JP7500013B2 - Printed Wiring Boards - Google Patents

Description

The present invention relates to a printed wiring board.

Patent Document 1 describes the production of a (lead-free) solder alloy by melting and adjusting the raw materials consisting of Sn, Ag, Cu, Ni, and a Sn-P alloy in an electric furnace, and containing 1.0 to 4.0% by weight of silver (Ag), 2.0% by weight or less of copper (Cu), 0.5% by weight or less of nickel (Ni), 0.2% by weight or less of phosphorus (P), with the remainder consisting of tin (Sn) and unavoidable impurities.

Patent No. 3296289

However, when soldering is performed using conventional solder products, it is difficult to achieve finer wiring patterns.
An object of the present invention is to provide a printed wiring board that enables finer wiring patterns to be formed.

The printed wiring board of the present invention includes a substrate and an electronic component soldered to the substrate with solder, and the solder is made using a solder product manufactured by a method including a heating step of melting a raw material containing tin as a main component and a metal element other than lead as a secondary component and a carboxylic acid having a carbon number of 10 to 20 by heating to form a molten metal, a removal step of removing solids having a diameter of more than 10 μm and present in the molten metal, which has been set at 230°C to 260°C, and a cooling step of solidifying the molten metal from which the solids have been removed by cooling and precipitating the carboxylic acid on the surface side.

The present invention aims to provide a printed wiring board that allows for finer wiring patterns.

1A and 1B are diagrams showing a solder product according to the present embodiment. 1A is a first example showing a state of conventional solder, and FIG. 1B is a first example showing a state of solder according to the present embodiment. 1A is a second example showing the state of conventional solder, and FIG. 1B is a second example showing the state of solder according to the present embodiment. 1A is a third example showing the state of conventional solder, and FIG. 1B is a third example showing the state of solder according to the present embodiment. 11A is a fourth example showing the state of conventional solder, and FIG. 11B is a fourth example showing the state of solder according to the present embodiment. 10A is a fifth example showing the state of conventional solder, and FIG. 10B is a fifth example showing the state of solder according to the present embodiment. 10A is a sixth example showing the state of conventional solder, and FIG. 10B is a sixth example showing the state of solder according to the present embodiment. 13A is a seventh example showing the state of conventional solder, and FIG. 13B is a seventh example showing the state of solder according to the present embodiment. 1A and 1B show an electronic component before it is soldered to a substrate. 8A is an eighth example showing the state of the conventional solder, and FIG. 8B is an eighth example showing the state of the solder of the present embodiment. FIG. 1 is a diagram showing a printed circuit board on which electronic components are mounted. 4 is a flowchart showing a manufacturing procedure of the solder product according to the present embodiment. FIG. 13 is a diagram for explaining an overview of the filtration process of step 30.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the size, thickness, and other dimensions of each part in the drawings referred to in the following description may differ from the actual dimensions.
[Definition of terms]
First, the definitions of some terms used in this embodiment will be explained.

(Lead-free solder)
In the present embodiment, the "lead-free solder" refers to a mixture of multiple metal elements containing tin (Sn) as a main component and metal elements other than lead (Pb) as secondary components.
Here, the metal element serving as the secondary component may be any metal element other than lead, such as copper (Cu), silver (Ag), bismuth (Bi), zinc (Zn), etc. Among these, it is preferable to use copper, which is available at low cost.
The metal element serving as the secondary component may contain not only one type but also two or more types (for example, silver and copper).
Although the "lead-free solder" of the present embodiment is called "lead-free," it may actually contain lead as an unavoidable impurity.
Furthermore, in addition to the above metal elements, the lead-free solder of the present embodiment contains a carboxylic acid having a carbon number of 10 to 20. As will be described in detail later, the inclusion of a carboxylic acid reduces the inclusion of solid matter such as oxides and needle-like crystals.

(Solder products)
In this embodiment, the "solder product" refers to an item used in soldering to join target metal materials with the above-mentioned "lead-free solder."
Here, examples of "solder products" include those in the form of plates or rods (ingots, plates, rods), lines (wires), and balls. Solder products may also contain flux. Thus, for example, solder products include paste-like cream solder made by kneading fine solder powder with flux, and thread-like solder threads containing flux in a core shape.

(Solder raw materials)
In the present embodiment, the "solder raw material" refers to a material used as a raw material when manufacturing the above-mentioned "solder product."
Here, examples of the "solder raw material" include the metal elements constituting the above-mentioned main and sub-components, and alloys thereof. Furthermore, examples of the "solder raw material" include the above-mentioned carboxylic acids having 10 to 20 carbon atoms. In addition, in this embodiment, solder scraps generated when soldering is performed using the above-mentioned "solder product" may be used as the "solder raw material". Furthermore, these "solder raw materials" (particularly solder scraps) may contain oxides of various metals and various impurities.

(Solder)
In the present embodiment, "solder" refers to the above-mentioned "solder product" that is transferred and adhered to the metal material to be joined as a result of joining by soldering.

