JP2002368391A - Wiring board, electronic apparatus and method for mounting electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring board capable of effectively avoiding firing of a substrate to ensure satisfactory reliability even if an electrolyte leaks out when being employed in a lithium ion battery pack and a lithium polymer battery pack used in a cellular telephone set or a notebook type PC, etc., and further being employed in a circuit board of a device main body employing these battery packs and various types of electronic apparatuses, and to provide an electronic device employing this wiring board and a method for mounting electronic components. SOLUTION: A coating 6 which is resistant to a depositable liquid is formed on at least a part where ion migration may occur, or a resin which is resistant to a depositable liquid covers at least a part where a conductor in which ion migration may occur is exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mounting a wiring board, electronic equipment and electronic components, for example, a lithium ion battery pack for a cellular phone, a notebook personal computer, and the like.
The present invention can be applied to a lithium polymer battery pack, a circuit board of an apparatus body using such a battery pack, and various electronic devices. According to the present invention, at least a portion where ion migration can occur can be formed by forming a film having resistance to a liquid that can adhere thereto, or at least an exposed portion of a conductor where ion migration can occur can be attached. By covering with a resin that is resistant to possible liquids,
Even when the electrolyte leaks out, ignition of the substrate is effectively avoided and sufficient reliability can be ensured.

[0002]

2. Description of the Related Art Conventionally, in portable electronic devices such as cellular phones and notebook computers, secondary batteries having high energy density and excellent long-term storage characteristics have been demanded. Batteries and nickel cadmium batteries have been used, and in recent years, lithium ion secondary batteries and lithium polymer secondary batteries having higher energy density have been used instead of these batteries.

In such a lithium ion secondary battery and a lithium polymer secondary battery, a control circuit and a protection circuit are configured by mounting electronic components on a wiring board, and the control circuit and the protection circuit are combined with a secondary battery cell. The battery pack is integrated. The lithium ion secondary battery and the lithium polymer secondary battery are protected from overcharge, overdischarge, and the like by these control circuits and protection circuits.

[0004]

A secondary battery used in such a battery pack is filled with an electrolytic solution. If the electrolytic solution leaks out, the wiring board is subjected to ion migration by ion migration. May ignite.

[0005] That is, in the case of ion migration, when a conductor such as a pattern, a land, or a test pin having a different potential is wetted by a liquid such as an electrolytic solution on a wiring board, a metal having the highest ionization tendency becomes an ion and becomes high. This is a phenomenon in which the metal ions elute from the potential-side conductor into the liquid, and the eluted metal ions move to the low-potential-side conductor due to Coulomb force to precipitate branch crystals (dendrites).

[0006] Such a branch-like crystal gradually grows toward the conductor on the high potential side, whereby the wiring board finally grows between the high potential side conductor and the low potential side conductor due to the growth of the branch crystal. Insulation cannot be maintained between the high-potential-side conductor and the low-potential-side conductor on the substrate surface, causing a short-circuit accident. Here, such a short circuit accident is instantaneous due to disappearance of the branch crystals due to heat generation,
This heat causes the lower insulating resin to be locally carbonized.

[0007] Such a branch-like crystal continues to grow everywhere between conductors having different potentials, so that localization of a wiring board causes local carbonization due to a short circuit accident. As a result, in the wiring board, the area of the carbonized portion gradually increases, and finally the conductors having different potentials are completely connected by the carbonized portion. In such a portion, a large current flows to generate heat, thereby functioning as a heater, increasing the temperature of the wiring board, and igniting the wiring board when the temperature rises above a predetermined temperature. In the lithium ion secondary battery pack, when the wiring board is ignited and the temperature of the secondary battery cell rises, gas may be ejected from the cell.

[0008] Such a phenomenon tends to occur more easily in a portion where the interval between conductors having different potentials is short and in a portion where the area exposed on the surface is large. Furthermore, this phenomenon occurs not only in the electrolyte solution of the lithium ion secondary battery but also in the electrolyte solution used for various batteries, and furthermore, salt water, vinegar, and citrus juice (eg, lemon juice) found in daily life. Etc. occur widely in liquids having ionic dielectric properties, and become more pronounced as the ion mobility increases.

