KR20010085422A - Lead frame and copper alloy to be used for lead frame - Google Patents

Abstract

PURPOSE: 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. CONSTITUTION: 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

LEAD FRAME AND COPPER ALLOY TO BE USED FOR LEAD FRAME}

The present invention relates to a copper alloy lead frame of a so-called resin sealed semiconductor package and a copper alloy having a novel surface layer structure.

The plastic package of a semiconductor device is mainstream because the package which seals a semiconductor chip with a thermosetting resin is excellent in economy and mass productivity. As the structure of a plastic package, DIP (Dual In-line Package) which was a lead-mounting mounting device was mainstream previously. At present, due to the demand for improvement in package density, surface mount devices such as small out-line package (SOP), quad flat package (QFP), etc. are becoming more and more mainstream. have. In addition, according to the recent demand for miniaturization of electronic components, a thin type of thin small out-line package (TSOP), thin quad flat package (TQFP), and ultra small outline in-line package (USOP) having a thickness of 0.5 mm Packages are also emerging.

In assembling these packages, the semiconductor chip is heat-compressed to the lead frame using Ag paste or the like, or the semiconductor chip is soldered or Ag soldered to the lead frame through a plating layer such as Au or Ag, and then the resin sealing is performed. After carrying out the resin sealing, the exterior lead is generally covered with an electroplating. The purpose of the exterior plating is to improve the corrosion resistance of the lead and to facilitate substrate mounting in a later mounting process. As a pretreatment for performing external electroplating, chemical polishing is performed. The purpose is to remove the oxide layer generated when the outer lead is heated when the sealing resin is cured in the previous step, and the thickness removed by chemical polishing is about several 탆. As the exterior plating material, a solder having good wettability is used. Solder has the lowest melting point as low as 183 ℃ in the process composition near 63 mass% Sn-37 mass% Pb, but also improves the wettability. It is necessary to raise hardness so that it will not generate | occur | produce, and it is common to make Sn concentration into 80 to 90 wt%.

The biggest problem regarding the reliability of these packages is a problem of package cracking or peeling occurring during surface mounting. The peeling mechanism of the package is caused by thermal stress during subsequent heat treatment when the adhesiveness between the resin and the die pad (the portion where the semiconductor chip is raised on the lead frame) is low after the semiconductor package is assembled. The mechanism of generating a package crack is as follows. After assembling the semiconductor package, the mold resin is more hygroscopic than the atmosphere, so that moisture is vaporized by heating at a later surface mount, and if there is a crack in the package, water vapor is applied to the peeling surface and the internal pressure is reduced. Acts as. This internal pressure may cause expansion of the package, or the resin may not crack the internal pressure. If a crack occurs in the package after surface mounting, moisture or impurities enter the corrosion and damage the chip, thereby impairing its function as a semiconductor. In addition, as the package is expanded, the appearance is poor and the product value is lowered. The problem of such a package crack and peeling becomes remarkable in recent years with the progress of the thin shape of a package.

Here, the problem of package cracking or peeling is due to poor adhesion between the resin and the die pad, but the biggest influence on the adhesion between the resin and the die pad is that the lead frame base material is die-bonded during the package assembly process. It is an oxide film formed on the surface of the base material in the thickness of tens to hundreds of nm before sealing the resin because it undergoes various heating processes such as -bonding) and wire bonding. Since the die pad surface is in contact with the lead frame base material and the resin through this oxide film, the adhesion between the oxide film and the lead frame base material has a significant effect on the adhesion between the resin and the lead frame base material.

However, as a raw material for lead frames, Fe-Ni-based alloys representing a 42% Ni-Fe alloy and copper alloys are used. 42% Ni-Fe alloy has been used as a material for ceramic packages because of its approximate coefficient of thermal expansion and has been used as a high reliability lead frame material in plastic packages. However, Fe-Ni-based alloys have disadvantages of lower electrical conductivity than Cu alloys, and are disadvantageous in response to the high heat dissipation and high speed signal transmission required in recent years. In this respect, copper alloy having high conductivity is advantageous in heat dissipation and high speed signal transmission, and it is possible to design a higher performance package.

However, since copper alloys are inferior to Fe-Ni alloys in the above-mentioned oxide film adhesiveness, peeling easily occurs between the resin and the die pad, and problems such as package cracking and peeling are likely to occur. Therefore, it is necessary to develop a copper alloy having high oxide film adhesion for producing a highly reliable package.

