Patent Description:
With the development of information technologies, various electronic products are increasingly appearing in people's daily life. A circuit board is a main component for an electronic product to implement each function. The circuit board generally includes a board body and an electronic component that is fastened to the board body by means of soldering. A tin solder leg used to fasten the electronic component exists on an outer surface of the board body.

When there is water or moisture entering the electronic device, the tin solder leg on the outer surface of the board body is often subject to dendrite corrosion in a case of electrification. The following describes a dendrite corrosion process. As shown in <FIG>, an anode tin solder leg is oxidized in water and dissolved to obtain a tin ion, and the tin ion moves to a cathode due to a potential difference between the anode and the cathode to obtain an electron, so as to form tin dendrite. As shown in <FIG>, continuous generation of dendrites easily causes a connection among different solder legs, and causes a short circuit, which causes a part of functions of an electronic product to fail, thereby affecting reliability of the electronic product.

In a related technology, to suppress dendrite corrosion of a solder leg on a circuit board, an outer surface of the circuit board is usually covered with an insulation layer, so as to prevent the solder leg from contacting water, thereby avoiding dendrite corrosion of the solder leg.

However, because each electronic component is installed on the board body, a geometric appearance of the outer surface of the circuit board is often complex. In addition, there are a relatively large quantity and variety of electronic components on the board body, and a radio frequency antenna and a relatively large quantity of electrical connection points, which cannot be covered by the insulation layer, are disposed on the outer surface of the board body. Therefore, a disposing process of the insulation layer is relatively complex, and consequently, costs of the electronic product are relatively high.

In addition, because there is a relatively low probability of water or moisture entering the electronic device, insulation layers of most electronic products do not function when in use. If an isolation layer is disposed on a circuit board for each electronic product, costs are further increased.

<CIT> relates to a printed circuit board, comprising a substrate comprising an insulating material; a plurality of conductive tracks attached to at least one surface of the substrate; a multi-layer coating deposited on the at least one surface of the substrate, the multi-layer coating covering at least a portion of the plurality of conductive tracks, the multi-layer coating comprising at least one layer formed of a halo-hydrocarbon polymer; and at least one electrical component connected by a solder joint to at least one conductive track, wherein the solder joint is soldered through the multi-layer coating such that the solder joint abuts the multi-layer coating.

<CIT> relates to a solution for dissolving noble metal alloys which include Sn from substrates in presence of refractory metal which must be retained on the substrate consisting essentially of (<NUM>) KI in an amount of at least <NUM> moles/liter, (<NUM>) I2 in an amount of at least <NUM> moles/liter, and (<NUM>) halogen ions selected from the group consisting of chloride and bromide ions in an amount of at least <NUM> moles/lite.

Document <NPL> reviews briefly recent advances in method of inhibiting the ECM of tin and tin-based solder alloys. Some candidate strategies for slowing down dendrite growth for tin and tin-based solder alloys have been elaborated.

<CIT> relates to a surface treatment method for solder joint comprising steps of: (<NUM>) making alkali buffer solution; (<NUM>) dipping products with solder joint into the alkali buffer solution for a period of time; and (<NUM>) rinsing the products to remove alkali remained thereon; whereby a passive layer is formed on a surface of the solder joint to inhibit the solder joint corrosion and dissolution during subsequent aqueous cleaning.

This application provides a circuit board, an electronic device, and a production method for a circuit board, so as to prevent dendrite corrosion of the circuit board, and production costs are relatively low.

According to a first aspect, this application provides a circuit board, including:.

The board body may include a substrate and a conducting layer, and the conducting layer is fastened to the substrate. A connector may be disposed on a surface of the substrate, one end of the connector is electrically connected to the conducting layer, the other end of the connector passes through the substrate and is located on an outer surface of the substrate, and the other end of the connector is configured to be electrically connected to a pin of the electronic component. Specifically, the connector may be a bonding pad. A material of the substrate is an insulation material, and the insulation material may be, for example, a resin, a glass fiber, or another insulation material. The conducting layer may be a copper foil, the conducting layer is configured to form wiring in the circuit board, or the conducting layer may be another conductive material. According to wiring distribution, the board body may be a single-layer board, dual-layer board, or multi-layer board. When the board body is a multi-layer board, the board body includes a multi-layer conducting layer and a multi-layer substrate, and the multi-layer conducting layer and the multi-layer substrate are alternately stacked. According to a property of the substrate, the board body may be a rigid board, or may be a flexible board. The board body in this embodiment of this application may be a printed circuit board (printed circuit board, PCB).

The electronic component may include, but is not limited to, a power management unit, a radio frequency integrated circuit, a radio frequency power amplifier, a wireless fidelity chip, a resistor, a capacitor, an inductor, a transistor, a processor, a memory, a camera, a flash lamp, a microphone, a speaker, a battery, and the like.

The electronic component may be a sheet-like component, and may be electrically connected to a board body by using a surface mount technology SMT.

The reaction particle may be disposed on the outer surface of the solder leg, or may be disposed on an entire outer surface of the board body and the solder leg, or may be disposed at a location, on the surface of the board body, where no solder leg is disposed and adjacent to the solder leg. The reaction particle of the circuit board provided in this embodiment of this application is adjacent to the solder leg for soldering the electronic component. When the circuit board is energized and in an environment with water, the reaction particle reacts with the solder leg to form an insoluble protection layer on the outer surface of the solder leg. In this way, the insoluble protection layer can isolate the solder leg from water, to prevent the solder leg from contacting water. In this way, when there is water on the circuit board, dendrite corrosion of the solder leg can be prevented.

In addition, in this embodiment of this application, the reaction particle only needs to be attached to a location adjacent to the solder leg on the surface of the board body, and may react with the solder leg when the circuit board is energized and in an environment with water, so that an insoluble protection layer is formed on the outer surface of the solder leg. In this embodiment of this application, a form, a density, a location, and the like of the reaction particle are not strictly and specifically required. Therefore, disposing of the reaction particle is not easily limited by a geometric appearance of the circuit board, and is not easily affected by a component that needs to be exposed outside, such as an antenna and an electrical connection point. Therefore, a disposing process of the reaction particle on the board body is more flexible, simple, and easy to operate, so that a production process of the circuit board and the electronic device is also simple, and production costs of the circuit board and the electronic device are relatively low.

In addition, a form of the reaction particle is relatively flexible, the reaction particle does not need to have an isolation function, and there is no need to set a very large density. Therefore, disposing of the reaction particle is not easy to cause an obstacle to radiation of an antenna, and a radiation function of the antenna is not easy to be affected, so that reliability of a wireless communication function of the electronic device is better.

In an optional design, the reaction particle is a compound, and anionic reducibility of the compound is higher than that of tin.

When reducibility of a substance is relatively high, that is, an electron loss capacity of the substance is relatively high, and the substance is more easily oxidized. A reducibility order of nonmetallic anions can be determined according to electronegativity/activity: S<NUM>->I->Br->B->Cl->OH->oxygenated acid ions>Sn<NUM>-.

Br-, B-, Cl- and oxygenated acid ions, and products produced by reaction between such ions and tin are easily dissolved in water, or cannot react with tin after oxidation. These ions are not suitable as anions for reaction particles. Therefore, the foregoing compound may be a sulfide, a complex of sulfur, an iodide, a complex of iodine, or a hydroxide.

In this embodiment, because anionic reducibility of the reaction particle is higher than that of tin, when electrochemical corrosion occurs, an electron loss capability of anion of the reaction particle is stronger than that of tin. The anion of the reaction particle is oxidized before tin, so as to suppress oxidization and dissolving of the tin solder leg, thereby further reducing a probability that the tin solder leg is oxidized and dissolved to a tin particle, and reducing a probability of dendrite corrosion of the solder leg.

In an optional design, the compound is a sulfide or an iodide.

In this embodiment, because anions in the sulfide and the iodide are sulfur ions and iodine ions, in an environment with water, the sulfur ions or the iodine ions can react with dissolved tin ions to form a precipitate, so as to form a tin disulfide protection layer or a tin tetraiodide protection layer on an outer surface of the tin solder leg.

In addition, after the sulfur ions or the iodine ions are oxidized to a sulfur or iodine elementary substance, the sulfur or iodine elementary substance may further react with the tin solder leg quickly to form a tin disulfide protection layer or a tin tetraiodide protection layer, thereby increasing a speed and a probability of forming the insoluble protection layer, so that the generated insoluble protection layer can better cover the outer surface of the solder leg to make the solder leg better isolated from water, and a probability of the solder leg being oxidized and dissolved is further reduced, thereby reducing a probability of dendrite corrosion of the solder leg.

In an optional design, the insoluble protection layer is a tin sulfide protection layer or a tin iodide protection layer.

Because tin sulfide or tin iodide is not dissolvable in water, when the insoluble protection layer is a tin sulfide protection layer or a tin iodide protection layer, the insoluble protection layer may be more reliably attached to the surface of the solder leg, and the insoluble protection layer may more reliably isolate the solder leg from water, thereby better preventing dendrite corrosion of the solder leg.

In an optional design, the reaction particle is disposed on the outer surface of the solder leg.

In this embodiment, the reaction particle is directly disposed on the outer surface of the solder leg, and the reaction particle is in contact with the solder leg. In this way, in a case of the circuit board in contact with water and energized, the reaction particle can react quickly with the solder leg to form an insoluble protection layer, and a probability of the solder leg being oxidized and dissolved is reduced, thereby reducing a probability of dendrite corrosion of the solder leg. In addition, in this embodiment, there is no need to dispose the reaction particle on the surface of the board body except the solder leg, thereby reducing impact of the reaction particle on the board body and making the circuit board more reliable.

