JP2020033628A - Electroless palladium plating solution and electroless palladium plating method and manufacturing method of electroless palladium plating solution - Google Patents

Abstract

To provide an electroless palladium plating solution capable of changing a phosphorus content from middle to low phosphorus in a plating film without changing a palladium source compound in the electroless palladium plating solution a concentration of a major component including a reducer including phosphorus, the electroless palladium plating providing not reduced plating speed and being stable as a plating solution.SOLUTION: An electroless palladium plating solution comprises a chloro ammine complex palladium salt, an inorganic sulfur compound, and ammonium compound, an amine compound, and a reducer including phosphorus.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electroless palladium plating solution, an electroless palladium plating method, and a method for producing an electroless palladium plating solution.

  As an electrical connection method between an electrode (pad) on a semiconductor element such as a transistor manufactured on a semiconductor wafer and an electrode on a mounting substrate or the like on which the semiconductor wafer is mounted, a wire diameter made of gold or the like is used for both electrodes. A wire bonding method for connecting via thin wires (wires) of about 20 μm to 50 μm, and forming protruding electrodes (bumps) on the electrodes (pads) and aligning them with electrode pads on the opposing substrate. A flip-chip method of mounting by mounting is known.

  When wire bonding is performed on an electrode (pad) of the semiconductor element, a method of forming a Ni / Pd / Au or Ni / Pd film on the electrode by electroless plating is used.

  To solder the IC to the substrate and the ICs by flip chip, UBM (Under Bump Metallurgy) is formed by vapor deposition or plating on the electrode pads of Al, Cu, Au, etc. formed on the IC. Then, a lead-free solder such as Sn-Ag or Sn-Ag-Cu is formed thereon by printing, ball mounting, or plating. A method of heating and bonding the same to an IC and a substrate similarly formed is used.

As a method of forming the UBM, the UBM is increasingly formed by an electroless plating method, which is expected to have a low cost. As a method of forming a UBM by electroless plating, a degreasing process or a soft etching process is performed in order to first clean a portion to be plated (pad or wiring) on a semiconductor wafer. Next, a catalyst application step is performed. The catalyst application step is a zincate treatment on the aluminum-based metal surface and a palladium treatment on the copper-based metal surface. Thereafter, a method of forming a UBM of a Ni / Au film by electroless nickel (Ni) plating and substitutional electroless gold (Au) plating is generally used.
When the plated wafer is exposed to high temperature or high humidity, Ni diffuses into the gold film and precipitates on the surface to form Ni oxide, which adversely affects solder wettability and wire bonding property. . In this case, electroless palladium (Pd) plating, which is a barrier layer for Ni diffusion, is generally performed between electroless nickel plating and substitutional electroless gold plating to form a Ni / Pd / Au film. .
In the present invention, the symbol “/” means the structure of a plurality of plating films formed in each plating step, and the order of the plating films depends on the order of plating from the base material side.

  In the Ni / Pd / Au plating film, the plating with the electroless pure Pd plating film is superior in the wire bonding property as compared with the plating with the electroless Pd-P plating film. On the other hand, the electroless pure Pd plating bath has poor bath stability as compared with the electroless Pd-P plating bath. Therefore, an electroless Pd-P plating solution which is excellent in bath stability and can form a plating film having excellent wire bonding performance is desired.

  Regarding the phosphorus content in the electroless palladium plating film, Non-Patent Document 1 describes a case where an electroless Pd-P alloy plating solution containing palladium chloride, ethylenediamine, thiodiglycolic acid, and sodium hypophosphite is used. Although the phosphorus content in the plating film was reduced by the addition of a small amount of thiodiglycolic acid, the concentration of thiodiglycolic acid showed a constant value in the concentration range of 50 mg / L to 200 mg / L. It is described that the concentration increased in proportion to the 0.2th power of the concentration of sodium phosphate, and that the higher the pH, the smaller the value.

