WO2008075851A1

WO2008075851A1 - Fabrication method of epoxy molding compound tablet and the epoxy molding compound tablet thereby and fabrication method of white emitting device thereby

Info

Publication number: WO2008075851A1
Application number: PCT/KR2007/006464
Authority: WO
Inventors: Eun Jung Seo
Original assignee: Seoul Semiconductor Co., Ltd.
Priority date: 2006-12-19
Filing date: 2007-12-12
Publication date: 2008-06-26

Abstract

The present invention provides a method of fabricating an epoxy molding compound (EMC) tablet containing a phosphor for use in transfer molding of a light emitting device. The method comprises the steps of pulverizing epoxy powder; forming an EMC by mixing the pulverized epoxy powder with phosphor powder; and fabricating the EMC into an EMC tablet. According to the present invention, the process of pulverizing the epoxy powder and the process of mixing the epoxy powder and the phosphor powder are separately performed. Thus, when transfer molding is performed, the phosphor can be uniformly distributed in an epoxy resin molded onto each LED regardless of the arranged position of each of printed circuit boards, thereby narrowing dispersion of the color coordinates of a white color and improving the degree of concentration on a target color coordinate. Therefore, it is possible to mass-produce light emitting devices with uniform luminous characteristics.

Description

FABRICATION METHOD OF EPOXY MOLDING COMPOUND

TABLET AND THE EPOXY MOLDING COMPOUND TABLET

THEREBY AND FABRICATION METHOD OF WHITE

EMITTING DEVICE THEREBY Technical Field

[1] The present invention relates to a method of fabricating a white light emitting device, and more particularly, to a method of fabricating an epoxy molding compound (EMC) tablet, which solves a phenomenon that dispersion of the color coordinates of a white color is widened due to fine particles of a phosphor upon fabrication of a white light emitting device through transfer molding, an EMC tablet fabricated by the method, and a method of fabricating a white light emitting device using the EMC tablet. Background Art

[2] Generally, a light emitting diode (LED) has advantages including an excellent monochromatic peak wavelength, excellent optical efficiency and feasibility of miniaturization, and thus, is widely used for displays and light sources. In particular, a white LED is positively utilized as a high-output, high-efficient light source that can substitute for a backlight of a display or an illumination device.

[3] For methods of implementing such a white LED, a wavelength-converting method in which a phosphor is applied to a blue or ultraviolet (UV) LED to perform conversion into a white color has been mainly used.

[4] For methods of applying a phosphor to a blue or UV LED, there are a method employing a dispensing process using a phosphor-containing liquid resin, and a method employing transfer molding.

[5] Since the dispensing process uses a liquid resin, there is a problem in that phosphor powder precipitates in the liquid resin while the liquid resin is cured.

[6] Meanwhile, the transfer molding is performed in such a manner that a phosphor is mixed with epoxy powder to make an EMC tablet and the EMC tablet is then molded onto a blue LED.

[7] By the transfer molding process, curing time is relatively shortened, thereby preventing deterioration of light conversion efficiency due to precipitation of phosphor powder, and improving productivity.

[8] However, a white LED fabricated using a conventional transfer molding process exhibits wide dispersion of the color coordinates of a white color. [9] In addition, since the molding epoxy is cured within a short time, it is difficult to adjust the distribution of the phosphor while the epoxy is cured. In view of characteristics of the transfer molding, several printed circuit boards (PCBs) are molded at a time using one EMC tablet, causing variations among the PCBs. The occurrence of variations among the PCBs causes wide dispersion of entire color coordinates.

[10] Due to the above problems, in spite of the advantages of the transfer molding, an actually fabricated white LED still partially emits white-blue or white-yellow light, and there is also difficulty in fabricating an LED with excellent light conversion efficiency. Disclosure of Invention Technical Problem

[11] An object of the present invention is to improve the degree of concentration on a target color coordinate by narrowing dispersion of the color coordinates of a white color when transfer molding is performed for chip LEDs. Technical Solution

[12] According to one aspect of the present invention for achieving the object, there is provided a method of fabricating an epoxy molding compound (EMC) tablet containing a phosphor for use in transfer molding of a light emitting device, comprising the steps of pulverizing epoxy powder; forming an EMC by mixing the pulverized epoxy powder with phosphor powder; and fabricating the EMC into an EMC tablet.