In an optional design, the reaction particle is dissolvable in water.

For example, the reaction particle may be any one of sodium sulfide, potassium sulfide, sodium iodide, potassium iodide, calcium iodide, or potassium hydroxide, but is not limited thereto.

In this embodiment, because the reaction particle is dissolvable in water, when the circuit board is in an environment with water, the reaction particle can be more evenly distributed in water after being dissolved in water, and can be more evenly distributed in water attached on the outer surface of the solder leg, so that the reaction particle in water can react with each part of the outer surface of the solder leg more evenly. Each part of the outer surface of the solder leg can quickly and evenly form an insoluble protection layer, so that each part of the outer surface of the solder leg cannot contact water, thereby reducing a probability of dendrite corrosion of the solder leg.

In an optional design, the reaction particle is attached to the surface of the board body in a form of powder or a particle.

In this embodiment, because a process of attaching the reaction particle in the form of powder or a particle to the surface of the board body is relatively simple, the reaction particle is attached to the surface of the board body in the form of powder or a particle, which may make a production process of the circuit board and an electronic device simpler, thereby reducing costs of the circuit board and the electronic device.

According to a second aspect, an embodiment of this application provides a circuit board, including a board body, an electronic component, and an insoluble protection layer. The electronic component is soldered to a surface of the board body by using soldering tin, and the insoluble protection layer is attached to an outer surface of the solder leg for soldering the electronic component, so as to isolate the solder leg from water. When the circuit board is energized and in an environment with water, the insoluble protection layer is a protection layer obtained from reaction between the solder leg and a reaction particle, which is disposed on the surface of the board body and adjacent to the solder leg.

The insoluble protection layer on the solder leg of the circuit board provided in this embodiment can isolate the solder leg from water, so that the solder leg does not contact water. In this way, when there is water on the circuit board, dendrite corrosion of the solder leg can be prevented.

In addition, the insoluble protection layer is obtained, when the circuit board is energized and in an environment with water, from reaction between the solder leg and the reaction particle on the surface of the board body. Therefore, the reaction particle only needs to be attached to a location adjacent to the solder leg on the surface of the board body, and the reaction particle may react with the solder leg when the circuit board is energized and in an environment with water, so that the insoluble protection layer is formed on the outer surface of the solder leg. In this embodiment of this application, a form, a density, a location, and the like of the reaction particle are not strictly and specifically required. Therefore, disposing of the reaction particle is not easily limited by a geometric appearance of the circuit board, and is not easily affected by a component that needs to be exposed outside, such as an antenna and an electrical connection point. Therefore, a disposing process of the reaction particle on the board body is more flexible, simple, and easy to operate, so that a production process of the circuit board and the electronic device is also simple, and production costs of the circuit board and the electronic device are relatively low.

Because a form of the reaction particle is relatively flexible, the reaction particle does not need to have an isolation function, and there is no need to set a very large density, in this case, disposing of the reaction particle is not easy to cause an obstacle to radiation of an antenna, and a radiation function of the antenna is not easy to be affected, so that reliability of a wireless communication function of the electronic device is better.

According to a third aspect, an embodiment of this application provides an electronic device, including a housing and the circuit board installed in the housing according to any one of the first aspect or the second aspect.

According to the electronic device provided in this embodiment, when the circuit board is energized and in an environment with water, a reaction particle reacts with a solder leg to form an insoluble protection layer on an outer surface of the solder leg. The insoluble protection layer can isolate the solder leg from water, to prevent the solder leg from contacting water. In this way, when there is water on the circuit board, dendrite corrosion of the solder leg can be prevented.

In addition, disposing of the reaction particle is not easily limited by a geometric appearance of the circuit board, and is not easily affected by a component that needs to be exposed outside, such as an antenna and an electrical connection point. Therefore, a disposing process of the reaction particle on a board body is more flexible, simple, and easy to operate, so that a production process of the circuit board and the electronic device is also simple, and production costs of the circuit board and the electronic device are relatively low.

According to a fourth aspect, an embodiment of this application provides a production method for a circuit board, where the method includes:.

In this embodiment, by using a soldering process such as reflow soldering, wave soldering, and dip soldering, the electronic component may be soldered to the board body by using soldering tin, or may be soldered by using another soldering process. This is not specifically limited in this application.

In this embodiment, the reaction particle may be disposed on the surface of the board body by using any one of a coating method, a printing method, a silk printing method, a soaking method, an atomization sedimentation method, a steam method, a vapor deposition method, a sputtering method, a spraying method, or 3D printing.

Optionally, a solution containing the reaction particle may be prepared, the solution containing the reaction particle is adsorbed on the surface of the board body, and the reaction particle is formed on the surface of the board body after drying. Alternatively, powder or a particle of the reaction particle may be directly attached to an outer surface of the board body by using a 3D printing method, a spraying method, a sputtering method, or the like.

According to the production method for a circuit board provided in this embodiment of this application, the reaction particle is disposed at a location, on the surface of the board body, which is adjacent to the solder leg for soldering the electronic component. When the circuit board is energized and in an environment with water, the reaction particle reacts with the solder leg to form an insoluble protection layer on the outer surface of the solder leg. In this way, the insoluble protection layer can isolate the solder leg from water, to prevent the solder leg from contacting water. In this way, when there is water on the circuit board, dendrite corrosion of the solder leg can be prevented.

In addition, in this embodiment of this application, the reaction particle only needs to be disposed at a location, on the surface of the board body, which is adjacent to the solder leg, and the reaction particle may react with the solder leg when the circuit board is energized and in an environment with water, so that an insoluble protection layer is formed on the outer surface of the solder leg. In this embodiment of this application, a form, a density, a location, and the like of the reaction particle are not strictly and specifically required. Therefore, disposing of the reaction particle is not easily limited by a geometric appearance of the circuit board, and is not easily affected by a component that needs to be exposed outside, such as an antenna and an electrical connection point. Therefore, a disposing process of the reaction particle on the board body is more flexible, simple, and easy to operate, so that a production process of the circuit board and the electronic device is also simple, and production costs of the circuit board and the electronic device are relatively low. In addition, a form of the reaction particle is relatively flexible, the reaction particle does not need to have an isolation function, and there is no need to set a very large density. Therefore, disposing of the reaction particle is not easy to cause an obstacle to radiation of an antenna, and a radiation function of the antenna is not easy to be affected, so that reliability of a wireless communication function of the electronic device is better.

In an optional design, the disposing a reaction particle at a location, on a surface of the board body, which is adjacent to a solder leg for soldering the electronic component to obtain the circuit board includes:.

The solution containing the reaction particle may be a saturated solution, or may be an unsaturated solution. For example, a volume ratio of the solution containing the reaction particle may be in a range from <NUM>% to <NUM>%, that is, the saturated solution containing the reaction particle of <NUM> to <NUM> volumes is added to <NUM> volumes of solvent (water or alcohol), to form the solution. The volume ratio of the solution containing the reaction particle may also be another ratio, which is not specifically limited in this application.

The solution containing the reaction particle may be an aqueous solution, or may be an alcoholic solution. The alcoholic solution is obtained by dissolving the reaction particle in alcohol, and the aqueous solution is obtained by dissolving the reaction particle in water.

An environment of the solution containing the reaction particle may be in an original state (that is, a liquid state) environment of a solution, or may be a steam environment or a vapor environment generated when a solution changes a physical form after processing such as evaporation or atomization.

In this embodiment, the solution containing the reaction particle is adsorbed on the board body and then dried to obtain the circuit board, so that the reaction particle can be conveniently disposed on the surface of the board body. In the solution of the reaction particle, the reaction particle is evenly distributed. Therefore, in this embodiment, the reaction particle disposed on the surface of the board body can further be more evenly distributed, so that when the circuit board is energized and meets water, an insoluble protection layer with good uniformity can be formed on each part of the surface of the solder leg, and each part of the outer surface of the solder leg cannot contact water, thereby reducing a probability of dendrite corrosion of the solder leg.

In an optional design, the placing the board body soldered with the electronic component in an environment of a solution containing the reaction particle includes:
soaking the board body soldered with the electronic component in the solution containing the reaction particle.

In this embodiment, the board body is directly soaked in the solution containing the reaction particle, and the solution may be adsorbed on the surface of the board body simply and conveniently. Therefore, a process for disposing the reaction particle on the surface of the board body is simpler, so that a production process of the circuit board and the electronic device is simpler, and production costs are lower.

In an optional design, the placing the board body soldered with the electronic component in an environment of a solution containing the reaction particle includes:.

In an optional design, the disposing a reaction particle at a location, on a surface of the board body, which is adjacent to a solder leg for soldering the electronic component includes:
disposing the reaction particle on the outer surface of the solder leg for soldering the electronic component.

In an optional design, before the disposing a reaction particle at a location, on a surface of the board body, which is adjacent to a solder leg for soldering the electronic component, the method further includes:
covering the surface of the board body on which the electronic component is installed with a barrier, where the barrier covers the board body except each solder leg, so as to prevent the reaction particle from being disposed on the surface of the board body except each solder leg. The barrier may be a dam board, a housing, a barrier film, and the like. A plurality of through-holes are disposed in the barrier, a size of each through-hole is corresponding to a size of each solder leg, and the through-hole is used to make the solder leg exposed, so as to facilitate disposing of the reaction particle.

