KR19980063303A - Manufacturing method of semiconductor lead frame - Google Patents

Abstract

The present invention provides a method for manufacturing a semiconductor lead frame, characterized in that the plating layer is formed on the substrate in an electroless manner. According to the present invention, it is possible to obtain a lead frame having a plating layer having a uniform thickness, regardless of the shape of the lead frame, while facilitating wastewater treatment and improving work efficiency.

Description

Manufacturing method of semiconductor lead frame

The present invention relates to a method for manufacturing a semiconductor lead frame, and more particularly, to a method for manufacturing a semiconductor lead frame capable of forming a plating layer having a uniform thickness regardless of the shape of the product.

The semiconductor lead frame is one of the core components of the semiconductor package together with the semiconductor chip, and simultaneously serves as a conductor connecting the inside and the outside of the semiconductor package and a support for supporting the semiconductor chip. Such a semiconductor lead frame may exist in various shapes according to a method of densification, high integration, and substrate mounting of a semiconductor chip.

The semiconductor lead frame is made of a plate-like material by a stamping process or an etching process to have a pad portion, an inner lead portion, and an outer lead portion. Here, the stamping process is a process of punching and forming a thin material into a predetermined shape by using a press mold apparatus which is sequentially transferred, and is widely used when mass producing lead frames. Etching is a chemical etching process that uses chemicals to corrode local parts of a material to form a product.

Typically, a semiconductor lead frame manufactured using the above two processes forms a semiconductor package by assembling other components, for example, a chip, which is a memory device. During the semiconductor package process, a metal material such as silver (Ag) is plated on the die pad part and the inner lead of the lead frame to maintain the wire bonding between the semiconductor chip and the lead frame inner lead and the die characteristics of the die pad in good condition. . In addition, solder molding, that is, tin-lead (Sn-Pb) plating, is performed on the external lead and a predetermined region in order to improve solderability for mounting the substrate after molding the resin protective film. However, if this process is carried out, after the protective film molding must be subjected to a wet treatment process, there is a problem that reduces the reliability of the finished product.

In order to solve the above problems, a pre-plated frame has been proposed. This method is a method of forming a lead frame by applying a material having excellent solder wettability in advance before the semiconductor package process.

1 is a cross-sectional view schematically showing a plated layer structure of a conventional lead frame.

Referring to this, a nickel (Ni) thin film layer 12 as an intermediate layer and a gold (Au) thin film layer 13 as an outermost plating layer are sequentially stacked on the substrate 11. This lead metal structure is symmetrically formed as described above also on the base metal lower surface.

In order to manufacture the lead frame having the structure as described above, first, the lead frame material of the thin plate is processed into a desired shape by a stamping process or an etching process. In this case, as the lead frame material, copper, nickel, iron, or an alloy thereof is used.

Thereafter, a lead frame is obtained by performing overflow plating with nickel on the substrate and overflow plating with gold thereon.

In the overflow plating, an electroplating method is used.

The electroplating method is a method of forcibly depositing a metal cation dissolved in a solution onto the surface of a to-be-plated object by supplying a negative electricity to the object to be plated. The metal cation receives electrons and precipitates in nucleus form on the surface of the object to be plated. The nucleus is unevenly deposited depending on the shape of the product, the current density and the concentration distribution of cations dissolved in the solution. When nuclei are generated at one point on the surface of the object to be plated, metals grow around the nucleus, and the growth rate is faster than that at which adjacent nuclei are formed.

When the plating layer is formed using the method as described above, there are the following problems.

First, the use of a plating solution based on the cyan compound in the plating has caused a problem of environmental pollution.

Second, in the case of plating a product having a fine pitch (pitch) there is a large variation in plating thickness for each part according to the current density gradient. When the thickness of the plating layer becomes nonuniform in this way, the characteristics of the lead frame are degraded.

Third, in the case of forming the gold plating layer as the outermost plating layer, when the vacancy of metal components such as nickel, iron, cobalt, copper, etc. is present in the gold plating layer, the wire bonding property is degraded, and thus the gold plating layer having a high purity of about 99.99% when gold plating is performed. There is a difficulty to secure.

The technical problem to be solved by the present invention is to provide a method for manufacturing a semiconductor lead frame having a plating layer having a uniform thickness, regardless of the shape of the lead frame by using a plating solution excluding the cyan bath to solve the above problems. .

1 is a view showing a plating layer structure of a lead frame according to the prior art.