[13] The pulverizing step may comprise a process of putting the epoxy powder into ajar and pulverizing the epoxy powder through ball milling, and the EMC forming step may comprise a process of putting the phosphor powder and the epoxy powder pulverized through the ball milling into the jar and mixing the epoxy powder and the phosphor powder with each other through ball milling.

[14] The ball milling for pulverizing the epoxy powder may be performed at 100 to 130 rpm for 20 to 40 minutes, and the ball milling for mixing the epoxy powder and the phosphor powder may be performed at 40 to 80 rpm for 20 to 40 minutes.

[15] According to another aspect of the present invention, there is provided a method of fabricating a white light emitting device by transfer-molding LED chips using an EMC containing a phosphor, comprising the steps of forming an EMC by mixing phosphor powder and epoxy powder with each other; transfer-molding a printed circuit board (PCB) substrate, which has the LED chips wire-bonded thereto, using the EMC; and performing sawing and barrel processes to divide the PCB substrate into individual white light emitting devices, wherein the EMC forming step comprises pulverizing the epoxy powder; forming the EMC by mixing the pulverized epoxy powder with the phosphor powder; and fabricating the EMC into an EMC tablet. [16] The pulverizing step may comprise a process of putting the epoxy powder into ajar and pulverizing the epoxy powder by performing ball milling at 100 to 130 rpm for 20 to 40 minutes, and the EMC forming step may comprise a process of putting the phosphor powder and the epoxy powder pulverized through the ball milling into the jar and mixing the epoxy powder and the phosphor powder by performing ball milling at 40 to 80 rpm for 20 to 40 minutes.

[17] According to a further aspect of the present invention, there is provided an EMC tablet containing a phosphor for use in transfer molding of a light emitting device, comprising epoxy powder pulverized through a pulverizing process; and phosphor powder mixed with the epoxy powder pulverized through the pulverizing process, wherein a mixture of the phosphor powder and the epoxy powder is fabricated into a tablet.

[18] The epoxy powder may be pulverized through first ball milling, and the phosphor powder may be mixed, through second ball milling, with the epoxy powder pulverized through the first ball milling.

[19] According to a still further aspect of the present invention, there is provided a method of fabricating an EMC tablet containing a phosphor for use in transfer molding of a light emitting device, comprising the steps of removing fine particles from phosphor powder; forming an EMC by mixing epoxy powder with the phosphor powder from which the fine particles have been removed; and fabricating the EMC into the EMC tablet using a jig.

[20] According to a still further aspect of the present invention, there is provided a method of fabricating a white light emitting device by transfer-molding LED chips using an EMC containing a phosphor, comprising the steps of forming an EMC by mixing phosphor powder with epoxy powder; transfer-molding a PCB substrate, which has the LED chips wire-bonded thereto, using the EMC; and performing sawing and barrel processes to the PCB substrate to divide the PCB substrate into individual white light emitting devices, wherein the EMC forming step comprises removing fine particles from the phosphor powder; forming an EMC by mixing the epoxy powder with the phosphor powder from which the fine particles have been removed; and fabricating the EMC into an EMC tablet.

[21] According to a still further aspect of the present invention, there is provided an

EMC tablet for use in transfer molding of a light emitting device, comprising phosphor powder from which fine particles have been removed in advance; and epoxy powder mixed with the phosphor powder from which the fine particles have been removed, wherein a mixture of the phosphor powder and the epoxy powder is fabricated into a tablet.

[22] The fine particles may fine particles of 5 D or less. Advantageous Effects

[23] According to the present invention, when an EMC tablet for use in transfer molding is fabricated, a first ball milling process of uniformly pulverizing epoxy powder and a second ball milling process of uniformly mixing phosphor powder with the epoxy powder uniformly pulverized through the first ball milling process are separately performed.

