Patent Publication Number: US-11024776-B2

Title: Filling material, resin composition, package, and light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of the U.S. patent application Ser. No. 15/852,823 filed on Dec. 22, 2017, which claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-250608, filed on Dec. 26, 2016, the contents of which are hereby incorporated by reference in their entirety 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates to a filling material, a resin composition, a package, and a light-emitting device. 
     2. Description of Related Art 
     Resin compositions containing light-reflecting substances are widely used for packages of light-emitting devices. With recent reduction in the size and thickness of light-emitting devices, improvement of the mechanical strength of resin compositions has been demanded. For example, Japanese Patent Publication No. 2002-294070 proposes a resin composition intended to have an improved mechanical strength by adding a fibrous filling material composed of wollastonite. 
     The above-mentioned wollastonite is obtained by milling a silicate mineral, which is a natural mineral, into a fibrous form and is used as a filling material for the resin composition. Accordingly, while mining the silicate mineral, mineral magnetite (Fe 3 O 4 ) may also be mined and incorporated as an unavoidable impurity. In addition, tools used for mining and milling the silicate mineral may wear away, resulting in iron being incorporated as an unavoidable impurity. Once the iron and magnetite (hereinafter referred to as “iron component”) is incorporated into the silicate mineral, it is difficult to remove them to obtain a pure wollastonite. If, for example, a resin composition containing the wollastonite containing those unavoidable impurities is used in a package of a light-emitting device, light emitted from a light-emitting element is likely to be absorbed in the iron component contained in the wollastonite, resulting in decreased light reflection of the package. This may lead to decreased light-extraction efficiency of the light-emitting device. 
     In view of the foregoing, Japanese Patent Publication No. 2015-5675 (hereinafter referred to as Patent Literature 2) proposes coating the surface of fibrous particles composed of wollastonite with a light-reflecting material and using the coated particles as a filling material. This proposal is directed to improvement in both the mechanical strength and the light reflectivity of the resin composition. 
     SUMMARY 
     According to an embodiment of the present disclosure, a filling material includes a base material and a coating material coating at least a portion of a surface of a particle of the base material. The base material comprises a first inorganic compound containing a Group II element. The coating material comprises a second inorganic compound containing the Group II element and is different from the first inorganic compound. 
     According to an embodiment of the present disclosure, a resin composition includes a light transmissive resin and the filling material dispersed in the resin. The resin has a refractive index lower than that of the base material and higher than that of the coating material. 
     Preferably, the base material has a refractive index of 1.60 to 1.80; the resin has a refractive index of 1.48 to 1.59; and the coating material has a refractive index of 1.35 to 1.47. 
     According to an embodiment of the present disclosure, a package has a recess for mounting a light-emitting element, wherein the recess has an inner surface having at least a portion comprising the resin composition. 
     According to an embodiment of the present disclosure, a light-emitting device includes the package and a light-emitting element mounted in the recess. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of embodiments of the invention and many of the attendant advantages thereof will be readily obtained by reference to the detailed description below when considered in connection with the accompanying drawings. 
         FIG. 1  is a perspective view showing a light-emitting device according to an embodiment of the present disclosure. 
         FIG. 2A  is a cross-sectional view taken along line IIA-IIA in  FIG. 1 . 
         FIG. 2B  is a schematic diagram of a resin composition according to the embodiment, partially enlarging region IIB shown in  FIG. 2A . 
         FIG. 3  is a flowchart for a method of manufacturing a light-emitting device according an embodiment of the present disclosure. 
         FIG. 4A  is a schematic cross-sectional view illustrating a particle of a first inorganic compound, which is an original material of a first filling material, in a method of manufacturing a light-emitting device according to an embodiment of the present disclosure. 
         FIG. 4B  is a schematic cross-sectional view illustrating a particle of a first inorganic compound after being subjected to a surface treatment step in a method of manufacturing a light-emitting device according to an embodiment of the present disclosure. 
         FIG. 4C  is a schematic cross-sectional view illustrating a particle of a first inorganic compound after being subjected to a heat treatment step in a method of manufacturing a light-emitting device according to an embodiment of the present disclosure. 
         FIG. 4D  is a schematic cross-sectional view illustrating another particle of a first inorganic compound after being subjected to a heat treatment step in a method of manufacturing a light-emitting device according to an embodiment of the present disclosure. 
         FIG. 5A  is a photograph of a first filling material before being subjected to the surface treatment in an example of the present disclosure. 
         FIG. 5B  is a photograph enlarging a part of the first filling material shown in  FIG. 5A . 
         FIG. 6A  is a photograph showing a first filling material that has been subjected to the surface treatment in the example. 