(wire)
The "wire" in this embodiment refers to an electric wire that at least partially includes the above-mentioned "solder product". The wire may be entirely made of the above-mentioned "solder product", or may partially use the above-mentioned "solder product". An example of a partially used wire is an electric wire in which a linear conductor is coated with the above-mentioned "solder product". The linear conductor is, for example, a copper wire. That is, in this case, the wire is a copper wire whose outer surface is coated with the above-mentioned "solder product". In addition, the wire may further include an insulating coating that covers the outer surface of the coated "solder product". The insulating coating is, for example, made of resin or the like. That is, the wire may be an insulated electric wire.

(soldered products)
In this embodiment, the "soldered product" refers to a product including those in which connected members are soldered together via the above-mentioned "solder product." Here, the connected members are a plurality of members that are connected by soldering, and are not particularly limited as long as they can be soldered. The connected members are, for example, members made of metal, members made of ceramics such as porcelain and glass, etc. Examples of connected members soldered together include printed circuit boards, electrical products using such printed circuit boards, ornaments such as pendants and brooches, stained glass, and housings in which metal plates are soldered together.

(Relationship between "lead-free solder,""solderproducts,""solder raw materials,""solder," and "soldering products")
Therefore, in this embodiment, a "solder product" made of "lead-free solder" is manufactured using a "solder raw material," and then this "solder product" is used to solder a target metal material, causing the "solder" to transfer and adhere to the metal material. The product manufactured by soldering using this "solder product" becomes a "soldered product."

(Flexible Printed Circuit Board)
The "flexible printed circuit board (FPC (Flexible Printed Circuits))" in this embodiment is a flexible printed circuit board. The "flexible printed circuit board" is, for example, a thin film, and has a structure in which an adhesive layer is formed on an insulating base film, and a conductor foil is further laminated on the adhesive layer. This "flexible printed circuit board" has a terminal for connecting to a connector or the like. This terminal can also be said to be an electrode. Conventionally, this terminal is generally in the form of a conductive foil covered with gold foil or the like. On the other hand, the terminal of the "flexible printed circuit board" in this embodiment is a conductive foil on which the above-mentioned "solder product" is coated. The conductive foil is, for example, a copper foil made of copper. That is, in this case, the terminal of the "flexible printed circuit board" is a copper foil on which the above-mentioned "solder product" is coated. Conventionally, in order to plate the gold foil, it is necessary to clean the plating bed, and the cleaning agent used for cleaning may remain after cleaning. The remaining cleaning agent causes defects such as poor contact, cracks, and deterioration of the joint. In this embodiment, the "solder product" can be covered without the need to clean the terminals beforehand. Therefore, no cleaning agent remains. This makes it difficult for such problems to occur, and furthermore, a _CO2 reduction effect can be expected. As will be described in detail later, in the case of solder using the "solder product" of this embodiment, a pattern can be formed with a narrow gap. Thus, similarly, the gap between multiple terminals of the "flexible printed circuit board" can also be made narrower.

(Electronic Components)
The "electronic component" in this embodiment is a component of an electronic circuit, and has a terminal that electrically connects to a board or other electronic components. The "electronic component" is not particularly limited, and may be, for example, a capacitor, a resistor, a sensor, a semiconductor, an integrated circuit, a connector, a micro LED (Micro LED Display) panel, or the like. This terminal can also be said to be an electrode. The terminal is coated with the above-mentioned "solder product" on the surface of the terminal. The conductor is a copper wire made of copper. That is, in this case, the terminal of the "electronic component" is a copper wire whose surface is coated with the above-mentioned "solder product". As will be described in detail later, in the case of solder using the "solder product" of this embodiment, component floating and crack occurrence can be suppressed. In addition, improvement of fluidity and wettability and uniform application amount can be realized. Therefore, similarly, when the "solder product" of this embodiment is coated on the terminal of the "electronic component", it is effective in suppressing component floating and crack occurrence, improving fluidity and wettability, and realizing a uniform application amount.

(molten metal)
In the present embodiment, the "molten metal" refers to a "solder raw material" that is a raw material for a "solder product" and is melted by heating.

[Solder products]
Next, the solder product according to this embodiment will be described.
1(a) and (b) are diagrams showing a solder product according to the present embodiment.
1A shows a solder product 20, and FIG. 1B shows an enlarged cross-sectional view of a surface portion of the solder product 20 shown in FIG. 1A.
As shown in FIG. 1( b ), the solder product 20 of the present embodiment includes a lead-free solder portion 21 and a surface layer 22 .

The lead-free solder portion 21 is mainly made of the lead-free solder described above. That is, it contains tin (Sn) as the main component and metal elements other than lead (Pb) as secondary components. Furthermore, the lead-free solder portion 21 of this embodiment contains less solid matter such as oxides and needle-shaped crystals than conventional solder.

The surface layer 22 is mainly composed of the above-mentioned carboxylic acid. In other words, the carboxylic acid is mainly distributed on the surface side of the solder product 20 to form the surface layer 22. The surface layer 22 covers the entire surface of the solder product 20. The carboxylic acid forms the surface layer 22 by being unevenly distributed on the surface side of the solder product 20, for example.

