JP3561231B2 - Manufacturing method of wiring board - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board on which electronic components such as a semiconductor element, a capacitance element, and a resistor are mounted, and a wiring board formed by applying a plating layer to a wiring conductor on the surface by an electroless method, and manufacturing the same. It is about the method.
[0002]
[Prior art]
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 of an aluminum oxide sintered body and having a substantially square plate-shaped insulator having a mounting portion for the electronic component, and an insulating member. It consists of a plurality of wiring layers made of a refractory metal material such as tungsten, molybdenum, and manganese, which are led out from the mounting part of the body to the outside, and semiconductor elements, capacitance elements, and resistors are mounted on the insulating mounting part. And the like, 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 circuit wiring of the external electric circuit board via solder or the like, and is simultaneously mounted on the wiring board. Each of the electrodes of the electronic component is electrically connected to a predetermined external electric circuit.
[0004]
Further, such a wiring board has a plating metal layer made of nickel, copper or the like adhered to the surface of the wiring layer, and has good wettability and bonding property of solder and bonding wires with respect to the wiring layer made of a high melting point metal material. And
[0005]
On the other hand, as a method of applying and forming a plating metal layer of nickel, copper, etc., it is difficult to form a lead wire for supplying power for plating due to the high density of wiring conductors accompanying the miniaturization of a wiring board. Electroless methods that do not require wires are being used extensively.
[0006]
Such deposition of a plating metal layer on a wiring conductor by an electroless method is performed by reductive precipitation of a metal such as nickel, copper or the like by a high melting point metal such as tungsten, molybdenum or manganese by an electroless method (autocatalytic type). Since it does not have catalytic activity, 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 immersed in an electroless plating solution. A method of applying a plating metal layer by using a method is adopted, and is generally performed as follows. That is,
First, prepare an insulating substrate having a wiring conductor on the surface,
Next, an additive such as a pH adjuster such as sodium hydroxide and potassium hydroxide is added to 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. The wiring conductor is immersed in an active solution formed by depositing and depositing a platinum group metal such as palladium on the surface of the wiring conductor,
Next, a complexing agent, a pH buffer, and a metal compound serving as a supply source of a plating metal such as nickel sulfate and copper sulfate and a reducing agent such as sodium hypophosphite, dimethylamine borane, and formalin are used as main components. Agents, stabilizers, etc., are immersed in an electroless plating solution, and nickel, copper and other metals are reduced and precipitated by the catalytic activity of platinum group metals such as palladium applied to the wiring conductor surface, A plating metal layer is selectively formed only on the surface of the wiring conductor.
[0007]
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 becomes a platinum group element such as palladium. Has the effect of sensitizing the deposition and deposition of platinum group elements such as palladium and platinum on the wiring conductor, and makes deposition and deposition easy and uniform. Further, in the inside of the plating metal layer adhered to the surface of the wiring conductor, a platinum group element such as palladium and platinum adhered to the surface of the wiring conductor and lead remain and are contained.
[0008]
[Problems to be solved by the invention]
Since the conventional wiring board contains lead in the plating metal layer as described above, when heat is applied to the plating metal layer such as nickel and copper, the lead moves and diffuses to the surface of the plating metal layer. There have been problems such as functional inconvenience of oxidizing and causing stain-like discoloration, and environmental and safety inconvenience that humans are harmed by lead in the plated metal layer.
[0009]
In order to solve the above problem, it is conceivable that lead is not contained in the active liquid. In this case, however, the surface of the wiring conductor made of a high melting point metal is coated with a platinum group element such as palladium or platinum. Due to insufficient sensitivity to deposition, it is not possible to uniformly and firmly deposit and deposit the platinum group element on the surface of the wiring conductor, and as a result, defects such as unevenness, This can cause problems.
[0010]
The present invention has been devised in order to solve the above problems, and an object of the present invention is to provide an electroless plating metal layer that is uniformly and firmly adhered on a wiring conductor, and that the plating metal layer It is an object of the present invention to provide a wiring board which does not contain lead and does not cause functional defects such as spot-like discoloration and does not harm the human body.
[0012]
[Means for Solving the Problems]
The method of manufacturing a wiring board according to the present invention includes: (1) a step of preparing an insulator having a wiring conductor made of a high melting point metal formed on a surface; and (2) a step of preparing the wiring conductor by using a platinum group element and oxycarboxylic acid. (3) immersing the wiring conductor in an active liquid, and applying a platinum group element to the surface of the wiring conductor to impart catalytic activity; and (3) the wiring conductor is mainly composed of a nickel compound and dimethylamine borane. Dipping in an electroless plating solution to form an electroless plating metal layer made of a nickel-boron alloy on the surface of the wiring conductor.
