Light-emitting unit and illumination device and image reading device using light-emitting unit
A light-emitting unit 20 has a light-emitting unit board 21 made of resin provided with a lead frame 22. The light-emitting unit board 21 is also provided with an open window 21a for mounting a light-emitting device. The lead frame 22 comprises a lead terminal section 22a, an inner lead section 22c, and a light-emitting device mounting and connecting section 22b which is exposed within the open window 21a. The light-emitting devices 23a, 23b, and 23c are bonded with the light-emitting device mounting and connecting section 22b, and electrodes of the light-emitting devices and the lead frame are connected by a metal wire 24, wherein the open window 21a is sealed by transparent resin. The lead frame 22 is made of iron-containing copper to improve heat radiation performance of the light-emitting unit board. By increasing maximum current to be supplied to the light-emitting diodes, it is possible to increase illumination brightness and to attain speedup of image reading.
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This application is a Divisional of 10/898,420 filed Jul. 23, 2004 which is a Divisional of 10/193,026 filed Jul. 9, 2002 and which application(s) are incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a light-emitting unit, an illumination device for illuminating a document, and a contact-type image reading device (i.e., an image sensor) incorporating the illuminating device therein.
2. Description of the Prior Art
A contact-type image sensor is used as a device for reading a document using facsimile terminal equipment, a copying machine, an image scanner, etc. This contact-type image sensor is provided with a line illumination device for linearly illuminating a document surface over a main scanning range.
The line illumination device using a light guide is known and disclosed, for example, in Japanese Unexamined Patent Publication No. HEI 8-163320 (1996) and Japanese Unexamined Patent Publication No. HEI 10-126581 (1998) (Japanese Patent No. 2999431) in which the line illumination device using a bar-shaped or plate-shaped light guide and an image reading device using such a line illumination device are described.
Structure of the light-emitting unit 102 is shown in
The lead frame 104 comprises a lead terminal section serving as an outer connecting terminal, an inner lead section, and a light-emitting device mounting and connecting section exposed within the window section 103. In the prior art, phosphor bronze is used as material for the lead frame 104, and silver paste formed by mixing resin with silver powder is used as material for the adhesive agent 106. An outer connecting terminal 104a of the lead frame 104 guided out of the light-emitting unit board 110 is adapted to solder the corresponding electric circuit.
If the brightness of the line illumination device is increased to increase the brightness of the illumination light for illuminating the reading surface of a document, it is possible to easily speed up the image reading. However, when an electric current sent to the light-emitting device is increased to increase the brightness of the line illumination device, calorific value of the light-emitting device is also increased accordingly. In this case, luminous efficiency decreases and as a result, there is a problem that it is difficult to increase the brightness.
When the electric current is supplied to the light-emitting device, junction temperature rises at the same time when light is emitted (i.e., heat is generated from the light-emitting device itself). Generated heat is transmitted or escapes to the side of the light-emitting unit board and finally radiated in the air. Accordingly, the rise of the junction temperature depends on the heat radiation characteristics of the light-emitting unit board and is substantially proportional to the supplied electric current. Namely, if the heat radiation characteristics of the light-emitting unit board are good or satisfactory, the rate of rise in the junction temperature becomes small.
On the other hand, to send an electric current to the light-emitting device (i.e., to turn on a light) at a high temperature leads to acceleration of deterioration of the light-emitting device. To lengthen the life, it is desirable that the temperature rise of the light-emitting device be controlled as much as possible. Accordingly, the better the heat radiation performance of the light-emitting unit board, the larger the maximum current which can be supplied to the light-emitting unit. The heat radiation performance of the light-emitting unit board varies with the shape, material or the like. In the prior art, phosphor bronze has been used for the material of the lead frame of the light-emitting unit board.
Namely, if the same level of brightness as before is required, the phosphor bronze can be used as the material for the lead frame, but the heat conductivity is not enough to obtain the higher or further brightness.
Solder used in the case where the outer connecting terminal of the lead frame is soldered to the corresponding electric circuit is generally an alloy of tin (Sn) and lead (Pb). However, there is a tendency to use the solder which does not contain the lead (i.e., lead-free solder) from the environmental point of view these days.