Surface technology vol.40, No.3, 1989, p.477-480

  The embodiment of the present invention changes the content of phosphorus in the plating film from medium phosphorus to low phosphorus without changing the concentration of a main component such as a compound serving as a palladium source of the electroless palladium plating solution or a reducing agent containing phosphorus. It is an object of the present invention to provide an electroless palladium plating solution, an electroless palladium plating method, and a method for producing an electroless palladium plating solution, which are capable of causing a plating rate not to be reduced and are stable as a plating solution. And

An embodiment of the present invention has the following configuration.
(1) An electroless palladium plating solution containing a chloroammine complex palladium salt, an inorganic sulfur compound, an ammonium compound, an amine compound, and a reducing agent containing phosphorus.
(2) the concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L,
The concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0040 mol / L with respect to the palladium-equivalent amount of the chloroammine complex palladium salt of 0.006 mol / L,
The concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L,
The concentration of the amine compound is 0.02 mol / L to 2.00 mol / L,
The electroless palladium plating solution according to (1), wherein the concentration of the phosphorus-containing reducing agent is from 0.027 mol / L to 2.000 mol / L.
(3) The method according to (2), wherein the concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0009 mol / L based on 0.006 mol / L of palladium in the chloroammine complex palladium salt. Electrolytic palladium plating solution.
(4) The method according to (2), wherein the concentration of the inorganic sulfur compound is 0.0010 mol / L to 0.0040 mol / L with respect to the palladium equivalent of 0.006 mol / L of the chloroammine complex palladium salt. Electrolytic palladium plating solution.
(5) The electroless palladium plating solution according to any one of (1) to (4), wherein the inorganic sulfur compound is thiodiglycolic acid or thioglycolic acid.
(6) The electroless palladium plating solution according to any one of (1) to (5), wherein the phosphorus-containing reducing agent is sodium hypophosphite or sodium phosphite.
(7) The electroless palladium plating solution according to any one of (1) to (6), further comprising an unsaturated dicarboxylic acid compound.
(8) An electroless palladium plating method of performing electroless palladium plating using the electroless palladium plating solution according to any one of (1) to (7).
(9) By adjusting the concentration of the inorganic sulfur compound contained in the electroless palladium plating solution, the phosphorus content of the obtained electroless palladium plating film is adjusted to 1.0% by mass or more and 4.0% by mass or less. The electroless palladium plating method according to the above (8).
(10) The electroless palladium plating solution comprises:
The concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L,
The concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0009 mol / L with respect to the palladium-equivalent amount of the chloroammine complex palladium salt of 0.006 mol / L,
The concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L,
The concentration of the amine compound is 0.02 mol / L to 2.00 mol / L,
The concentration of the phosphorus-containing reducing agent is 0.027 mol / L to 2.000 mol / L,
The electroless palladium plating method according to the above (8) or (9), wherein the content of phosphorus in the obtained electroless palladium plating film is from 3.0% by mass to 4.0% by mass.
(11) The electroless palladium plating solution comprises:
The concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L,
The concentration of the inorganic sulfur compound is 0.0010 mol / L to 0.0040 mol / L with respect to the palladium equivalent of 0.006 mol / L of the chloroammine complex palladium salt;
The concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L,
The concentration of the amine compound is 0.02 mol / L to 2.00 mol / L,
The concentration of the phosphorus-containing reducing agent is 0.027 mol / L to 2.000 mol / L,
The electroless palladium plating method according to the above (8) or (9), wherein the content of phosphorus in the obtained electroless palladium plating film is 1.0% by mass or more and less than 3.0% by mass.
(12) A method for producing an electroless palladium plating solution in which a chloroammine complex palladium salt, an inorganic sulfur compound, an ammonium compound, an amine compound, and a reducing agent containing phosphorus are dissolved in water.

  The electroless palladium plating solution according to the embodiment of the present invention is a compound serving as a palladium source, and the content of phosphorus in a plating film is changed from medium phosphorus to low phosphorus without changing the concentration of a main component such as a reducing agent containing phosphorus. It can be changed, the plating rate does not decrease, and the plating solution is stable.