In this embodiment, by using the barrier, the board body except the solder leg can be covered, so as to prevent the reaction particle from being disposed on a part except the solder leg, thereby reducing impact of the reaction particle on the circuit board except the solder leg, and improving structural stability and reliability of the circuit board.

In an optional design, the disposing a reaction particle at a location, on a surface of the board body, which is adjacent to a solder leg for soldering the electronic component includes:
sputtering, by using a sputtering method, and adsorbing the reaction particle at the location, on the surface of the board body, which is adjacent to the solder leg for soldering the electronic component.

A process of disposing the reaction particle on the surface of the board body by using the sputtering method may be specifically: filling a vacuum coating chamber with a proper amount of argon gas, placing a target material of the reaction particle at a location close to a cathode, applying a voltage between a cathode board and an anode board, and rapidly increasing energy of an electron emitted from a surface of the cathode board by means of acceleration of an electric field. A high-energy electron can collide with the argon gas to decompose a positive argon ion. Under an effect of the electric field, the argon ion moves to the cathode board and the target material of the reaction particle to bombard a surface of the target material of the reaction particle, and the reaction particle in the target material of the reaction particle obtains energy from bombardment, and is finally discharged from the target material of the reaction particle to sputter on the board body.

In this embodiment, the reaction particle may be directly sputtered and adsorbed on the surface of the board body by using the sputtering method, and no drying or another subsequent processing process is required, so that a production process of the circuit board has fewer steps and a simpler process. In addition, by using the sputtering method, the board body is always in a dry environment, so that a process of disposing the reaction particle does not affect another part of the circuit board, and reliability of the circuit board is higher. In addition, by using the sputtering method, a film of the reaction particle with a more uniform thickness and better densification can be formed on the surface of the board body, so that when the circuit board is energized and meets water, an insoluble protection layer with better uniformity can be formed on the solder leg.

In an optional design, the method further includes:
energizing the circuit board and placing the circuit board in an environment with water, so that the reaction particle reacts with the solder leg to form the insoluble protection layer on the outer surface of the solder leg.

In this implementation, when the circuit board is energized, the circuit board is soaked in water, or water is sprayed on the circuit board, or the circuit board is placed in vapor or water after atomization, so that the reaction particle reacts with the solder leg to form the insoluble protection layer on the outer surface of the solder leg.

In this implementation, the circuit board may be energized first, and then placed in an environment with water, or the circuit board may be placed in an environment with water first and then energized, or the circuit board is energized, and at the same time, placed in an environment with water. This is not specifically limited in this application.

In this embodiment, the insoluble protection layer is formed on the outer surface of the solder leg, and the solder leg can be isolated from water, so that dendrite corrosion of the solder leg can be prevented.

In an optional design, the disposing a reaction particle at a location, on a surface of the board body, which is adjacent to a solder leg for soldering the electronic component, and energizing the circuit board and placing the circuit board in an environment with water includes:
energizing the board body on which the electronic component is installed, and placing the board body in an environment of a solution containing the reaction particle, so that the reaction particle reacts with the solder leg to form the insoluble protection layer on the outer surface of the solder leg, to obtain the circuit board.

In this embodiment, when the board body is energized, the board body is placed in the environment of the solution containing the reaction particle. In this way, when the reaction particle is attached to the surface of the board body, the insoluble protection layer is formed on the outer surface of the solder leg. In this way, a process of forming the insoluble protection layer is simultaneously performed with the process of disposing the reaction particle, which reduces a production process step of the circuit board, and makes a production process of the circuit board simpler.

In an optional design, the method further includes:
cleaning and drying the circuit board formed with the insoluble protection layer.

Specifically, the circuit board may be cleaned by using an ultrasonic cleaning machine, or may be cleaned by using a washing machine. A cleaning solution may be water, or may be an alcoholic solution.

In this embodiment, the reaction particle remaining on the circuit board, the reaction particle and the solder leg, and an intermediate product generated in a process of water reaction may be washed off, so that impact of these substances on performance of the circuit board can be reduced.

Because anions in the sulfide and the iodide are sulfur ions and iodine ions, after the sulfur ions or the iodine ions are oxidized to a sulfur or iodine elementary substance, the sulfur or iodine elementary substance may further react with the tin solder leg quickly to form a tin disulfide protection layer or a tin tetraiodide protection layer, thereby increasing a speed and a probability of forming the insoluble protection layer, so that the generated insoluble protection layer can better cover the outer surface of the solder leg to make the solder leg better isolate from water, and a probability of the solder leg being oxidized and dissolved is further reduced, thereby reducing a probability of dendrite corrosion of the solder leg.

Meanings represented by reference numerals of the accompanying drawings are respectively as follows:.

Clearly, the described embodiments are only some, but not all, embodiments of this application.

In the description of this application, it should be noted that, unless otherwise specified and limited, the terms "install", "connection", and "connect" should be understood in a broad sense, for example, may be a fastened connection, may be a detachable connection, or may be integrally connected; may be a mechanical connection, may be an electrical connection, or may communicate with each other; may be directly connected, or may be indirectly connected by using an intermediate medium, or may be connected inside two components or an interaction relationship between the two components. A person of ordinary skill in the art may understand a specific meaning of the foregoing term in this application according to a specific situation.

In the description of this application, it should be understood that an orientation or location relationship indicated by the terms "upper", "lower", "side", "inner", "outer", "top", "bottom" is an installation-based orientation or location relationship, which is merely intended to facilitate description and simplify description of this application, and is not intended to indicate or imply that the referred apparatus or component must have a specific orientation, and be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on this application.

It should be further noted that in the embodiments of this application, a same reference numeral indicates a same component part or a same part. For a same part in the embodiments of this application, only one part or component may be used as an example in the figure to mark a reference numeral. It should be understood that, for another same part or component, the reference numeral is also applicable.

In the following, the terms "first", "second", and the like are used only for description purposes, and cannot be understood to indicate or imply relative importance or implicitly indicate the quantity of indicated technical features. Therefore, a feature defined as "first", "second", or the like may explicitly or implicitly include one or more of the features.

In the description of this application, it should be noted that the term "and/or" is merely an association relationship that describes an associated object, and indicates that three relationships may exist. For example, A and/or B may indicate three conditions that only A exists, A and B exist simultaneously, or only B exists.

It should be further noted that in the embodiments of this application, a same reference numeral indicates a same component part or a same part. For a same part in this embodiment of this application, only one part or component may be used as an example in the figure to mark a reference numeral. It should be understood that, for another same part or component, the reference numeral is also applicable.

A circuit board is a main component for an electronic product to implement various functions. The circuit board generally includes a board body and an electronic component that is fastened to the board body by soldering of soldering tin. A tin solder leg used to fasten the electronic component exists on an outer surface of the board body. When there is water or moisture entering the electronic device, the tin solder leg on the outer surface of the board body is often subject to dendrite corrosion in a case of electrification. The following describes a dendrite corrosion process of a solder leg.

<FIG> is a schematic diagram of a process in which dendrite corrosion occurs on a solder leg of a circuit board, and <FIG> is a physical diagram of a solder leg of a circuit board after dendrite corrosion;.

As shown in <FIG>, when a board body <NUM> of a circuit board is energized, a solder leg <NUM> connected to a positive electrode of a power supply is an anode (that is, the "+" electrode in <FIG>), and a solder leg <NUM> connected to a negative electrode of the power supply is a cathode (that is, the "-" electrode in <FIG>). When the circuit board is in an environment with water <NUM>, the solder leg <NUM> is easily subject to electrochemical corrosion, and the electrochemical corrosion can cause an anodic solder leg <NUM> to be oxidized and dissolved.

A specific process of the electrochemical corrosion is as follows: The anodic solder leg <NUM> loses electrons and is oxidized to tin ions, and oxidation reaction occurs on the anode. Oxygen of the cathode obtains electrons and combines with water to form a hydroxide ion, and reduction reaction occurs on the cathode. Because tap water is usually sterilized by chlorine gas, chlorine gas can be dissolved in water to form hydrogen chloride, so tap water is usually slightly acidic. Hydrogen ions exist in tap water. When a hydrogen ion exists in the water <NUM>, the cathode may be further subject to reaction in which the hydrogen ion obtains electrons to generate hydrogen gas.

A reaction equation of anode reaction during an electrochemical corrosion process is Sn - 2e = Sn<NUM>+;
a reaction equation of cathode reaction during the electrochemical corrosion process is <NUM>+ + 2e = H<NUM>, O<NUM> + <NUM><NUM>O + 4e = 4OH-.

After a tin ion is generated due to electrochemical corrosion, as shown in <FIG>, because the tin ion is a cation, the tin ion moves toward the cathode due to an electric potential difference between the anode and the cathode. Because there is a relatively large quantity of electrons at the cathode, the tin ion easily obtains electrons at the cathode to restore and generate a tin elementary substance, the tin elementary substance generates a dendrite <NUM> at the cathode, and dendrite corrosion occurs. A reaction equation for reducing the tin ion to generate the tin elementary substance at the cathode is Sn<NUM>+ + 2e = Sn↓.

As shown in <FIG>, continuous generation of the dendrite <NUM> easily causes a connection among different solder legs <NUM>, and causes a short circuit, which causes a part of functions of an electronic product to fail, thereby affecting reliability of the electronic product.

