Printed circuit board assembly

A printed circuit board substrate includes an insulation matrix and a waterproof layer. The insulation matrix includes a first surface and a second surface at an opposite side thereof to the first surface. The waterproof layer is formed in the insulation matrix and is arranged between the first surface and the second surface for blocking water from passing therethrough in a thicknesswise direction of the insulation matrix.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to flexible printed circuit boards (PCBs) and, particularly, to a printed circuit board substrate and a printed circuit board having the same.

2. Description of Related Art

Nowadays, flexible printed circuit boards (FPCBS) are widely used in portable electronic devices such as mobile phones, digital cameras, and personal digital assistants (PDAS). In some electronic devices, certain parts are movable relative to a main body. In these electronic devices, FPCBS can maintain an electrical connection between the main body and the movable parts due to their flexibility.

FPCBS can be manufactured by at least a base film using a wetting process, such as cleaning, developing, etching, electro-plating, etc. The base film includes an insulation film and a copper film. For example, a process for manufacturing electrical traces of the FPCB includes the following steps. Firstly, the base film is cleaned in a cleaning solution to remove surface oils of the copper film. Secondly, a photo-resist layer is formed on the surface of the copper film. Thirdly, the photo-resist layer is exposed to a light beam using a mask having a predetermined pattern. Thus, one portion of photo-resist layer is covered by the mask, and the other portion of photo-resist layer is not covered and irradiated by the light beam. When the photo-resist layer is made of a positive photo-resist, the uncovered photo-resist layer (i.e. the exposed photo-resist layer) is changed to be soluble in a developing agent. Fourthly, the base film having the photo-resist layer is developed in the developing agent. During the developing process, the exposed photo-resist layer is dissolved in the developing agent, and the residual photo-resist layer forms a patterned photo-resist layer. Thus, one portion of the copper film is covered by the pattered photo-resist layer, and the other portion of the copper film is exposed to the outside. Fifthly, the base film having the patterned photo-resist layer is arranged in an etching solution, and the copper film not covered by the photo-resist layer is dissolved by the etching solution. As a result, the residual copper film covered by the photo-resist layer forms a copper trace. Finally, the photo-resist layer covering the copper trace is eliminated, thereby obtaining the desired electrical traces of the FPCB.

In the process mentioned above, the base film is exposed in liquid solutions (e.g., the cleaning solution, the developing agent, the etching solution) repeatedly, and the liquid solution may inevitably penetrate into the base film. Thus, an original characteristic of the base film may be changed, thereby affecting the quality of the FPCB manufactured by such base film. Furthermore, when the copper film is made into copper traces, molecules (e.g., water molecules) or other ions of the liquid solution may migrate from the insulation film to the copper traces to react with the copper traces. That is, an ion migration phenomena has happened between the insulation film and the copper traces. As a result, a quality of the copper traces may be affected, e.g., causing an open circuit phenomena or a short circuit phenomena.

What is need, therefore, is PCB substrate which can resist/avoid the happening of the ion migration phenomena. What is also need is a PCB having the PCB substrate.

SUMMARY OF THE INVENTION

An embodiment of printed circuit board substrate includes an insulation matrix and a waterproof layer. The insulation matrix includes a first surface and a second surface at an opposite side thereof to the first surface. The waterproof layer is formed in the insulation matrix and is arranged between the first surface and the second surface for blocking water from passing therethrough in a thicknesswise direction of the insulation matrix.

Advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will now be described in detail below and with reference to the drawings.

Referring toFIG. 1, an insulation film10, in accordance with a first preferred embodiment, is shown. The insulation film10is used as a printed circuit board substrate and includes an insulation matrix11, and a waterproof layer20formed in the insulation matrix11. The insulation matrix11includes a first surface12and a second surface14on opposite sides of the insulation matrix11. At least one waterproof layer20is formed between the first surface12and the second surface14to separate/divide the first surface12and the second surface14from each other along a thickness (height) of the insulation matrix11, thereby preventing molecules or ions migrating/seeping/leaking between the first surface12and the second surface14. In other words, the waterproof layer20is provided to avoid an ion migration phenomena happening between the first surface12and the second surface14. In order to realize the separation/division the first surface12and the second surface14, a projection area of the waterproof layer20along the thickness of the insulation matrix11is equal to a vertical sectional area of the insulation matrix11, where the waterproof layer20is located.

The waterproof layer20is made of waterproof materials such as an aluminum foil. When used as the waterproof layer20, the aluminum foil has many advantages, such as excellent waterproof characteristics, light weight, non-magnetic, low oxidation activity, corrosion resistance, and so on. Therefore, the waterproof layer20made of aluminum foil is adopted in the insulation matrix11to add the corresponding advantages of the aluminum foil to the waterproof20.