An electroless nickel plating film obtained using the electroless palladium plating solution of Example 1, an electroless palladium plating film formed on the electroless nickel plating film, and formed on the electroless palladium plating film FIG. 3 is a diagram showing an AES depth profile of a semiconductor wafer having a plated electroless gold plating film. An electroless nickel plating film obtained using the electroless palladium plating solution of Example 2, an electroless palladium plating film formed on the electroless nickel plating film, and formed on the electroless palladium plating film FIG. 3 is a diagram showing an AES depth profile of a semiconductor wafer having a plated electroless gold plating film. An electroless nickel plating film obtained using the electroless palladium plating solution of Example 3, an electroless palladium plating film formed on the electroless nickel plating film, and formed on the electroless palladium plating film FIG. 3 is a diagram showing an AES depth profile of a semiconductor wafer having a plated electroless gold plating film. An electroless nickel plating film obtained using the electroless palladium plating solution of Example 4, an electroless palladium plating film formed on the electroless nickel plating film, and formed on the electroless palladium plating film FIG. 3 is a diagram showing an AES depth profile of a semiconductor wafer having a plated electroless gold plating film. It is a graph which shows the relationship between the phosphorus content in the electroless palladium plating film obtained using the electroless palladium plating solution of Examples 1-4, and the concentration of thiodiglycolic acid in the electroless palladium plating solution. 4 is an optical micrograph of a fractured surface after a solder shear strength test in the evaluation of solder properties in Example 1. 5 is an optical micrograph of a fractured surface after a solder shear strength test in the evaluation of solder characteristics in Example 2. 5 is an optical micrograph of a fractured surface after a solder shear strength test in the evaluation of solder characteristics in Example 3. 9 is an optical micrograph of a fractured surface after a solder shear strength test in the evaluation of solder properties in Example 4. 5 is a SIM image of an electroless palladium plating film obtained using the electroless palladium plating solution of Example 1 after FIB cross-section processing. 6 is a SIM image of an electroless palladium plating film obtained by using the electroless palladium plating solution of Example 2 after FIB cross-section processing. 9 is a SIM image of an electroless palladium plating film obtained using the electroless palladium plating solution of Example 3 after FIB cross-section processing. 9 is a SIM image of an electroless palladium plating film obtained using the electroless palladium plating solution of Example 4 after FIB cross section processing.

The electroless palladium plating solution of the present invention contains a chloroammine complex palladium salt, an inorganic sulfur compound, an ammonium compound, an amine compound, and a reducing agent containing phosphorus.
The electroless palladium plating solution of the present invention can change the phosphorus content in the deposited palladium plating film from low to medium phosphorus by changing the concentration of the inorganic sulfur compound that is a bath stabilizer. Thus, the crystallinity can be changed.
By adjusting the concentration of the inorganic sulfur compound in the electroless palladium plating solution, the phosphorus content in the deposited electroless palladium plating film can be reduced to 2% by mass or less. Can provide a plating film that is both good.
Further, the electroless palladium plating solution contains a reducing agent containing phosphorus and has high solution stability.
In the present invention, the medium phosphorus having a phosphorus content of the electroless palladium plating film refers to a material having a phosphorus content of 3% by mass or more and 6% by mass or less, and low phosphorus means that the phosphorus content is low. Less than 3% by mass.

In the case of performing electroless plating of Ni / Pd / Au specifications in forming the UBM, the concentration of phosphorus, which is an eutectoid element in the palladium plating film, may be required widely from low to high phosphorus.
By adjusting the concentration of the phosphorus-containing reducing agent in the electroless Pd-P plating solution, the phosphorus content in the deposited plating film can be changed within a certain range. For example, in order to lower the phosphorus concentration in the plating film, the phosphorus concentration in the plating solution may be reduced. However, if the concentration of phosphorus in the plating solution is reduced to such an extent that a low-phosphorus plating film is obtained, the plating rate is reduced. Also, by increasing the pH of the plating solution, the phosphorus concentration in the plating film can be lowered, but increasing the pH of the plating solution decreases the bath stability.
Further, the phosphorus-free type reducing agent can reduce the phosphorus concentration to 0%, but the stability of the plating solution is lowered. For stable production of the plating film, it is desirable that the bath stability is high.
Therefore, an electroless palladium plating solution that can reduce the phosphorus concentration in the plating film to low phosphorus, particularly 2% by mass or less, does not slow down the plating rate, and has excellent bath stability has not been obtained.
On the other hand, the electroless palladium plating solution of the present invention can reduce the phosphorus content in the plating film by increasing the concentration of the inorganic sulfur compound in the electroless palladium plating solution. Further, even if the concentration of the inorganic sulfur compound is increased, the bath stability does not decrease. Also, when the concentration of the inorganic sulfur compound is increased, the plating speed is increased, so that the plating process time can be shortened. With the palladium plating solution of the present invention, the phosphorus content in the plating film can be changed more broadly (to a low phosphorus range) without lowering the stability and plating rate of the plating solution. Moreover, the inorganic sulfur compound can change the phosphorus content in the plating film at a lower amount.