[0013]
According to the method for manufacturing a wiring board of the present invention, the platinum group element necessary for applying the electroless plating metal layer is contained inside the electroless plating metal layer applied to the wiring conductor, Since lead-free material can be used, 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, and lead is contained in the plating metal layer. The problem of discoloration of the plated metal layer and harm to the human body caused by the inclusion in the plating metal layer can also be effectively prevented.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing one embodiment in which a wiring board according to 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. The insulator 1 and the wiring conductor 2 form a wiring board 4 on which the semiconductor element 3 is mounted.
[0015]
The insulator 1 is made of an electrically insulating material such as a silicon carbide sintered body such as an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, etc., and the semiconductor element 3 is mounted on the upper surface thereof. A large number of wiring conductors 2 made of a refractory metal such as tungsten, molybdenum, and manganese are formed from the mounting portion on which the semiconductor element 3 is mounted to the lower surface.
[0016]
The insulator 1 has a semiconductor element 3 mounted on a mounting portion, and each electrode of the semiconductor element 3 is electrically connected to a wiring conductor 2 exposed on the mounting portion via a solder ball 5. The portion led out to the lower surface of the insulator 2 is electrically connected to the circuit wiring of the external electric circuit board via solder or the like.
[0017]
As shown in the cross-sectional view of FIG. 2, the wiring conductor 2 has a plating metal layer 6 applied to the surface thereof by an electroless method.
[0018]
The plating metal layer 6 functions to improve the wettability, bonding strength, and bonding property of the solder to the wiring conductor 2 and is made of a nickel-boron alloy.
[0019]
In the present invention, it is important that the plating metal layer 6 contains a platinum group element and does not contain lead.
[0020]
This prevents lead contained in the plating metal layer 6 of the nickel-boron plating layer from moving and diffusing to the surface of the plating metal layer 6 due to heat or the like, thereby causing stain-like discoloration or harm to the human body. To do 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.
[0021]
The platinum group element does not need to be applied in a film form along the surface of the wiring conductor 2, and is substantially constant, such as a portion along a grain boundary of crystal grains of a high melting point metal forming the wiring conductor. It is sufficient that the plating metal layer 6 is 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 in a granular or fragmented manner.
[0022]
Further, as the platinum group element, palladium or platinum, particularly palladium, is preferable, and is suitable for forming a good adhesion on the surface of the wiring conductor 2 made of a high melting point metal, such as nickel and copper, by electroless method. Good catalytic activity can be imparted to them.
[0023]
Furthermore, when the surface of the plating metal layer 6 made of a nickel-boron alloy is covered with a gold plating layer (not shown), the wiring board 4 effectively prevents oxidation corrosion of the plating metal layer 6. And the wettability of the solder to the wiring conductor 2 can be further improved. Therefore, it is preferable that the surface of the plating metal layer 6 of the wiring board 4 is further covered 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 covering the plating metal layer is weak, and if it exceeds 0.8 μm, the brittle intermetallic layer between the tin and gold in the solder. Objects tend to be generated in large quantities and the solder bonding strength 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.
[0024]
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. A bowl-shaped lid 9 made of metal or ceramics is joined to the upper surface of the insulator 1 via a sealing material such as glass, resin, or brazing material. The semiconductor device as a product is completed by housing 3 in an airtight manner.
[0025]
Next, a method for manufacturing the above-described wiring board will be described with reference to FIGS. 1 and 2 have the same reference numerals.
[0026]
First, an insulator 1 having a wiring conductor 2 made of a high melting point metal provided on a surface shown in FIG. 3A is prepared.
[0027]
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. It has a mounting part for mounting, and the semiconductor element is mounted on the mounting part.
[0028]
In the case where the insulator 1 is made of, for example, an aluminum oxide sintered body, a suitable organic binder and a solvent are added to a raw material powder such as aluminum oxide, silicon oxide, calcium oxide, and magnesium oxide, and the mixture is mixed to form a slurry. A ceramic green sheet (green ceramic sheet) is obtained by forming a ceramic slurry and forming the ceramic slurry into a sheet by employing a sheet forming technique such as a doctor blade method or a calendar roll method which is well known in the art. The green sheet is formed by cutting or punching into an appropriate shape, laminating a plurality of the green sheets, and finally firing the laminated ceramic green sheets at a temperature of about 1600 ° C. in a reducing atmosphere.
[0029]
The wiring conductor 2 is made of a high melting point metal material such as tungsten, molybdenum, manganese or the like, and 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 a ceramic as an insulator 1. The green sheet is printed and applied in a predetermined pattern in advance by a well-known screen printing method so that the green sheet is adhered and formed from the mounting portion of the insulator 1 to the lower surface.