         FIG. 6B  is a photograph enlarging a part of the first filling material shown in  FIG. 6A . 
         FIG. 7A  is a photograph showing a first filling material that has been subjected to the heat treatment at a temperature of 850° C. in an example of the present disclosure. 
         FIG. 7B  is a photograph enlarging a part of the first filling material shown in  FIG. 7A . 
         FIG. 8A  is a photograph showing a first filling material that has been subjected to the heat treatment at a temperature of 900° C. in an example of the present disclosure. 
         FIG. 8B  is a photograph enlarging a part of the first filling material shown in  FIG. 8A . 
         FIG. 9A  is a photograph showing a first filling material that has been subjected to the heat treatment at a temperature of 950° C. in an example of the present disclosure. 
         FIG. 9B  is a photograph enlarging a part of the first filling material shown in  FIG. 9A . 
         FIG. 10A  is a photograph showing a first filling material that has been subjected to the heat treatment at a temperature of 970° C. in an example of the present disclosure. 
         FIG. 10B  is a photograph enlarging a part of the first filling material shown in  FIG. 10A . 
         FIG. 11A  is a photograph showing a first filling material that has been subjected to the heat treatment at a temperature of 1000° C. in an example of the present disclosure. 
         FIG. 11B  is a photograph enlarging a part of the first filling material shown in  FIG. 11A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a description is given of a light-emitting device according to an embodiment of the present disclosure. 
     The drawings referenced in the following description schematically show the embodiment. Thus, the scale of members, distances between members, positional relations between members or the like may be presented in an exaggerated manner, and illustration of a part of a member may be omitted. Furthermore, the scale and distances between members may not match between a perspective view and its corresponding cross-sectional view. In the description below, members that are the same or analogous are given the same name or number in principle, and duplicative detailed descriptions are appropriately omitted. 
     It is to be noted that, in a light-emitting device and a method of manufacturing the device according to the embodiment, interpretation of directions like “up”, “down”, “left”, and “right” should be interchanged according to the situation. It is to be noted that, directions like “up” and “down” are used to represent relative positions between constituent elements in a drawing referenced for explanation and are not intended to specify the absolute positions unless otherwise stated. 
     A particle diameter is, unless otherwise stated, indicated by an average particle diameter determined as a Fisher Sub Sieve Sizer&#39;s No. (F.S.S.S.No.) using an air permeation method. Specifically, under an environment of a temperature of 25° C. and a humidity of 70%, 1 cm 3  of a sample is measured and packed in a special tubular vessel and then a dry air is passed through the vessel at a constant pressure. The specific surface area is obtained based on the difference in the pressure and converted to the average particle diameter. 
     Embodiment 
     Configuration of Light-Emitting Device 
     A description is given of the configuration of a light-emitting device according to an embodiment with reference to  FIGS. 1 to 2B .  FIG. 1  is a perspective view illustrating the configuration of the light-emitting device according to the embodiment.  FIG. 2A  is a cross-sectional view taken along line IIA-IIA of  FIG. 1 , illustrating the configuration of the light-emitting device according to the embodiment.  FIG. 2B  is a schematic diagram illustrating a enlarged view of region IIB of a resin-molded body in the light-emitting device shown in  FIG. 2A . 
     In  FIGS. 1 and 2A , XYZ-axis coordinates are indicated for the sake of illustration. The X-axis is in a longitudinal direction of the light-emitting device  1  having an elongated, substantially rectangular parallelepiped shape; the Y axis is in a lateral direction of the light-emitting device  1 ; and the Z-axis is in a thickness direction of the light-emitting device  1 . 
     The light-emitting device  1  according to the embodiment includes a package  2  having a recess  2   a , a light-emitting element  3  mounted on a bottom surface  2   b  of the recess  2   a , and a light-transmissive sealing member  4  disposed in the recess  2   a  to seal the light-emitting element  3 . The package  2  includes a pair of lead electrodes  21  and a resin-molded body  22  holding the pair of lead electrodes  21 . 
     The external shape of the light-emitting device  1  is an elongated, substantially rectangular parallelepiped shape and has a thin thickness, which corresponds to the dimension of the light-emitting device  1  in the Z-axis direction. The light-emitting device  1  has an end surface located furthest in the negative Z-axis direction and serving as a mounting surface. The recess  2   a  of the light-emitting device  1  is formed such as to have an opening at an end side of the light-emitting device  1  located furthest in the negative Y-axis direction. Thus, the light-emitting device  1  is suitable to the side-view mounting in which the light-emitting device  1  emits light in a direction parallel to the mounting surface. 