[0009] A resist film is usually formed on the wiring board by a resist treatment, and the resist film protects the wiring pattern. However, the resist film has a property of being dissolved by the electrolyte of the lithium ion secondary battery, and accordingly, the ignition of the wiring board due to the adhesion of the electrolyte as described above cannot be effectively prevented by the resist film.

[0010] The present invention has been made in view of the above points, and even when the electrolyte leaks out, it is possible to effectively avoid ignition and ensure sufficient reliability of the wiring board. Another object of the present invention is to propose a method for mounting electronic devices and electronic components using the wiring board.

[0011]

According to the first aspect of the present invention, in order to solve the above-mentioned problems, the invention is applied to a wiring board, and at least a portion where ion migration can occur is provided.
Form a coating that is resistant to liquids that may adhere.

The invention according to claim 8 is applied to a mounting method of an electronic component, and after the mounting of the electronic component, at least an exposed portion of the conductor capable of generating ion migration is exposed to a liquid that may adhere. Cover with a resin that is resistant to this.

According to the first aspect of the present invention, by forming a film having resistance to a liquid that may adhere to at least a portion where ion migration can be applied, the film is applied to the wiring board. For conductors covered by such coatings, the coatings are prevented from eroding, the coatings prevent direct liquid contact, and further prevent the permeation of the liquids over a long period of time to generate metal ions. Can be prevented. This prevents the occurrence of ion migration between the wiring patterns on the wiring board, thereby effectively preventing ignition and ensuring sufficient reliability even when the electrolyte leaks out. can do.

According to the configuration of the eighth aspect, the present invention is applied to a mounting method of an electronic component, and after the mounting of the electronic component, at least an exposed portion of the conductor where ion migration can occur can be attached to the liquid. By covering with a resin that is resistant to water, the portion covered with the resin can be prevented from penetrating the liquid for a long time and elution of metal ions can be prevented, thereby preventing the occurrence of ion migration. can do. Thus, even when the electrolyte leaks out, ignition can be effectively avoided and sufficient reliability can be ensured.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate.

(1) Configuration of Embodiment FIG. 1 is a plan view showing a component mounting wiring board in a lithium ion battery pack according to an embodiment of the present invention.
The component mounting wiring board 1 is formed by mounting components on the wiring board 2, connecting the cable 3, and coating with a predetermined resin 4.

Here, the wiring board 2 has four wiring pattern layers.
FIG. 2 shows a component mounting surface (FIG. 2A), and a back surface of the component mounting surface (FIG. 2).
As shown in (B)), a film 6 having resistance to a liquid that may adhere instead of the resist film formed by the resist process is formed.

Here, the coating 6 having a resistance to a potential liquid is a coating that does not dissolve at least to a liquid that may adhere, which is a liquid that generates ion migration, and that has a long term. It is a coating that can prevent the permeation of this liquid and prevent the elution of metal ions and the movement of metal ions. In this embodiment, such a target liquid is an electrolyte of a lithium ion battery, and the coating 6 except for the land 7 of the wiring board 2 includes a surface including a portion where ion migration can occur, and Created on the entire back surface. Specifically, in this embodiment, the coating 6 is an ink (for example, an acrylic resin or an epoxy resin) that is printed on the surface of a general wiring board and used for marking a component number, a component mounting position, and the like.
Is formed by silk printing, which is the same step as the marking printing, and is formed with a sufficient film thickness. In this way, the display of the part number and the like, which is the original purpose of this type of printing, is also displayed together with a blank character on the coating 6, thereby making it possible to increase the number of steps as compared with the conventional method. , So that the reliability can be further improved.

On the other hand, in coating after component mounting, it is difficult to cover with the coating 6 as described above.
The process is performed so as to cover all exposed conductors including at least all exposed portions of the conductor where ion migration can occur. Specifically, the process is performed so as to cover a land which is a conductor portion to be mounted on a component, a conductor of an electronic component arranged on the land, and a solder which is an electrical connection member of the land and the conductor. Further, in this coating, similarly to the coating 6, a resin having resistance to a liquid that may adhere thereto is applied. That is, it is a resin material that does not dissolve depending on the electrolytic solution, and that can prevent the penetration of the electrolytic solution to prevent generation of metal ions and migration of metal ions, and adheres to the coating film 6 with sufficient strength. It is performed by applying resin. Specifically, in this embodiment, HC-1000 (manufactured by Dow Corning Toray Silicone Co., Ltd.), which is a silicon-based coating material, was applied to this resin.