In addition to the above, the following performance is required for the lead frame material. First, from the request for thinner packages, it is necessary to thin the lead frame material, and as a result, thin materials of 0.15 mm and 0.125 mm have become mainstream in recent years. Such thinning and narrowing of the lead frame lowers the rigidity of the entire frame and the lead and causes deformation of the inner lead in the assembling process and deformation of the outer lead during device mounting. In order to prevent such a problem, higher strength is required for the leadframe material to be used. In addition, various characteristics such as excellent etching property and press formability necessary for pattern formation of the lead frame and high reliability of the solder joint after mounting are required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a copper alloy lead frame having improved oxide film adhesion and improved package heat dissipation and operating speed in order to cope with problems of package cracking and peeling, and a copper alloy having a novel polar surface structure. I am doing it.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the evaluation method of a polar surface layer.

2 is an explanatory diagram of an X-ray diffraction method according to a conventional method.

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

The inventors of the present invention have conducted a intensive study on the relationship between the oxide film adhesion of the copper alloy and the crystal orientation of the polar surface of the base material, which are not particularly subjected to the oxide film removal treatment by polishing or the like. It was discovered that the oxide film adhesiveness can be improved by doing so. The specific method is described below.

In the copper alloy lead frame of the present invention, in the crystal orientation of the polar surface evaluated by the X-ray diffraction (XRD) thin film method, the ratio of the {100} peak intensity to the {111} peak intensity is set to 0.04 or less, so that the oxide film adhesion Characterized in that improved. The lead frame may be any lead frame sealed by resin, but in particular, a lead frame in which precious metal, nickel, or the like is plated on an adhesive surface with a semiconductor chip before resin sealing is preferable.

The copper alloy may be any copper alloy for a lead frame, and the crystal orientation particularly characterized by the present invention is realized by copper alloys of various component systems such as particle dispersion type and precipitation hardening type. However, particularly preferable copper alloys contain Cr: 0.04 to 0.4%, Zr: 0.03 to 0.25%, and Zn: 0.06 to 2.0% by mass ratio, and the balance consists of Cu and unavoidable impurities (hereinafter, The same) for the copper alloy, Cr: 0.04 to 0.4%, Zr: 0.03 to 0.25%, and Zn: 0.06 to 2.0%, and further in the group consisting of Ni, Sn, In, Mn, P, Mg and Si Copper alloy containing 0.01 to 1.0% in total of one kind or two or more kinds selected, 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 Copper alloy containing: 0.1 to 0.8%, Cr: 0.04 to 0.4%, Zr: 0.03 to 0.25%, Zn: 0.06 to 2.0%, Fe: 0.1 to 1.8%, Ti: 0.1 to 0.8%, Furthermore, the copper alloy which contains 0.01-1.0% in total of 1 type, or 2 or more types chosen from the group which consists of Ni, Sn, In, Mn, P, Mg, and Si is preferable.

In addition, the crystal orientation of the polar surface layer of the lead frame measured by XRD (X-ray diffraction) means, for example, the Co tube (RINT2000) manufactured by Rikakudenki Co., Ltd. Using a tube, the scanning surface 2θ is perpendicular to the sample and includes the rolling direction RD, and the incident angle α of the X-rays is incident at an angle of 5 ° with respect to the sample surface. 1, the integral intensity of the {111} plane and the intensity of the peak of the diffraction line peak from the {200} plane are respectively determined by scanning (2θ), and these ratios are calculated and evaluated.

In the conventional X-ray diffraction measurement method, as shown in Fig. 2, the relationship in which the incidence angle and the opposite angle of the X-ray with respect to the sample surface are equal is maintained. Therefore, in an actual apparatus, the tube which is the X-ray generating source is fixed, and when the sample surface is at an angle of θ with respect to the angle of incidence, the sample surface is such that the counter tube is 2 θ with respect to the incident line. And the counter tube rotates. At this time, in a conventional method, the measurement target surface is always a plane parallel to the sample surface. In the case of the thin film method, the angle of incidence is fixed, so that the display with α is used to distinguish from θ, and for 2θ, In the sense of the position of the counter tube with respect to the line, since it is the same as a normal method, it displays similarly. In this case, however, the difference from the conventional method is that, as shown in FIG. 3, the measurement target surface becomes a plane at which the angle of incidence is opposite to the angle of incidence, and thus changes with 2θ rather than a plane parallel to the sample plane. .

In the pole surface layer, since it receives the friction from the rolling rolls strongly, it has a crystal orientation different from that inside. Therefore, in order to evaluate the crystal orientation of the pole surface layer, the X-ray diffraction by the above-described thin film method is necessary.

Regarding the crystal orientation of copper alloy rolling, it has long been known that (110) [112] is the main rolling orientation (Progress in Metal Physics, I. By Bruce Chalmers, 1949, p. 297).