On the other hand, since material resin for the light-emitting unit board must stand the heat when soldered, polybutylene terephthalate (PBT) has been used in the prior art. A melting point of the polybutylene terephthalate is 200 ˜ 210° C. and there was no problem because the melting point of a conventional solder (i.e., an alloy of tin and lead) is 186° C. However, since the melting point of the lead-free solder is 210 ˜ 230° C., heat resistance is not enough in the case of polybutylene terephthalate (PBT).
By increasing the brightness of the light-emitting unit which is incorporated in the line illumination device, it is possible to speed up image reading, but there is caused a new problem that the luminous efficiency decreases when the temperature is high.
SUMMARY OF THE INVENTIONIt is therefore an object of the present invention to improve these problems.
A light-emitting unit according to a first invention is provided, in which a lead frame disposed on a light-emitting unit board on which a light-emitting device is mounted is made of a copper alloy or an aluminum alloy of which the heat conductivity is250 W/(m·K) or more.
The copper alloy includes beryllium bronze or iron-containing copper. A specific composition ratio of the iron-containing copper is as follows: Iron (Fe): 0.02 ˜ 0.5 wt %; phosphorus (P): 0.005 ˜ 0.10 wt %; the rest: copper (Cu)
By setting iron and phosphorus at the above ratio, it is possible to increase the strength while maintaining the heat conductivity high.
More desirable composition ratio of iron and phosphorus is as follows: Fe: 0.05 ˜ 0.15 wt %; P: 0.015 ˜ 0.04 wt %; the rest: Cu
In addition to the above, material with high heat conductivity includes pure metal such as gold, silver, aluminum, copper, or tungsten. However, gold and silver are expensive and not realistic. Aluminum and copper are not sufficient in strength and tungsten is hard to be processed.
In particular, the heat conductivity of the iron-containing copper with the above composition ratio is about 364 W/(m·K) and high. Accordingly, if the lead frame is formed using the iron-containing copper, it is possible to improve the heat radiation performance of the light-emitting unit board. In this manner, even though the electric current supplied to the light-emitting device is increased, it is possible to decrease the temperature rise of the light-emitting device and increase the illumination brightness.
Further, when thickness of the lead frame of the light-emitting unit is t (mm), thickness of the light-emitting unit board is T (mm), thickness of the light-emitting device is D (mm), and height of a bonding wire is d (mm), it is desirable that the relationship among them be 0.1 mm≦t≦(T−D−d). Especially desirable range is T/2 ≦t≦(T−D−d).
Still further, when width of the lead frame of the light-emitting unit is W (mm), an interval of the lead frame is P (mm), and thickness of the lead frame is t (mm), it is desirable that the relationship among them be P/2≦W≦(P−t). Especially desirable range is (P−2t)≦W≦(P−t).
The light-emitting unit according to a second invention is provided, in which at least a translucent light-emitting device, specifically a blue or green light-emitting diode (LED) is bonded with the lead frame by a transparent resin or a white resin. It is however to be noted that when bonding by the transparent resin is made, the lead frame surface existing thereunder has been silver-plated.
The silver plating or the white resin has a reflection factor higher than silver paste. Accordingly, by having such a structure, light emitted from the light-emitting device is efficiently emitted from the front surface thereof and as a result, quantity of light entering the light guide increases.
The light-emitting unit according to a third invention is provided, in which as material for the light-emitting unit board, resin is used of which the heat resistant temperature is higher than a melting point of lead-free solder which is used when soldering the lead frame to an electric circuit. Specifically, it is desirable that the resin such as polyphthalamide resin, polyphenylene sulfide resin, or liquid crystal polymer be used.
A melting point of the lead-free solder is 210 ˜ 230° C. Since the melting point of the polyphthalamide resin is 290° C., that of polyphenylene sulfide resin (PPS) is 260 ˜ 270° C., and that of the liquid crystal polymer is 220 ˜ 230° C., each of them can fully stand the temperature in the case of soldering.
An illumination device using the light-emitting unit includes the illumination device in which a light-emitting unit is provided on the end face of a bar-shaped light guide, and light incident from the light-emitting unit is emitted from a light-emitting surface provided along the longitudinal direction while reflecting the light by the inner surface of the bar-shaped light guide or the illumination device in which the light-emitting unit is provided on the side of a plate-shaped light guide in the direction of the thickness, and light incident from the light-emitting unit is emitted from the upper or lower surface of the plate-shaped light guide while reflecting the light by the inner surface of the plate-shaped light guide.
