LENS FOCUSING METHOD AND OPTICAL MODULE

A lens focusing method includes the following steps. A holder is disposed on a printed circuit board, such that the holder surrounds an image sensor that is on the printed circuit board. A lens assembly is rotated to position in the holder through a first thread of the holder and a second thread of the lens assembly. A tilt of the holder is adjusted, such that an optic axis of the lens assembly is perpendicular to the image sensor. The lens assembly is rotated to move to a focal plane in a vertical direction through the first and second threads again.

RELATED APPLICATIONS

This application claims priority to Taiwanese Application Serial Number 104126851, filed Aug. 18, 2015, which is herein incorporated by reference.

BACKGROUND

Field of Invention

The present invention relates to a lens focusing method and an optical module.

Description of Related Art

In the current market of various electronic products, many products have extensively utilized optical modules that have lenses to receive image information. For example, optical modules having lenses may be assembled to cellular phones, notebook computers, cameras, and equipment of medical science.

During assembly of an optical module, in order to form a good image generated by an image sensor after a lens assembly is installed, a thread focusing method or an active alignment (AA) focusing method is often utilized to adjust the focal length of the lens assembly. When the thread focusing method is used, the lens assembly is connected to a holder that is fixed on a printed circuit board through the threads of the lens assembly and the holder. Thereafter, the lens assembly is rotated to a focal plane. However, in this method, when the holder or the image sensor is not evenly assembled to the printed circuit board, the optic axis of the lens assembly is not perpendicular to the image sensor, such that the corner region of an image is easily fuzzy.

When the active alignment focusing method is used, the lens assembly is clamped into the holder and is moved to a focal plane. Thereafter, the tilt of the lens assembly is adjusted to a position that the optic axis is perpendicular to the image sensor. Subsequently, glue is dispensed to fix the lens assembly. However, in this method, when the tilt of the lens assembly is adjusted, it is possible to leave the focal plane, such that the central region of an image easily has poor resolution.

SUMMARY

An aspect of the present invention is to provide a lens focusing method.

According to an embodiment of the present invention, a lens focusing method includes the following steps. A holder is disposed on a printed circuit board, such that the holder surrounds an image sensor that is on the printed circuit board. A lens assembly is rotated to position in the holder through a first thread of the holder and a second thread of the lens assembly. A tilt of the holder is adjusted, such that an optic axis of the lens assembly is perpendicular to the image sensor. The lens assembly is rotated to move to a focal plane in a vertical direction through the first and second threads again.

Another aspect of the present invention is to provide an optical module.

According to an embodiment of the present invention, an optical module includes a printed circuit board, an image sensor, a holder, and a lens assembly. The image sensor is located on the printed circuit board. The holder is located on the printed circuit board and surrounds the image sensor. The holder has an accommodating space and a first thread, and the first thread is located on the wall surface of the holder facing the accommodating space. At least a portion of the lens assembly is located in the accommodating space and has a second thread. The holder is oblique relative to the printed circuit board, such that an optic axis of the lens assembly is perpendicular to the image sensor.

In the aforementioned embodiments of the present invention, the lens assembly is combined with the holder through the first and second threads. When the tilt of the holder is adjusted, the lens assembly is shifted along with the holder (e.g., a left shift or a right shift). Hence, the lens assembly may be adjusted to a position that the optic axis thereof is perpendicular to the image sensor. After the tilt of the holder is adjusted, the lens assembly may be rotated to move in a vertical direction in the holder (e.g., up and down). Therefore, the lens assembly may be adjusted to a position of the focal plane. As a result, the lens focusing method and the optical module of the present invention can improve not only the resolution of the corner region of an image, but also the resolution of the central region of an image.

DETAILED DESCRIPTION

FIG. 1is a flow chart of a lens focusing method according to one embodiment of the present invention. The lens focusing method includes the following steps. In step S1, a holder is disposed on a printed circuit board, such that the holder surrounds an image sensor that is on the printed circuit board. Thereafter, in step S2, a lens assembly is rotated to position in the holder through a first thread of the holder and a second thread of the lens assembly. Subsequently, in step S3, a tilt of the holder is adjusted, such that an optic axis of the lens assembly is perpendicular to the image sensor. Finally, in step S4, the lens assembly is rotated to move to a focal plane in a vertical direction through the first and second threads again.