In a related technology, to suppress dendrite corrosion of the solder leg <NUM> on the circuit board, an outer surface of the circuit board is usually covered with an insulation layer, so as to prevent the solder leg <NUM> from contacting water <NUM> to cause dissolution, thereby avoiding dendrite corrosion of the solder leg <NUM>.

However, when each electronic component is installed on the circuit board, a geometric appearance of the outer surface of the circuit board is often complex. In addition, there are a relatively large quantity and variety of electronic components on the circuit board, and a radio frequency antenna and a relatively large quantity of electrical connection points, which cannot be covered by the insulation layer, are disposed on the outer surface of the circuit board. Therefore, a disposing process of the insulation layer is relatively complex, and consequently, costs of an electronic product are relatively high.

To solve the foregoing problem, embodiments of this application provide a circuit board, an electronic device, and a production method for a circuit board, so as to reduce costs of the electronic device, and further prevent dendrite corrosion of a solder leg on the circuit board.

The following describes an electronic device and a circuit board provided in embodiments of this application.

In the embodiments of this application, the electronic device may be a device with a circuit board, such as a mobile phone (for example, a common mobile phone or a foldable mobile phone), a wireless headset, a wristband, a smart sound box, a tablet computer, a notebook computer, a desktop computer, a watch, a digital camera, a personal digital assistant (personal digital assistant, PDA), a point of sales (point of sales, POS), an in-vehicle computer, a television, a router, a drone, and the like, but is not limited thereto. In the embodiments of this application, a mobile phone is used as an example for description.

<FIG> is a schematic diagram of a structure of an electronic device according to an embodiment of this application. As shown in <FIG>, the electronic device includes a housing <NUM>, a display screen <NUM>, and a circuit board <NUM>. The display screen <NUM> and the circuit board <NUM> are installed on the housing <NUM>.

Specifically, the housing <NUM> may include a frame and a rear cover, and the frame surrounds a periphery of the display screen <NUM>, and surrounds a periphery of the rear cover. The display screen <NUM> and the rear cover are disposed at intervals. The circuit board <NUM> may be installed in a cavity formed among the display screen <NUM>, the frame, and the rear cover. The housing <NUM> may be a metal housing <NUM>, a metal housing <NUM> such as a magnesium alloy or stainless steel. In addition, the housing <NUM> may be a plastic housing <NUM>, a glass housing <NUM>, a ceramic housing <NUM>, or the like, but is not limited thereto.

The display screen <NUM> may be a light emitting diode (light emitting diode, LED) display screen, a liquid crystal display (liquid crystal display, LCD), an organic light-emitting diode (organic light-emitting diode, OLED) display screen, a touch panel-liquid crystal display (touch panel-liquid crystal display, TP-LCD), or the like, but is not limited thereto. In addition, the display screen <NUM> may further be a foldable screen (a flexible screen).

<FIG> is a schematic diagram of a structure of the circuit board <NUM> of the electronic device shown in <FIG>. As shown in <FIG>, the circuit board <NUM> includes a board body <NUM>, an electronic component <NUM>, and a reaction particle <NUM>.

The electronic component <NUM> is soldered to a surface of the board body <NUM> by using soldering tin, the reaction particle <NUM> is disposed on the surface of the board body <NUM>, and the reaction particle <NUM> is adjacent to a solder leg <NUM> for soldering the electronic component <NUM>. When the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> reacts with the solder leg <NUM> to form an insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>, and the insoluble protection layer <NUM> isolates the solder leg <NUM> from contacting water to prevent dendrite corrosion of the solder leg <NUM>.

The board body <NUM> may also be referred to as a circuit board. The board body <NUM> may include a substrate and a conducting layer, and the conducting layer is fastened to the substrate. A connector may be disposed on a surface of the substrate, one end of the connector is electrically connected to the conducting layer, the other end of the connector passes through the substrate and is located on an outer surface of the substrate, and the other end of the connector is configured to be electrically connected to a pin of the electronic component <NUM>. Specifically, the connector may be a bonding pad. A material of the substrate is an insulation material, and the insulation material may be, for example, a resin, a glass fiber, or another insulation material. The conducting layer may be a metal foil, for example, a copper foil. The conducting layer is configured to form wiring in the circuit board <NUM>, or the conducting layer may be another conductive material.

According to wiring distribution, the board body <NUM> may be a single-layer board, dual-layer board, or multi-layer board. When the board body <NUM> is a multi-layer board, the board body <NUM> includes a multi-layer conducting layer and a multi-layer substrate, and the multi-layer conducting layer and the multi-layer substrate are alternately stacked. According to a property of the substrate, the board body <NUM> may be a rigid board, or may be a flexible board. The board body <NUM> in this embodiment of this application may be a printed circuit board (printed circuit board, PCB).

The electronic component <NUM> may include a power management unit (power management unit, PMU), a radio frequency integrated circuit (radio frequency integrated circuit, RFIC), a radio frequency power amplifier (radio frequency power amplifier, RFPA), a wireless-fidelity (wireless-fidelity, WIFI) chip, a resistor, a capacitor, an inductor, a transistor, a processor, a memory, a camera, a flash lamp, a microphone, a speaker, a battery, and the like, but is not limited thereto. The electronic component <NUM> may be electrically connected to the board body <NUM>. Specifically, an electrical connection end of the electronic component <NUM> may be soldered to a connector (for example, a bonding pad) on the board body <NUM>, so as to implement electrical connection between the electronic component <NUM> and the board body <NUM>. There is the solder leg <NUM> on the surface of the board body <NUM> for soldering the electronic component <NUM> on the board body <NUM>. Solder for soldering the electronic component <NUM> is soldering tin.

Optionally, the electronic component <NUM> may be a sheet-like component, and the sheet-like component may be electrically connected to the board body <NUM> by using a surface mount technology (surface mount technology, SMT). The SMT is a circuit installation and connection technology in which a sheet-like component is attached and installed on the surface of the board body <NUM>, and implement soldering and assembly by using a soldering process such as reflow soldering or dip soldering. The SMT has a feature of high production efficiency, high reliability of installing the electronic component <NUM>, and high assembly density. The sheet-like component is a new micro component without leads or with short leads, and is a dedicated component for the SMT.

The reaction particle <NUM> may be disposed at a location, on the surface of the board body <NUM>, where the solder leg <NUM> is not disposed, and the reaction particle <NUM> is adjacent to the solder leg <NUM>, that is, there is a distance between the reaction particle <NUM> and the solder leg <NUM>. It may be understood that the distance between the reaction particle <NUM> and the solder leg <NUM> should not be too long, to ensure that when the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> can react with the solder leg <NUM> to form the insoluble protection layer <NUM>. For example, the distance between the reaction particle <NUM> and the solder leg <NUM> may be <NUM>, <NUM>, or <NUM>, but is not limited thereto.

When there is a distance between the reaction particle <NUM> and the solder leg <NUM>, if the circuit board <NUM> is in an environment with water, the reaction particle <NUM> can move in water due to an electric potential difference between cathodic and anodic solder legs <NUM>, so as to move to a location contacting the solder leg <NUM> to react with the solder leg <NUM> to form the insoluble protection layer <NUM>.

In a specific embodiment, the reaction particle <NUM> may be disposed on the outer surface of the solder leg <NUM>, that is, the distance between the reaction particle <NUM> and the solder leg <NUM> is <NUM>. The reaction particle <NUM> is directly disposed on the outer surface of the solder leg <NUM>, and the reaction particle <NUM> contacts the solder leg <NUM>. In this way, in a case in which the circuit board <NUM> meets water and is energized, the reaction particle <NUM> may react rapidly with the solder leg <NUM> to form the insoluble protection layer <NUM>, and a probability of the solder leg <NUM> being oxidized and dissolved is reduced, thereby reducing a probability of dendrite corrosion of the solder leg <NUM>. In addition, in this embodiment, there is no need to dispose the reaction particle <NUM> on the surface of the board body <NUM> except the solder leg <NUM>, thereby reducing impact of the reaction particle <NUM> on the board body <NUM> and making the circuit board <NUM> more reliable.

In a specific embodiment, the reaction particle <NUM> may alternatively be attached to an entire outer surface of the board body <NUM> and the solder leg <NUM>, so that a disposing process of the reaction particle <NUM> is simpler.

The insoluble protection layer <NUM> is not dissolvable in water, is attached to the outer surface of the solder leg <NUM>, and covers the outer surface of the solder leg <NUM>, so as to isolate the solder leg <NUM> from water.

The reaction particle <NUM> may be attached to the outer surface of the solder leg <NUM> in a form of a film, a particle, or powder. The reaction particle <NUM> may form a film with relatively good densification on the outer surface of the solder leg <NUM>, or may be attached to the outer surface of the solder leg <NUM> in a form of a particle or powder dispersedly. In this embodiment of this application, the reaction particle <NUM> can react with the solder leg <NUM> to form the insoluble protection layer <NUM> that covers the surface of the solder leg <NUM>, and a specific disposing form of the reaction particle <NUM> is not limited.

Because a process of attaching the reaction particle <NUM> in the form of powder or a particle to the surface of the board body <NUM> is relatively simple, the reaction particle <NUM> is attached to the surface of the board body <NUM> in the form of the powder or particle, which may make a production process of the circuit board <NUM> and the electronic device simpler, thereby reducing costs of the circuit board <NUM> and the electronic device.

The reaction particle <NUM> may be attached to the surface of the board body <NUM> or the surface of the solder leg <NUM> by using an intermolecular adsorption force, so that when the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> can move away from an attachment surface and move more flexibly due to a potential difference between the anode and the cathode, to react with the solder leg <NUM> to form the insoluble protection layer <NUM> more evenly, so that the formed insoluble protection layer <NUM> covers the outer surface of the solder leg <NUM> more evenly.