     In the light-emitting device  1  according to the embodiment, the resin-molded body  22  of the package  2  is formed using a resin composition  20  containing a resin  201  containing a first filling material  202  for improving the mechanical strength of the resin  201 . The first filling material  202  may contain a fibrous base material  202   a  and a coating material  202   b  coated on the surface of the base material  202   a  to enhance light reflectivity. The resin composition  20  may further contain a second filling material  203  for enhancing light reflectivity or other filling materials. 
     Package 
     The package  2  includes the pair of lead electrodes  21  and the resin-molded body  22  that holds the pair of lead electrodes  21  such that the pair of lead electrodes are spaced apart from each other. In the present embodiment, the opening of the recess  2   a  of the package  2  opens laterally in a direction parallel to the end surface located furthest in the negative Z-axis direction and serving as the mounting surface. The bottom surface  2   b  of the recess  2   a  is formed substantially perpendicular to the mounting surface. 
     The bottom surface  2   b  of the recess  2   a  is constituted by the pair of lead electrodes  21  and the resin-molded body  22 ; and side surfaces of the recess  2   a  are constituted by sidewalls  22   a  of the resin-molded body  22 . One pair of the sidewalls  22   a  located opposite in the Z-axis direction and constituting upper and lower side surfaces of the recess  2   a  have a smaller thickness than the other pair of the sidewalls  22   a  located opposite in the X-direction and constituting lateral side surfaces of the recess  2   a.    
     The light-emitting element  3  is arranged in the recess  2   a . The sidewalls  22   a  are formed such as to surround the light-emitting element  3 . The sidewalls  22   a  are formed to have inner surfaces inclined at a predetermined angle relative to the bottom surface  2   b  such that the recess  2   a  expands from the bottom surface  2   b  to the opening of the recess  2   a . With this structure, light emitted from the light-emitting element  3  in lateral directions thereof is reflected by the sidewalls  22   a  toward the opening and extracted from the package  2 . 
     The resin-molded body  22  comprises the resin composition  20  having good light-reflecting properties so that the light from the light-emitting element  3  is reflected by the resin-molded body  22  and efficiently extracted from the opening of the recess  2   a.    
     Recently, packages have been made thinner and thinner in response to an increasing demand for smaller light-emitting devices. For this reason, specifically, it is desirable that the resin-molded body  22  surrounding the light-emitting element  3  has a portion having a thickness of 100 μm or less, or more desirably a thickness of 50 μm or less. 
     In the package  2  according to the present embodiment, the opening of the recess  2   a  is of an oval shape. The package  2  can be formed to have a small outer dimension in the thickness direction without changing the dimensions of the recess  2   a , by forming the pair of sidewalls  22   a  extending in the lengthwise direction of the opening of the recess  2   a  to have a small thickness. This structure enables making the light-emitting device  1  thin. 
     The sidewalls  22   a  can have necessary mechanical strength even when formed to have a small thickness, by being formed of the resin composition  20  containing the fibrous first filling material  202 . The sidewalls  22   a  exhibits necessary light reflectivity even when formed to have a small thickness, because the coating material  202   b  for enhancing light reflectivity is provided in the first filling material  202 . 
     Although the opening of the recess  2   a  of the package  2  in the present embodiment is of an oval shape, the shape of the opening may be a circular shape, an elliptical shape, or other polygonal shape. 
     Lead Electrode 
     The lead electrodes  21  are wiring lines for connecting an external power source and the light-emitting element  3 . The pair of lead electrodes  21  of the package  2  in the present embodiment correspond to an anode and a cathode of the light-emitting element  3 . When a plurality of light-emitting elements  3  are to be mounted, three or more lead electrodes  21  may be provided according to the electrical connection manner of the light-emitting elements  3 . 
     The pair of lead electrodes  21  is formed in the bottom surface  2   b  of the recess  2   a  such as to be exposed from the resin-molded body  22 . The pair of lead electrodes  21  is arranged such as to occupy a half or more of the area of the bottom surface  2   b  of the recess  2   a . The light-emitting element  3  is connected with the pair of lead electrodes  21  at portions thereof exposed on the bottom surface  2   b , via electrically conductive members such as wires and solder. In the present embodiment, the light-emitting element  3  is bonded to the pair of lead electrodes  21  at the portions thereof exposed on the bottom surface  2   b.    
     Each of the pair of lead electrodes  21  has an outer portion projecting out of the resin-molded body  22  and bent to be arranged on a lower surface of the package  2 , i.e., the mounting surface. The light-emitting device  1  is bonded to an external circuit board or the like via the outer portions of the pair of lead electrodes  21  arranged on the lower surface of the package  2 . 