Further, by incorporating the line illumination device in an image reading device, it is possible to increase the illumination brightness of a document and attain the speedup of image reading.
BRIEF DESCRIPTION OF THE DRAWINGSThe above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.
A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. As shown in
As shown in
A shown in
In this line illumination device 10, light from the light-emitting source is introduced into the light guide 11 from one end (i.e., the light incident surface) of the light guide 11. Light transmitted through the light guide 11 is scattered by the light-scattering pattern 11b formed on the back of the light guide and then, the scattered light is caused to emit from the light-emitting surface 11a (see
The intensity of light incident from the light-emitting source is high or large on the side near the light-incident surface, while the light intensity is low or small as light goes further away from the light-incident surface. Now, as shown in
As shown in
A light-emitting unit board 21 is made by insert-molding a lead frame 22 onto a board resin and provided with an open window 21a for mounting light-emitting devices 23 (23a, 23b, and 23c). In particular, the light-emitting devices 23a and 23c are blue or green light-emitting diodes (LED), while the light-emitting device 23b is a red light-emitting diode (LED).
In the present embodiment, the light-emitting unit board 21 uses the resin such as polyphthalamide resin, polyphenylene sulfide resin, or liquid crystal polymer of which the heat-resistant temperature is higher than a melting point of lead-free solder described below as its material.
The lead frame 22 consists of a section (i.e., a lead terminal section) 22a exposed to supply the light-emitting devices 23 with an electric current from the outside, a section (i.e., a light-emitting device mounting and connecting section) 22b exposed within the open window 21a for mounting the light-emitting devices 23, and a section (i.e., an inner lead section) 22c hidden within the board resin. The lead terminal section 22a is soldered to the corresponding circuit (not shown). In the present embodiment, bonding is made using the lead-free solder.
The surface of the lead frame 22 is provided with silver plating to increase a reflection factor and to improve wire-bonding strength.
The light-emitting unit 20 is constructed in such a manner that the light-emitting devices 23 (i.e., 23a, 23b, and 23c) are bonded onto the lead frame 22b (i.e., the light-emitting device mounting and connecting section) exposed within the open window 21a of the light-emitting unit board 21. The light-emitting devices 23 (23a, 23b, and 23c) and the lead frame 22b are connected by a metal wire 24 and then, sealed by transparent resin 25. A through-bore 26 provided on the light-emitting unit board 21 is used to secure the light-emitting unit 20 to the light guide casing 12 when the line illumination device is assembled.
Phosphor bronze has been used as the material for the lead frame 22, but in the present embodiment, iron-containing copper is used instead. A comparison of the iron-containing copper with the conventional material is made below:
Composition (unit: wt/%)
Heat conductivity [unit: W/(m·k)]
The iron-containing copper has the heat conductivity close to that i.e., 391 W/(m·k) of pure copper.
As shown in
On the other hand, the red light-emitting device 23b is provided with a non-transparent GaAs substrate. Since there are provided electrodes on both the surface and the back of the substrate, only one metal wire 24 is provided as shown in
As described above, by using the transparent resin 27 as an adhesive agent, light transmitted through the light-emitting device among light emitted from the light-emitting device 23a or 23c is reflected by silver plating provided on the surface of the lead frame 22b. Then, the light is again transmitted through the light-emitting device and emitted from the front surface, resulting in increasing quantity of light.
White resin (e.g., epoxy resin or silicon resin) can be used in place of the transparent resin 27. In this case, the reflecting surface is the surface of the white resin in place of the silver plating provided on the surface of the lead frame 22b. Accordingly, when the white resin is used, the surface of the lead frame 22b is not necessarily provided with the silver plating.
FIGS. 12 (a) and (b) are graphs showing experimental results of the relationship between a kind of adhesive resin and the output of LED regarding the green LED and Blue LED. As is apparent from these graphs, it is to be noted that when transparent or white resin is used as an adhesive agent, the LED output remarkably improves compared with conventional silver paste.