As a result, the surface layer 22 plays a role as a protective layer for the lead-free solder portion 21. In other words, the surface layer 22 prevents oxygen and moisture in the air from reaching the lead-free solder portion 21. Therefore, the surface layer 22 can be said to be an oxidation-resistant film or a water-resistant film. Therefore, when the solder product 20 is, for example, cream solder, it can be stored at room temperature. Conventionally, cream solder is prone to oxidation and moisture absorption, so it has been common to store it at low temperatures using a refrigerator or the like. On the other hand, the cream solder of this embodiment is less prone to oxidation and moisture absorption because the surface layer 22 is present in the solder powder contained therein. Therefore, it can be stored at room temperature. In addition, it has a long shelf life and is less likely to be lost, so it has excellent environmental performance and can be expected to reduce _CO2 emissions.

As mentioned above, the carboxylic acid has a carbon number of 10 or more and 20 or less. If the carbon number is less than 10, the carboxylic acid is less likely to form the surface layer 22. If the carbon number is more than 20, the carboxylic acid is less likely to disperse in the molten metal. In this case, too, the carboxylic acid is less likely to form the surface layer 22.

However, it is more preferable that the carboxylic acid is a fatty acid having 12 to 16 carbon atoms. Among these, it is even more preferable that the carboxylic acid is a monovalent fatty acid having 12 to 16 carbon atoms. Among these, it is particularly preferable that the carboxylic acid is a monovalent saturated fatty acid having 12 to 16 carbon atoms.

Examples of monovalent saturated fatty acids include lauric acid (CH ₃ -(CH ₂ ) ₁₀ -COOH) having 12 carbon atoms, myristic acid (CH ₃ -(CH ₂ ) ₁₂ -COOH) having 14 carbon atoms, pentadecylic acid (CH ₃ -(CH ₂ ) ₁₃ -COOH) having 15 carbon atoms, and palmitic acid (CH ₃ -(CH ₂ ) ₁₄ -COOH) having 16 carbon atoms.
Among monovalent fats, palmitic acid having 16 carbon atoms is particularly preferred. Palmitic acid has a melting point of 62.9°C and a boiling point of 351°C to 352°C, and exists as a molten liquid in the soldering temperature range of 200°C to 300°C, and is likely to adhere to the surface after the solder has solidified. In this case, palmitic acid can be said to be compatible with lead-free solder. In addition, the fluidity of the solder during soldering is improved. If the carbon number is more than 16 or if the carbon number is less than 16, the solder may not be in a molten liquid state in the soldering temperature range. In addition, the fluidity of the solder during soldering is likely to be lower than that of palmitic acid.
Palmitic acid is contained in, for example, coconut oil or coconut oil waste, and can be extracted from these. Therefore, in this respect, palmitic acid can be said to be a plant-derived material and a renewable raw material. In addition, palmitic acid has little effect on human skin and is excellent in safety. Palmitic acid may be extracted from other raw materials instead of being extracted from coconut oil or the like, or may be produced by chemical synthesis.

Examples of monovalent fatty acids that are not monovalent saturated fatty acids include monovalent unsaturated fatty acids, such as oleic acid (CH ₃ -(CH ₂ ) ₇ -CH=CH-(CH ₂ ) ₇ -COOH), linoleic acid (CH 3 -(CH 2 ) ₄ -CH=CH-CH 2 -CH=CH-(CH ₂ ) 7 -COOH), and linolenic acid (CH _{3 -CH 2} -CH=CH-CH ₂ -CH=CH-CH ₂ -CH=CH-CH ₂ -CH=CH-(CH ₂ ) ₇ -COOH), which have ₁₈ carbon _atoms .
Furthermore, examples of fatty acids that are not monobasic fatty acids include dibasic fatty acids that are dicarboxylic acids, such as sebacic acid (HOOC-(CH ₂ ) ₈ -COOH) having 10 carbon atoms and tridecanedioic acid (HOOC-(CH ₂ ) ₁₁ -COOH) having 13 carbon atoms.
Furthermore, examples of carboxylic acids having 10 to 20 carbon atoms, rather than 12 to 16 carbon atoms, include sebacic acid ( _CH3- ( _CH2 ) ₈ -COOH) having 10 carbon atoms, stearic acid ( _CH3- ( _CH2 ) ₁₆ -COOH) having 18 carbon atoms, and arachidic acid ( _CH3- ( _CH2 ) ₁₈ -COOH) having 20 carbon atoms.

The thickness of the surface layer 22 is, for example, 1 nm or more and 1 μm or less. The surface layer 22 is, for example, a monolayer of carboxylic acid. When the surface layer 22 is a monolayer of carboxylic acid, the thickness of the surface layer 22 is, for example, 1 nm or more and 4 nm or less. However, it may not be a monolayer, and as a result, the thickness may be thicker than this. When the surface layer 22 is a monolayer of palmitic acid, the thickness of the surface layer 22 is about 2.5 nm.

[Solder]
Next, the solder according to the present embodiment will be described, along with a printed circuit board using the solder according to the present embodiment.
The conventional solder described below is a lead-free solder having a composition of 0.7 wt. % copper and the remainder tin, while the solder of the present embodiment is a lead-free solder containing the above-mentioned carboxylic acid.