In an ethylenediamine complex bath using palladium chloride as a palladium source, even if the addition concentration of the inorganic sulfur compound is changed in a concentration range of 50 mg / L to 200 mg / L, the phosphorus content in the obtained plating film is constant. The value of was shown. However, in the bath of the present invention using a chloroammine complex palladium salt as a palladium source, it has been found that by changing the concentration of the inorganic sulfur compound, the phosphorus content of the obtained plating film changes.
When the inorganic sulfur compound acts on the coordination of the palladium metal chloroammine complex, the oxidation-reduction potential of the palladium metal chloroammine complex changes. As a principle of electroless plating, the difference between the oxidation-reduction potential of the metal chloroammine complex and the oxidation-reduction potential of the reducing agent corresponds to the reaction energy. Therefore, it is considered that the precipitation reaction rate of the electroless palladium plating changes, and the phosphorus content of the Pd-P plating changes by changing the eutectoid rate of phosphorus, which is an eutectoid element.

In the electroless palladium plating solution of the present invention, the concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L, and the concentration of the inorganic sulfur compound is the palladium conversion amount of the chloroammine complex palladium salt. 0.0003 mol / L to 0.0040 mol / L with respect to 0.006 mol / L, the ammonium compound concentration is 0.1 mol / L to 2.0 mol / L, and the amine compound concentration is 0.1 mol / L to 2.0 mol / L. It is preferably from 02 mol / L to 2.00 mol / L, and the concentration of the phosphorus-containing reducing agent is preferably from 0.027 mol / L to 2.000 mol / L.
In the electroless palladium plating solution, if the concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0009 mol / L with respect to 0.006 mol / L of the palladium-equivalent amount of the chloroammine complex palladium salt, The content of phosphorus in the electrolytic palladium plating film is 3.0% by mass or more and 4.0% by mass or less, and an amorphous Pd-P film is obtained.
In the electroless palladium plating solution, when the concentration of the inorganic sulfur compound is 0.0010 mol / L to 0.0040 mol / L with respect to 0.006 mol / L of palladium equivalent of the chloroammine complex palladium salt, The content of phosphorus in the electrolytic palladium plating film is 1.0% by mass or more and less than 3.0% by mass, and a crystalline Pd-P film is obtained.

Hereinafter, the components of the electroless palladium plating solution of the present invention will be described.
<Chloroammine complex palladium salt>
As the chloroammine complex palladium salt, dichlorodiamminepalladium, dichlorotetraamminepalladium, tetrachloropalladiumtetraamminepalladium, or the like can be used.
The concentration of the chloroammine complex palladium in the plating solution is preferably from 0.001 mol / L to 0.200 mol / L, more preferably from 0.002 mol / L to 0.020 mol / L.
When the concentration is 0.001 mol / L or more, the plating rate does not decrease. Even if the concentration exceeds 0.200 mol / L, the effect is saturated, so that the concentration is preferably 0.200 mol / L or less.

<Inorganic sulfur compound>
The inorganic sulfur compound acts as a bath stabilizer, and preferably uses thiodiglycolic acid, thioglycolic acid, sodium thiosulfate, sodium sulfite, or the like, and more preferably uses thiodiglycolic acid or thioglycolic acid. preferable.

The concentration of the inorganic sulfur compound in the plating solution is preferably 0.0003 mol / L to 0.0040 mol / L, more preferably 0.0003 mol / L to 0.0030 mol, based on the palladium equivalent of the chloroammine complex palladium salt of 0.006 mol / L. / L is more preferred.
When the concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0040 mol / L with respect to 0.006 mol / L in terms of palladium of the chloroammine complex palladium salt, the phosphorus content in the palladium plating film is reduced. It can be 1.0% by mass or more and 4.0% by mass or less.
When the concentration of the inorganic sulfur compound is 0.0003 mol / L or more with respect to the palladium equivalent of the chloroammine complex palladium salt of 0.006 mol / L, the plating solution is stabilized, and palladium precipitates in the plating solution. Can be suppressed. The effect obtained by adding the inorganic sulfur compound to the plating solution (stabilization of the plating solution and suppression of the deposition of phosphorus in the plating film) is saturated at about 0.0040 mol / L. 0040 mol / L or less is preferable.