In recent years the more precise measurement,

(H.Hu and S. Goodman: Trans, AIME, 227 (1963), (627). In these measurements, the X-rays were obtained by invading tens of micrometers from the surface, which is roughly equivalent to the bulk). Although the average properties of the film were captured, there has been no knowledge about the crystal orientation of the surface layer of the polar surface layer having a surface thickness of about 1 μm, the study of the relationship between the orientation and the oxide film adhesion, and the crystal orientation of the surface layer.

Moreover, in order to obtain the crystal orientation mentioned above, it turned out that what is necessary is just to control the rolling conditions of the final cold rolling which are generally performed by 20 to 80% of a process process. In other words, it has been found that the {100} peak strength is lowered when the thickness of the oil film of the rolling oil introduced between the roll and the material becomes thick. As a rolling condition for this, if the roll diameter of the final pass of cold rolling is 100 mm or more, the rolling speed is 200 m / min or more, and the viscosity of rolling oil is 5 cSt or more, ie, 0.05 cm <2> / s or more, {{}} It was found that the ratio of the peak intensity was less than 0.04.

As mentioned above, although the use mainly as a lead frame of a semiconductor package was demonstrated, the alloy of this invention can also be used for the other application which apply | coats a surface protection film directly, omitting the process of a base material grinding etc.

Hereinafter, the preferable copper alloy composition of this invention is demonstrated. The percentage here is mass%.

Cr is precipitated in the base metal to improve the strength by performing aging treatment after solution treatment of the alloy. If the content is less than 0.04%, the desired effect by this action cannot be obtained and more than 0.4%. If it is contained, coarse Cr remains in the base material after commercialization. As a result, the etching property is deteriorated. For the above reason, the Cr content is preferably 0.04 to 0.4%.

Although Zr has the effect of forming a compound with Cu by aging treatment to precipitate in the base metal and strengthening the base metal, the desired effect by the above action cannot be obtained when the content is less than 0.03%. In addition, when Zr is contained in excess of 0.25%, coarse unused Zr remains in the mother material after solution treatment, resulting in deterioration of the etching property. Therefore, the Zr content is preferably 0.03 to 0.25%.

Zn is a component to be added because it serves to improve the thermal peeling resistance of the solder and the adhesion of the oxide film, but when the content is less than 0.06%, the desired effect by the above action cannot be obtained. In addition, when Zn is added in excess of 2.0%, the conductivity decreases. Therefore, the Zn content is preferably 0.06 to 2.0%.

Ti and Fe are added as necessary because they form an intermetallic compound of Ti and Fe in the base material when the alloy is aged, and as a result have an effect of further improving the alloy strength. If it is less than 0.1%, the desired strength by the above action cannot be obtained. Moreover, when Ti content exceeds 0.8% or Fe content exceeds 1.8%, the coarse interference | inclusion which has Ti and Fe as a main component remain | survives and etching property is remarkably impaired. Therefore, the Ti content is preferably 0.1 to 0.8%, and the Fe content is preferably 0.1 to 1.8%.

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 two or more kinds are added as necessary, but the content is 0.01% in total. If it is less than the desired effect by the above-described action is not obtained, and if the total amount exceeds 1.0%, the conductivity of the alloy is significantly reduced. Therefore, as for content of Ni, Sn, In, Mn, P, Mg, and Si which single addition or two or more types of complex addition are made, 0.01 to 1.0% is preferable in total amount.

(Example)

Next, the effect of this invention is concretely demonstrated by the Example which shows a preferable composition range.

First, copper (Cu) or oxygen-free copper (Cu) as the main raw material, copper chromium master alloy, copper zirconium mother alloy, zinc, titanium, mild steel, nickel, tin, indium, manganese, magnesium, silicon, copper phosphorus master alloy Was prepared as a raw material, and the copper alloys of the various component compositions shown in Tables 1 and 3 were melted in a vacuum or in an Ar atmosphere in a high frequency melting furnace, and cast into an ingot having a thickness of 30 mm. Each of these ingots were then treated in the order of hot working and solution treatment, first cold rolling, aging treatment, final cold rolling (processing degree 50%) under the conditions shown in Tables 1 and 3, and strain removal annealing. And a plate having a thickness of 0.15 mm.

The evaluation method is described below. First, the crystal orientation of each produced sheet was evaluated by the method described above using an X-ray diffraction apparatus. Next, the oxide film adhesion was evaluated by a tape peeling test. 20 x 50 mm of test pieces were cut out from each plate and heated at a predetermined temperature in the air for 5 minutes, and then a commercially available tape (trade name: 3M # 851) was attached and detached from the test piece surface on which the oxide film was formed. At this time, when the heating temperature was changed every 20 ° C., the lowest temperature at which the oxide film was peeled off was determined to be the oxide film peeling temperature. In addition, the strength was measured by measuring the tensile strength by the tensile test, and the conductivity was performed by obtaining the electrical conductivity.