In the following description, the aforesaid steps will be described in detail.

FIG. 2is a top view of a printed circuit board110and an image sensor120according to one embodiment of the present invention. As shown inFIG. 2, the image sensor120is located on the printed circuit board110. The image sensor120may be fixed to the printed circuit board110by surface mount technology (SMT), such that the image sensor120is electrically connected to the printed circuit board110. In addition, a light-curing adhesive130may be dispensed to the printed circuit board110, such that the light-curing adhesive130surrounds the image sensor120. In this embodiment, preferably, the image sensor120may be a CMOS chip or a CCD chip, and the light-curing adhesive130may be an ultraviolet curing adhesive, but the present invention is not limited in this regard.

FIG. 3is a schematic view of a holder140and a lens assembly150after being disposed on the printed circuit board110shown inFIG. 2. As shown inFIG. 2andFIG. 3, after the light-curing adhesive130surrounds the image sensor1.20, the holder140may be disposed on the printed circuit board110, such that the holder140surrounds the image sensor120that is on the printed circuit board110. The light-curing adhesive130is utilized to adhere the holder140to the printed circuit board110. In this embodiment, the holder140has an accommodating space141and a first thread142, and the lens assembly150has a second thread152. After the holder140is adhered to the printed circuit board110, the lens assembly150may be rotated to position in the holder140through the first and second threads142,152, but the present invention is not limited in this regard.

In another embodiment, the lens assembly150may be rotated to position in the holder140first, and then the lens assembly150and the holder140are together assembled to the printed circuit board110, such that the holder140is adhered to the printed circuit board110by the light-curing adhesive130.

FIG. 4is a schematic view of the holder140shown inFIG. 3after being clamped by a robotic arm210. As shown inFIG. 3andFIG. 4, after the lens assembly150is assembled to the holder140, the robotic arm210may clamp the holder140. In this embodiment, due to manufacturing errors, the image sensor120is obliquely located on the printed circuit board110. Since the light-curing adhesive130is not exposed by a light (e.g., an ultraviolet light) that corresponds to the wavelength of the light-curing adhesive130yet for previous curing and a baking process is not performed on the light-curing adhesive130in a high temperature yet for thermal curing, the holder140is only temporally positioned on the printed circuit board110. When the holder140on the printed circuit board110receives a force, the tilt of the holder140still can be adjusted. In this embodiment, the robotic arm210is utilized to clamp the holder140to adjust the tilt of the holder140.

FIG. 5is a schematic view of the holder140shown inFIG. 4after being adjusted the tilt thereof. As shown inFIG. 4andFIG. 5, when the tilt of the holder140is adjusted, the lens assembly150is shifted along with the holder140(e.g., a left shift or a right shift), so that the lens assembly150may be adjusted to a position that the optic axis L of the lens assembly150is perpendicular to the image sensor120. In addition, when the robotic arm210adjust the tilt of the holder140, an included angle between the optic axis L of the lens assembly150and the image sensor120may be detected. Until the optic axis L of the lens assembly150is perpendicular to the image sensor120, the tilt of the holder140is stopped adjusting. As a result, due to the optic axis L of the lens assembly150perpendicular to the image sensor120, the resolution of the corner region of an image that is formed by the image sensor120may be improved.

In this embodiment, since the image sensor120is oblique downward at the right side ofFIG. 5, the holder140is also oblique downward at the right side ofFIG. 5after the robotic arm210adjusts the holder140. In fact, the tilt of the holder140can be adjusted in six-axial directions (i.e., x, y, z, θx, θy, and θz directions) by the robotic arm210to ensure that the image sensor120in different oblique states can be perpendicular to the optic axis L of the lens assembly150after the lens assembly150is adjusted.