<Ammonium compound>
Ammonium compounds are used for buffer applications.
As the ammonium compound, ammonia, ammonium chloride, ammonium hydroxide and the like can be preferably used.
The concentration of the ammonium compound in the plating solution is preferably from 0.1 mol / L to 2.0 mol / L, and more preferably from 0.15 mol / L to 1.00 mol / L.

<Amine compound>
The amine compound plays a role as a ligand of palladium.
Examples of the amine compound include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, benzylamine, methylenediamine, ethylenediamine, tetramethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and hexamethylenetetramine. Can be.
The concentration of the amine compound in the plating solution is preferably from 0.02 mol / L to 2.00 mol / L, more preferably from 0.05 mol / L to 1.00 mol / L.

<Reducing agent containing phosphorus>
The phosphorus-containing reducing agent preferably contains any of hypophosphorous acid, phosphorous acid, and salts thereof. Examples of the salts of hypophosphorous acid and phosphorous acid include sodium hypophosphite and sodium phosphite, and it is preferable to use sodium hypophosphite or sodium phosphite.
The concentration of the reducing agent in the plating solution is preferably from 0.027 mol / L to 2.00 mol / L, and more preferably from 0.04 mol / L to 0.50 mol / L.
The phosphorus content of the plating film also changes depending on the concentration of the phosphorus-containing reducing agent, and the lower the concentration of the reducing agent, the lower the phosphorus content of the plating film. When reducing the phosphorus content to improve wire bonding properties, the phosphorus content can also be reduced by reducing the content of the reducing agent contained in the plating solution. When the concentration is lower than 0.027 mol / L, the plating rate is reduced. When the concentration of the reducing agent was 0.027 mol / L or more, it was difficult to reduce the phosphorus content of the plating film to 2% by mass or less when no inorganic sulfur compound was added.
Even when the electroless palladium plating solution of the present invention contains a reducing agent of 0.027 mol / L or more, by adjusting the concentration of the inorganic sulfur compound, the phosphorus content of the obtained plating film can be reduced to 2% by mass. The plating rate can be reduced to below, and the plating rate does not decrease, and the plating solution is excellent in stability.

<Other ingredients>
The electroless palladium plating solution of the present invention preferably contains an unsaturated dicarboxylic acid compound. Including an unsaturated dicarboxylic acid compound has an effect of suppressing hydrogen embrittlement.
Examples of the unsaturated dicarboxylic acid compound include maleic acid, fumaric acid, citraconic acid, mesaconic acid, and anhydrides, salts and derivatives thereof, and maleic acid is preferred.
The concentration of the unsaturated dicarboxylic acid compound in the plating solution is preferably 0.030 mol / L to 2.000 mol / L, and more preferably 0.100 mol / L to 1.000 mol / L.

Further, the electroless palladium plating solution of the present invention may optionally contain a pH buffer. Phosphate compounds are particularly preferred as the pH buffer.
Examples of the phosphoric acid compound include phosphoric acid, pyrophosphoric acid, or an alkali metal salt, alkaline earth metal salt, ammonium salt, alkali metal dihydrogen phosphate, alkaline earth metal dihydrogen phosphate, or dibasic phosphate thereof. Examples include ammonium hydrogen, a dialkali metal hydrogen phosphate, a dialkaline earth metal hydrogen phosphate, and a diammonium hydrogen phosphate. The concentration of the phosphoric acid compound in the plating solution is preferably from 0.01 g / L to 200 g / L, more preferably from 0.1 g / L to 100 g / L.

The pH of the electroless palladium plating solution of the present invention is preferably 7 to 9.
The phosphorus content of the plating film varies depending on the pH, and the higher the pH, the lower the phosphorus content. However, even when the pH was increased to 11, it was difficult to reduce the phosphorus content in the plating film to 2% by mass or less when the inorganic sulfur compound was not added. In addition, when the pH is 11 or more, the liquid stability decreases. By using the plating solution of the present invention, the content of phosphorus in the plating film can be reduced to 2% by mass or less even at pH 7 to 9.
Further, the plating temperature is preferably from 40C to 70C. If the temperature is too low, the plating rate will be low, and if it is too high, the liquid stability will decrease.