Tables 3 and 4 show the results of the evaluation. For this example, good oxide film adhesion could be obtained. In addition, each comparative example is an example in which the {100} orientation of the pole surface layer is out of an appropriate range and the oxide film adhesiveness is inferior because the rolling conditions are not suitable.

As described above, the copper alloy of the present invention significantly improves the heat dissipation and high-speed operation of the semiconductor package compared with the 42 alloy (42% Ni-Fe alloy), and further improves the adhesion of the oxide film, thereby improving the reliability of the package. A fall can also be suppressed.

Claims (13)

The {100} peak strength ratio of the {111} peak strength of the copper alloy crystal constituting the pole surface layer, which was obtained by evaluating the copper alloy leadframe base material pole surface layer by the XRD thin film method, was characterized in that the resin was sealed. Copper alloy leadframe. The copper alloy lead frame according to claim 1, wherein the copper alloy lead frame includes a resin sealing part and a metal plated outer lead part, and the base material pole layer of the resin sealing part has a peak strength ratio of 0.04 or less. The copper alloy according to claim 1 or 2, wherein the copper alloy contains Cr: 0.04 to 0.4%, Zr: 0.03 to 0.25%, and Zn: 0.06 to 2.0% by mass ratio, and the balance Cu and inevitable impurities. Copper alloy lead frame, characterized in that made. The copper alloy according to claim 1 or 2, wherein the copper alloy contains Cr: 0.04 to 0.4%, Zr: 0.03 to 0.25%, and Zn: 0.06 to 2.0% by mass ratio, and further includes Ni, Sn, A copper alloy lead frame comprising 0.01 to 1.0% of one or two or more selected from the group consisting of In, Mn, P, Mg, and Si, with the balance being Cu and unavoidable impurities. The copper alloy of claim 1 or 2, wherein the copper alloy has a mass ratio of 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: 0.1. A copper alloy lead frame containing -0.8%, the remainder being made of Cu and unavoidable impurities. The copper alloy according to claim 1 or 2, wherein the copper alloy has a mass ratio of 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: 0.1. It contains -0.8%, Furthermore, it contains 0.01-1.0% of 1 type, or 2 or more types chosen from the group which consists of Ni, Sn, In, Mn, P, Mg, and Si in total amount, and remainder is Cu and an unavoidable thing. Copper alloy lead frame, characterized in that consisting of red impurities. Rolled surface poles containing Cr: 0.04 to 0.4%, Zr: 0.03 to 0.25% and Zn: 0.06 to 2.0% by mass ratio, the balance consisting of Cu and unavoidable impurities and evaluated by XRD thin film method A copper alloy, wherein the ratio of the {100} peak strength to the {111} peak strength of the copper alloy crystal constituting the surface layer is 0.04 or less. By mass ratio, it contains Cr: 0.04-0.4%, Zr: 0.03-0.25% and Zn: 0.06-2.0%, and is further selected from the group which consists of Ni, Sn, In, Mn, P, Mg, and Si. {111} peak of the copper alloy crystal constituting the rolled surface pole surface layer containing 0.01 to 1.0% of one kind or two or more kinds in total, the remainder consisting of Cu and unavoidable impurities and evaluated by XRD thin film method Copper alloy, characterized in that the {100} peak strength ratio to strength is 0.04 or less. By mass ratio, it contains Cr: 0.04-0.4%, Zr: 0.03-0.25%, Zn: 0.06-2.0%, Fe: 0.1-1.8%, and Ti: 0.1-0.8%, and remainder is Cu and an unavoidable impurity. And a {100} peak strength ratio with respect to {111} peak strength of the copper alloy crystal constituting the rolled surface pole surface layer obtained by evaluation by the XRD thin film method, wherein the copper alloy is 0.04 or less. By mass ratio, it contains Cr: 0.04-0.4%, Zr: 0.03-0.25%, Zn: 0.06-2.0%, Fe: 0.1-1.8%, and Ti: 0.1-0.8%, and further Ni, Sn, In Rolling containing 1% or 2% or more selected from the group consisting of Mn, P, Mg, and Si in a total amount of 0.01 to 1.0%, the balance consisting of Cu and an unavoidable impurity, evaluated by the XRD thin film method A copper alloy, wherein the ratio of the {100} peak strength to the {111} peak strength of the copper alloy crystal constituting the surface pole surface layer is 0.04 or less. The copper alloy according to any one of claims 7 to 10, wherein the copper alloy is used for a lead frame. The final cold rolling according to any one of claims 7 to 10, wherein the final pass is rolled at a diameter of 100 mm or more, a rolling speed of 200 m / min or more, and a viscosity of the rolling oil of 0.05 cm 2 / s or more. Copper alloy to be made. 12. The copper alloy according to claim 11, wherein the final pass is cold rolled 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.