The reaction particle <NUM> may alternatively be attached to the surface of the board body <NUM> in a bonding manner or in another manner, which is not specifically limited in this application.

The reaction particle <NUM> may be an elementary substance, or may be a compound. A tin compound that is not dissolvable in water generally includes: tin sulfide and tin iodide. Therefore, the reaction particle <NUM> may be a sulfur or iodine elementary substance, or the reaction particle <NUM> may be a compound such as sulfide or iodide. The reaction particle <NUM> may be a pure substance, or may be a compound.

For example, the reaction particle <NUM> may include: a combination of one or more of an iodine elementary substance, a sulfur elementary substance, sodium sulfide, magnesium sulfide, potassium sulfide, sodium iodide, potassium iodide, and calcium iodide, and is not limited thereto. When the reaction particle <NUM> includes only one of the foregoing substances, the reaction particle <NUM> is a pure substance. When the reaction particle <NUM> includes a plurality of the foregoing substances, the reaction particle <NUM> is a compound. To facilitate disposing of the reaction particle <NUM>, the reaction particle <NUM> may be an elementary substance. When the circuit board <NUM> is energized and has water, the reaction particle <NUM> can react with the solder leg <NUM> (that is, tin) to form a precipitate, and a specific component of the reaction particle <NUM> is not limited.

Because dendrite corrosion is reaction that occurs only in an environment with water, when the circuit board <NUM> is in an environment which has no water or is dry, there is no chemical reaction between the reaction particle <NUM> on the surface of the solder leg <NUM> and the solder leg <NUM>, that is, the reaction particle <NUM> and the solder leg <NUM> remain their own states. In this way, intermediate substances generated by chemical occurrence between the solder leg <NUM> and the reaction particle <NUM> can be reduced, so that impact of these intermediate substances on performance of the circuit board <NUM> can be reduced.

In this embodiment of this application, when the circuit board <NUM> is energized and is in an environment with water, the reaction particle <NUM> may react with at least one solder leg <NUM> to form an insoluble protection layer <NUM> on an outer surface of the solder leg <NUM>. Because reduction reaction occurs at the cathode in a reaction process, and the solder leg <NUM> and the reaction particle <NUM> are usually easy to have oxidization reaction, the reaction particle <NUM> generally chemically reacts with the solder leg <NUM> to form an insoluble protection layer <NUM> at the anode, and the reaction particle <NUM> at the cathode generally does not chemically react with the solder leg <NUM> to form an insoluble protection layer <NUM>. Therefore, when the circuit board <NUM> is energized and is in an environment with water, the insoluble protection layer <NUM> can generally be formed on the surface of the solder leg <NUM> at each anode, and the insoluble protection layer <NUM> is generally not easily formed on the surface of the solder leg <NUM> at each cathode. Because the solder leg <NUM> at the cathode is not to be oxidized and dissolved, even if the surface of the solder leg <NUM> at the cathode does not form the insoluble protection layer <NUM>, the solder leg <NUM> at the cathode is not to be dissolved to cause electrochemical corrosion.

<FIG> is another schematic diagram of a structure of the circuit board <NUM> of the electronic device shown in <FIG>.

In this embodiment of this application, the electronic component <NUM> shown in <FIG> may be soldered to the board body <NUM>, and a plurality of electronic components <NUM> shown in <FIG> may be soldered to the board body <NUM>.

When the plurality of electronic components <NUM> shown in <FIG> are soldered to the board body <NUM>, electrochemical reaction may occur between two solder legs <NUM> with different polarities of a same electronic component <NUM>, and electrochemical reaction may also occur between two solder legs <NUM> with opposite polarities corresponding to two adjacent electronic components <NUM>.

The reaction particle <NUM> of the circuit board <NUM> provided in this embodiment of this application is adjacent to the solder leg <NUM> for soldering the electronic component <NUM>. When the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>. In this way, the insoluble protection layer <NUM> can isolate the solder leg <NUM> from water, to prevent the solder leg <NUM> from contacting water. In this way, when there is water on the circuit board <NUM>, dendrite corrosion of the solder leg <NUM> can be prevented.

In addition, in this embodiment of this application, the reaction particle <NUM> only needs to be attached to a location, on the surface of the board body <NUM>, adjacent to the solder leg <NUM>, and may react with the solder leg <NUM> when the circuit board <NUM> is energized and in an environment with water, so that the insoluble protection layer <NUM> is formed on the outer surface of the solder leg <NUM>. In this embodiment of this application, a form, a density, a location, and the like of the reaction particle <NUM> are not strictly and specifically required. Therefore, disposing of the reaction particle <NUM> is not easily limited by a geometric appearance of the circuit board <NUM>, and is not easily affected by a component that needs to be exposed outside, such as an antenna and an electrical connection point. Therefore, a disposing process of the reaction particle <NUM> on the board body <NUM> is more flexible, simple, and easy to operate, so that a production process of the circuit board <NUM> and the electronic device is also simple, and production costs of the circuit board <NUM> and the electronic device are relatively low.

In addition, a form of the reaction particle <NUM> is relatively flexible, the reaction particle <NUM> does not need to have an isolation function, and there is no need to set a very large density. Therefore, disposing of the reaction particle <NUM> is not easy to cause an obstacle to radiation of the antenna, and a radiation function of the antenna is not easy to be affected, so that reliability of a wireless communication function of the electronic device is better.

In one implementation, the reaction particle <NUM> may be a compound, and anionic reducibility of the compound is higher than that of tin.

When reducibility of a substance is relatively high, that is, an electron loss capacity of the substance is relatively high, and the substance is more easily oxidized.

A capability of an elementary substance to gain and lose electrons can be evaluated by electronegativity. Electronegativity is a relative scale of a capability of an atom of each element in the periodic table of elements to attract an electron. When electronegativity of an element is higher, a tendency of attracting an electron is higher, and a nonmetallic attribute is stronger. In the periodic table of elements, electronegativity of elements from left to right increases in a same period, and electronegativity of elements from top to bottom decreases in a same main group. Therefore, elements with high electronegativity are concentrated in the upper right corner of the periodic table of elements, and elements with low electronegativity are concentrated in the lower left corner.

A nonmetallic element with higher electronegativity is more active, and a metallic element with lower electronegativity is more active. Because a substance that reacts with tin to generate a tin compound is a nonmetallic element, a reducibility order of nonmetallic anions can be determined according to electronegativity/activity: S<NUM>->I->Br->B->Cl->OH->oxygenated acid ions>Sn<NUM>-. Products are Br and B after Br- and B- lose electrons, and a product generated by reaction between which Br and tin is easy to dissolve in water. B is not easy to react with tin, and B- is also not easy to react with a tin ion to generate a stable compound. Products of oxidized Cl- and oxygenated acid ions are water and gas, and water and gas cannot react with tin to generate an insoluble protection layer <NUM>. A compound generated after Cl- and oxygenated acid ions combine with tin ions is easy to dissolve in water, so Br-, B-, Cl- and oxygenated acid ions cannot react with tin or tin ions to generate an insoluble protection layer <NUM> when losing electrons and not losing electrons.

OH- can react with tin ions to generate Sn(OH)<NUM>. Because Sn(OH)<NUM> is difficult to dissolve in water, when less water is on the circuit board <NUM>, generally, an insoluble protection layer can be formed on the surface of the solder leg <NUM> by Sn(OH)<NUM>.

Products are S and I<NUM> after S<NUM>- and I- lose electrons. S and I<NUM> can react with tin to generate SnS<NUM> and SnI<NUM>. SnS<NUM> and SnI<NUM> are not dissolvable in water, so that SnS<NUM> and SnI<NUM> are easy to form an insoluble protection layer <NUM> on the surface of the solder leg <NUM>. The reaction particle <NUM> may be a sulfide, an iodide, a complex containing iodine (such as iohexol), or a complex containing sulfur. Anion of the sulfide and the complex containing sulfur is S<NUM>-, and anion of the iodide and the complex containing iodide is I-.

For a specific compound component of the reaction particle <NUM>, refer to the foregoing compound.

In this embodiment of this application, when the reaction particle <NUM> is a sulfide or an iodide, because reducibility of a sulfur ion and an iodine ion is higher than that of tin, the sulfur ion and the iodine ion can be oxidized before tin, to suppress oxidization and dissolving of tin into the tin ion, so as to suppress electrochemical corrosion on the tin solder leg <NUM> to form a dendrite. In addition, after a sulfur ion or an iodine ion is oxidized to a sulfur or iodine elementary substance, the sulfur or iodine elementary substance may further react with the tin solder leg <NUM> to form a tin sulfide protection layer or a tin iodide protection layer, thereby improving a probability of forming the insoluble protection layer <NUM>, so that the generated insoluble protection layer <NUM> can better cover the outer surface of the solder leg <NUM> to make the solder leg <NUM> better isolate from water, and a probability of the solder leg <NUM> being oxidized and dissolved is further reduced, thereby reducing a probability of dendrite corrosion of the solder leg <NUM>.

In this embodiment, because anionic reducibility of the reaction particle <NUM> is higher than that of tin, when electrochemical corrosion occurs, an electron loss capability of anion of the reaction particle <NUM> is stronger than that of tin. The anion of the reaction particle <NUM> is oxidized before tin, so as to suppress oxidization and dissolving of the tin solder leg <NUM>, thereby further reducing a probability that the tin solder leg <NUM> is oxidized and dissolved to a tin particle, and reducing a probability of dendrite corrosion of the solder leg <NUM>.