The illumination device 30 is provided with the light-emitting unit 20 on the side of a plate-shaped light guide 31 made of transparent acrylic resin in the direction of the thickness. The plate-shaped light guide 31 is housed within a white casing 32. A white reflection plate 33 is provided on the upper surface of the light guide 31 serving as a reflection surface, while a diffusion sheet 34 is provided on the lower surface of the light guide 31 serving as a light-emitting surface.
As described above, according to a first invention, it is possible to improve heat radiation performance of the light-emitting unit board. Accordingly, even though an electric current supplied to the light-emitting device is caused to increase, it is possible to decrease the rise in temperature of the light-emitting device and increase the illumination brightness. Further, when the line illumination device according to the present invention is incorporated in the image reading device, it is possible to increase the illumination brightness of the document and attain the speedup of the image reading.
According to a second invention, the transparent resin or the white resin is used in place of the conventional silver paste as the adhesive agent for bonding the light-emitting device with the lead frame. Accordingly, by causing the light going or escaping backward out of the translucent light-emitting device board to reflect forward, it is possible to improve the luminous efficiency and increase the illumination brightness.
As a result, by incorporating the line illumination device according to the present invention in the image reading device, it is possible to increase the illumination brightness of the document and also attain the speedup of the image reading.
According to a third invention, the light-emitting unit board is made of heat resisting resin such as polyphthalamide resin, polyphenylene sulfide resin, or liquid crystal polymer. Accordingly, it is possible for the light-emitting unit board to fully stand the heat in the case where the lead frame is bonded with the corresponding circuit using the lead-free solder and to improve the reliability.
Claims
1. A light-emitting unit having a light-emitting device mounted on a light-emitting unit board which is provided with a lead frame, wherein the lead frame is made of a copper alloy or an aluminum alloy of which the heat conductivity is 250 W/(m·K) or more.
2. The light-emitting unit according to claim 1, wherein the copper alloy is iron-containing copper having composition of Fe: 0.02 ˜ 0.5 wt %; P: 0.005 ˜ 0.10 wt %; and the rest: Cu
3. A light-emitting unit having a light-emitting device mounted on a light-emitting unit board which is provided with a lead frame, wherein the light-emitting unit board is made of resin of which the heat resistant temperature is higher than a melting point of lead-free solder which is used when the lead frame is soldered onto an electric circuit.
4. The light-emitting unit according to claim 3, wherein the resin is polyphthalamide resin, polyphenylene sulfide resin, or liquid crystal polymer.
5. An illumination device designed to emit light incident from a light-emitting unit which is provided on an end face of a bar-shaped light guide in the longitudinal direction from a light-emitting surface provided along the longitudinal direction while reflecting the light by the inner surface of the bar-shaped light guide, wherein the light-emitting unit is specified by claim 1.
6. An illumination device designed to emit light incident from a light-emitting unit which is provided on a side of a plate-shaped light guide in the direction of the thickness from the upper or lower surface of the plate-shaped light guide while reflecting the light by the inner surface of the plate-shaped light guide, wherein the light-emitting unit is specified by claim 1.
7. An image reading device comprising the illumination device according to claim 5, a line image sensor, and a rod lens array for converging the reflected light or transmitted light from a document on the line image sensor, wherein each of them is incorporated within a frame.
8. An image reading device comprising the illumination device according to claim 6, a line image sensor, and a rod lens array for converging the reflected light or transmitted light from a document on the line image sensor, wherein each of them is incorporated within a frame.
9. An illumination device designed to emit light incident from a light-emitting unit which is provided on an end face of a bar-shaped light guide in the longitudinal direction from a light-emitting surface provided along the longitudinal direction while reflecting the light by the inner surface of the bar-shaped light guide, wherein the light-emitting unit is specified by claim 3.
10. An illumination device designed to emit light incident from a light-emitting unit which is provided on a side of a plate-shaped light guide in the direction of the thickness from the upper or lower surface of the plate-shaped light guide while reflecting the light by the inner surface of the plate-shaped light guide, wherein the light-emitting unit is specified by claim 3.
Type: Application
Filed: Mar 7, 2007
Publication Date: Jul 5, 2007
Applicant: Nippon Sheet Glass Co., Ltd. (Osaka-shi)
Inventors: Yoshiyuki Uemura (Osaka-shi), Tomihisa Saito (Osaka-shi)
Application Number: 11/714,948
International Classification: F21L 4/00 (20060101);