After the tilt of the holder140is adjusted, the holder140is oblique relative to the printed circuit board110. Hence, a gap132may be formed between the holder140and the printed circuit board110. At this time, the gap132may be filled with additional light-curing adhesive130to prevent one side of the holder140from suspending.

FIG. 6is a schematic view of the gap132shown inFIG. 5after being filled with the light-curing adhesive130and after the light-curing adhesive130is cured. As shown inFIG. 5andFIG. 6, after the tilt of the holder140is adjusted and the light-curing adhesive130is dispensed in the gap132, a light corresponding to the wavelength of the light-curing adhesive130can be utilized to irradiate the light-curing adhesive130(e.g., an ultraviolet light), such that the light-curing adhesive130is pre-cured. Thereafter, the light-curing adhesive130is baked (e.g., 80° C.), such that the light-curing adhesive130is cured to fix the holder140to the printed circuit board110. As a result, the holder140can maintain its tilt on the printed circuit board110. After the light-curing adhesive130is cured, the lens assembly150may be rotated (e.g., in a direction D1) to move to a focal plane in a vertical direction (e.g., in a direction D2) through the first and second threads142,152again. Until the lens assembly150is on the focal plane, the lens assembly150is stopped rotating. In addition, when the lens assembly150is moved in the vertical direction, an image of the image sensor may be detected. When the central region of the image is in the clearest state, it is referred that the lens assembly150is just located on the focal plane, and the lens assembly150may be stopped rotating. As a result, due to the lens assembly150on the focal plane, the resolution of the central region of an image may be improved.

FIG. 7is a schematic view of the lens assembly150and the holder140shown inFIG. 6after being fixed by glue160. As shown inFIG. 6andFIG. 7, after the lens assembly150is moved to the focal plane, the glue160may be utilized to fix the lens assembly150to the holder140. As a result, the lens assembly150can be hold at the position of the focal plane in the holder140, and the optical module100of the present invention is obtained.

The optical module100includes the printed circuit board110, the image sensor120, the holder140, and the lens assembly150. The image sensor120is located on the printed circuit board110. The holder140is located on the printed circuit board110and surrounds the image sensor120. The holder140has the accommodating space141and the first thread142, and the first thread142is located on the wall surface of the holder140facing the accommodating space141. At least a portion of the lens assembly150is located in the accommodating space141. The portion of the lens assembly150in the accommodating space141has the second thread152that may be coupled to the first thread142. The holder140is oblique relative to the printed circuit board110, such that the optic axis L of the lens assembly150is perpendicular to the image sensor120.

In the lens focusing method and the optical module100of the present invention, the holder140is combined with the lens assembly150through the first and second threads142,152. When the tilt of the holder140is adjusted, the lens assembly150is shifted along with the holder140(e.g., a left shift or a right shift). Hence, the lens assembly150may be adjusted to a position that the optic axis L of the lens assembly150is perpendicular to the image sensor120. After the tilt of the holder140is adjusted, the lens assembly150may be rotated to move in a vertical direction in the holder140(e.g., up and down). Therefore, the lens assembly150may be adjusted to a position of the focal plane. As a result, the lens focusing method and the optical module100of the present invention can improve not only the resolution of the corner region of an image, but also the resolution of the central region of an image.

In this embodiment, the optical module100may further include the light-curing adhesive130. The light-curing adhesive130is between the holder140and the printed circuit board110to adhere the holder140to the printed circuit board110. The surface144of the holder140facing the printed circuit board110has a first edge145and a second edge146that is opposite to the first edge145, and a distance H1between the first edge145and the printed circuit board110is greater than a distance H2between the second edge146and the printed circuit board110. In other words, as shown inFIG. 7, a thickness H1of the light-curing adhesive130between the first edge145and the printed circuit board110is greater than a thickness H2of the light-curing adhesive130between the second edge146and the printed circuit board110.

Moreover, the optical module100may further include the glue160. The glue160is between the lens assembly150and the holder140to adhere the lens assembly150to the holder140.