In a specific embodiment, the reaction particle <NUM> may be salt. The salt refers to a compound combined by a metallic ion or an ammonium ion (NH<NUM>+) with an acid radical ion or a nonmetallic ion, and is usually neutral in acid-base property. Because the acid-base property of salt is neutral, when the reaction particle <NUM> is salt, corrosion on the circuit board <NUM> may be reduced, so that reliability of the circuit board <NUM> is higher. For example, the reaction particle <NUM> may be potassium sulfide, sodium iodide, potassium iodide, or the like, but is not limited thereto.

In one implementation, the reaction particle <NUM> may be a substance that is dissolvable in water. For example, the reaction particle may be any one of sodium sulfide, potassium sulfide, sodium iodide, potassium iodide, calcium iodide, or potassium hydroxide, but is not limited thereto. Because the reaction particle <NUM> is dissolvable in water, when the circuit board <NUM> is in an environment with water, the reaction particle <NUM> can be more evenly distributed in water after being dissolved in water, and can be more evenly distributed in water attached on the outer surface of the solder leg <NUM>, so that the reaction particle <NUM> in water can react with each part of the outer surface of the solder leg <NUM> more evenly. Each part of the outer surface of the solder leg <NUM> can quickly and evenly form the insoluble protection layer <NUM>, so that each part of the outer surface of the solder leg <NUM> cannot contact water, thereby reducing a probability of dendrite corrosion of the solder leg <NUM>.

The following describes, by using a specific example, a process in which when the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> in this embodiment of this application.

<FIG> is a schematic diagram in which the reaction particle <NUM> of the circuit board <NUM> shown in <FIG> is a potassium iodide particle, and reaction occurs when the circuit board <NUM> is energized and in an environment with water <NUM>. Two solder legs <NUM> in <FIG> may be two solder legs <NUM> with different polarities of a same electronic component <NUM> in <FIG>, or may be two solder legs <NUM> with different polarities corresponding to two adjacent electronic components <NUM> in <FIG>. In this example, when the circuit board <NUM> is in an environment with water, the potassium iodide particle is easily dissolved in water <NUM> and decomposed into iodine ions and potassium ions.

The reaction particle <NUM> is disposed on the outer surface of the solder leg <NUM>. As shown in <FIG>, when the circuit board <NUM> is in an environment with water <NUM>, water <NUM> is attached to an outer surface of the board body <NUM> and the solder leg <NUM>. When the circuit board <NUM> is energized, one solder leg <NUM> is an anode (that is, a "+" electrode in <FIG>), and another solder leg <NUM> is a cathode (that is, a "-" electrode in <FIG>).

A specific reaction process is as follows: Tin of the solder leg <NUM> at the anode loses an electron to become a tin ion, an iodine ion loses an electron to become an iodine elementary substance, and the iodine elementary substance reacts with the tin of the solder leg <NUM> to form a tin iodide insoluble substance. The tin ion moves to the cathode due to the potential difference between the anode and the cathode. Oxygen at the cathode obtains an electron and combines with water <NUM> and a potassium ion to form potassium hydroxide. Tin which has moved to the cathode obtains an electron and reacts to form a tin elementary substance.

A reaction equation of anode reaction during the reaction is: Sn - 2e = Sn<NUM>+, I- - 2e = I<NUM>, 2I<NUM> + Sn = SnI<NUM>↓; and
a reaction equation of cathode reaction during the reaction is: <NUM>+ + 2e = H<NUM>↑, O<NUM> + <NUM><NUM>O + <NUM>+ + 4e = 4KOH, Sn<NUM>+ + 2e = Sn↓.

In a reaction process, because reducibility of an iodine ion is stronger than that of tin, the iodine ion at the anode can be rapidly oxidized to generate an iodine elementary substance, and react with the tin of the solder leg <NUM> to generate a tin iodide insoluble substance. In this way, when tin at the anode is oxidized but dissolved in a small amount, a tin iodide protection layer may be formed on a surface of the solder leg <NUM> at the anode, thereby isolating the solder leg <NUM> from reacting with water. Because dissolved tin at the anode is in a small amount, a quantity of tin ions moving to the cathode is also very small, and a small quantity of tin elementary substances can be restored and generated at the cathode. Therefore, a quantity of dendrites generated at the cathode is also very small, and dendrite generation can be effectively suppressed.

In a reaction process, as shown in <FIG>, the iodine ion at the cathode can move toward the anode due to the potential difference between the anode and the cathode, so that an iodine ion concentration at the anode is greater, and a tin iodide protection layer generated at the anode has better densification, so that the generated tin iodide protection layer can better isolate the solder leg <NUM> from water.

<FIG> is a schematic diagram in which the reaction particle <NUM> of the circuit board <NUM> shown in <FIG> is a sodium sulfide particle, and reaction occurs when the circuit board <NUM> is energized and in an environment with water. A reaction process of the example shown in <FIG> is similar to that of the example shown in <FIG>. For a specific process, refer to the foregoing detailed description of <FIG>. When the circuit board <NUM> is in an environment with water <NUM>, sodium sulfide is easily dissolved in water and decomposed into sulfur ions and sodium ions. A reaction equation of chemical reaction occurring in the example shown in <FIG> is as follows: A reaction equation of anode reaction during the reaction is: Sn - 2e = Sn<NUM>+, S<NUM>- - 2e = S, <NUM> + Sn = SnS<NUM>↓; and
a reaction equation of cathode reaction during the reaction is: <NUM>+ + 2e = H<NUM>↑, O<NUM> + <NUM><NUM>O + 4Na+ + 4e = 4NaOH, Sn<NUM>+ + 2e = Sn↓.

In a reaction process, because reducibility of a sulfur ion is stronger than that of tin, the sulfur ion at the anode can be rapidly oxidized to generate a sulfur elementary substance, and react with the tin of the solder leg <NUM> to generate a tin sulfide insoluble substance. A principle of suppressing dendrite generation when the reaction particle <NUM> is sulfide is similar to that of iodide, and details are not described herein again.

In an implementation, the circuit board <NUM> of the foregoing electronic device may include a board body <NUM>, an electronic component <NUM>, and an insoluble protection layer <NUM>. The electronic component <NUM> is soldered to a surface of the board body <NUM> by using soldering tin, and the insoluble protection layer <NUM> is attached to an outer surface of a solder leg <NUM> for soldering the electronic component <NUM>, to isolate the solder leg <NUM> from contacting water, thereby preventing dendrite corrosion of the solder leg <NUM>. The insoluble protection layer <NUM> is a protection layer obtained when the reaction particle <NUM>, which is disposed on the surface of the board body <NUM> and adjacent to the solder leg <NUM>, reacts with the solder leg <NUM> when the circuit board <NUM> is energized and in an environment with water.

The insoluble protection layer <NUM> may be a tin iodide protection layer or a tin sulfide protection layer. A specific implementation method and a beneficial effect in this embodiment are similar to the implementation method and the beneficial effect of the circuit board <NUM> containing the reaction particle <NUM> in the foregoing embodiment, and details are not described herein again.

<FIG> is a schematic flowchart of a production method for a circuit board <NUM> according to an embodiment of this application.

This application further provides a production method for a circuit board <NUM>. As shown in <FIG>, the method includes the following steps S10 and S20.

Step S10: Soldering of an electronic component <NUM> on a board body <NUM> by using soldering tin.

By using a soldering process such as reflow soldering, wave soldering, and dip soldering, the electronic component <NUM> may be soldered to the board body <NUM> by using soldering tin, or may be soldered by using another soldering process. This is not specifically limited in this application. Specifically, a pin of the electronic component <NUM> may be electrically connected to a connector of the board body <NUM>, and then the pin is fastened to the connector by soldering, so that the pin of the electronic component <NUM> is securely electrically connected to the board body <NUM>. Alternatively, a sheet-like component may be soldered to the board body <NUM> by using an SMT. <FIG> is a schematic diagram of a process of a production method for a circuit board according to an embodiment of this application.

As shown in <FIG>, after the electronic component <NUM> is soldered to the board body <NUM> by using soldering tin, a structure shown in (a) in <FIG> is obtained, and the electronic component <NUM> and the board body <NUM> are fastened by using a solder leg <NUM>.

Step S20: Dispose a reaction particle <NUM> at a location, on a surface of the board body <NUM>, which is adjacent to the solder leg <NUM> for soldering the electronic component <NUM>.

By performing step S20, the circuit board <NUM> may be obtained.

A structure shown in (b) in <FIG> of the circuit board <NUM> is obtained by disposing the reaction particle <NUM> at the location, on the surface of the board body <NUM>, which is adjacent to the solder leg <NUM> for soldering the electronic component <NUM>.

When the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> reacts with the solder leg <NUM> to form an insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>, and the insoluble protection layer <NUM> isolates the solder leg <NUM> from contacting water to prevent dendrite corrosion of the solder leg <NUM>. A structure in which the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM> is shown in (c) in <FIG>.

In this embodiment, when there is no water on the circuit board <NUM>, a structure of the circuit board <NUM> is shown in (d) in <FIG>. The structure shown in (d) in <FIG> is the same as the structure shown in (b) in <FIG>.