In this way, in the component mounting wiring board 1, even if the electrolytic solution adheres, the electrolytic solution is prevented from adhering to the conductor surface, which is the site where the branch-like crystal is generated. Even in such cases, ignition is effectively avoided and sufficient reliability can be ensured.

(2) Operation of the Embodiment In the above-described configuration, the component mounting wiring board 1 is applied to a lithium ion battery pack. The electrolyte may adhere.

In the component mounting wiring board 1, even when such an electrolytic solution adheres, the front and rear surfaces of the wiring board, including the portions where ion migration can occur, are formed.
Since the coating 6 having resistance to the liquid that may adhere thereto is formed on the entire surface excluding the lands where the components are mounted, the wiring pattern covered with the coating 6 has a long term. Furthermore, elution of metal ions can be prevented. Thereby, ignition between such conductors can be effectively avoided and sufficient reliability can be ensured.

Further, in the component mounting wiring board 1, the exposed portions such as lands which are difficult to cover with the coating 6 are
After the components are mounted, similarly, the components are coated with a resin having resistance to a liquid that may adhere thereto, so that the leaked electrolyte is held so as not to come into contact with the conductor at any location. Thus, in this embodiment, even when a large amount of electrolyte leaks, ignition can be effectively avoided and sufficient reliability can be ensured.

Specifically, the component-mounted wiring board 1 is connected to a lithium-ion battery cell, housed in a resin mold case to form a battery pack, and then fully charged, and the component-mounted wiring board 1 An experiment was conducted by applying 1 [cc] of the electrolytic solution. When the wiring board 2 was left standing for one week and checked, no scorch was found on the board and no trace of ignition could be confirmed, thereby confirming that safety was ensured. Incidentally, the applied electrolyte was completely volatilized and dried.

Similarly, after a battery pack was prepared and fully charged, 1 [cc] of lemon juice was applied to conduct an experiment.
As a result of leaving it for one week and checking, it was found that the substrate was scorched and there was no trace of ignition. In this case, safety was confirmed. In this case, the lemon juice was completely dried.

In these comparative experiments, when a resist film was arranged in place of the film 6 and the coating process was omitted and left as it was, the electrolyte solution was applied and the lemon juice was applied. In either case,
Substrate ignition was confirmed. In particular, when the electrolytic solution was applied, the resist was dissolved, and scorching was observed in the pattern under the resist.

In this embodiment, the coating film 6 and the coating treatment are performed by using the ink which is printed on the substrate surface and used for marking the part number, the component mounting position, and the like. By being formed with a sufficient film thickness by silk printing, which is the same process as such printing, it is possible to effectively avoid firing of the substrate without changing the conventional manufacturing process of the wiring board at all, and to obtain sufficient reliability. Nature can be secured.

In the coating 6, the part number, etc., which is the original purpose of this type of printing, is indicated by a blank character so that the marking is not printed again.
It is possible to display a component mounting position and the like, whereby the number of steps for forming a resist film is reduced as compared with the related art, so that the steps can be simplified and the reliability can be further improved.

(3) Effects of the Embodiment According to the above configuration, a film having resistance to a liquid that may adhere is formed at least at a portion where ion migration can occur, thereby providing such a film. Even in the case where the electrolytic solution leaks out from a portion where a thin film is formed, ignition of the substrate can be effectively avoided and sufficient reliability can be secured.

In these configurations, the coating 6 is formed by printing ink used for marking the wiring board, thereby effectively avoiding ignition of the board without any change in the conventional wiring board manufacturing process. As a result, sufficient reliability can be secured.

In these configurations, a coating is formed on the entire surface of the wiring board except for parts where components are to be mounted, and markings are formed by characters on the coating, so that the components can be mounted again without printing the markings. The position and the like can be displayed.

In these structures, by forming a film by silk printing, a sufficient film thickness can be ensured and sufficient reliability can be ensured.

Further, by covering at least an exposed portion of the conductor where ion migration can occur with a resin having resistance to a liquid that may adhere thereto,
Even in the case where the electrolyte leaks from these exposed parts, it is possible to effectively avoid ignition of the substrate and secure sufficient reliability.