* Description of the symbols for the main parts of the drawings *

Substrate 12. Interlayer Thin Film

13. Outermost plating layer

In order to achieve the above object, the present invention provides a method of manufacturing a semiconductor lead frame, the method of manufacturing a semiconductor lead frame for forming a metal plating layer on the substrate, characterized in that the plating layer is formed by an electroless plating method.

In the present invention, the plating layer of the lead frame is formed by using an electroless plating method. Electroless plating, also called chemical plating, is a plating method in which a metal is precipitated on a product by a reducing agent in a solution containing metal ions, which is an electronic product such as a memory disk, an insulator (ceramic) plating, and hard chromium. Electroless nickel on top, plating on office equipment and computer parts, etc. are used.

Hereinafter, the principle of the electroless plating will be briefly described.

Scheme 1

As shown in Scheme 1, the electrons released when the reducing agent is oxidized are received by the metal ions, and the metal is deposited on the object to be plated. When the material is a metal, a substitution reaction occurs initially, but the plating continues as soon as a reduction reaction occurs due to autocatalytic reaction.

Unlike the conventional electroplating, this plating method can form a plated film having a uniform thickness even on a subject in a depressed state.

Hereinafter, the manufacturing method of the lead frame using the electroless plating method of the present invention will be described.

First, prepare an electroless plating solution. At this time, the plating liquid contains a metal salt and a reducing agent as main components, and contains a pH adjuster, a reducing agent, a complexing agent, an accelerator, a stabilizer, an improving agent, and the like as auxiliary components. Herein, the metal salt refers to a salt containing a metal to be deposited. Nickel chloride or nickel sulfate is used to plate the nickel layer, and palladium chloride or palladium fluoride is used to plate the palladium layer. do.

The reducing agent refers to a drug that reduces electrons to a metal by supplying electrons to metal ions. The reducing agent belongs to sodium hypophosphite, sodium borohydride, hydrazine, and the like, and the reducing agent mainly has a large reducing effect in alkali.

The pH adjuster serves to adjust the rate of plating, reduction efficiency, stability and the like, which includes caustic soda, caustic, ammonia water, sulfuric acid, hydrochloric acid and the like.

The buffer refers to a substance used to control (buffer) the pH change as the metal ions are reduced to the metal, and include a salt or an acid having a small dissociation function such as sodium acetate, boric acid, and carbonic acid.

In neutral or alkaline solutions, metals such as nickel and copper are converted to their hydroxides to precipitate out. When ammonia water is added to this precipitate, the ammonia water acts simultaneously as a complexing agent and a pH adjusting agent so that the metals do not precipitate even in alkali. Sodium acetate, ethylene glycol and the like are used as complexing agents, which are also pH buffers as described above.

The accelerator is a substance for inhibiting the generation of hydrogen gas while promoting the plating rate and making the precipitation of metal more efficient, and fluoride, sulfide and the like belong to this.

The stabilizer serves to suppress the reduction reaction outside the surface to be plated. That is, it inhibits the natural decomposition of the plating solution and prevents the generation of hydrogen gas by reacting with the precipitation and reducing agent caused by the aging of the plating solution. Substances that play this role include lead chlorides, sulfides and nitrates.

The modifier serves to improve the state of the plating layer which gives glossiness, and usually a trace amount of surfactant is added.

By preparing the electroless plating solution, the plating layer forming method according to an exemplary embodiment of the present invention will be described.

First, the copper thin film material is subjected to electroless copper plating to form a copper plating layer. Electroless nickel plating is performed on the substrate to form a nickel plating layer. Then, electroless palladium plating is performed on the substrate on which the nickel plating layer is formed to form a palladium plating layer as the outermost plating layer. It is preferable to form a palladium plating layer as an outermost plating layer here compared with forming a gold plating layer, for the following reason.

First, palladium (standard electrode potential: + 0.987V) is easier to substitute and reduce precipitation than gold (standard electrode potential: + 1.2V).

Secondly, palladium is electrically conductive, and the palladium plated layer can be efficiently applied to contacts under elasticity, that is, to connectors of semiconductor printed circuit boards or contacts of electronic switches.

Third, the palladium plating layer may reduce the plating layer formation cost by replacing the gold plating layer for the purpose of preventing discoloration and improving solderability.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

Example 1

Copper and copper alloy substrates were degreased and activated. Then, on the substrate at a pH of about 5,0 and a temperature of 90 ° C, 26 g / l of nickel sulfate, 26 g / l of sodium acetate, 15 g / l of sodium citrate, 16 g / l of sodium hypophosphite and 3 to 5 ppm of thiourea The electroless plating using the plating liquid containing was performed and the nickel plating layer was formed.

