conductivity is low, it cannot be used as a lead frame material.

  Copper alloys having various component compositions were melted in the atmosphere and partly desulfurized and melted to cast ingots having a thickness of 30 mm. Then, it processed in the process of homogenization annealing, cold rolling, recrystallization annealing, cold rolling, and strain relief annealing, and was set as the board of thickness 0.15mm. Table 3 shows the analysis results of various component compositions and the results of measuring the size of the inclusions that were maximized within the observation range by chemically polishing the material surface.

  With respect to each alloy thus obtained, the plating property was evaluated. In the evaluation method, the surface of the material was chemically polished, and the surface 10 mm × 10 mm after polishing was observed with an optical microscope, and the size of the inclusion that became the maximum within the observation range was measured. The plating property is “X” when the surface of the sample is subjected to silver plating with a thickness of 5 μm, and then the surface of the silver plating is observed, and a protrusion having a size of 10 μm or more is observed, and “○” when it is not observed. It was determined.

Invention Example No. In Nos. 15 to 17, since the chemical composition is within the scope of the present claims and the S concentration is controlled, the size of the inclusions is within the scope of the present claims, and therefore, good silver plating properties are obtained.
On the other hand, Comparative Example No. In 18-20, since the S content exceeds the scope of this patent claim, the inclusion becomes coarser as the number of inclusions increases, and the size of the inclusion is 1 μm from the surface. Since it comes off, generation | occurrence | production of 10 micrometers or more protrusion is seen by silver plating.

Claims (4)

Lead with excellent uniform plating characteristics, characterized by satisfying the following relationship with respect to the size of inclusions (hereinafter referred to as “D”) existing in the depth from the outermost layer (hereinafter referred to as “L”) Copper alloy for frame,
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm. Ni: 1.0 to 4.8% by mass, Si: 0.2 to 1.4% by mass as basic components, and further Mg, Zn, Sn, Fe, Ti, Zr, Cr, Al, P, Mn 1 or more selected from the group of Ag and Be in a total amount of 0.005 to 2% by mass, with the balance being substantially Cu, precipitates such as Ni ₂ Si, Cu—S, Mg—S, The lead frame copper alloy having excellent uniform plating properties, characterized in that the oxide of the component composition satisfies the following relationship with respect to the depth (L) from the outermost layer and the size (D) of the precipitates:
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm. Cr: 0.05 to 1.0% by mass, Zr: 0.03 to 0.25% by mass as basic components, and further selected from the group of Mg, Zn, Fe, Al, P, Mn, Co and Ni The total amount of one or more of the above is 0.01 to 1.0%, the balance is substantially Cu, and precipitates such as Cr and Cu-Zr and oxides of component compositions are deep from the outermost layer ( L) and the size of the precipitate (D) satisfying the following relationship, the copper alloy for lead frames excellent in uniform plating properties,
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm. Sn: 3.5 to 11% by mass, P: 0.03 to 0.35% by mass, S: 0.001% by mass or less, the balance being made of Cu and its inevitable impurities, A copper alloy for lead frames with excellent uniform plating properties, characterized in that the oxide satisfies the following relationship with respect to the depth (L) from the outermost layer and the size (D) of the precipitates:
When 0.1 ≦ L, D ≦ 0.1 μm
When 0.1 <L ≦ 5 μm, D <L
When 5 μm <L ≦ 10 μm, D ≦ 5 μm.