In step S20, the reaction particle may be disposed on the surface of the board body <NUM> by using any one of a coating method, a printing method, a soaking method, an atomization sedimentation method, a steam method, a vapor deposition method, a sputtering method, a spraying method, 3D printing, and the like.

Optionally, a solution containing the reaction particle may be prepared, the solution containing the reaction particle is adsorbed on the surface of the board body <NUM>, and the reaction particle <NUM> is formed on the surface of the board body <NUM> after drying. Alternatively, powder or a particle of the reaction particle <NUM> may be directly attached to an outer surface of the board body <NUM> by using a 3D printing method, a spraying method, a sputtering method, or the like.

Optionally, a coating containing the reaction particle may be prepared, and the coating is painted or printed on the surface of the board body <NUM>. Specifically, an epoxy group, an acrylic group, or a polyurethane base may be used as a major resin, and reaction particles such as potassium iodide, sodium iodide, and sodium sulfide which have a volume ratio of <NUM>%-<NUM>% are mixed into the major resin, to obtain the coating containing the reaction particle. A volume ratio of the reaction particle in the coating may also be another ratio, which is not limited in this application.

During a process of soldering the circuit board, to prevent a problem such as a bridging short circuit during soldering, solder resist ink is generally coated on the outer surface of the board body to protect the board body. In this embodiment of this application, a reaction particle with a volume ratio of <NUM>%-<NUM>% may be added to the solder resist ink. When the solder resist ink is coated on the board body, the reaction particle may also be coated on the surface of the board body.

The reaction particle <NUM> may be a compound, and anionic reducibility of the compound is higher than that of tin. In this way, when electrochemical corrosion occurs, an electron loss capability of anion of the reaction particle <NUM> is stronger than that of tin. The anion of the reaction particle <NUM> is oxidized before tin, so as to suppress oxidization and dissolving of the tin solder leg <NUM>, thereby further reducing a probability that the tin solder leg <NUM> is oxidized and dissolved to a tin particle, and reducing a probability of dendrite corrosion of the solder leg <NUM>.

Specifically, the compound may be a sulfide or an iodide, and the insoluble protection layer <NUM> formed on the solder leg <NUM> is a tin sulfide protection layer or a tin iodide protection layer.

In the production method for a circuit board <NUM> provided in this embodiment of this application, because the reaction particle <NUM> is disposed at the location, on the surface of the board body <NUM>, which is adjacent to the solder leg <NUM> for soldering the electronic component <NUM>, when the circuit board <NUM> is energized and in an environment with water, the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>. In this way, the insoluble protection layer <NUM> can isolate the solder leg <NUM> from water, to prevent the solder leg <NUM> from contacting water. In this way, when there is water on the circuit board <NUM>, dendrite corrosion of the solder leg <NUM> can be prevented.

<FIG> is another flowchart of a production method for a circuit board according to an embodiment of this application. In a specific embodiment, as shown in <FIG>, step S20 may be implemented according to the following steps S21 and step S22.

Step S21: Place the board body <NUM> soldered with the electronic component <NUM> in an environment of a solution containing the reaction particle, so that the solution of the reaction particle is adsorbed on the surface of the board body <NUM>.

Step S22: Dry the board body <NUM> on which the solution containing the reaction particle is adsorbed, to obtain the circuit board <NUM>.

In this embodiment, the reaction particle <NUM> may be a substance that is dissolvable in water. For a specific component of the reaction particle <NUM>, refer to the foregoing embodiment description of the circuit board <NUM>.

The solution containing the reaction particle may be a saturated solution, or may be an unsaturated solution. For example, a volume ratio of the solution containing the reaction particle may be in a range from <NUM>% to <NUM>%, that is, the saturated solution containing the reaction particle <NUM> of <NUM> to <NUM> volumes is added to <NUM> volumes of solvent (water or alcohol), to form the solution. A volume ratio range of the solution containing the reaction particle may also be another ratio, such as <NUM>%-<NUM>% or <NUM>%-<NUM>%, which is not specifically limited in this application.

The solution containing the reaction particle may be an aqueous solution, or may be an alcoholic solution. The alcoholic solution is obtained by dissolving the reaction particle <NUM> in alcohol, and the aqueous solution is obtained by dissolving the reaction particle <NUM> in water.

In an optional implementation, step S21 may be implemented according to the following steps: After the solution containing the reaction particle is distilled, steam containing the reaction particle <NUM> is obtained, and the board body <NUM> soldered with the electronic component <NUM> is placed in the obtained steam. In this example, a steam generator may be used to convert the solution containing the reaction particle into steam.

In an optional implementation, step S21 may alternatively be implemented according to the following step: Soak the board body <NUM> soldered with the electronic component <NUM> in the solution containing the reaction particle.

<FIG> is a schematic diagram of an operation of disposing a reaction particle <NUM> on a board body <NUM> in a production method for a circuit board <NUM> according to an embodiment of this application.

As shown in <FIG>, a solution <NUM> containing the reaction particle may be put into a box <NUM>, and each board body <NUM> soldered with the electronic component <NUM> may be placed on a placing rack of a lifting mechanism <NUM>. Each board body <NUM> soldered with the electronic component <NUM> may be placed in the solution <NUM> containing the reaction particle by using the lifting mechanism <NUM>, and each board body <NUM> soldered with the electronic component <NUM> may be lifted from the solution. In this way, the solution <NUM> containing the reaction particle may be attached to a surface of each board body <NUM> soldered with the electronic component <NUM>.

In this embodiment, the board body <NUM> is directly soaked in the solution <NUM> containing the reaction particle, and the solution may be adsorbed on the surface of the board body <NUM> simply and conveniently. Therefore, a process for disposing a reaction particle <NUM> on the surface of the board body <NUM> is simpler, so that a production process of the circuit board <NUM> and an electronic device is simpler, and production costs are lower.

In an optional embodiment, step S21 may alternatively be implemented according to the following step: Atomize the solution <NUM> containing the reaction particle, and place the board body <NUM> soldered with the electronic component <NUM> in the atomized solution.

<FIG> is another schematic diagram of an operation of disposing a reaction particle <NUM> on a board body <NUM> in a production method for a circuit board <NUM> according to an embodiment of this application.

As shown in <FIG>, the solution <NUM> containing the reaction particle may be delivered into an atomizer <NUM> by using a pipeline <NUM>, and atomized by using the atomizer <NUM>. Mist sprayed from the atomizer <NUM> is sprayed into the box <NUM>. Each board body <NUM> soldered with the electronic component <NUM> is placed on the placing rack of the lifting mechanism <NUM>, and each board body <NUM> soldered with the electronic component <NUM> is placed in the mist in the box <NUM> by using the lifting mechanism <NUM>. Then, each board body <NUM> soldered with the electronic component <NUM> is lifted from the box <NUM>. In this way, the solution <NUM> containing the reaction particle may be attached to the surface of each board body <NUM> soldered with the electronic component <NUM>.

In this embodiment, the board body <NUM> is placed in the atomized solution <NUM> of the reaction particle, so that a process for disposing the reaction particle <NUM> on the surface of the board body <NUM> is simple and convenient. Therefore, a production process of the circuit board <NUM> and an electronic device is simpler, and production costs are lower.

In addition, because a density of the atomized solution is relatively low, the board body <NUM> is placed in the atomized solution, which can make the board body <NUM> not too wet after the solution <NUM> of the reaction particle is adsorbed on the board body <NUM>, so that the board body <NUM> can be quickly dried. Therefore, production efficiency of the circuit board <NUM> is improved, and a probability that the solution <NUM> of the reaction particle soaks inside each electronic component <NUM> to make the electronic component <NUM> damaged is reduced, so that reliability of the circuit board <NUM> and the electronic device is higher, and a fault rate is lower.

In the foregoing step S22, the board body <NUM> on which the solution <NUM> containing the reaction particle is adsorbed may be placed in a drying stove for drying. A drying temperature may be lower than <NUM>, that is, drying is performed at a low temperature, to reduce impact of a high temperature on each component of the circuit board <NUM>.

In this embodiment, the solution <NUM> containing the reaction particle is adsorbed on the board body <NUM> and then dried to obtain the circuit board <NUM>, so that the reaction particle <NUM> can be conveniently disposed on the surface of the board body <NUM>. In the solution <NUM> of the reaction particle, the reaction particle <NUM> is evenly distributed. Therefore, in this embodiment, the reaction particle <NUM> disposed on the surface of the board body <NUM> can further be more evenly distributed, so that when the circuit board <NUM> is energized and meets water, an insoluble protection layer <NUM> with good uniformity can be formed on each part of the surface of the solder leg <NUM>, and each part of the outer surface of the solder leg <NUM> cannot contact water, thereby reducing a probability of dendrite corrosion of the solder leg <NUM>.

In an implementation, step S20 may be implemented according to the following step: Sputter, by using a sputtering method, and adsorb the reaction particle <NUM> at a location, on the surface of the board body <NUM>, which is adjacent to the solder leg <NUM> for soldering the electronic component <NUM>.

<FIG> is another schematic diagram of an operation of disposing a reaction particle <NUM> on a circuit board <NUM> in a production method for a circuit board <NUM> according to an embodiment of this application.