  The electroless palladium plating solution of the present invention can be obtained by dissolving a chloroammine complex palladium salt, an inorganic sulfur compound, an ammonium compound, an amine compound, and a phosphorus-containing reducing agent in water.

The electroless palladium plating method of the present invention performs electroless palladium plating using the above-described electroless palladium plating solution of the present invention. What is necessary is just to immerse the object to be plated in the electroless palladium plating solution of the present invention.
By adjusting the concentration of the inorganic sulfur compound in the electroless palladium plating solution, the phosphorus content of the obtained electroless palladium plating film can be adjusted.
The concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L, and the concentration of the inorganic sulfur compound is 0.0003 mol with respect to 0.006 mol / L of the chloroammine complex palladium salt in terms of palladium. / L to 0.0040 mol / L, the concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L, and the concentration of the amine compound is 0.02 mol / L to 2.00 mol / L. In an electroless palladium plating solution in which the concentration of a reducing agent containing phosphorus is 0.027 mol / L to 2.000 mol / L, the concentration of the inorganic sulfur compound is 0.006 mol in terms of palladium of a chloroammine complex palladium salt. /0.001 mol / L to 0.0009 mol / L with respect to / The content of phosphorus is 3.0 wt% or more in indium plating film becomes 4.0 mass% or less, the amorphous Pd-P. When the concentration of the inorganic sulfur compound is 0.0010 mol / L to 0.0040 mol / L with respect to 0.006 mol / L in terms of palladium of the chloroammine complex palladium salt, the resulting electroless palladium plating film has The phosphorus content becomes 1.0% by mass or more and less than 3.0% by mass, and becomes crystalline Pd-P. The crystalline Pd-P has better wire bonding properties than the amorphous Pd-P.

In general, with respect to wire bonding properties, a pure palladium plating film has lower hardness and excellent bonding properties than a Pd-P plating film.
However, with respect to flip-chip mountability, the pure palladium plating film is more likely to break the IMC layer, and the Pd-P plating film is more excellent in flip-chip mountability than the pure palladium plating film.
The low phosphorus type Pd-P plating film obtained by using the electroless palladium plating solution of the present invention can have a low phosphorus content, and thus has excellent wire bonding properties. Therefore, using the electroless palladium plating solution of the present invention, it is possible to obtain a plating film excellent in both flip chip mounting property and wire bonding property.

  Examples of the object to be plated include electronic components such as a semiconductor bump and a package substrate on which a semiconductor is mounted, a printed wiring board, and the like, and the electroless palladium plating solution of the present invention is used as the plating for bonding and the plating for UBM formation. In particular, it can be suitably used for electroless palladium plating inserted between electroless nickel plating and electroless gold plating.

  The present invention is not limited to each embodiment, and can be embodied by modifying the components without departing from the scope of the invention. Various inventions can be formed by appropriately combining a plurality of components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.

The present invention will be further described by the following examples and comparative examples.
(Examples 1 to 4)
In the electroless palladium plating solution, the concentration of thiodiglycolic acid was adjusted to 40 mg / L (0.0003 mol / L), 75 mg / L (0.0005 mol / L), or 150 mg / L (0. (0010 mol / L) and 300 mg / L (0.0020 mol / L) to prepare the electroless palladium plating solutions of Examples 1 to 4.
・ Electroless palladium plating solution 0.006mol / L (1.6g / L) dichlorotetraamminepalladium
Thiodiglycolic acid 0.0003 mol / L (40 mg / L) (Example 1)
0.0005 mol / L (75 mg / L) (Example 2)
0.0010 mol / L (150 mg / L) (Example 3)
0.0020 mol / L (300 mg / L) (Example 4)
Ammonium chloride 0.1869 mol / L (10 g / L)
50% ammonia water 0.0042 mol / L (0.15 g / L)
Ethylenediamine 0.2362mol / L (14g / L)
Sodium hypophosphite-hydrate 0.0944 mol / L (10 g / L)
Maleic acid 0.1723mol / L (20g / L)
Diammonium hydrogen phosphate 0.1514 mol / L (20 g / L)
pH 7.5