[24] Thus, it is possible to prevent the conventional problem of wide dispersion of the color coordinates of a white color due to fine particles of 5 D or less of phosphor powder which are formed while the epoxy powder and phosphor powder are put into a jar and then subjected to a ball milling process.

[25] Accordingly, when transfer molding is performed, the phosphor can be uniformly distributed in an epoxy resin molded onto each LED regardless of the arranged position of each of PCBs, thereby narrowing dispersion of the color coordinates of a white color and improving the degree of concentration on a target color coordinate. Therefore, it is possible to mass-produce light emitting devices with uniform luminous characteristics.

[26] In addition, according to the present invention, when an EMC tablet for use in transfer molding is fabricated, a process of removing fine particles (preferably, fine particles of 5 D or less) from phosphor powder is performed in advance.

[27] Thus, there is no fine particle of the phosphor powder that is conventionally a cause of wide dispersion of the color coordinates of a white color in a white light emitting device fabricated using transfer molding. Accordingly, when transfer molding is performed, the phosphor can be uniformly distributed in an epoxy resin molded onto each LED regardless of the arranged position of each of PCBs, thereby narrowing dispersion of the color coordinates of a white color and improving the degree of concentration on a target color coordinate. Therefore, it is possible to mass-produce light emitting devices with uniform luminous characteristics.

[28]

Brief Description of the Drawings

[29] Fig. 1 is a flowchart illustrating a process of fabricating a white LED by performing transfer molding using an EMC tablet containing a phosphor, according to an embodiment of the present invention.

[30] Fig. 2 is a flowchart illustrating a process of fabricating an EMC tablet containing a phosphor, according to an embodiment of the present invention.

[31] Figs. 3 to 5 are graphs of respective PCBs of white LEDs fabricated using an EMC tablet generated by putting epoxy powder and a phosphor together and performing ball milling at 80 rpm for 80 minutes, according to comparative examples. [32] Figs. 6 to 8 are graphs of respective PCBs of white LEDs fabricated by performing transfer molding using an EMC tablet containing a phosphor, according to embodiments of the present invention, showing improvement in dispersion of the color coordinates of a white color.

[33] Fig. 9 is a flowchart illustrating a process of fabricating a white LED by performing transfer molding using an EMC tablet containing a phosphor, according to another embodiment of the present invention.

[34] Fig. 10 is a flowchart illustrating a process of fabricating an EMC tablet containing a phosphor, according to another embodiment of the present invention.

[35] Fig. 11 is a graph of a white LED that is fabricated using an EMC tablet fabricated without performing a process of removing fine particles of 5 D or less, according to a comparative example.

[36] Fig. 12 is a graph of a white LED fabricated by performing transfer molding using an EMC tablet containing a phosphor, according to another embodiment of the present invention, comparatively showing improvement in dispersion of the color coordinates of a white color. Best Mode for Carrying Out the Invention

[37] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[38] Fig. 1 is a flowchart illustrating a process of fabricating a white LED by performing transfer molding using an EMC tablet containing a phosphor, according to an embodiment of the present invention; and Fig. 2 is a flowchart illustrating a process of fabricating an EMC tablet containing a phosphor, according to an embodiment of the present invention.

[39] Referring to Fig. 1, phosphor powder and epoxy powder are mixed to form an EMC

(SlO).

[40] Referring to Fig. 2, the process of fabricating an EMC tablet is initiated with a process of putting epoxy powder into ajar, subsequently putting a suitable amount of balls thereinto, and performing ball milling at high speed during a short time so as to pulverize coarse particles of the epoxy powder into uniform fine particles (Sl 1). Here, the ball milling process for pulverizing only the epoxy powder is called a first ball milling process.

[41] The first ball milling process is properly performed at 100 to 300 rpm for about 20 to 40 minutes, preferably for about 30 minutes.

