JP2002161370A - Wiring board and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a surface of a metal plated layer tarnishes. SOLUTION: The wiring board comprises having a wiring conductor 2 consisting of a high melting point metal, which is formed on an insulator 1, having an electroless plated metal layer 6 which is applied on the wiring conductor 2, and including platinum group elements and excluding lead inside the above electroless metal plated layer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board on which electronic components such as semiconductor elements, capacitance elements, resistors and the like are mounted, wherein a plating layer is applied to a wiring conductor on the surface by an electroless method. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a wiring board on which electronic components such as a semiconductor element, a capacitor element, and a resistor are mounted is generally formed in a substantially square plate shape made of an aluminum oxide sintered body and having a mounting portion for electronic components. It is composed of an insulator and a plurality of wiring layers made of a refractory metal material such as tungsten, molybdenum, and manganese that are led out from the mounting portion of the insulator to the outside. Capacitive element,
An electronic component such as a resistor is mounted, and each electrode of the electronic component is electrically connected to a wiring layer via a conductive connecting material such as solder or a bonding wire.

[0003] Such a wiring board is mounted on the external electric circuit board by connecting a portion led out of the wiring conductor to the circuit wiring of the external electric circuit board via solder or the like, and at the same time, is mounted on the wiring board. Each electrode of the electronic component mounted on the tower is electrically connected to a predetermined external electric circuit.

In such a wiring board, a plating metal layer of nickel, copper, or the like is formed on the surface of the wiring layer, and the wettability and bonding property of the solder and the bonding wire with respect to the wiring layer made of a high melting point metal material. And so on.

[0005] On the other hand, the method of depositing and forming a plating metal layer of nickel, copper, or the like is that it is difficult to form a lead wire for supplying plating power due to the high density of wiring conductors accompanying the miniaturization of a wiring board. Therefore, an electroless method that does not require a lead wire is being widely used.

[0006] The formation of a plating metal layer on a wiring conductor by such an electroless method is performed by an electroless method (autocatalytic type) in which a refractory metal such as tungsten, molybdenum, manganese or the like is formed of a metal such as nickel or copper. Since it does not have catalytic activity against reduction precipitation by palladium, usually, first, a platinum group element such as palladium or platinum is applied to the surface of the wiring conductor to impart catalytic activity, and then the wiring conductor is placed in an electroless plating solution. And a method of applying a plating metal layer by immersion in a metal plate, which is generally performed as follows. That is, first, an insulating substrate having a wiring conductor on its surface is prepared, and then, an aqueous solution mainly containing a metal compound serving as a supply source of a platinum group element such as palladium chloride and a lead compound such as lead chloride is prepared. The wiring conductor is immersed in an active solution containing an additive such as a pH adjuster such as sodium or potassium hydroxide, and a platinum group metal such as palladium is deposited and deposited on the surface of the wiring conductor. A complexing agent, a pH buffering agent, and a stabilizer in an aqueous solution mainly containing a metal compound serving as a supply source of a plating metal such as nickel and copper sulfate and a reducing agent such as sodium hypophosphite, dimethylamine borane, and formalin. Immersed in an electroless plating solution containing a metal such as palladium, and by reducing and precipitating metals such as nickel and copper by the catalytic activity of a platinum group metal such as palladium applied to the surface of the wiring conductor. Selective The plated metal layer is deposited and formed.

The lead compound contained in the above-mentioned active solution is first adsorbed on the surface of the wiring conductor when the wiring conductor made of a high melting point metal is immersed in the active solution, and the surface of the wiring conductor is made of palladium or the like. It has the effect of sensitizing the deposition and deposition of platinum group elements, and makes deposition and deposition of platinum group elements such as palladium and platinum on wiring conductors easy and uniform. Further, inside the plating metal layer deposited on the surface of the wiring conductor, palladium deposited on the surface of the wiring conductor,
Platinum group elements such as platinum and lead remain and are contained.

[0008]

In the conventional wiring board, lead is contained in the plated metal layer as described above.
When heat is applied to the plating metal layer of nickel, copper, etc., lead moves and diffuses to the surface of the plating metal layer, oxidizes it, and causes a discoloration like a stain. As a result, there is a problem in that it causes harm to the human body and causes a safety problem.

In order to solve the above problem, it is conceivable that lead is not contained in the active solution.
Since the surface of the wiring conductor made of a high melting point metal is insufficiently sensitive to deposition and deposition of platinum group elements such as palladium and platinum, the platinum group element is uniformly and strongly deposited and deposited on the surface of the wiring conductor. As a result, a problem such as unevenness, chipping, blistering, or the like occurs in the plated metal layer.