(4) Other Embodiments In the above-described embodiment, the case where a film is formed by silk printing has been described. However, the present invention is not limited to this, and various printing methods may be used as necessary. A coating can be created.

Further, in the above-described embodiment, the case where the marking is formed by the characters without the coating film has been described. However, the present invention is not limited to this, and the marking may be formed again by printing. Where a coating is formed and where no coating is formed, in the printing process of this coating,
The marking may be created in the same manner as a normal wiring board.

Further, in the above-described embodiment, the case where the coating is formed by printing the ink for marking has been described. However, the present invention is not limited to this. Various inks having resistance to the ink can be widely applied.

In the above-described embodiment, the case where a film is formed on the entire surface of the wiring board except for the land has been described. However, the present invention is not limited to this, and ion migration can be generated as necessary. You may make it a coat | cover only about a site | part.

In the above-described embodiment, the case where a film is formed and a coating process is performed has been described. However, the present invention is not limited to this. For example, even if a land is exposed, the distance is large. In this case, since the progress of ion migration is significantly reduced, only the coating may be provided as necessary. Even when a film is not formed, the same effect as in the above-described embodiment can be obtained by coating the entire surface, for example, so that only the coating process may be performed.

In the above-described embodiment, the case where the coating treatment is performed with the silicon-based coating agent has been described. However, the present invention is not limited to this. For example, a liquid that may adhere, such as a fluorine-based coating agent, is used. Resins having a high resistance to the above can be widely applied.
Incidentally, SE9189L (manufactured by Dow Corning Toray Silicone Co., Ltd.), TSE3975C (manufactured by GE Silicone Co., Ltd.), KE3494 (manufactured by Shin-Etsu Chemical Co., Ltd.)
, The same effect was confirmed.

In the above embodiment, the case where the present invention is applied to a lithium ion secondary battery pack has been described. However, the present invention is not limited to this and can be widely applied to various electronic devices.

[0041]

According to the present invention, by forming a film having resistance to a liquid that may adhere to at least a portion where ion migration can occur, or at least a conductor capable of generating ion migration. By covering the exposed area with a resin that is resistant to liquids that may adhere, even if the electrolyte leaks out, the ignition of the substrate is effectively avoided and sufficient reliability is achieved. Can be secured.

[Brief description of the drawings]

FIG. 1 is a plan view showing a component mounting wiring board according to an embodiment of the present invention.

FIG. 2 is a plan view showing a wiring board applied to the component mounting wiring board of FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Component mounting wiring board, 2 ... Wiring board, 3 ... Cable, 4 ... Resin, 6 ... Coating, 7 ... Land

Claims (10)

[Claims] 1. A wiring board on which a desired electronic component is mounted, wherein at least a portion where ion migration can occur, a coating having resistance to a liquid that may adhere thereto is arranged. . 2. The wiring board according to claim 1, wherein the coating is formed by printing ink used for marking the wiring board. 3. The wiring board according to claim 1, wherein the coating is formed on an entire surface of the wiring board except for a component mounting portion, and a marking is formed by a character cut out of the coating. 4. The method according to claim 1, wherein said coating is made by silk printing.
The wiring board according to claim 1. 5. The semiconductor device according to claim 1, wherein after mounting the electronic component, at least an exposed portion of the conductor where ion migration can occur is covered with a resin having resistance to a liquid that may adhere thereto. The wiring board as described. 6. The wiring board according to claim 5, wherein the resin is a fluorine-based or silicon-based coating agent. 7. An electronic device, wherein an electronic component is mounted on the wiring board according to claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6. 8. A mounting method of an electronic component for mounting a desired electronic component on a wiring board, wherein after mounting the electronic component, at least an exposed portion of a conductor capable of generating ion migration may be attached to a liquid. A method for mounting an electronic component, characterized in that the electronic component is covered with a resin having resistance to the electronic component. 9. The method according to claim 8, wherein the resin is a fluorine-based or silicon-based coating agent. 10. The wiring board according to claim 8, wherein the wiring board is formed at least in a portion where ion migration can occur, with a film having resistance to a liquid that may adhere thereto. How to mount electronic components.