[42] For the uniform pulverization of the particles of the epoxy powder in the first ball milling process, as the particles of the epoxy powder are pulverized more uniformly, they can be mixed more uniformly with a phosphor. [43] When the first ball milling process is completed, a suitable amount of a phosphor is put into the jar in which the epoxy powder uniformly pulverized through the first ball milling process is contained, and ball milling is then performed at low speed during a short time so that the epoxy powder and the phosphor are uniformly mixed to form an EMC (S 12). Here, the ball milling process performed for mixing the epoxy powder and the phosphor is called a second ball milling process.

[44] The second ball milling process is properly performed at 40 to 80 rpm for about 20 to 40 minutes, preferably for about 30 minutes.

[45] Performing the second ball milling process at low speed when the epoxy powder and the phosphor are mixed with each other is to prevent the phosphor from being pulverized into fine particles during the ball milling.

[46] In addition, the reason why the ball milling process is performed separately via the first ball milling process of pulverizing the epoxy powder and the second ball milling process of mixing the epoxy powder and the phosphor with each other is that the phosphor may be pulverized into fine particles while the epoxy powder is pulverized by putting the epoxy powder and the phosphor together and subsequently performing the ball milling.

[47] The reason to prevent the phosphor from being pulverized into fine particles is as follows. If phosphor powder is pulverized into fine particles of 5 D or less due to the ball milling, the fine particles of 5 D or less may be a cause of wide dispersion of the color coordinates of a white color during transfer molding.

[48] During transfer molding, the EMC tablet is injected under pressure. At this time, fine particles of 5 D or less are pushed far away due to the pressure and gathered at a distal end.

[49] Thus, when several PCBs are arranged and then subjected to transfer molding thereon, a phosphor in an epoxy resin molded onto each LED is not uniform according to the arranged position of each of the PCBs. This results in a luminous characteristic by which a yellow-cyan color becomes stronger far away from a transfer molding injection port. Therefore, to prevent formation of fine particles of 5 D or less of the phosphor that causes the above result, phosphor powder is put into the jar just at the time of the second ball milling process, which is separate from the first ball milling process for pulverizing the epoxy powder, so that the phosphor powder is mixed with the epoxy powder uniformly pulverized through the first ball milling process.

[50] When an EMC is formed by performing the ball milling for a suitable time duration, the EMC is fabricated into an EMC tablet using a jig (S 13).

[51] When the EMC tablet is prepared, blue LED chips and Zener diodes are die- attached to a PCB substrate by means of a paste, and chip pads and the PCB substrate are wire-bonded using Au wires (S20). [52] After the wire-bonding process, the PCB substrate is preheated for several seconds to several minutes (S30).

[53] After preheating the PCB substrate to a certain extent, the PCB substrate to which the blue LED chips have been wire-bonded is transfer-molded with the EMC tablet containing the phosphor (S40).

[54] Thereafter, the molded PCB substrate is subjected to sawing and barrel processes so as to be divided into individual white LEDs (S50).

[55] Figs. 3 to 5 are graphs of respective PCBs of white LEDs fabricated using an EMC tablet generated by putting epoxy powder and a phosphor together and performing ball milling at 80 rpm for 80 minutes, according to comparative examples.

[56] Figs. 6 to 8 are graphs of respective PCBs of white LEDs fabricated by performing transfer molding using an EMC tablet containing a phosphor, according to embodiments of the present invention, showing improvement in dispersion of the color coordinates of a white color.

[57] Referring to Figs. 3 to 8, it can be understood that dispersion of the color coordinates of a white color in each of PCBs of white LEDs is narrowed and thus more improved when transfer molding is performed using the EMC tablet fabricated through the first ball milling process of pulverizing epoxy powder and the second ball milling process of mixing the epoxy powder with a phosphor, according to an embodiment of the present invention, as compared with the comparative examples.

[58] Fig. 9 is a flowchart illustrating a process of fabricating a white LED by performing transfer molding using an EMC tablet containing a phosphor, according to another embodiment of the present invention; and Fig. 10 is a flowchart illustrating a process of fabricating an EMC tablet containing a phosphor, according to another embodiment of the present invention.

[59] Referring to Fig. 9, phosphor powder and epoxy powder are mixed to form an EMC

(SI lO).