Thereafter, at a pH of about 9 and a temperature of 90 ° C., it contained [Pd (NH ₃ ) ₄ ] Cl ₂ 5.4 g / l, EDTA-2Na 33.6 g / l, ammonia water 350 g / l and hydrazine 0.3 g / l. Electroless plating was performed using a hydrazine plating bath to form a palladium plating layer. At this time, the deposition rate of palladium was about 25.4 µm / hr.

Example 2

The alloy 42 material (Fe-Ni 42%) substrate was degreased and activated. Then, at a pH of about 12.0, at room temperature, CuSO ₄ 29 g / l, 37% HCHO 166 ml / l, sodium carbonate 25 g / l, Rochelle salt (C ₄ H ₄ O ₆ NaK) 140 g / l, and NaOH 40 g Electroless plating was carried out using a plating bath containing / l to form a copper plating layer.

Then, the nickel plating layer was formed on the board | substrate with which the copper plating layer was formed using the electroless nickel plating solution on condition of pH about 5,0 and the temperature of 90 degreeC. Here, the electroless nickel plating solution is composed of 26 g / l nickel sulfate, 26 g / l sodium acetate, 15 g / l sodium citrate, 16 g / l sodium hypophosphite and 3 to 5 ppm thiourea.

On the substrate on which the copper plating layer and the nickel plating layer were sequentially formed, a pH of about 8.0 and a temperature of 30 ml of a gold plating solution containing 10 g of gold chloride, 5 g of sodium chloride, and 800 ml of water at 80 ° C., 22.5 g of tartaric acid, and 300 g of sodium hydroxide were formed. , Electroless plating was carried out with 70 ml of a reducing solution containing 380 ml of alcohol and 600 ml of water to form a gold plating layer.

Example 3

After the alloy 42 material (containing 43 wt% nickel) substrate was degreased and activated, a copper plating layer was formed using an electroless copper plating solution.

Thereafter, electroplating using Ni 6450 (Germany degussa) plating solution was performed on the copper plating layer to form a nickel plating layer. Then, 30 ml of a gold plating solution containing 10 g of gold chloride, 5 g of sodium chloride, and 800 ml of water was used. Electroless plating was performed with 70 ml of a reducing solution containing 22.5 g of tartaric acid, 300 g of sodium hydroxide, 380 ml of alcohol, and 600 ml of water to form a gold plating layer.

Comparative example

The substrate of alloy 42 (containing 43 wt% nickel) was degreased and activated, followed by electroplating to form a copper plating layer.

Thereafter, an electroplating process using a nickel 6450 (Germany Degussa) plating solution was performed on the copper plating layer to form a nickel plating layer, and then a gold plating layer was formed by electroplating.

Thickness variation of the plating layer obtained according to Examples 1-3 and Comparative Examples was measured to determine the thickness uniformity of each part. As a result, unlike the case of the plated layer (comparative example) formed by the electroplating method, it was found that the thickness of the plated layer (the example) formed by the electroless method was hardly varied.

On the other hand, the nickel plating layer is preferably formed using the electroless plating method as in Examples 1 and 2. However, the nickel plated layer has a thicker plating thickness than other metal plated layers, and since the change of the plated layer characteristics according to the plating method is not so large, even if only the nickel plated layer is formed by the electroplating method as described in Example 3, the overall lead There is little negative effect on frame characteristics. In particular, since the gold plating layer, which is a precious metal plating layer, is further formed on the nickel plating layer, the deterioration of the characteristics of the lead frame caused by the thickness variation of the nickel plating layer is suppressed.

According to the present invention, the following effects can be obtained.

First, since the cyanide plating solution used in the prior art is not used, wastewater treatment is easy and the environmental pollution problem is solved.

Second, regardless of the shape of the lead frame, it is possible to obtain a lead frame having a plating layer of uniform thickness. Therefore, it is possible to suppress the degradation of the characteristics of the lead frame caused by the thickness variation.

Third, when plating the semiconductor lead frame by the electroplating method, a high level of technical skill is required for the fine pitch of the patterning, so that side effects such as low density and low integration due to the reduction of the work efficiency due to the complexity of the design and the reduction of the application range can be suppressed. This can maximize the efficiency of the work process.

Claims (1)

In the method of manufacturing a semiconductor lead frame to form a metal plating layer on the substrate, The plating layer is a method of manufacturing a semiconductor lead frame, characterized in that formed by electroless plating.