[0010] The present invention has been devised to solve the above problems, and an object thereof is to provide an electroless plating metal layer uniformly and firmly adhered on a wiring conductor,
It is an object of the present invention to provide a wiring board which does not contain lead in the plated metal layer and does not cause functional defects such as spot discoloration and does not harm the human body.

[0011]

A wiring board according to the present invention is a wiring board formed by forming a wiring conductor made of a high melting point metal on an insulator and applying an electroless plating metal layer on the surface of the wiring conductor. In addition, the electroless plating metal layer contains a platinum group element therein and is free of lead.

Further, the method for manufacturing a wiring board according to the present invention comprises:
(1) a step of preparing an insulator having a wiring conductor made of a refractory metal on the surface; and (2) immersing the wiring conductor in an active liquid containing a platinum group element and oxycarboxylic acid as main components; A step of depositing a platinum group element on the surface of the wiring conductor to impart catalytic activity; and (3) immersing the wiring conductor in an electroless plating solution to deposit an electroless plating metal layer on the surface of the wiring conductor. And the step of causing

According to the wiring board of the present invention, the platinum group element necessary for depositing the electroless plating metal layer is contained inside the electroless plating metal layer deposited on the wiring conductor. Since lead is not contained, good catalytic activity is imparted to the wiring conductor by the action of the platinum group element, and the electroless plating metal layer can be uniformly applied only to the wiring conductor,
In addition, it is possible to effectively prevent problems such as spot discoloration of the plating metal layer and harm to a human body caused by lead contained in the plating metal layer.

[0014]

Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing an embodiment in which the wiring board of the present invention is applied to a package for housing a semiconductor element for housing a semiconductor element, wherein 1 is an insulator, and 2 is a wiring conductor. A wiring board 4 for mounting the semiconductor element 3 on the insulator 1 and the wiring conductor 2 is formed.

The insulator 1 is made of an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, or the like.
It is made of an electrically insulating material such as a silicon carbide sintered body, and has a mounting portion on which the semiconductor element 3 is mounted on its upper surface, and a large number of tungsten, molybdenum, and manganese from the mounting portion on which the semiconductor element 3 is mounted to the lower surface. The wiring conductor 2 made of a high melting point metal such as that described above is adhered and formed.

In the insulator 1, the semiconductor element 3 is mounted on the mounting portion, and each electrode of the semiconductor element 3 is electrically connected to the wiring conductor 2 exposed on the mounting portion via the solder ball 5, Further, a portion of the wiring conductor 2 extending to the lower surface of the insulator 1 is electrically connected to circuit wiring of an external electric circuit board via solder or the like.

As shown in the sectional view of FIG. 2, a plating metal layer 6 is applied to the surface of the wiring conductor 2 by an electroless method.

The plated metal layer 6 serves to improve the wettability, bonding strength, and bonding property of the solder to the wiring conductor 2, and is made of high-purity nickel having a nickel content of 99.9% by weight or more. , A nickel-phosphorus alloy, a nickel-boron alloy, copper, an alloy containing copper as a main component, or the like.

In the present invention, it is important that the plating metal layer 6 contains a platinum group element and does not contain lead.

This is because the lead contained in the plating metal layer 6 such as the nickel-boron plating layer moves and diffuses to the surface of the plating metal layer 6 due to heat or the like, causing stain-like discoloration or harm to the human body. This is to prevent that. In this case, a platinum group element such as palladium or platinum has a function of providing a catalyst necessary for depositing the plating metal layer 6 on the wiring conductor 2 by an electroless method, and is deposited and deposited on the surface of the wiring conductor 2. However, since the platinum group element is harder to oxidize than lead and has extremely low toxicity, it migrates and diffuses to the surface of the plating metal layer 6 to cause stain discoloration. It does not occur or harm the human body.

The platinum group element does not need to be applied in the form of a film along the surface of the wiring conductor 2, but may be located along the grain boundaries of the crystal grains of the refractory metal forming the wiring conductor. The plating metal layer 6 can be uniformly deposited on the surface of the wiring conductor 2 with the platinum group element as a base point, as long as the plating metal layer 6 is applied uniformly and at a substantially constant interval in a granular or fragmented manner. .

As the platinum group element, palladium or platinum, particularly palladium, is preferable. The platinum group element is favorably adhered to the surface of the wiring conductor 2 made of a high melting point metal, and is coated with a metal such as nickel or copper by an electroless method. Good catalytic activity can be imparted to deposit formation.