[60] Referring to Fig. 10, the process of fabricating an EMC tablet is initiated with a process of removing fine particles of 5 D or less from the phosphor powder (S 111).

[61] The reason why the fine particles of 5 D or less are removed from the phosphor powder is that the fine particles of 5 D or less may be a cause of wide dispersion of the color coordinates of a white color during transfer molding.

[62] During transfer molding, the EMC tablet is injected under pressure. At this time, fine particles of 5 D or less are pushed far away due to the pressure and gathered at a distal end.

[63] Thus, when several PCBs are arranged and then subjected to transfer molding thereon, a phosphor in an epoxy resin molded onto each LED is not uniform according to the arranged position of each of the PCBs. This results in a luminous characteristic by which a yellow-cyan color becomes stronger far away from a transfer molding injection port. Thus, the fine particles of 5 D or less that cause the above result are required to be removed in advance.

[64] The fine particles of 5 D or less can be removed from phosphor powder by means of various methods. For example, a method employing specific gravity and a method employing a sieve may be used.

[65] In the method employing specific gravity, phosphor powder is put into a solvent such as alcohol and then left alone for a certain time duration, e.g., 30 minutes, so that fine particles of 5 D or less float on the solvent, and coarse particles of greater than 5 D sink down. Thus, the fine particles of 5 m or less floating on the solvent are scummed.

[66] In the method employing a sieve, phosphor powder is strained through a sieve to remove the fine particles of 5 D or less.

[67] After the fine particles of 5 D or less are removed from phosphor powder, epoxy powder and the phosphor powder from which the fine particles of 5 D or less have been removed are put into a jar, a suitable amount of balls are put thereinto, and ball milling is then performed to form an EMC with the epoxy powder and the phosphors mixed together (S 112).

[68] When the EMC is formed by performing the ball milling for a suitable time duration, the EMC is fabricated into an EMC tablet using a jig (Sl 13).

[69] When the EMC tablet is prepared, blue LED chips and Zener diodes are die- attached to a PCB substrate by means of a paste, and chip pads and the PCB substrate are wire-bonded using Au wires (S 120).

[70] After the wire-bonding process, the PCB substrate is preheated for several seconds to several minutes (S 130).

[71] After preheating the PCB substrate to a certain extent, the PCB substrate to which the blue LED chips have been wire-bonded is transfer-molded with the EMC tablet containing the phosphor (S 140).

[72] Thereafter, the molded PCB substrate is subjected to sawing and barrel processes so as to be divided into individual white LEDs (S 150).

[73] Fig. 11 is a graph of a white LED that is fabricated using an EMC tablet fabricated without performing a process of removing fine particles of 5 D or less, according to a comparative example; and Fig. 12 is a graph of a white LED fabricated by performing transfer molding using an EMC tablet containing a phosphor, according to another embodiment of the present invention, comparatively showing improvement in dispersion of the color coordinates of a white color.

[74] Referring to Figs. 11 and 12, it can be understood that dispersion of the color coordinates of a white color in the white LED is narrowed and thus more improved when transfer molding is performed using the EMC tablet without fine particles of 5 D or less according to the other embodiment of the present invention, as compared with the comparative example.

[75] The present invention is not limited to the embodiments described above but various modifications and changes can be made thereto by those skilled in the art and fall within the scope and spirit of the present invention defined by the appended claims.

[76] For example, although the embodiments of the present invention have been described in connection with fabrication of a whit LED capable of emitting white light by transfer-molding a blue LED chip, it is also possible to fabricate a white LED capable of white light by transfer-molding a UV LED chip.

[77] Further, although the embodiments of the present invention have been described in connection with fabrication of a whit LED capable of emitting white light by transfer- molding a blue LED chip, the present invention can be applied to fabrication of various white light emitting devices having luminous ranges in addition to the white LED.

[78] Moreover, although the embodiments of the present invention have been described in connection with fabrication of a whit LED capable of emitting white light by transfer-molding a blue LED chip, the present invention can be applied to fabrication of multi-color light emitting devices capable of emitting light with a white color and various colors based on a blue LED chip or UV LED chip.