Fig. 2(a) is a first example showing the state of the conventional solder, and Fig. 2(b) is a first example showing the state of the solder of this embodiment.
Here, a case is shown in which a plurality of patterns P are formed on a printed wiring board with a predetermined electrode width F and a predetermined gap G by solder. In this case, the electrode width F is 10 μm. The predetermined gaps G are 5 μm, 10 μm, 20 μm, 40 μm, 80 μm, 160 μm, and 320 μm. FIG. 2(a) shows a case in which each pattern P is formed by conventional solder 20a, and FIG. 2(b) shows a case in which each pattern P is formed by solder 20b using the solder product 20 of the present embodiment.

2(a) and 2(b), in the solder 20a in FIG. 2(a), adjacent patterns P are short-circuited when the gap G is 20 μm or less. In other words, a so-called solder bridge Br occurs. In contrast, the solder 20b in FIG. 2(b) can form all patterns P. That is, for example, when soldering electrodes of electronic components, it means that even if the gap between the electrodes is narrow, the electrodes can be soldered without short-circuiting. This is because the conventional solder 20a contains solids such as oxides and needle-like crystals, while the solder 20b of the present embodiment contains a small amount of these solids and needle-like crystals. That is, in the conventional solder 20a, it is difficult to form a pattern P with a narrow gap G because the conventional solder 20a contains more solids and needle-like crystals. On the other hand, in the solder 20a of the present embodiment, it is easier to form a pattern P with a narrow gap G because the solids and needle-like crystals are small.
One of the features of the solder product 20 of the present embodiment is that the solder using the solder product 20 has good fluidity and better wettability to the printed wiring than conventional solder. Therefore, the solder is less likely to bulge out from the pattern P.

Fig. 3(a) is a second example showing the state of the conventional solder, and Fig. 3(b) is a second example showing the state of the solder of this embodiment.
Here, an electrode 112a of an electronic component 112 is soldered to a pad 111a of a substrate 111. Fig. 3(a) shows a case where soldering is performed using a conventional solder 20a, and Fig. 3(b) shows a case where soldering is performed using a solder 20b using the solder product 20 of this embodiment. A solder resist 250 is formed to prevent the solder 20a, 20b from adhering. The solder 20a, 20b adhere to areas other than the solder resist 250. The function of the solder resist 250 is the same in the examples described below.

Also, the solder product 20 of this embodiment has good fluidity and better wettability to the pads 111a and electrodes 112a than the conventional solder product, as in the case of FIG. 2. Therefore, when comparing FIG. 3(a) and FIG. 3(b), the solder 20a of FIG. 3(a) has poor fluidity and poor wettability to the pads 111a and electrodes 112a, so they do not bond unless the amount of solder 20a attached is large. On the other hand, the solder 20b of FIG. 3(b) has good fluidity and good wettability to the pads 111a and electrodes 112a, so they bond even if the amount of solder 20b attached is small. Therefore, the amount of solder 20b used during soldering is reduced. Therefore, a _CO2 reduction effect can also be expected.

Fig. 4(a) is a third example showing the state of the conventional solder, and Fig. 4(b) is a third example showing the state of the solder of this embodiment.
Here, a case is shown in which solder is coated onto pads 111a of a substrate 111. Comparing Fig. 4(a) and Fig. 4(b), Fig. 4(a) shows a case in which coating is performed with conventional solder 20a, while Fig. 4(b) shows a case in which coating is performed with solder 20b using the solder product 20 of the present embodiment.

Comparing FIG. 4(a) and FIG. 4(b), the surface of solder 20b in FIG. 4(b) is smoother than that of solder 20a in FIG. 4(a). This is because solder 20b has better fluidity and wettability to pad 111a than solder 20a, and contains a smaller amount of solids such as oxides and needle-shaped crystals.

Fig. 5(a) is a fourth example showing the state of the conventional solder, and Fig. 5(b) is a fourth example showing the state of the solder of this embodiment.
Here, an electrode 112a of an electronic component 112 is soldered to a pad 111a of a substrate 111, and the pad 111a and the electrode 112a are coated with solder. Fig. 5(a) shows a case where soldering is performed using a conventional solder 20a, and Fig. 5(b) shows a case where soldering is performed using a solder 20b that uses the solder product 20 of this embodiment.

Comparing FIG. 5(a) and FIG. 5(b), the solder 20a in FIG. 5(a) has poor fluidity and poor wettability to the pads 111a and electrodes 112a, so unless the amount of solder 20a applied is large, they cannot be bonded and further coated. In contrast, the solder 20b in FIG. 5(b) has good fluidity and good wettability to the pads 111a and electrodes 112a, so even if the amount of solder 20b applied is small, they can be bonded and further coated.

Fig. 6(a) is a fifth example showing the state of the conventional solder, and Fig. 6(b) is a fifth example showing the state of the solder of this embodiment.
Here, an electrode 112a of an electronic component 112 is shown soldered to a pad 111a of a substrate 111. Fig. 6(a) shows a case where soldering is performed using a conventional solder 20a, and Fig. 6(b) shows a case where soldering is performed using a solder 20b that uses the solder product 20 of the present embodiment.