     The lead electrodes  21  may have any shape depending on the shape of the package  2 . For example, the lead electrodes  21  may have a plate-like form, a block-like form, or a film-like form, and may have a wavy surface or an uneven surface. The lead electrodes  21  may each have a uniform thickness, or may each partially have a thick portion and/or a thin portion. Although not particularly limited, the lead electrodes  21  preferably have a wide width for the purpose of improving heat dissipation. Although not particularly limited, the material of the lead electrodes  21  preferably has comparatively high electrical conductivity and comparatively high thermal conductivity. The lead electrodes  21  made of such a material allows for efficient dissipation of the heat generated by the light-emitting element  3  to the outside. For example, preferably, the material for the lead electrodes  21  is a material having a large thermal conductivity of about 200 W/m·K or more, a material having a comparatively large mechanical strength, or a material easy to punch or etch. Specific examples of the material for the lead electrodes  21  include: metals such as copper, aluminum, gold, silver, tungsten, iron, and nickel; and alloys such as iron-nickel alloys and phosphor bronze. Preferably, the lead electrodes  21  have surfaces plated with a metal having good light-reflecting properties, such as silver and aluminum, to efficiently extract light from the light-emitting element  3  mounted on the lead electrodes  21 . Preferably, the plated surface has a glossiness of 0.2 to 2.0, from the viewpoint of light extraction efficiency and manufacturing cost. 
     Resin-Molded Body 
     The resin-molded body  22  is formed to provide the recess  2   a , the purpose of which is to hold the lead electrodes  21  and mount the light-emitting element  3  together with the lead electrodes  21 . In the resin-molded body  22 , at least the sidewalls  22   a  constituting the side surfaces of the recess  2   a  comprises the resin composition  20  having good mechanical strength and light reflectivity. 
     The resin-molded body  22  may be formed by a known resin molding method, such as transfer molding, injection molding, compression molding, and extrusion molding. 
     Resin Composition 
     The resin composition  20  includes the light-transmissive resin  201  containing the first filling material  202  for improving mechanical strength and light reflectivity. The resin composition  20  in the present embodiment may include the second filling material  203  for further improving light reflectivity. 
     The resin composition  20  may include additional materials conventionally used for synthetic resins in addition to the first filling material  202  and the second filling material  203 , so long as the preferred characteristics of those filling materials are not impaired. Examples of such additional materials include: inorganic filling materials such as talc, silica, and zinc oxide; flame retardants; plasticizers; diffusing agents; dyes; pigments; releasants; ultraviolet absorbers; antioxidants; thermostabilizers; and combinations of the foregoing. Herein, the pigments include white pigments. 
     Resin 
     Preferably, the resin  201  contains a resin material having good light-transmissive properties. Examples of such a resin material include thermoplastic resins, such as liquid crystal polymers, polyamide resins, polyphthalamide resins, and polybutylene terephthalates. Alternatively, the resin  201  may be a thermosetting resin, examples of which include epoxy resins and silicone resins. Thermoplastic resins are very inexpensive compared to ceramics, and thus are useful in providing low-cost light-emitting devices. Thermosetting resins have better heat resistance than thermoplastic resins, and thus are useful in providing light-emitting devices having good heat resistance. 
     First Filling Material 
     The first filling material  202  is a granular filler to be contained in the resin  201  to enhance the mechanical strength of the resin-molded body  22  using the resin composition  20 . Preferably, the particles of the first filling material  202  are of an elongated shape, such as a fibrous shape, a needle-like shape, or a stick-like shape, from the viewpoint of enhancing the mechanical strength of the resin-molded body  22 . In addition, the particles of the first filling material preferably have a certain size. If the particles of the first filling material  202  are too large, the resin-molded body  22  may have a surface with unevenness, which causes insufficient adhesion to the sealing member  4 , resulting in a separation between the resin-molded body  22  and the sealing member  4 . Under the condition that the total volume of the first filling material  202  in the resin-molded body  22  is the same, the smaller the volume of each individual particle of the first filling material  202 , the larger the total surface area of the first filling material  202 . The larger the total surface area of the first filling material  202  in the resin-molded body  22 , the greater the light reflectivity of the resin-molded body  22 . 
     Taking the above into account, the average fiber diameter, i.e., minor diameter, of the particles of the first filling material  202  is preferably from 0.1 μm to 30 μm, more preferably from 0.1 μm to 15 μm, or still more preferably from 2 μm to 7 μm; the average fiber length, i.e., major diameter, of the particles of the first filling material  202  is preferably from 1 μm to 100 μm, more preferably from 3 μm to 100 μm, or still more preferably from 20 μm to 50 μm; and the average aspect ratio, i.e., ratio of major diameter to minor diameter, of the particles of the first filling material  202  is preferably 3 or more, more preferably from 3 to 50, or still more preferably from 5 to 30. 