Further, the wiring board 4 is made of a plated metal layer made of pure nickel, a nickel-phosphorus alloy, a nickel-boron alloy, copper, an alloy mainly containing copper, etc., having a nickel content of 99.9% by weight or more. 6 is coated with a gold plating layer (not shown), it is possible to effectively prevent oxidative corrosion of the plating metal layer 6 and to further improve the wettability of the solder to the wiring conductor 2. It can be. Therefore, the wiring board 4 is provided with the plated metal layer 6.
It is preferable to further cover the surface with a gold plating layer. In this case, if the thickness of the gold plating layer is less than 0.03 μm, the effect of coating the plating metal layer is weak, and if the thickness exceeds 0.8 μm, the brittle intermetallic layer between tin and gold in the solder. Objects tend to be generated in large quantities, and the bonding strength of the solder tends to deteriorate. Therefore, it is preferable that the thickness of the gold plating layer be in the range of 0.03 μm to 0.8 μm.

Thus, according to the wiring board of the present invention, the semiconductor element 3 is mounted on the mounting portion of the insulator 1 and each electrode of the semiconductor element 3 is electrically connected to the wiring layer 2 via the solder ball 5. Thereafter, a bowl-shaped lid 9 made of metal or ceramics is bonded to the upper surface of the insulator 1 via a sealing material such as glass, resin, brazing material, or the like. The semiconductor device as a product is completed by housing the semiconductor element 3 in an airtight manner.

Next, a method for manufacturing the above-described wiring board will be described with reference to FIGS. FIG.
The same parts as those in FIG. 2 are denoted by the same reference numerals.

First, an insulator 1 having a wiring conductor 2 made of a refractory metal on the surface shown in FIG. 3A is prepared.

The insulator 1 is a substantially square plate made of an electrically insulating material such as an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body and a silicon carbide sintered body. There is a mounting portion for mounting the semiconductor element, and the semiconductor element is mounted on the mounting portion.

When the insulator 1 is made of, for example, a sintered body of aluminum oxide, a suitable organic binder and a solvent are added to a raw material powder of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide or the like and mixed. A ceramic green sheet (green ceramic sheet) is formed by forming a slurry-like ceramic slurry and forming the ceramic slurry into a sheet by employing a sheet forming technique such as a doctor blade method or a calender roll method which is well known in the art.
After that, the ceramic green sheet is formed into an appropriate shape by cutting or punching, and a plurality of the green sheets are laminated. Finally, the laminated ceramic green sheets are heated at a temperature of about 1600 ° C. in a reducing atmosphere. It is manufactured by firing.

The wiring conductor 2 is made of a high melting point metal material such as tungsten, molybdenum, manganese or the like. A metal paste obtained by adding a suitable organic binder or a solvent to a high melting point metal powder such as tungsten is mixed with the insulator 1. The ceramic green sheet is printed and applied in a predetermined pattern in advance by a well-known screen printing method, so that the insulator 1 is adhered and formed from the mounting portion to the lower surface.

Next, palladium, platinum,
Immersion in an active solution containing at least one platinum group element composed of rhodium, ruthenium and iridium and at least one oxycarboxylic acid such as citric acid and malic acid as shown in FIG. As shown, the catalytic activity is imparted by depositing the platinum group element 8 on the surface of the wiring conductor. However, in the figure, the platinum group element 8 is exaggerated from the actual scale for explanation.

In the above-mentioned active solution, the platinum group element acts to impart catalytic activity to the surface of the wiring conductor 2 by adhering to the surface of the wiring conductor 2, and the plating metal layer 6 is formed on the wiring conductor 2 in a later step. It is possible to selectively and uniformly adhere to the surface of the substrate.

The oxycarboxylic acid has an important function of enabling the platinum group element 8 to be adhered to the surface of the wiring conductor 2 without containing lead in the active liquid. That is, the oxycarboxylic acid such as citric acid acts on the surface of the wiring conductor 2 made of a high melting point metal such as tungsten, and oxidizes and complexes the high melting point metal on the surface portion of the wiring conductor 2 to elute into the active liquid. It acts to reduce and precipitate the platinum group element by replacing the trace of elution with tungsten or the like. This is presumably because the stability of the complex of an organic acid such as citric acid to a metal is higher for a high melting point metal such as tungsten than for an activator such as a platinum group element. By adding the oxycarboxylic acid to the active solution in this way, the platinum group element can be easily and uniformly applied to the surface of the wiring conductor 2 without adding lead as a sensitizing agent to the active solution. It can be applied.

When the active liquid is, for example, palladium as a platinum group element, a palladium compound such as palladium chloride or palladium sulfate and an oxycarboxylic acid (carboxylic acid having a hydroxy group) such as citric acid or malic acid are used. A solution obtained by adding additives such as a pH adjusting agent such as hydrochloric acid, borohydrofluoric acid, sodium hydroxide, and potassium hydroxide to an aqueous solution mainly containing The concentration of palladium in the active solution is preferably set to about 20 to 80 ppm because high concentrations may cause problems such as segregation of palladium.