6(a) and 6(b), the solder 20a in Fig. 6(a) has a larger amount and is therefore more likely to contain solid matter such as oxides, needle-like crystals, and voids Df. In contrast, the solder 20b in Fig. 6(b) has a smaller amount than the solder 20b in Fig. 6(a), and is therefore less likely to contain solid matter such as oxides, needle-like crystals, and voids Df.
In addition, since the solder 20b is less likely to contain solid matter such as oxides, needle-like crystals, and voids Df, the solder 20b has a higher bonding strength than the solder 20a.

Fig. 7(a) is a sixth example showing the state of the conventional solder, and Fig. 7(b) is a sixth example showing the state of the solder of this embodiment.
Here, an electrode 112a of an electronic component 112 is shown soldered to a pad 111a of a substrate 111. In this case, the change over time after soldering is illustrated. Fig. 7(a) shows the case where soldering is performed using a conventional solder 20a, and Fig. 7(b) shows the case where soldering is performed using a solder 20b that uses the solder product 20 of this embodiment.

7(a) and 7(b), the solder 20a in FIG. 7(a) is prone to cracks Kr. This is because when the solder 20a is subjected to vibration or expands or contracts due to temperature changes, if it contains solids such as oxides, needle-like crystals, and voids Df, cracks Kr are likely to occur. That is, if an alternating load occurs on a printed circuit board or the like, and deterioration occurs over the long term, the conductive environment of the solder may break, and the conductive function may be lost. Then, the occurrence of cracks Kr makes the solder 20a prone to oxidation. On the other hand, the solder 20b in FIG. 7(b) is unlikely to contain solids such as oxides, needle-like crystals, and voids Df. Therefore, cracks Kr are unlikely to occur, and as a result, changes over time are unlikely to occur. And because cracks Kr are unlikely to occur, the solder 20b is unlikely to oxidize. Also, on the surface of the solder 20b, carboxylic acid forms a surface layer 22, as in the case described in FIG. 1(b). As a result, the surface layer 22 acts as an oxidation-resistant film, suppressing oxidation of the solder 20b and making it even less susceptible to changes over time.

Conventionally, soldering may be performed using a nitrogen reflow device in a nitrogen environment that excludes oxygen. This method can suppress the generation of dross, which is an oxide of solder, during soldering. Therefore, improvement can be expected when soldering with a narrow pitch P as described in FIG. 2. However, it is difficult to improve to the level of the solder 20b of this embodiment. In addition, since conventional solder contains solid matter and needle-like crystals, it is ineffective in suppressing the cracks Kr. In addition, since there is no surface layer 22, it is ineffective in suppressing changes over time due to oxidation.
It should be noted that the use of a nitrogen reflow device to form the solder 20b in this embodiment is not excluded, and it is expected that the generation of dross can be further suppressed compared to when this device is not used.

Fig. 8(a) is a seventh example showing the state of the conventional solder, and Fig. 8(b) is a seventh example showing the state of the solder of this embodiment.
Here, an electrode 112a of an electronic component 112 is shown soldered to a pad 111a of a substrate 111. Fig. 8(a) shows a case where soldering is performed using a conventional solder 20a, and Fig. 8(b) shows a case where soldering is performed using a solder 20b that uses the solder product 20 of the present embodiment.

Comparing FIG. 8(a) and FIG. 8(b), the solder 20a in FIG. 8(a) contains solids such as oxides, needle-like crystals, and voids Df, which makes it easy for the electronic component 112 to float up from the board 111. In contrast, the solder 20b in FIG. 8(b) is less likely to contain solids such as oxides, needle-like crystals, and voids Df. Therefore, component floating is less likely to occur.

9(a) and 9(b) show the electronic component 112 before it is soldered to the substrate 111. FIG.
Here, the electronic component 112 has electrodes 112a coated with solder in advance. In this state, the electronic component 112 may be further soldered and bonded to the substrate 111, as shown in FIG.
9(a) shows a case where coating is performed with conventional solder 20a, and FIG. 9(b) shows a case where coating is performed with solder 20b using the solder product 20 of the present embodiment.

9(a) and 9(b), the surface of the solder 20b in Fig. 9(b) is smoother than that of the solder 20a in Fig. 9(a). This is because the solder 20b has better fluidity and wettability to the pad 111a than the solder 20a.
Furthermore, since the solder 20b in FIG. 9B is coated more uniformly than the solder 20a in FIG. 9A, component lifting is less likely to occur and voids Df and cracks Kr are less likely to occur.

Fig. 10(a) is an eighth example showing the state of the conventional solder, and Fig. 9(b) is an eighth example showing the state of the solder of this embodiment.
Here, a printed circuit board before electronic components are mounted is shown. This printed circuit board is also called a printed circuit board. Fig. 10(a) shows a conventional printed circuit board 200, and Fig. 10(b) shows a printed circuit board 200 using the solder product 20 of this embodiment.

The conventional printed circuit board 200 shown in FIG. 10(a) has a copper pattern 220 formed as a wiring pattern on a substrate 210. This copper pattern 220 is formed as a thin film on the substrate 210, and is an example of a wiring pattern layer that forms a wiring pattern. Nickel plating 230 and gold plating 240 are then layered on the copper pattern 220. In addition, a solder resist 250 is formed to prevent adhesion of the solder 20a. The nickel plating 230 and gold plating 240 are formed to improve the durability of the printed circuit board 200.