The insulation film10can be used to manufacture either rigid or flexible PCBS. Generally, the PCBS are composed of at least one base film. The base film includes an insulation film and a copper film formed on at least one surface of the insulation film. A thickness of the insulation film is in a range from about 7 mils to about 8 mils (1 mil equals to about 25.4 micrometers), and the thickness of the waterproof layer20have a thickness in a range from about 3 micrometers to about 25 micrometers. It is to be understood that any potential variances in the thickness of the waterproof layer20are considered to be within the scope of the present insulation film10, so long as the waterproof layer20prevents the ion migration phenomenon from happening between the first surface12and the second surface14.

The insulation matrix11can be made of a resin or a prepreg. The resin includes phenolic resin, epoxy resin, polytetrafluoroethylene (PTFE) resin, polymide resin, and so on. The prepreg is a semi-hardened composite sheet made of a fiberglass cloth and one of the above resins. The fiberglass cloth is soaked in one of the resins, e.g., epoxy resin, and is dried, thereby yielding an epoxy prepreg.

The insulation film10of the present embodiment is manufactured using a laminating method. First, one waterproof layer20and two insulation matrixes11are provided. Second, the waterproof layer20is clamped between the two insulation matrixes11. Finally, the two insulation matrixes11with the waterproof layer20clamped therebetween are laminated by a laminating device, thereby yielding a desired insulation film10. In the present embodiment, the two insulation matrixes11are two fiberglass cloths, and the waterproof layer20is an aluminum foil. Moreover, two or more of the waterproof layer20can be configured between two insulation matrixes11correspondingly to manufacture various insulation films10.

In other preferred embodiments, the insulation films10may have a multi-layered configuration composed of a number of waterproof layers20and a number of matrixes11laminated in an alternating manner correspondingly. In the multi-layered configuration, the insulation matrix11may be resin, prepreg, or the combination thereof. For example, the insulation film10includes three insulation matrixes11and two waterproof layers20clamped between adjacent two insulation matrixes11correspondingly. In the three insulation matrixes11, one of the three insulation matrixes11is epoxy prepreg, while the remained of the three insulation matrixes11are epoxy resins. It is to be understood that any potential variances in the configuration of the insulation matrix11are considered to be within the scope of the insulation film10, as long as at least one waterproof layer20is provided in the insulation film10to prevent the ion migration phenomenon from happening between the first surface12and the second surface14.

Referring toFIG. 2, a base film100for manufacturing flexible printed circuit board (FPCB), in accordance with a second embodiment, is shown. The base film100is used as a printed circuit board substrate and includes an insulation film110, an electrically conductive layer120formed on at least one surface of the insulation film110, and at least one waterproof layer130. The insulation film110includes a first surface111and a second surface112on opposite sides of the insulation film110. The electrically conductive layer120is formed on the first surface111. The waterproof layer130is formed between the first surface111and the second surface112to separate/divide the first surface111and the second surface112from each other along a thickness (height) of the insulation film110, thereby preventing molecules or other ions from migrating/seeping/leaking between the first surface111and the second surface112. In order to achieve this separation/division, a projection area of the waterproof layer130along the thickness (height) of the insulation film110is equal to a vertical sectional area of the insulation film110, where the waterproof layer130is positioned. When wetting processes such as clearing, etching, electro-plating and so on, is performed on the base film100, the waterproof layer130prevents molecules or other ions migrating from the second surface112to the first surface111and further reacting with the electrically conductive layer120. As a result, a natural characteristic of the electrically conductive layer120cannot be affected or changed. Especially, when the electrically conductive layer120is made into electrical traces, the electrical traces cannot be affected (e.g., cannot causing an open circuit phenomena or a short circuit phenomena).

In the present embodiment, the insulation film110is a rectangular sheet, and the waterproof layer130is a flat aluminum foil. The waterproof layer130is parallel to the first surface111and the second surface112, and is arranged between the first surface111and the second surface112. In the present embodiment, the projection area of the waterproof layer130along the thickness (height) of the insulation film110is equal to a surface area of the waterproof layer130. Therefore, the surface area of the waterproof layer130is identical with that of either the first surface111or the second surface112. Thus, the waterproof layer130separates/divides the first surface111and the second surface112along the thickness (height) of the insulation film110. It is to be understood that any potential variances in the shape of the waterproof layer130are considered to be within the scope of the present base film100, as long as the projection area of the waterproof layer130along the thickness of the insulation film110is equal to a vertical sectional area of the insulation film110, where the waterproof layer130is located.