Electroless nickel nickel plating, electroless palladium plating, and electroless gold plating were performed on a pad material AlCu, a pattern wafer having a pad diameter of 300 μm, and an AlCu plate as described below.
<Preparation of plating film>
Alkaline degreasing (made by JX Metal, WBD-400)
(50 ° C, 5min)
→ Nitric acid cleaning (30%, 25 ° C, 30s)
→ zincate (JX metal, WBZ-200)
(25 ° C, 30 seconds)
→ Nitric acid cleaning (30%, 25 ° C, 15s)
→ zincate (JX metal, WBZ-200)
(25 ° C, 15s)
→ Electroless nickel plating (made by JX Metal, UBN-18)
(80 ° C, pH 4.6, 15 min, P content 7%)
→ Electroless palladium plating (the above electroless palladium plating solution, 50 ° C, 6 minutes)
→ Electroless gold plating (made by JX Metal, FA-210)
(75 ° C, pH 7.0, 12 min)
(Washing process of 1 min is inserted between all processes)

The phosphorus content of the palladium plating film of the plated AlCu plate was measured by AES analysis. The obtained results are shown in Table 1, and graphs are shown in FIGS. 1A to 1D.
FIG. 2 is a graph showing the relationship between the concentration of thiodiglycolic acid and the phosphorus content in the palladium plating film.

Solder property evaluation Sn-Ag-Cu solder balls (600 µm diameter) were mounted on the pads of the plated wafer that had been plated above, and after forming solder bumps by reflow (once) under the following conditions, A test was conducted to evaluate the solder shear strength and fracture mode.
Reflow heating conditions Temperature: Peak top 245 ° C, heating at 240 ° C or higher for 40 seconds Atmosphere: Nitrogen atmosphere (oxygen concentration: 600 ppm to 800 ppm)
Solder ball used: Sn-3% Ag-0.5% Cu (600 μm diameter)
Solder shear test condition Solder shear speed: 100 μm / sec
Solder share height: 15μm from plating / solder joint surface
Table 1 shows the results of the obtained solder shear strength.
The fracture surface on the substrate side after the solder shear strength test was observed, and the fracture mode was evaluated. FIGS. 3A to 3D show optical microscope photographs of the fracture surface on the substrate side after the solder shear strength test in Examples 1 to 4. In Example 1 (FIG. 3A), a portion where the lower surface appears to be rough corresponds to an intermetallic compound (IMC layer) breakdown. In Example 1, broken solder and destruction of the intermetallic compound were observed, and in Example 4, broken solder was observed. It can be seen that the lower the phosphorus concentration in the palladium film, the lower the ratio of destruction of the IMC layer, and the harder it is to form an IMC layer.
The low phosphorus type Pd-P plating film obtained by using the electroless palladium plating solution of Examples 3 and 4 is the medium phosphorus type Pd obtained by using the electroless palladium plating solution of Examples 1 and 2. -Flip chip mountability was superior to -P plating film.
Therefore, the low-phosphorus-type Pd-P plating film obtained using the electroless palladium plating solution of Examples 3 and 4 has good flip chip mounting and wire bonding properties under the above test conditions. I understand.

After the FIB cross-section processing of the plated wafer, SIM image observation was performed to determine whether the obtained electroless palladium plating film was crystalline Pd-P or amorphous Pd-P. 4A to 4D show SIM images of Examples 1 to 4. From the bottom of the image, an AlCu pad, a nickel plating film, a palladium plating film, and a gold plating film are formed. When the palladium plating film is crystalline Pd-P, a channeling contrast is seen, while in the case of amorphous Pd-P, the whole is seen as a uniform gray.
Table 1 shows the determination results.

  In the SIM image observation, the thickness of the obtained palladium plating film was measured. The plating film obtained by using the electroless palladium plating solution of Example 4 was about 1.4 times as thick as the plating film obtained by using the electroless palladium plating solution of Example 1. This indicates that the plating rate using the electroless palladium plating solution of Example 4 was about 1.4 times the plating rate using the electroless palladium plating solution of Example 1.

In the electroless palladium plating used in Example 1, an electroless palladium plating solution was prepared in which the concentration of thiodiglycolic acid was changed as shown in Table 2 below, and heated at 70 ° C. for 24 hours to improve the solution stability. evaluated. The symbol "分解" indicates that no decomposition was caused by heating, and the symbol "x" indicates that decomposition occurred.
When the concentration of thiodiglycolic acid was 0.0002 mol / L or less, decomposition was confirmed by heating at 70 ° C. for 24 hours.