The printed circuit board 200 of this embodiment shown in FIG. 10(b) is similar to FIG. 10(a) in that a copper pattern 220 is applied as a circuit pattern on a board 210, and a solder resist 250 is formed. In contrast, the printed circuit board 200 of this embodiment differs in that a solder coat 260 is coated on the copper pattern 220. The solder coat 260 is made of solder 20b. The solder coat 260 is formed as a thin film on the copper pattern 220, and is an example of a solder layer that contains solder.

In other words, the printed circuit board 200 of this embodiment does not require nickel plating 230 and gold plating 240, and can be substituted with the less expensive solder coating 260. Since the solder coating 260 of this embodiment is made of solder 20b, it is less likely to contain solid matter such as oxides, needle-like crystals, and voids Df. In addition, since the surface layer 22 is formed as a protective layer on the solder coating 260, it is less likely to change over time, and the printed circuit board 200 is less likely to change over time. Therefore, the nickel plating 230 and gold plating 240 are no longer necessary.

Moreover, the printed circuit board 200 of the present embodiment may further include electronic components 112 mounted thereon. This printed circuit board is also called a printed wiring board.
FIG. 11 is a diagram showing a printed circuit board 200 on which an electronic component 112 is mounted.
In this case, the electronic component 112 is soldered to the solder coat 260. Specifically, the electrode 112a of the electronic component 112 is soldered to the solder coat 260 by the solder 20b. In this case, when soldering with the solder 20b, the solder 20b and the solder coat 260 are both melted once and then integrated and solidified. Therefore, as shown in the figure, they are no longer distinguishable. In this case, the solder 20b constituting the solder coat 260 and the solder 20b to be soldered may have the same composition, or may have different compositions within the above-mentioned range. However, regardless of the composition, the solder coat 260 and the solder 20b that do not contain coarse solids or needle-like crystals are more likely to improve the joint strength.
Also, the electronic component 112 may be joined to the conventional printed circuit board 200 shown in FIG. 10(a) by the solder 20b. In this case, the printed circuit board 200 before mounting the electronic component 112 is the same as the conventional one, but by using the solder 20b of the present embodiment during soldering, the joint strength is improved and the solder 20b is less likely to change over time. That is, the solder 20b is less likely to contain solids such as oxides, needle-like crystals, voids Df, etc., compared to the conventional solder 20a. Therefore, the degree of adhesion of the joint between the printed circuit board 200 and the electronic component 112 is improved, and the joint strength is more likely to be improved. As a result, the solder 20b is less likely to change over time.

[Method of manufacturing solder product 20]
Next, a method for manufacturing the solder product 20 according to the present embodiment will be described.
FIG. 12 is a flow chart showing the manufacturing procedure of the solder product 20 according to the present embodiment.

First, a preparation step is carried out to prepare solder raw materials that are the raw materials for the solder product 20 (step 10).
In step 10, a solder raw material containing tin as a main component and metal elements other than lead is prepared as a solder raw material. At this time, it is desirable that the composition ratio of each metal element is basically the same as the composition ratio in the target solder product 20. Note that the solder raw material prepared in step 10 may actually contain lead as an unavoidable impurity. Also, in step 10, a carboxylic acid having a carbon number of 10 to 20 is prepared as a solder raw material.

Next, a heating step is performed (step 20) in which the solder raw material prepared in step 10 is heated and melted into a molten metal.
In step 20, the temperature may be set as appropriate as long as the above-mentioned solder raw material melts, but when manufacturing a solder product 20 made of so-called lead-free solder, it is desirable to set the temperature at approximately 300°C to 400°C.

The carboxylic acids, such as palmitic acid, have the effect of absorbing oxygen in the molten metal. This prevents solids, such as oxides, and needle-like crystals from being mixed into the solder product. The amount of oxygen in the solder product 20 is also reduced. The solder 20b is also less susceptible to oxidation during the soldering process. As a result, when the solder 20b is used in this embodiment, voids Df are less likely to occur.
Furthermore, when palmitic acid is used as the carboxylic acid, the oxygen adsorption capacity is particularly excellent.

Next, a filtration process is carried out (step 30), in which the molten metal obtained in step 20 is filtered using a filter (details of which will be described later). In the following description, the molten metal obtained by carrying out step 20 may be referred to as the "molten metal before filtration," and the molten metal obtained by carrying out step 30 may be referred to as the "molten metal after filtration." Details of step 30 will be described later.

Then, a cooling step is performed (step 40) in which the filtered molten metal obtained in step 30 is cooled and solidified to form the solder product 20. At this time, the carboxylic acid is precipitated on the surface side of the solder product 20 to form a surface layer 22.
In step 40, it is possible to select an appropriate cooling method depending on the shape (ingot, wire, ball, etc.) of the solder product 20 to be obtained. For example, when an ingot-shaped solder product 20 is to be obtained, the molten metal after the above-mentioned filtration may be poured into a mold made of iron oxide or the like and allowed to solidify.

[Details of the filtration process]
FIG. 13 is a diagram for explaining an outline of the filtration process in step 30.
Here, Fig. 13(a) is a diagram for explaining an overview of a filtration device 10 used in the filtration step. Fig. 13(b) is a diagram for explaining a configuration example of a filter 12 (details of which will be described later) provided in the filtration device 10. Fig. 13(c) is a diagram for explaining another configuration example of the filter 12.