     The content of the first filling material  202  in the resin composition  20  is preferably from 5 to 70 percent by mass, or more preferably from 10 to 70 percent by mass. The inclusion of the first filling material  202  within these content ranges may enable the resin-molded body  22  to satisfy high levels of requirements in terms of obtaining mechanical properties and optical properties required of the package  2  of the light-emitting device  1 . 
     Note that the first filling material  202  may contain two or more kinds of materials whose particles have different shapes. 
     Preferably, the elongated-shaped particles of the first filling material  202  are randomly oriented in the resin-molded body  22 , which may make the mechanical strength of the resin-molded body  22  close to isotropic. Further, making both the resin-molded body  22  and the sealing member  4  have isotropic mechanical strength makes them have the same behavior in terms of their expansions and contractions due to temperature changes, which may inhibit the occurrence of a separation between the resin-molded body  22  and the sealing member  4  at an interface therebetween. 
     Meanwhile, the elongated-shaped particles of the first filling material  202  may be arranged in the resin-molded body  22  so as to be oriented in a predetermined direction. Because the resin composition  20  is filled into a mold with a predetermined pressure when molding the resin-molded body  22 , the particles of the first filling material  202  may be oriented in the same direction, which makes the formed resin-molded body  22  have an anisotropic mechanical strength. This may enhance the mechanical strength of the resin-molded body  22  in a predetermined direction. 
     Base Material and Coating Material 
     To enhance the light reflectivity of the resin composition  20 , in the first filling material  202 , the surface of the base material  202   a  is coated with the coating material  202   b  having good light-transmissive properties. Preferably, the coating material  202   b  has better light-transmissivity than the base material  202   a . More preferably, the base material  202   a  has a refractive index higher than that of the resin  201 , and the coating material  202   b  has a refractive index lower than that of the resin  201 . Such a configuration makes the resin composition  20  have a higher light reflectance compared to a case in which the first filling material  202  is solely composed of a base material  202   a  not coated with the coating material  202   b.    
     The coating material  202   b  may be disposed such as to coat at least a portion of the surface of each particle of the base material  202   a . It is, however, preferable that the coating material  202   b  be disposed such as to coat the entire surface of each particle of the base material  202   a  to enhance the light reflectivity of the resin composition  20 . 
     Wollastonite, a kind of calcium silicate, can be used as the first filling material  202  to enhance the mechanical strength. As described above, wollastonite generally contains iron as an unavoidable impurity. When iron is mixed into the wollastonite as an impurity, the iron is likely to absorb light from the light-emitting element  3  and light obtained by converting the wavelength of the light from the light-emitting element  3  by phosphors or the like. An interface between a filler and the resin  201  reflects light according to the difference between the refractive indices of the filler and the resin  201 . A portion of the light incident on the interface propagates into the filler and is absorbed by the iron impurity. For this reason, use of a resin composition  20  containing a filler including wollastonite may result in poor light reflectivity. 
     For example, it is preferable that the base material  202   a  have a refractive index of from 1.60 to 1.80, the resin  201  have a refractive index of from 1.48 to 1.59, and the coating material  202   b  have a refractive index of from 1.35 to 1.47. Use of materials satisfying these conditions may enhance light reflectivity. 
     A description is given of an example in which: wollastonite (refractive index: 1.63) is used as the base material  202   a ; calcium fluoride (refractive index: 1.43) is used as the coating material  202   b ; and polyamide resin (refractive index: 1.50) is used as the resin  201 . 
     In a comparative example of resin composition in which a filler containing the wollastonite but not containing the coating material  202   b  is used, the difference in the refractive index between the filler and the resin  201  is 0.13, and the refractive index of the filler is greater than that of the resin  201 . Accordingly, the light propagating in the resin  20  is reflected at an interface between the filler and the resin  201  with a reflectance according to the difference in the refractive index. 
     In the example in which the filler of the wollastonite coated with the coating material  202   b  of calcium fluoride is used, the resin  201  and the coating material  202   b  have an interface therebetween having a difference of 0.07 in the refractive index, and the coating material  202   b  and the base material  202   a  have an interface therebetween having a difference of 0.20 in the refractive index. Namely, the example has an interface between the coating material  202   b  and the base material  202   a  whose difference in the refractive index is greater than that of the interface between the filler and the resin  201  in the resin composition of the comparative example. In addition, the example also has an interface between the resin  201  and the coating material  202   b . Those interfaces efficiently reflect light, resulting in reduction in the amount of light that propagates into the base material  202   a  and is absorbed therein. Therefore, the configuration of the example may improve light reflectivity of the resin composition  20 . 