Also, as shown in the above Non-patent Document 1,
Palladium chloride 0.01mol / L
Ethylenediamine 0.08mol / L
Thiodiglycolic acid 0-200mg / L
Sodium hypophosphite 0.06mol / L
pH 8
Bath temperature 50 ℃
In the example using the electroless palladium plating solution, it is described that the phosphorous content of a plating film obtained in a concentration range of 50 to 200 mg / L of thiodiglycolic acid showed a constant value.
On the other hand, when the electroless palladium plating solution of the present invention was used, the content of phosphorus in the plating film was changed by changing the concentration of thiodiglycolic acid, and the content of phosphorus was 2 mass%. It can be seen that a plating film of not more than% was obtained.

Claims (12)

  An electroless palladium plating solution containing a chloroammine complex palladium salt, an inorganic sulfur compound, an ammonium compound, an amine compound, and a reducing agent containing phosphorus. The concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L,
The concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0040 mol / L with respect to the palladium-equivalent amount of the chloroammine complex palladium salt of 0.006 mol / L,
The concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L,
The concentration of the amine compound is 0.02 mol / L to 2.00 mol / L,
The electroless palladium plating solution according to claim 1, wherein the concentration of the phosphorus-containing reducing agent is 0.027 mol / L to 2.000 mol / L.   3. The electroless palladium plating solution according to claim 2, wherein the concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0009 mol / L with respect to 0.006 mol / L of palladium equivalent of the chloroammine complex palladium salt. 4. .   3. The electroless palladium plating solution according to claim 2, wherein the concentration of the inorganic sulfur compound is 0.0010 mol / L to 0.0040 mol / L with respect to 0.006 mol / L of the chloroammine complex palladium salt. .   The electroless palladium plating solution according to any one of claims 1 to 4, wherein the inorganic sulfur compound is thiodiglycolic acid or thioglycolic acid.   The electroless palladium plating solution according to any one of claims 1 to 5, wherein the phosphorus-containing reducing agent is sodium hypophosphite or sodium phosphite.   The electroless palladium plating solution according to any one of claims 1 to 6, further comprising an unsaturated dicarboxylic acid compound.   An electroless palladium plating method for performing electroless palladium plating using the electroless palladium plating solution according to claim 1.   The content of phosphorus in the obtained electroless palladium plating film is adjusted to 1.0% by mass or more and 4.0% by mass or less by adjusting the concentration of the inorganic sulfur compound contained in the electroless palladium plating solution. 9. The electroless palladium plating method according to 8. The electroless palladium plating solution,
The concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L,
The concentration of the inorganic sulfur compound is 0.0003 mol / L to 0.0009 mol / L with respect to the palladium equivalent of the chloroammine complex palladium salt of 0.006 mol / L;
The concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L,
The concentration of the amine compound is 0.02 mol / L to 2.00 mol / L,
The concentration of the phosphorus-containing reducing agent is 0.027 mol / L to 2.000 mol / L,
The electroless palladium plating method according to claim 8 or 9, wherein the content of phosphorus in the obtained electroless palladium plating film is 3.0% by mass or more and 4.0% by mass or less. The electroless palladium plating solution,
The concentration of the chloroammine complex palladium salt is 0.001 mol / L to 0.200 mol / L,
The concentration of the inorganic sulfur compound is 0.0010 mol / L to 0.0040 mol / L with respect to the palladium equivalent of the chloroammine complex palladium salt of 0.006 mol / L;
The concentration of the ammonium compound is 0.1 mol / L to 2.0 mol / L,
The concentration of the amine compound is 0.02 mol / L to 2.00 mol / L,
The concentration of the phosphorus-containing reducing agent is 0.027 mol / L to 2.000 mol / L,
The electroless palladium plating method according to claim 8 or 9, wherein the content of phosphorus in the obtained electroless palladium plating film is 1.0% by mass or more and less than 3.0% by mass.   A method for producing an electroless palladium plating solution in which a chloroammine complex palladium salt, an inorganic sulfur compound, an ammonium compound, an amine compound, and a phosphorus-containing reducing agent are dissolved in water.