(Configuration of Filtration Device)
The filtering device 10 includes a container 11 to which the unfiltered molten metal 1 is supplied and which stores the unfiltered molten metal 1, a filter 12 attached to the container 11 and which filters the unfiltered molten metal 1 to discharge filtered molten metal 2, and a heater 13 which heats the filter 12. Here, in the example shown in Fig. 13(a), it is assumed that the temperature of the molten metal 1 before filtration is a pre-filtration temperature T1, and the temperature of the molten metal 2 after filtration is a post-filtration temperature T2.

〔container〕
The container 11 has, for example, a cylindrical shape, and two openings provided in the container 11 are arranged so as to face in the vertical direction (up and down direction). The container 11 may be made of any material, but from the viewpoint of suppressing the inclusion of oxides and the like in the molten metal 1 before filtration, it is preferable to use a metal material rather than a ceramic material. Furthermore, among various metal materials, it is preferable to use a stainless steel material, in particular SUS316L, from the viewpoint of reducing the inclusion of the metal in the molten metal 1 before filtration.

〔filter〕
The filter 12 is, for example, plate-shaped (disk-shaped) and is attached to close the bottom of the above-mentioned container 11. The mesh size s of the filter 12 in this embodiment is set to 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. In particular, it is set to 1 μm or less. The filter 12 may be made of any material (for example, inorganic material, metal material, organic material), but from the viewpoint of suppressing the inclusion of oxides and the like in the molten metal 1 before filtration, it is preferable to use a metal material rather than a ceramic material. Among various metal materials, from the viewpoint of reducing the melting into the molten metal 1 before filtration, it is preferable to use a stainless steel material, particularly SUS316L. Furthermore, when the filter 12 made of a metal material is adopted, as long as the above-mentioned mesh size s can be obtained, either a wire mesh made by weaving metal wires or a punched metal made by drilling holes in a metal plate may be adopted. However, it is preferable to use a wire mesh as the filter 12, which can easily obtain a smaller mesh size s. In addition, when a wire mesh is used as the filter 12, it is preferable to use a wire mesh that has been subjected to a sintering process in order to suppress deviation of the mesh openings s. Examples of organic materials that can be used as the filter 12 include various aramid resins and carbon fibers.

When a wire mesh is used as the filter 12, various weaving methods may be used, such as plain weave, twill weave, plain tatami weave, and twill tatami weave. Here, FIG. 13(b) shows an example of a filter 12 using a plain weave, and FIG. 13(c) shows an example of a filter 12 using a twill weave. As shown in these, when the diameter (width) of the metal wire (wire) used in each is the wire width w, the gap between two adjacent wires is the mesh size s. Note that in the examples shown in FIGS. 13(b) and (c), the mesh size s is larger than the wire width w, but this is not limited to this, and the mesh size s and the wire width w may be equal, or the mesh size s may be smaller than the wire width w.

〔heater〕
The heater 13 heats the filter 12 by using a heat source other than the unfiltered molten metal 1. Therefore, the heater 13 may directly heat the filter 12 by passing electricity or the like, or may indirectly heat the filter 12 by thermal conduction via the container 11 or another member not shown.

[Relationship between pre-filtration temperature and post-filtration temperature]
Here, the relationship between the pre-filtration temperature T1 of the pre-filtration molten metal 1 and the post-filtration temperature T2 of the post-filtration molten metal 2 will be described.
As described above, in the heating process of step 20, the solder raw material is melted by being heated to about 300° C. to 400° C. However, the pre-filtration temperature T1 of the pre-filtration molten metal 1 is about 230° C. to 260° C., more preferably about 235° C. to 250° C., and the maximum temperature is slightly lower than that during melting.
On the other hand, the post-filtration temperature T2 of the filtered molten metal 2 is desirably set to about 230° C. to 260° C. If the post-filtration temperature T2 is too low, the filtered molten metal 2 will start to solidify during or immediately after the filtration process, resulting in a significant decrease in the production efficiency of the solder product 20.

(Operation of the filtration device)
Next, the operation of the filtration device 10 in the filtration process of step 30 will be described in more detail.
First, in the heating process of step 20, the temperature of the unfiltered molten metal 1 obtained by heating the solder raw material to 300° C. to 400° C. is adjusted to a pre-filtration temperature T1 (230° C. to 260° C.). In addition, the filter 12 is heated in advance using the heater 13.

Next, the unfiltered molten metal 1, whose temperature has been adjusted to the unfiltered temperature T1, is poured from above into the container 11 to which the filter 12 is attached. Then, most of the unfiltered molten metal 1 poured into the container 11 passes through the filter 12 and falls downward due to the action of gravity, becoming the filtered molten metal 2. At this time, pressure may be applied to the unfiltered molten metal 1 present in the container 11 and on the filter 12, as necessary. When applying pressure, it is preferable to use a gas such as nitrogen (a gas inert to the unfiltered molten metal 1), which is unlikely to oxidize the unfiltered molten metal 1 and which can apply pressure isotropically to the unfiltered molten metal 1.