     Note that, because the coating material  202   b  has a lower refractive index than the resin  201 , total reflection according to the Snell&#39;s law does not occur in the light incident from the coating material  202   b  to the interface between the coating material  202   b  and the resin  201 . That means the light propagating in the coating material  202   b  is transmitted to the resin  201  in a comparatively efficient manner, which may enhance the light reflectivity of the resin composition  20 . 
     As the material for the base material  202   a , a first inorganic compound containing a Group II element may be used. Preferably, the Group II element is Ca or Mg. Specifically, examples of the first inorganic compound include calcium silicate and magnesium silicate. In particular, a wollastonite composed of calcium metasilicate, which is a kind of calcium silicate, can be easily processed into fibrous particles by crushing, and thus is preferred as the base material  202   a  of the first filling material  202  in terms of enhancing the mechanical strength of the resin composition  20 . 
     As the material for the coating material  202   b , a second inorganic compound containing the Group II element contained in the chemical composition of the first inorganic compound, which is used for the base material  202   a , may be used. Preferably, the second inorganic compound has a smaller refractive index than the first inorganic compound and the resin  201  used in the resin composition  20 . 
     Specifically, the second inorganic compound is preferably selected from the group consisting of a fluoride, a phosphate, and a sulfate which includes the Group II element. For example, when the Group II element is Ca, examples of the second inorganic compound include calcium fluoride (CaF 2 ), calcium hydrogen phosphate (CaHPO 4 ), and calcium sulfate (CaSO 4 ). When the Group II element is Mg, examples of the second inorganic compound include magnesium fluoride (MgF 2 ), magnesium hydrogen phosphate (MgHPO 4 ), and magnesium sulfate (MgSO 4 ). 
     To further improve the mechanical strength or the like of the resin-molded body  22 , the first filling material  202  may be subjected to a known surface treatment using a silane coupling agent or a titanium coupling agent. As the agent for use in the surface treatment, a silane coupling agent, in particular, amino silane is preferred. Surface treatment with a silane coupling agent or the like improves adhesion between the first filling material  202  and the resin  201 , and thus enhances the mechanical strength of the resin-molded body  22 . In addition, the surface treatment improves sliding properties of the surface of the first filling material  202 , and thus improves fluidity of the resin composition  20  before being cured. Due to the improved fluidity, when molding the resin composition  20 , the resin composition  20  before being cured can be distributed throughout a mold cavity. 
     Second Filling Material 
     The second filling material  203  is a filler that is added to the resin composition  20  when the resin composition  20  is required to have a light reflectivity higher than that imparted by the first filling material  202 . The second filling material  203  may be arranged in the resin-molded body  22  molded using the resin composition  20  so that the second filling material  203  may be uniformly dispersed in the resin-molded body  22  or unevenly distributed and concentrated at or near an surface of the resin-molded body  22 . Preferably, the second filling material  203  has insulation properties. The second filling material  203  having insulation properties prevents the pair of lead electrodes  21  from being shorted via the second filling material  203 . Thus, the second filling material  203  can be contained in the resin-molded body  22  at a comparatively high content. 
     Preferably, the material for the second filling material  203  has a refractive index largely different from that of the resin  201  used in the resin composition  20 . For example, particles of titanium oxide (TiO 2 ) or aluminum oxide (Al 2 O 3 ) may be used for the second filling material  203 . The diameter of the particles of the second filling material  203  is preferably in a range of 0.08 μm to 10 μm, or more preferably in a range of 0.1 μm to 5 μm, so as to obtain light-scattering effects at high efficiency. The content of the second filling material  203  in the resin composition  20  is preferably 10 percent by mass to 60 percent by mass, or more preferably 20 percent by mass to 50 percent by mass, so as to enhance light reflectivity within a range where the formability of the resin composition  20  is not impaired. 
     Light Emitting Element 
     The light-emitting element  3  may be made by forming a semiconductor such as GaAlN, ZnS, ZnSe, SiC, GaP, GaAlAs, AlN, InN, AlInGaP, InGaN, GaN, or AlInGaN on a sapphire substrate or the like as a light-emitting layer. Of these, a nitride-based compound semiconductor element having a peak emission wavelength in a short wavelength range from a ultraviolet region to a visible light region (360 nm to 550 nm) may be used. Even when a light-emitting element  3  having high light emission output is used, because the resin-molded body  22  has high light reflectivity by containing the first filling material  202  in which the surface of the base material  202   a  is coated by the coating material  202   b , the light from the light-emitting element  3  may not be able to penetrate into the resin-molded body  22 . Accordingly, it may be possible to inhibit degradation of the resin-molded body  22  due to light, and thus improve the light resistance of the package  2 . 