As shown in <FIG>, a process of disposing the reaction particle <NUM> on the surface of the board body <NUM> by using the sputtering method may be specifically: filling a vacuum coating chamber (not shown in the figure) with a proper amount of argon gas, placing a target material <NUM> of the reaction particle at a location close to cathode, applying a voltage between a cathode board <NUM> and an anode board <NUM> (a coating chamber wall), and rapidly increasing energy of an electron emitted from a surface of the cathode board <NUM> by means of acceleration of an electric field. A high-energy electron can collide with the argon gas to decompose a positive argon ion. Under an effect of the electric field, the argon ion moves to the cathode board <NUM> and the target material <NUM> of the reaction particle to bombard a surface of the target material <NUM> of the reaction particle, and the reaction particle <NUM> in the target material <NUM> of the reaction particle obtains energy from bombardment, and is finally discharged from the target material <NUM> of the reaction particle to sputter on the board body <NUM>.

Optionally, as shown in <FIG>, the sputtering method may be a magnetron sputtering method. The magnetron sputtering method is that a plurality of magnets <NUM> with different polarities are disposed in the vacuum coating chamber. The magnets <NUM> with different polarities form a magnetic field, and electrons can move helically along a magnetic line of the magnetic field. Therefore, a movement path of electrons is increased, a probability of colliding between the electron and argon gas is improved, and a quantity of the reaction particle <NUM> sputtered from the target material <NUM> of the reaction particle is increased, so that sputtering efficiency is higher and an sputtering effect can be more uniform.

In this embodiment, the reaction particle <NUM> may be directly sputtered and adsorbed on the surface of the board body <NUM> by using the sputtering method, and no drying or another subsequent processing process is required, so that a production process of the circuit board <NUM> has fewer steps and a simpler process. In addition, by using the sputtering method, the board body <NUM> is always in a dry environment, so that a process of disposing the reaction particle <NUM> does not affect another part of the circuit board <NUM>, and reliability of the circuit board <NUM> is higher. In addition, by using the sputtering method, a film of the reaction particle <NUM> with a more uniform thickness and better densification can be formed on the surface of the board body <NUM>, so that when the circuit board <NUM> is energized and meets water, an insoluble protection layer <NUM> with better uniformity can be formed on the solder leg <NUM>.

In an implementation, step S20 may be implemented according to the following step: Dispose the reaction particle <NUM> on the outer surface of the solder leg <NUM> soldered with the electronic component <NUM>.

In this implementation, the reaction particle <NUM> may be disposed on the outer surface of the solder leg <NUM>, and the reaction particle is not disposed on the surface of the board body <NUM> except the outer surface of the solder leg <NUM>. In this way, in a case in which the circuit board <NUM> meets water and is energized, the reaction particle <NUM> may react rapidly with the solder leg <NUM> to form the insoluble protection layer <NUM>, and a probability of the solder leg <NUM> being oxidized and dissolved is reduced, thereby reducing a probability of dendrite corrosion of the solder leg <NUM>. In addition, there is no need to dispose the reaction particle <NUM> on the surface of the board body <NUM> except the solder leg <NUM>, so that impact of the reaction particle <NUM> on the board body <NUM> can be reduced, and the circuit board <NUM> can be more reliable.

Specifically, as shown in <FIG>, before step S21, that is, before step S20, the production method for the circuit board <NUM> may further include the following step S40.

Step <NUM>: Cover the surface of the board body <NUM> on which the electronic component <NUM> is installed with a barrier, where the barrier covers the board body <NUM> except each solder leg <NUM>, so as to prevent the reaction particle <NUM> from being disposed on the surface of the board body <NUM> except each solder leg <NUM>.

The barrier may be a dam board, a housing, a barrier film, and the like. A plurality of through-holes are disposed in the barrier, a size of each through-hole is corresponding to a size of each solder leg <NUM>, and the through-hole is used to make the solder leg <NUM> exposed, so as to facilitate disposing of the reaction particle <NUM>.

In this embodiment, by using the barrier, the board body <NUM> except the solder leg <NUM> may be covered, so as to prevent the reaction particle <NUM> from being disposed on a part except the solder leg <NUM>, thereby reducing impact of the reaction particle <NUM> on the circuit board <NUM> except the solder leg <NUM>, and improving structural stability and reliability of the circuit board <NUM>.

In an implementation, as shown in <FIG>, the production method for the circuit board <NUM> may further include the following step S30.

Step S30: Energize the circuit board <NUM>, and place the circuit board <NUM> in an environment with water, so that the reaction particle <NUM> reacts with the solder leg <NUM> to form an insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>.

Specifically, in this implementation, when the circuit board <NUM> is energized, the circuit board <NUM> is soaked in water, or water is sprayed on the circuit board <NUM>, or the circuit board <NUM> is placed in vapor or water after atomization, so that the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>.

In this implementation, the circuit board <NUM> may be energized first, and then placed in an environment with water, or the circuit board <NUM> may be placed in an environment with water first, and then energized, or the circuit board <NUM> may be energized, and at the same time, placed in an environment with water. This is not specifically limited in this application.

For a process in which the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>, refer to the foregoing specific description of the embodiment of the circuit board <NUM>.

In this embodiment, when the board body <NUM> is energized, the board body <NUM> is placed in an environment of the solution <NUM> containing the reaction particle. In this way, when the reaction particle <NUM> is attached to the surface of the board body <NUM>, the insoluble protection layer <NUM> is formed on the outer surface of the solder leg <NUM>. In this way, a process of forming the insoluble protection layer <NUM> is simultaneously performed with a process of disposing the reaction particle <NUM>, which reduces a production process step of the circuit board <NUM>, and makes a production process of the circuit board <NUM> simpler.

In an implementation, step S20 and step S30 may be implemented according to the following steps:
energizing the board body <NUM> on which the electronic component <NUM> is installed, and placing the board body <NUM> in an environment of the solution <NUM> containing the reaction particle, so that the reaction particle <NUM> reacts with the solder leg <NUM> to form the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>, to obtain the circuit board <NUM>.

<FIG> is another schematic diagram of a process of a production method for a circuit board <NUM> according to an embodiment of this application. As shown in <FIG>, the board body <NUM> on which the electronic component <NUM> is installed may be energized first, so that the board body <NUM> on which the electronic component <NUM> is installed changes from a state (a) in <FIG> to a state (b) in <FIG>. Then the energized board body <NUM> is placed in the solution <NUM> containing the reaction particle, so that the solution <NUM> containing the reaction particle is attached to the solder leg <NUM>. The board body <NUM> on which the solution containing the reaction particle is attached is shown in (c) in <FIG>, and a structure is shown in (d) in <FIG> after the reaction particle <NUM> on the surface of the solder leg <NUM> at the anode reacts with the solder leg <NUM> to form the insoluble protection layer <NUM>.

<FIG> is still another schematic diagram of a process of a production method for a circuit board <NUM> according to an embodiment of this application. As shown in <FIG>, the board body <NUM> on which the electronic component <NUM> is installed may be first placed in the solution <NUM> containing the reaction particle, so that the board body <NUM> on which the electronic component <NUM> is installed changes from a state (a) in <FIG> to a state (b) in <FIG> in which the solution <NUM> containing the reaction particle is attached to the solder leg <NUM>. Then the circuit board <NUM> is energized, so that the circuit board <NUM> becomes a state (c) in <FIG>. A structure is shown in (d) in <FIG> after the reaction particle <NUM> on the surface of the solder leg <NUM> at the anode reacts with the solder leg <NUM> to form the insoluble protection layer <NUM>.

In this implementation, step S20 and step S30 are combined into one step for implementation, that is, the step of disposing the reaction particle <NUM> on the board body <NUM> is simultaneously performed with the step of forming the insoluble protection layer <NUM> on the outer surface of the solder leg <NUM>.

In this implementation, the board body <NUM> is placed in an environment of the solution <NUM> containing the reaction particle, which can make not only the solution <NUM> of the reaction particle be attached to the surface of the solder leg <NUM>, but also the circuit board <NUM> be in an environment with water, so that the insoluble protection layer <NUM> can be formed on the outer surface of the solder leg <NUM>.

In this implementation, a process of forming the insoluble protection layer <NUM> is simultaneously performed with a process of disposing the reaction particle <NUM>, which reduces a production process step of the circuit board <NUM>, and makes a production process of the circuit board <NUM> simpler.

In an implementation, after the insoluble protection layer <NUM> is formed, the production method for the circuit board <NUM> may further include the following step: cleaning and drying the circuit board <NUM> formed with the insoluble protection layer <NUM>.

Specifically, the circuit board <NUM> may be cleaned by using an ultrasonic cleaning machine, or may be cleaned by using a washing machine. A cleaning solution may be water, or may be an alcoholic solution.

In this embodiment, the reaction particle <NUM> remaining on the circuit board <NUM>, the reaction particle <NUM> and the solder leg <NUM>, and an intermediate product generated in a process of water reaction may be washed off, so that impact of these substances on performance of the circuit board <NUM> can be reduced.

Claim 1:
A circuit board, comprising:
a board body (<NUM>);
an electronic component (<NUM>), soldered to a surface of the board body (<NUM>) by using soldering tin, wherein a solder leg (<NUM>) is formed on the surface of the board body (<NUM>); and
a reaction particle (<NUM>), disposed on the surface of the board body (<NUM>) and adjacent to the solder leg (<NUM>), wherein when the circuit board is energized and in an environment with water, the reaction particle (<NUM>) reacts with the solder leg (<NUM>) to form an insoluble protection layer (<NUM>) on an outer surface of the solder leg (<NUM>), and the insoluble protection layer (<NUM>) isolates the solder leg (<NUM>) from water, wherein the reaction particle (<NUM>) is a compound, and anionic reducibility of the compound is higher than that of tin, and wherein the reaction particle (<NUM>) is dissolvable in water.