[0030]
Next, the wiring conductor 2 is made to have an activity mainly composed of at least one of the platinum group elements composed of palladium, platinum, rhodium, ruthenium, and iridium and at least one of oxycarboxylic acids such as citric acid and malic acid. As shown in FIG. 3B, the substrate is immersed in a liquid, and a platinum group element 8 is applied to the surface of the wiring conductor to impart catalytic activity. However, in the figure, the platinum group element 8 is exaggerated from the actual scale for explanation.
[0031]
In the active liquid, the platinum group element acts to impart catalytic activity to the surface of the wiring conductor 2 by being applied to the surface of the wiring conductor 2, and the plating metal layer 6 is applied to the surface of the wiring conductor 2 in a later step. This enables selective and uniform deposition.
[0032]
Further, 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 including 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 a platinum group element by replacing the trace of elution with tungsten or the like. This is presumed to be because the stability of the complex of an organic acid such as citric acid to a metal is higher for a refractory metal such as tungsten than for an activator such as a platinum group element. By adding 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.
[0033]
For example, when palladium is used as the platinum group element, the active liquid mainly includes a palladium compound such as palladium chloride and palladium sulfate and an oxycarboxylic acid (carboxylic acid having a hydroxy group) such as citric acid and malic acid. A solution obtained by adding additives such as a pH adjuster such as hydrochloric acid, borohydrofluoric acid, sodium hydroxide, and potassium hydroxide to an aqueous solution as a component can be used. The concentration of palladium in the active solution is preferably set to about 20 to 80 ppm because a high concentration may cause problems such as segregation of palladium.
[0034]
In addition, the active liquid preferably has an acidic liquidity, and particularly preferably has a pH of 1 to 3, in order to effectively replace tungsten with palladium by the action of oxycarboxylic acid. In order to adjust the pH of the active solution to a predetermined range, a pH adjuster such as hydrochloric acid, borohydrofluoric acid, sodium hydroxide, or potassium hydroxide may be appropriately added to the active solution for adjustment.
[0035]
Next, the wiring conductor 2 is immersed in an electroless plating solution, and the electroless plating metal layer 6 is deposited and applied to the surface of the wiring conductor 2 using the platinum group element as a catalyst.
[0036]
The plating metal layer is made of a nickel-boron alloy, and has an effect of improving solder wettability and bonding property with respect to the wiring conductor 2.
[0037]
The electroless plating solution contains a nickel compound serving as a nickel supply source such as nickel sulfate and a boron-based reducing agent made of dimethylamine borane as the main components because the electroless plating metal layer 6 is made of a nickel-boron alloy. An electroless nickel plating solution to which a complexing agent, a stabilizer, a pH buffer and the like are added can be used. In this case, the nickel (ion) in the electroless nickel plating solution is reduced to metallic nickel as the reducing agent is oxidatively decomposed by the catalytic action of the platinum group element 8 previously deposited on the surface of the wiring conductor. Then, the plating metal layer 6 made of a nickel-boron alloy is formed by eutectoid deposition on the surface of the wiring conductor 2 together with boron generated by the decomposition of the reducing agent. 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 with respect to the subsequent reduction and precipitation of nickel by a reducing agent. Even if the platinum group element which is a catalyst is not exposed and in contact with the liquid, the reductive precipitation and deposition reaction of nickel can be continuously performed.
[0038]
When a gold plating layer (not shown) is applied to the surface of the plating metal layer 6, the wiring conductor 2 on which the plating metal layer 6 is applied is coated with a gold compound such as potassium potassium cyanide and ethylenediamine tetraethylene. A method of immersing in a substitution type electroless gold plating solution containing a complexing agent such as acetic acid (EDTA) as a main component for a predetermined time can be used.
[0039]
Note that the wiring board of the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the wiring board of the present invention is applied to a semiconductor element housing package for housing a semiconductor element, but may be applied to other uses such as a hybrid integrated circuit board.
[0040]
【The invention's effect】
According to the method for manufacturing a wiring board of the present invention, the platinum group element necessary for applying the electroless plating metal layer is contained inside the electroless plating metal layer applied to 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, and the lead is plated. It is possible to prevent problems such as spot discoloration of the plated metal layer and harm to the human body caused by being contained in the 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 main 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

Claims (1)

(1) a step of preparing an insulator having a wiring conductor made of a high melting point metal formed on the surface thereof; and (2) immersing the wiring conductor in an active liquid mainly containing a platinum group element and oxycarboxylic acid. Applying a platinum group element to the surface of the wiring conductor to impart catalytic activity, and (3) immersing the wiring conductor in an electroless plating solution containing nickel compound and dimethylamine borane as main components, Depositing an electroless plating metal layer made of a nickel-boron alloy on the surface of the wiring conductor.

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