The active liquid is preferably acidic, and the pH is particularly preferably in the range of 1 to 3, in order to effectively replace tungsten and palladium by the action of oxycarboxylic acid. . In order to adjust the pH of the active solution to a predetermined range, the hydrochloric acid, borohydrofluoric acid,
The pH may be adjusted by appropriately adding a pH adjuster such as sodium hydroxide or potassium hydroxide to the active solution.

Next, the wiring conductor 2 is immersed in an electroless plating solution, and the electroless plating metal layer 6 is deposited on the surface of the wiring conductor 2 using the platinum group element as a catalyst, and is deposited.

The plating metal layer has a nickel content of
99.9% by weight or more of pure nickel, nickel-phosphorus alloy, nickel-boron alloy, copper, alloy containing copper as a main component, etc., to improve the wettability of the solder to the wiring conductor 2, the bonding property, etc. Works.

For example, when the electroless plating metal layer 6 is made of a nickel-boron alloy, the electroless plating solution includes a nickel compound serving as a nickel supply source such as nickel sulfate and a boron-based material such as dimethylamine borane. An electroless nickel plating solution containing a reducing agent as a main component and a complexing agent, a stabilizer, a pH buffering agent, and the like added thereto can be used. In this case, nickel (ion) in the electroless nickel plating solution is reduced to metallic nickel as the reducing agent is oxidized and decomposed by the catalytic action of the platinum group element 8 previously deposited on the surface of the wiring conductor. And eutectoid deposition on the surface of the wiring conductor 2 together with boron generated by the decomposition of the reducing agent,
A plating metal layer 6 made of a nickel-boron alloy is formed. Note that once nickel (boron alloy) starts to be deposited on the surface of the wiring conductor 2, the deposited nickel itself has catalytic activity for the subsequent reduction and precipitation of nickel by a reducing agent. Even if the platinum group element as a catalyst is not exposed and in contact with the liquid, the nickel can be continuously reduced and deposited and deposited.

When a gold plating layer (not shown) is applied on the surface of the plating metal layer 6, the wiring conductor 2 on which the plating metal layer 6 is applied is made of a gold compound such as potassium potassium cyanide. Alternatively, a method of dipping in a substitution type electroless gold plating solution containing a complexing agent such as ethylenediaminetetraacetic acid (EDTA) as a main component for a predetermined time can be used.

The wiring board of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, in the above embodiment, the wiring board of the present invention is applied to a package for housing a semiconductor element for housing a semiconductor element, but may be applied to other uses such as a hybrid integrated circuit board.

[0040]

According to the wiring board of the present invention, the platinum group element necessary for depositing the electroless plating metal layer is contained inside the electroless plating metal layer deposited on the wiring conductor. However, since lead is not contained, good catalytic activity is imparted to the wiring conductor by the action of the platinum group element, and the electroless plating metal layer can be uniformly applied only to the wiring conductor,
In addition, it is possible to prevent problems such as spot-like discoloration of the plating metal layer and harm to the human body caused by lead contained in the plating metal layer.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a wiring board of the present invention.

FIG. 2 is an enlarged view of a main part of the wiring board shown in FIG.

3 (a) to 3 (c) are enlarged cross-sectional views of essential parts in each step for explaining a method of manufacturing the wiring board shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulator 2 ... Wiring conductor 3 ... Semiconductor element 4 ... Wiring board 5 ... Solder ball 6 ... Plating metal layer 7 ... Lid 8 Platinum group elements

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H05K 3/24 H01L 23/14 MF term (Reference) 4E351 AA07 BB01 BB23 BB24 BB33 BB35 CC07 DD17 DD19 DD20 DD58 GG11 GG20 4K022 AA02 AA42 BA04 BA08 BA14 BA16 BA18 BA31 BA32 BA35 CA06 CA21 CA23 DA01 DB01 5E343 AA02 AA23 BB16 BB38 BB39 BB40 BB44 BB49 BB71 CC72 DD33 GG20

Claims (2)

[Claims] 1. A wiring board comprising a wiring conductor made of a high melting point metal formed on an insulator and an electroless plating metal layer applied to a surface of the wiring conductor, wherein the electroless plating metal layer is A wiring board, which contains a platinum group element and contains no lead. (2) a step of preparing an insulator having a wiring conductor made of a refractory metal formed on a surface thereof; and (2) a step of preparing the wiring conductor mainly containing a platinum group element and oxycarboxylic acid. A step of immersing the wiring conductor in a catalytic solution by applying a platinum group element to the surface of the wiring conductor to impart catalytic activity thereto; and (3) immersing the wiring conductor in an electroless plating solution to form a coating on the surface of the wiring conductor. A method of manufacturing a wiring board, comprising the step of applying an electrolytic plating metal layer.