Claims

[1] A method of fabricating an epoxy molding compound (EMC) tablet containing a phosphor for use in transfer molding of a light emitting device, the method comprising the steps of: pulverizing epoxy powder; forming an EMC by mixing the pulverized epoxy powder with phosphor powder; and fabricating the EMC into an EMC tablet.

[2] The method as claimed in claim 1, wherein the pulverizing step comprises a process of putting the epoxy powder into ajar and pulverizing the epoxy powder through ball milling, and the EMC forming step comprises a process of putting the phosphor powder and the epoxy powder pulverized through the ball milling into the jar and mixing the epoxy powder and the phosphor powder with each other through ball milling.

[3] The method as claimed in claim 2, wherein the ball milling for pulverizing the epoxy powder is performed at 100 to 130 rpm for 20 to 40 minutes, and the ball milling for mixing the epoxy powder and the phosphor powder is performed at 40 to 80 rpm for 20 to 40 minutes.

[4] A method of fabricating a white light emitting device by transfer-molding LED chips using an EMC containing a phosphor, the method comprising the steps of: forming an EMC by mixing phosphor powder and epoxy powder with each other; transfer-molding a printed circuit board (PCB) substrate using the EMC, the

LED chips being wire-bonded to the PCB substrate; and performing sawing and barrel processes to divide the PCB substrate into individual white light emitting devices, wherein the EMC forming step comprises: pulverizing the epoxy powder; forming the EMC by mixing the pulverized epoxy powder with the phosphor powder; and fabricating the EMC into an EMC tablet.

[5] The method as claimed in claim 4, wherein the pulverizing step comprises a process of putting the epoxy powder into ajar and pulverizing the epoxy powder by performing ball milling at 100 to 130 rpm for 20 to 40 minutes, and the EMC forming step comprises a process of putting the phosphor powder and the epoxy powder pulverized through the ball milling into the jar and mixing the epoxy powder and the phosphor powder by performing ball milling at 40 to 80 rpm for 20 to 40 minutes.

[6] An EMC tablet containing a phosphor for use in transfer molding of a light emitting device, comprising: epoxy powder pulverized through a pulverizing process; and phosphor powder mixed with the epoxy powder pulverized through the pulverizing process, wherein a mixture of the phosphor powder and the epoxy powder is fabricated into a tablet.

[7] The EMC tablet as claimed in claim 6, wherein the epoxy powder is pulverized through first ball milling, and the phosphor powder is mixed, through second ball milling, with the epoxy powder pulverized through the first ball milling.

[8] A method of fabricating an EMC tablet containing a phosphor for use in transfer molding of a light emitting device, the method comprising the steps of: removing fine particles from phosphor powder; forming an EMC by mixing epoxy powder with the phosphor powder from which the fine particles have been removed; and fabricating the EMC into the EMC tablet using a jig.

[9] The method as claimed in claim 8, wherein the fine particles are fine particles of

5 D or less.

[10] A method of fabricating a white light emitting device by transfer-molding LED chips using an EMC containing a phosphor, the method comprising the steps of: forming an EMC by mixing phosphor powder with epoxy powder; transfer-molding a PCB substrate using the EMC, the LED chips being wire- bonded to the PCB substrate; and performing sawing and barrel processes to the PCB substrate to divide the PCB substrate into individual white light emitting devices, wherein the EMC forming step comprises: removing fine particles from the phosphor powder; forming an EMC by mixing the epoxy powder with the phosphor powder from which the fine particles have been removed; and fabricating the EMC into an EMC tablet.

[11] The method as claimed in claim 10, wherein the fine particles are fine particles of 5 D or less.

[12] An EMC tablet for use in transfer molding of a light emitting device, comprising: phosphor powder from which fine particles have been removed in advance; and epoxy powder mixed with the phosphor powder from which the fine particles have been removed, wherein a mixture of the phosphor powder and the epoxy powder is fabricated into a tablet.

[13] The EMC tablet as claimed in claim 12, wherein the fine particles are fine particles of 5 D or less.