A thickness of the waterproof layer130is determined by the thickness of the insulation110. In the present embodiment, the thickness of the insulation film110is in a range from about 7 mils to about 8 mils (1 mil is about 25.4 micrometers). So the thickness of the waterproof layer130is in a range from about 3 micrometers to about 25 micrometers. Certainly, any potential variances in the thickness of the waterproof layer130are considered to be within the scope of the present base film100, as long as the waterproof layer130can provide the waterproof function between the opposite surfaces of the insulation film110. For example, in some base films, the thickness of the waterproof layer130can be larger than 25 micrometers or less than 3 micrometers.

The insulation film110can be made of a resin, a prepreg or a combination thereof. In the present embodiment, the insulation film110is made of prepreg, the electrically conductive layer120is a copper foil, and the waterproof layer130is an aluminum foil.

A method for manufacturing the base film100includes the following steps. Firstly, two prepreg sheets, a waterproof layer130and one electrically conductive layer120are provided. Secondly, the waterproof layer130is clamped between two prepreg sheets. Thirdly, two prepreg sheets with the waterproof layer130clamped therebetween are laminated by a laminating device, thereby yielding the desired insulation film110having the waterproof layer130. Finally, the electrically conductive layer120is laminated on one surface of the insulation film110to obtain the desired base film100. Certainly, two prepreg sheets, one waterproof layer130and one electrically conductive layer120can be laminated all at once to form the base film100.

Referring toFIG. 3, a base film200for manufacturing FPCB, in accordance with a third embodiment, is shown. The base film200includes an insulation film210, a copper layer220formed on one surface of the insulation film210, and a waterproof layer230formed in the insulation film210. The insulation film210is a rectangular sheet and includes a first surface211and a second surface212opposite to the first surface211. The waterproof layer230is a flat sheet of aluminum foil and is slant across in between (e.g., oblique to) the first surface211and the second surface212. A projection area of the waterproof230along a horizontal parallel to the first and second surfaces211and212is equal to the area of either the first surface211or the second surface212. Thus, the waterproof layer230partitions the first surface211and the second surface212along the thickness of the insulation film210.

Referring toFIG. 4, a base film300for manufacturing FPCB, in accordance with a fourth embodiment, is shown. The base film300includes an insulation film310, a copper layer320formed on one surface of the insulation film310, and a waterproof layer330formed in the insulation film310. The insulation film310is a rectangular sheet and includes a first surface311and a second surface312opposite to the first surface311. The waterproof layer330is a wave-shaped aluminum foil and is arranged between the first surface311and the second surface312. As a whole, the waterproof layer330is parallel to the first and second surfaces311,312. A projection area of the waterproof330along a horizontal parallel to the first and second surfaces311,312is equal to the area of either the first surface311or the second surface312. Thus, the waterproof layer330separates/divides the first surface311and the second surface312along the thickness of the insulation film310.

Referring toFIG. 5, a FPCB400, in accordance with a fifth embodiment, is shown. The FPCB400can be manufactured by at least one of the above-mentioned base film. In the present embodiment, the FPCB400is manufactured by laminating one double-sided FPCB and one single-sided FPCB. In detail, the FPCB400includes a first FPCB410(i.e., a double-sided FPCB), a second FPCB420(i.e., a single-sided FPCB), and an adhesive layer430for adhering the first FPCB410and the second FPCB420together.

The first FPCB410includes a first insulation film411, two first traces412, and a first waterproof layer413. The first insulation film411is a rectangular sheet and includes a first surface411aand a second surface411bon opposite sides of the first insulation film411. The waterproof layer413is arranged between the first surface411aand the second surface411b. The waterproof layer413is a flat aluminum foil and is parallel to the first surface411aand the second surface411b. Two first traces412are separately formed on the first surface411aand the second surface411b.

The second FPCB420includes a second insulation film421, a second trace422, and a second waterproof layer423. The second insulation film421is a rectangular sheet and includes a third surface421aand a fourth surface421bon opposite sides of the second insulation film421. The waterproof layer433is arranged between the third surface421aand the fourth surface421b. The waterproof layer423is wave-shaped and is parallel to the third surface421aand the fourth surface421b, as a whole. The second trace422is formed on the second surface421bof the second insulation film421.

The insulation films and the base films can be used in rigid printed circuit boards, flexible printed circuit boards, or rigid-flexible printed circuit boards. In those printed circuit boards, the insulation film thereof includes the waterproof layer. During the wetting processes (e.g., clearing, etching, electro-plating and so on) for manufacturing those printed circuit boards, the waterproof layer prevents molecules (e.g., water molecules) or other ions from migrating opposite surfaces of the insulation film and reacting with the electrically conductive layer or traces. Thus, a stability of the manufacturing process can be improved, and the printed circuit boards with excellent water-resistance characteristic have been obtained.