The filter 12 is heated by the heater 13 while the unfiltered molten metal 1 is being filtered, preventing the molten metal from solidifying within the filter 12. Note that the heater 13 only serves the function of assisting the molten metal to pass through the filter 12, and it is desirable not to heat the molten metal excessively so that the pre-filtration temperature T1 of the molten metal 1 in the vessel 11 exceeds the set temperature (230°C to 260°C). Note that filtration may be performed not only once, but multiple times.

The filtered molten metal 2 obtained by passing through the filter 12 is turned into the solder product 20 by the cooling process described above. Meanwhile, residue (not shown) that did not pass through the filter 12 remains on the filter 12. Then, after the filtering process is performed and heating by the heater 13 is terminated, the filter 12 with the residue adhering thereto is removed from the container 11 and discarded. A new filter 12 is then attached to the container 11.

In the embodiment described above, the solder product 20 contains a carboxylic acid having 10 to 20 carbon atoms. This adsorbs oxygen during the manufacturing process of the solder product 20, suppressing the generation of solids such as oxides and needle-like crystals. This allows the solder pattern to be finer, as shown in FIG. 2. Furthermore, as shown in FIG. 3 and other figures, the solder has good fluidity and good wettability to electrodes and substrates, allowing the amount of adhesion to be reduced. And, as shown in FIG. 6 and other figures, the amount of solids, needle-like crystals, and voids Df is reduced, and the generation of cracks Kr can be suppressed. This makes the solder product less susceptible to changes over time and has excellent durability.

After the solder product 20 is formed, the carboxylic acid exists on the surface of the solder product 20 as a surface layer 22, which acts as a protective layer. This makes the solder 20b less susceptible to deterioration over time due to oxidation or moisture absorption, and has excellent durability.

10, when the solder 20b is used for the printed circuit board 200, the nickel plating 230 and the gold plating 240 are not required. This is also expected to have a _CO2 reduction effect.
In addition, by containing a carboxylic acid having a carbon number of 10 or more and 20 or less, the generation of solid matter such as oxides and needle-like crystals can be suppressed, so depending on the performance required of the solder product 20, it may not be necessary to perform the filtration process of step 30 described above.

In recent years, especially in the field of smartphones, the wiring patterns on printed wiring boards that are the subject of soldering have become increasingly finer (thinner). For this reason, the so-called L/S (line/space) value on printed wiring boards has been below 100 μm for several years, and recently, 10 μm/10 μm is being considered.

When soldering a printed wiring board with an L/S set to 10 μm/10 μm, if there are needle-shaped objects with a diameter of just under 10 μm in the solder product 20 that is the source of the solder, there is a concern that the above-mentioned solder bridge Br may occur. For this reason, when taking such a problem into consideration, it is desirable to use a filter 12 with a mesh size s set to 5 μm or less in the filtration process of step 30, as in the above-mentioned Examples 1 and 2.

[others]
Here, a binary solder product 20 containing tin (main component) and copper (secondary component) called Sn-Cu system is used as an example for explanation. However, similar results have been obtained with other solder products 20 containing tin as the main component, which will not be described in detail here.
Here, examples of binary solder products 20 other than Sn-Cu include Sn-Ag, Sn-Bi, and Sn-Zn. Examples of ternary solder products 20 include Sn-Ag-Cu, Sn-Ag-Bi, Sn-Ag-In, Sn-Zn-Bi, and Sn-Zn-Al. Examples of quaternary solder products 20 include Sn-Ag-Cu-Bi and Sn-Ag-In-Bi. Examples of quinary solder products 20 include Sn-Ag-Cu-Ni-Ge. Similar results can be obtained with hexa- or higher-element solder products 20.

In addition, although the method of filtering the molten metal obtained by melting the solder raw material using the filter 12 has been described as an example, the present invention is not limited to this. For example, a method such as centrifugation or solid-liquid separation may be used to remove solids and needle-like crystals that are present in the molten metal and have a diameter of more than 10 μm (more preferably, a diameter of more than 5 μm, even more preferably, a diameter of more than 3 μm, and particularly preferably, a diameter of more than 1 μm).

1...molten metal before filtration, 2...molten metal after filtration, 10...filter, 11...container, 12...filter, 13...heater, 20...solder product, 20a, 20b...solder, 21...lead-free solder part, 22...surface layer, 111...substrate, 111a...pad, 112...electronic component, 112a...electrode, 200...printed circuit board, 210...substrate, 220...copper pattern, 230...nickel plating, 240...gold plating, 250...solder resist, 260...solder coat, Kr...crack

Claims (1)

A substrate;
an electronic component soldered to the substrate;
Equipped with
The solder is
A heating process of melting a raw material containing tin as a main component and a metal element other than lead and a carboxylic acid having a carbon number of 10 to 20 as a secondary component by heating to obtain a molten metal;
A removal step of removing solid matter having a diameter of more than 10 μm and present in the molten metal from the molten metal set at 230° C. to 260° C.;
a cooling step of cooling the molten metal from which the solid matter has been removed to solidify the molten metal and precipitating the carboxylic acid on a surface side of the molten metal;
A printed wiring board using a solder product manufactured by the manufacturing method of a solder product comprising the steps of: