JP2001244400A - Lead frame and copper alloy for lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the problems of a package and crack by improving oxide adhesion of copper alloy which is used for a lead frame of a resin sealed semiconductor package. SOLUTION: The copper alloy has a 100} peak intensity ratio less than 0.04 against 111} peak intensity of the copper alloy crystal which consists of top layer. The top layer is of base metal of the copper alloy lead frame that is evaluated by XRD thin film law.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper alloy lead frame for a so-called resin-sealed semiconductor package and a copper alloy having a novel surface layer structure.

[0002]

BACKGROUND OF THE INVENTION Plastic packages for semiconductor devices have become the mainstream packages in which a semiconductor chip is sealed with a thermosetting resin because of their excellent economy and mass productivity. For the structure of the plastic package, DIP, which was previously a lead mounting device
(Dual inline package) was the mainstream. At present, SOP (Small Outline Package), QF
P (quad flat package) and the like gradually become mainstream, and QFPs, which can cope with an increase in input / output signals in particular, are frequently used. Furthermore, with the recent demand for miniaturization of electronic components, thin type such as 1 mm thick TSOP (Thin Small Outline Package) and TQFP (Think Quad Flat Package) and 0.5 mm thick USOP (Ultra Small Outline Package) Packages have also appeared.

In assembling these packages,
After bonding the semiconductor chip to the lead frame by using an Ag paste or the like, or by soldering or Ag brazing through a plating layer of Au, Ag, and the like, and then performing resin sealing and resin sealing In general, the outer leads are generally covered by electroplating.
The purpose of the exterior plating is to improve the corrosion resistance of the leads and to facilitate the mounting of the substrate in a later mounting step. As a pretreatment for performing exterior electroplating, chemical polishing is performed. The purpose of this is to remove the oxide layer generated by heating the outer leads when the sealing resin is cured in the previous step, and the thickness to be removed by chemical polishing is about several μm. As a material for exterior plating,
Solder with good solder wettability is used. The solder has the lowest melting point of 183 ° C. and good wettability in the eutectic composition around 63% by mass Sn-37% by mass Pb, but solder scraps are generated when the outer leads are squeezed in the subsequent trimming process. It is necessary to increase the hardness so as not to cause the problem, and the Sn concentration is generally set to 80 to 90 wt%.

[0004] The biggest problem concerning the reliability of these packages is the problem of package cracking and peeling occurring during surface mounting. The mechanism of the package separation is caused by thermal stress at the time of heat treatment when the adhesiveness between the resin and the die pad (the portion on which the semiconductor chip of the lead frame is mounted) is low after the semiconductor package is assembled. The mechanism of occurrence of package cracks is as follows. After assembling the semiconductor package, since the mold resin absorbs moisture from the atmosphere, moisture evaporates during heating in surface mounting later, and if there is a crack inside the package, water vapor is applied to the peeled surface to act as an internal pressure. The package may swell due to the internal pressure, or the resin may not withstand the internal pressure and crack.
If cracks occur in the package after surface mounting, moisture and impurities penetrate and corrode the chip, impairing the function as a semiconductor. In addition, when the package swells, the appearance becomes poor and the commercial value is lost. Such problems of package cracking and peeling have become remarkable in recent years as packages have become thinner.

[0005] The problem of package cracking and peeling is caused by poor adhesion between the resin and the die pad. The most significant effect on the adhesion between the resin and the die pad is that various types of lead frame base materials are used. Is a oxide film formed to a thickness of several tens to several hundreds nm on the surface of the base material before plating with Ag or the like. Therefore, since the copper alloy and the resin are in contact with each other via the oxide film on the die pad surface, the oxide film has a significant effect on the adhesiveness between the resin and the lead frame base material.

By the way, as a material for a lead frame,
Fe-Ni alloys represented by a 42% Ni-Fe alloy and copper alloys are used. The 42% Ni-Fe alloy has been conventionally used as a material for ceramic packages because of its thermal expansion coefficient being close to that of ceramics, and has also been used as a highly reliable lead frame material in plastic packages. However, Fe-Ni-based alloys have a drawback that their electrical conductivity is lower than that of Cu alloys, and are disadvantageous in responding to recent demands on packages for high heat dissipation and high-speed signal transmission. In this regard, a copper alloy having high conductivity is advantageous in heat dissipation and high-speed signal transmission, and a higher-performance package can be designed.

Regarding the crystal orientation of copper alloy rolling, (11)
0) It has long been known that [112] is the main rolling direction, and it is known from (Progress in Metal Physics, 1. By B
ruceChalmers, 1949, p. 297). In recent years, more precise measurements have been expressed (H. Huand S. Goo
dman: Trans. AIME, 227 (1963), (62
7). In these measurements, X-rays were obtained by penetrating from the surface to several tens of μm, and almost the average properties of the bulk were captured. However, the crystal orientation of the surface layer of about 1 μm on the surface was studied. There has been no study on the relationship with the oxide film adhesion and the crystal orientation of the surface layer.

[0008]

However, the copper alloy is inferior to the Fe-Ni alloy in the adhesiveness of the oxide film as described above, so that the copper alloy is apt to peel off between the resin and the die pad, causing problems such as package cracking and peeling. It was easy. Therefore, development of a copper alloy having high adhesion to an oxide film for manufacturing a highly reliable package has been required.

[0009] In addition to the above, the following performance is required for the lead frame material. First, in order to reduce the thickness of the package, it is necessary to reduce the thickness of the lead frame material.
A thin material such as 25 mm is mainly used. Such thinning and narrowing of the lead frame lowers the rigidity of the entire frame and the leads, and causes deformation of the inner leads during the assembly process and deformation of the outer leads during device mounting. To prevent such troubles, higher strength is required for the lead frame material used. Further, a variety of characteristics are required, such as having excellent etching properties and press workability required for forming a lead frame pattern, and high reliability of a solder joint after mounting.

SUMMARY OF THE INVENTION The present invention provides a copper alloy lead frame having improved oxide film adhesion and improved heat dissipation and operation speed of a package, and a novel extreme surface layer structure in order to address the problem of package cracking and peeling. It is intended to provide a copper alloy having the same.

[0011]

Means for Solving the Problems The inventors of the present invention have made intensive studies on the relationship between the adhesion of an oxide film of a copper alloy which is not subjected to an oxide film removal treatment such as polishing and the crystal orientation of the extreme surface of a base material. As a result, it has been surprisingly found that it is possible to improve the oxide film adhesion by controlling the crystal orientation of the copper alloy extreme surface layer. The specific method is described below.

[0012] The copper alloy lead frame of the present invention is preferably made of XRD.
In the crystal orientation of the extreme surface evaluated by the thin film method of
The oxide film adhesion is improved by setting the ratio of the {100} peak intensity to the {111} peak intensity to 0.04 or less. The lead frame may be any lead frame that is resin-sealed, but is particularly preferably a lead frame in which the surface to be bonded to the semiconductor chip is plated with a noble metal or nickel before resin sealing.

The copper alloy may be any copper alloy for a lead frame. In particular, the crystal orientation characteristic of the present invention is realized by a copper alloy of various components such as a particle dispersion type and a precipitation hardening type. Is done. However, particularly preferred copper alloys are: Cr: 0.04-0.4%, Z:
r: 0.03% to 0.25%, and Zn: 0.06 to
Copper alloy containing 2.0%, the balance being Cu and unavoidable impurities (hereinafter the same applies to the remainder), Cr:
0.04 to 0.4%, Zr: 0.03% to 0.25%,
And Zn: 0.06 to 2.0%.
one or more selected from the group consisting of i, Sn, In, Mn, P, Mg and Si in a total amount of 0.01 to
Copper alloy containing 1.0%, Cr: 0.04 to 0.4
%, Zr: 0.03% to 0.25%, Zn: 0.06 to
2.0%, Fe: 0.1 to 1.8%, and Ti: 0.
Copper alloy containing 1 to 0.8% and Cr: 0.0
4 to 0.4%, Zr: 0.03% to 0.25%, Zn:
0.06 to 2.0%, Fe: 0.1 to 1.8%, Ti:
0.1-0.8%, and Ni, Sn, I
A copper alloy containing one or more selected from the group consisting of n, Mn, P, Mg and Si in a total amount of 0.01 to 1.0% is preferred.

Incidentally, the crystal orientation of the extreme surface layer of the lead frame by XRD (X-ray diffraction) means that the crystal orientation is, for example, an X-ray diffractometer RINT2000 manufactured by Rigaku Corporation.
o Using a bulb, the 2θ scanning plane is perpendicular to the sample, and the rolling direction (R
D), and the incident angle (α) of the X-rays is made to be incident at an angle of 5 ° to the sample surface (FIG. 1). The integrated intensity of the peak of the diffraction line from the {200} plane is obtained, and these ratios are calculated and evaluated. In a normal X-ray diffraction measurement method, as shown in FIG. 2, a relationship is maintained in which the incident angle and the reflection angle of the X-ray are equal to the sample surface. For this reason,
In an actual device, when the tube as an X-ray source is fixed and the sample surface is at an angle of θ to the incident line, the sample surface and the counter tube rotate so that the counter tube is at 2θ to the incident line. I do.
At this time, in the usual method, the measurement target surface is always a surface parallel to the sample surface. In the case of the thin-film method, the angle of incidence is fixed, so that it is denoted by α to distinguish it from θ.
Since θ is the same as the ordinary method in terms of the position of the counter tube with respect to the incident line, the same indication is given. However, in this case, the difference from the normal method is that the surface to be measured is not the sample surface but changes with 2θ as shown in FIG. Since the extreme surface layer is strongly affected by the friction from the rolling roll, it has a different crystal orientation from that of the inside. Therefore, to evaluate the crystal orientation of the extreme surface layer, X-ray diffraction by the above-mentioned thin film method is necessary.

In addition, it has been found that the above-mentioned crystal orientation can be obtained by controlling the rolling conditions of the final cold rolling generally performed in a 20-80% processing step. That is,
It has been found that the {100} peak strength decreases when the oil film thickness of the rolling oil introduced between the roll and the material increases. As rolling conditions for this, the roll diameter of the last pass of the cold rolling is 100 mm or more, and the rolling speed is 200
When the rolling oil viscosity was 5 cSt or more, that is, 0.05 cm ² / s or more, the ratio of {100} peak intensity to {111} peak intensity was 0.04 or less when the viscosity of the rolling oil was not less than m / min. As described above, mainly the use as a lead frame of a semiconductor package has been described, but the alloy of the present invention can also be used in other uses in which a surface protection film is directly applied without using a process such as polishing of a base material.
Hereinafter, preferred copper alloy compositions of the present invention will be described. Here, the percentage is% by mass.

[0016] Cr is subjected to aging treatment after solution treatment of the alloy to precipitate in the base material to improve the strength. If the content is less than 0.04%, the desired effect due to this effect is obtained. No effect is obtained, while if it exceeds 0.4%, coarse Cr remains in the base material after commercialization.
As a result, the etching properties deteriorate. For the above reasons, the Cr content is preferably 0.04 to 0.4%.

Zr has a function of forming a compound with Cu by aging treatment and precipitating in the base material to strengthen it.
If the content is less than 0.03%, the desired effect cannot be obtained by the above operation. On the other hand, if Zr is contained in excess of 0.25%, coarse undissolved Zr will remain in the base material after the solution treatment, resulting in a decrease in etching properties. Therefore, the Zr content is 0.03-0.2.
5% is preferred.

Zn is a component to be added because it has an effect of improving the heat-peeling resistance of the solder and the adhesion of the oxide film. No effect can be obtained. On the other hand, if Zn is added in excess of 2.0%, the electrical conductivity will be reduced. Therefore, the Zn content is preferably 0.06 to 2.0%.

Ti and Fe are added as necessary to form an intermetallic compound of Ti and Fe in the base material when the alloy is aged, and to exert an effect of further improving the alloy strength as a result. However, if the content of each of them is less than 0.01%, the desired strength cannot be obtained by the above action. On the other hand, if the Ti content exceeds 0.8% or Fe
If the content exceeds 1.80%, coarse inclusions containing Ti and Fe as main components remain, which significantly impairs the etching property. Therefore, the Ti content is 0.01 to 0.1.
8% and the Fe content are preferably 0.01 to 0.18%.

Ni, Sn, In, Mn, P, Mg and Si act as follows. All of these components have the effect of improving the strength mainly by solid solution strengthening without significantly lowering the conductivity of the alloy. Therefore, one or more of these components are added as necessary. If the total content is less than 0.01%, the desired effect cannot be obtained by the above-mentioned action, while if the total content exceeds 1.0%, the conductivity of the alloy is significantly reduced. For this reason,
Ni, S added alone or in combination of two or more
The total content of n, In, Mn, P, Mg and Si is preferably 0.01 to 1.0%.

[0021]

EXAMPLES Next, the effects of the present invention will be specifically described with reference to examples showing preferred composition ranges. First, electrolytic copper (C
u) or oxygen-free copper (Cu) as the main raw material, copper chromium mother alloy, copper zirconium mother alloy, zinc, titanium, mild steel,
Nickel, tin, indium, manganese, magnesium, silicon, and copper phosphorus mother alloys were used as auxiliary raw materials, and copper alloys of various component compositions shown in Tables 1 and 3 were melted in a high-frequency melting furnace in a vacuum or in an Ar atmosphere. It was cast into an ingot having a thickness of 30 mm. Next, each of these ingots was subjected to hot working and solution treatment, first cold rolling, aging treatment, Table 1,
The final cold rolling (deformation ratio: 50%) under the conditions shown in No. 3 was performed in the order of annealing and strain relief annealing to obtain a plate having a thickness of 0.15 mm.

The evaluation method will be described below. First, the crystal orientation of each of the prepared plate materials was evaluated by the above-described method using an X-ray diffractometer. Next, the oxide film adhesion was evaluated by a tape peeling test. A test piece of 20 × 50 mm was cut out from each plate material, heated at a predetermined temperature in the atmosphere for 5 minutes, then a commercially available tape (trade name: 3M # 851) was attached to the surface of the test piece on which the oxide film was formed, and peeled off. At this time, when the heating temperature was changed in steps of 20 ° C., the lowest temperature at which the oxide film was peeled off was determined and defined as the oxide film peeling temperature. Also,
The strength was determined by measuring the tensile strength in a tensile test, and the conductivity was determined by determining the conductivity.

Tables 3 and 4 show the evaluation results. In this example, good oxide film adhesion was obtained. On the other hand, in each of the comparative examples, the {100} orientation of the extreme surface layer was out of the proper range due to inappropriate rolling conditions, and the adhesion of the oxide film was poor.

[0024]

As described above, the copper alloy of the present invention dramatically improves the heat dissipation and high-speed operation of the semiconductor package as compared with the 42 alloy, and further enhances the adhesion of the oxide film by improving the adhesion of the oxide film. A decrease in reliability can also be suppressed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an evaluation method of an extreme surface layer.

FIG. 2 is an explanatory diagram of an X-ray diffraction method by a normal method.

FIG. 3 is an explanatory diagram of an X-ray diffraction method using a thin film method.

FIG. 4 shows alloy compositions of Examples 1 to 4 and Comparative Examples 1 to 4,
A chart showing the final rolling conditions and the crystal orientation of the extreme surface layer (Table
1).

FIG. 5 is a table (Table 2) showing the tensile strength, conductivity and oxide film adhesion of Table 1.

FIG. 6 is a table (Table 3) showing alloy compositions, final rolling conditions, and crystal orientation of an extreme surface layer of Examples 5 to 17 and Comparative Examples 5 to 7.

FIG. 7 is a table (Table 4) showing the tensile strength, conductivity and oxide film adhesion of Table 3.

[Procedure amendment]

[Submission Date] March 3, 2000 (200.3.3)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2 ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 30, 2000 (2005.3
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005] Here, the problem of package cracking and peeling is caused by poor adhesion between the resin and the die pad. The most significant effect on the adhesion between the resin and the die pad is that the lead frame base material is formed of a package. The oxide film is formed on the surface of the base material to a thickness of several tens to several hundreds of nm before plating with Ag or the like because it has undergone a heating step such as die bonding or wire bonding during the seed assembling step. Therefore, since the copper alloy and the resin are in contact with each other via the oxide film on the die pad surface, the oxide film has a significant effect on the adhesiveness between the resin and the lead frame base material.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

Regarding the crystal orientation of copper alloy rolling, (11)
0) It has long been known that [112] is the main rolling direction, and it is known from (Progress in Metal Physics, 1. By B
ruceChalmers, 1949, p. 297). With more precise measurements in recent years, (H. Huand S. Goodman: Tran
s. AIME, 227 (1963), 627). In these measurements, X-rays were obtained by penetrating from the surface to several tens of μm, and almost the average properties of the bulk were captured. However, the crystal orientation of the surface layer of about 1 μm on the surface was studied. There has been no study on the relationship with the oxide film adhesion and the crystal orientation of the surface layer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C22C 9/10 C22C 9/10 H01L 23/48 H01L 23/48 V

Claims (12)

[Claims] 1. A copper alloy lead frame base material having an XR
A copper alloy lead having a {100} peak intensity ratio to a {111} peak intensity of the copper alloy crystal constituting the extreme surface layer, which is 0.04 or less, which is evaluated and evaluated by a D thin film method. flame. 2. A copper alloy lead frame including a resin-sealed portion and a metal-plated outer lead portion, wherein a base material surface layer of the resin-sealed portion has a peak intensity ratio of 0.04 or less. Item 6. A copper alloy lead frame according to Item 1. 3. The method according to claim 1, wherein the copper alloy contains Cr:
3. The method according to claim 1, comprising 0.04 to 0.4%, Zr: 0.03 to 0.25%, and Zn: 0.06 to 2.0%, the balance being Cu and unavoidable impurities. Copper alloy lead frame. 4. The method according to claim 1, wherein the copper alloy contains Cr:
0.04 to 0.4%, Zr: 0.03 to 0.25%, and Zn: 0.06 to 2.0%.
one or more selected from the group consisting of i, Sn, In, Mn, P, Mg and Si in a total amount of 0.01 to
3. The copper alloy lead frame according to claim 1, which contains 1.0% and the balance consists of Cu and unavoidable impurities. 5. The method according to claim 1, wherein the copper alloy contains Cr:
0.04 to 0.4%, Zr: 0.03 to 0.25%, Z
The composition according to claim 1, wherein n: 0.06 to 2.0%, Fe: 0.1 to 1.8%, and Ti: 0.1 to 0.8%, with the balance being Cu and unavoidable impurities. 2. The copper alloy lead frame according to 2. 6. The copper alloy according to claim 1, wherein the mass ratio of Cr:
0.04 to 0.4%, Zr: 0.03 to 0.25%, Z
n: 0.06 to 2.0%, Fe: 0.1 to 1.8%, T
i: contains 0.1 to 0.8%, and further contains Ni, Sn,
The method according to claim 1, wherein one or more selected from the group consisting of In, Mn, P, Mg and Si contains 0.01 to 1.0% in total, and the balance consists of Cu and unavoidable impurities. 2. The copper alloy lead frame according to 2. 7. Cr: 0.04 to 0.4 in mass ratio.
%, Zr: 0.03 to 0.25%, and Zn: 0.0
6 to 2.0%, with the balance being Cu and unavoidable impurities, and {100} with respect to the {111} peak intensity of the copper alloy crystal constituting the surface layer of the rolled surface, evaluated and evaluated by the XRD thin film method.銅 A copper alloy having a peak intensity ratio of 0.04 or less. 8. Cr: 0.04 to 0.4 by mass ratio.
%, Zr: 0.03 to 0.25%, and Zn: 0.0
6 to 2.0%, and further contains Ni, Sn, In, M
one or more selected from the group consisting of n, P, Mg and Si, in a total amount of 0.01 to 1.0%,
The balance consists of Cu and unavoidable impurities, and the ratio of the {100} peak intensity to the {111} peak intensity of the copper alloy crystal constituting the pole surface of the rolled surface determined by the XRD thin film method is 0.04 or less. A copper alloy, characterized in that: 9. Cr: 0.04 to 0.4 by mass ratio.
%, Zr: 0.03 to 0.25%, Zn: 0.06 to
2.0%, Fe: 0.1 to 1.8%, and Ti: 0.
{100} with respect to the {111} peak intensity of the copper alloy crystal constituting the surface layer of the rolled surface determined by the XRD thin film method, containing 1 to 0.8% with the balance being Cu and inevitable impurities. A copper alloy having a peak intensity ratio of 0.04 or less. 10. Cr: 0.04 to 0.1 in mass ratio.
4%, Zr: 0.03 to 0.25%, Zn: 0.06 to
2.0%, Fe: 0.1 to 1.8%, Ti: 0.1 to
0.8%, Ni, Sn, In, Mn,
One or more selected from the group consisting of P, Mg and Si contains 0.01 to 1.0% in total, and the balance consists of Cu and unavoidable impurities, and was evaluated by the XRD thin film method. A copper alloy having a {100} peak intensity ratio to a {111} peak intensity of 0.04 or less, which is determined by the above method. 11. The method according to claim 5, wherein the copper alloy is used for a lead frame.
Copper alloy described in the item. 12. The final cold rolling under the condition that the roll diameter of the final pass is 100 mm or more, the rolling speed is 200 m / min or more, and the viscosity of the rolling oil is 0.05 cm ² / s or more. 12. The copper alloy according to any one of 7 to 11.