     Incidentally, it may also be possible to use a light-emitting element having a peak emission wavelength in a long wavelength range of visible light (551 nm to 780 nm). 
     A plurality of the light-emitting elements  3  may be used. Using light-emitting elements  3  having different emission colors allows for providing a light-emitting device  1  having a wide color reproduction range. For example, two light-emitting elements  3  capable of emitting green light, one light-emitting element  3  capable of emitting blue light, and one light-emitting element  3  capable of emitting red light may be used. 
     To use the light-emitting device  1  for pixels of a full-color display device, it is preferable that the emission wavelength of the red light-emitting element  3  be from 610 nm to 700 nm, the emission wavelength of the green light-emitting elements  3  be from 495 nm to 565 nm, and the emission wavelength of the blue light-emitting element  3  be from 430 nm to 490 nm. When the light-emitting device  1  is configured to emit white mixed-color light, taking into account the complementary relation in the emission wavelength between the color of the light-emitting element  3  and the color of the fluorescent substance contained in the sealing member  4 , and the deterioration of the sealing member  4  caused by the optical output of the light-emitting element  3 , the emission wavelength of the light-emitting elements  3  is preferably 400 nm or more and 530 nm or less, or more preferably 420 nm or more and 490 nm or less. 
     Sealing Member 
     The sealing member  4  is disposed in the recess  2   a  of the package  2  to seal the light-emitting element  3 , the lead electrodes  21 , and wires connecting the light-emitting element  3  and the lead electrodes  21 , which are arranged in the recess  2   a . Optionally, the sealing member  4  may be omitted. However, the sealing member  4  serves to protect the sealed members from degradation due to moisture and gases, and damages due to physical contacts. 
     The material usable for the sealing member  4  is not limited. However, it is preferable that the sealing member  4  has good light-transmissive properties. Examples of such a material include: resin material such as silicone resins and epoxy resins, and inorganic materials such as glass. 
     The sealing member  4  may contain: fluorescent substance that performs wavelength conversion on the light from the light-emitting element  3 , and light-reflecting substance that scatters the light from the light-emitting element  3 . As the light-reflecting substance, the same materials as the above-described materials for the second filling material  203  may be used. 
     As the fluorescent substance, one that absorbs the light from the light-emitting element  3  and converts the absorbed light to light having a wavelength different from that of the absorbed light may be used. For example, it is preferable to employ a material selected from the group consisting of: aluminum-garnet based phosphors; nitride-based phosphors, oxynitride-based phosphors, and sialon-based phosphors which are activated mainly with a lanthanoid element such as Eu or Ce; alkaline-earth halogen apatite phosphors, alkaline-earth metal boric acid halogen phosphors, alkaline-earth metal aluminate phosphors, alkaline-earth silicate, alkaline-earth sulfide, alkaline-earth thiogallates, alkaline-earth silicon nitrides, and germanates which are activated mainly with a lanthanoid element such as Eu and/or a transition-metal element such as Mn; rare-earth aluminates and rare-earth silicates which are activated mainly with a lanthanoid element such as Ce; organic compounds and organic complexes which are activated mainly with a lanthanoid element such as Eu; and mixtures thereof. 
     Method of Manufacturing Light-Emitting Device 
     Next, a description is given of a method of manufacturing the filling materials, resin composition, package, and light-emitting device with reference to  FIGS. 1 to 4D .  FIG. 3  is a flowchart illustrating the flow of a method of manufacturing the light-emitting device according to the embodiment.  FIG. 4A  is a schematic cross-sectional view illustrating a particle of a first inorganic compound, which is the material for the first filling material in the method of manufacturing the light-emitting device according to the embodiment.  FIG. 4B  is a schematic cross-sectional view illustrating the particle of the first filling material which has been subjected to a surface treatment step in the method of manufacturing the light-emitting device according to the embodiment.  FIG. 4C  is a schematic cross-sectional view illustrating an example of the particle of the first filling material which has been subjected to a heat treatment step in the method of manufacturing the light-emitting device according to the embodiment.  FIG. 4D  is a schematic cross-sectional view illustrating another example of a particle of the first filling material which has been subjected to the heat treatment step in the method of manufacturing the light-emitting device according to the embodiment. 
     Note that the example of the particle of the first filling material shown in  FIG. 4C  indicates that the surface of the base material is entirely coated by coating material, and the another example of the particle of the first filling material shown in  FIG. 4D  indicates that the surface of the base material is partially coated by coating material. 
     The method of manufacturing a light-emitting device according to the present embodiment includes: a filling material preparation step S 10 , a mixing step S 21 , a resin-molded body forming step S 31 , a light-emitting element mounting step S 40 , and a sealing member forming step S 50 . The filling material preparation step S 10  includes: a surface treatment step (first step) S 11  and a heat treatment step (second step) S 12 . 
     The filling material preparation step S 10  and the mixing step S 21  are included in a resin composition preparation step S 20 . The resin composition preparation step S 20  and the resin-molded body forming step S 31  are included in a package preparation step S 30 . 
     Hereinafter, a detailed description is given of each step. 
     Filling Material Preparation Step 
     The filling material preparation step S 10  is a step for preparing the first filling material  202 , and includes the surface treatment step (first step) S 11  and the heat treatment step (second step) S 12 . 
     Surface Treatment Step (First Step) 
     The surface treatment step S 11  performs a chemical surface treatment on a granular base material  202   a  comprising a first inorganic compound in order to form particles comprising a second inorganic compound through self-assembly thereof on the surface the base material  202   a . The particles of the second inorganic compound become the coating material  202   b.    
     As an example, a description is given of a case in which fibrous particles of wollastonite (CaSiO 3 ) are used as the base material  202   a  comprising the first inorganic compound and calcium fluoride (CaF 2 ) is used as the second inorganic compound. In this case, an aqueous solution of ammonium fluoride is used as an agent to synthesize calcium fluoride, i.e., the second inorganic compound, from wollastonite, i.e., the first inorganic compound. 
     Dispersing particles of the wollastonite in the aqueous solution of ammonium fluoride produces calcium fluoride on the surface of the particles of the wollastonite, through the chemical reaction represented by the following formula:
 
CaSiO 3 +2NH 4 F→CaF 2 +SiO 2 +2NH 3 +H 2 O
 
     The produced calcium fluoride self-assembles into particles thereof on the surfaces of the particles of the wollastonite. The particles of the calcium fluoride serve as the coating material  202   b.    
     Note that, because the particles of calcium fluoride, i.e., coating material  202   b , are formed on the surface of the wollastonite, i.e., base material  202   a , through self-assembly, the particles of the coating material  202   b  and the base material  202   a  are continuously formed without defining a clear interface therebetween. 
     Specifically, fibrous wollastonite, i.e., the base material  202   a , is added into the aqueous solution of ammonium fluoride, and then the aqueous solution is stirred to form a suspension therein in which the wollastonite is uniformly dispersed. Preferably, the stirring is performed gently so as not to destroy the shape of the wollastonite. While stirring the suspension, reaction is made in a predetermined period of time at a predetermined temperature so as to produce particles of calcium fluoride on the surfaces of wollastonite particles, i.e., the base material  202   a.    
     Preferably, the particles of the coating material  202   b  produced in the surface treatment step S 11  are nanoscale particles having a particle diameter (mode diameter) of 5 nm to 700 nm, or more preferably 5 nm to 500 nm. Nanoscale particles of a substance are known to have a melting point lower than that of the substance in a bulk state (for example, when the particle size is of the order of several micrometers or more), according to the size of the particles. Accordingly, the coating material  202   b  being nanoscale particles allows itself to melt at a lower temperature in the next heat treatment step S 12 . 
     Note that the above-mentioned diameter of the particles of the coating material  202   b  can be measured using a photograph taken with a scanning electron microscope (SEM). 
     The diameter of the particles of the coating material  202   b  produced in the surface treatment step S 11  can be controlled by the conditions of the above-mentioned reaction, such as temperature, duration, concentration of agent, and pH. The conditions of the reaction are determined so that the dimensions of the particles of the base material  202   a  are controlled within a range such that the particles of the base material  202   a  may serve as a filler for enhancing the mechanical strength of the resin composition  20 . 
     The first filling material  202 , in which the particles of the coating material  202   b  have been formed on the surface of the base material  202   a  by the chemical surface treatment, may be subjected to dehydration, drying, and dry sieving steps, and then processed in the heat treatment step S 12 . 
     Heat Treatment Step (Second Step) 
     The heat treatment step S 12  heats the first filling material  202  which has been subjected to the chemical surface treatment in the surface treatment step S 11 , so as to make the particles of the coating material  202   b  melt, thereby expanding the surface area of the base material  202   a  coated by the coating material  202   b.    
     In this step, the first filling material  202  is heated to a temperature at which the base material  202   a  does not melt but the coating material  202   b  melts. For example, when the base material  202   a  is wollastonite, its melting point is about 1500° C. When the coating material  202   b  is calcium fluoride, its melting point is 1418° C. Thus, when the size of the particles of coating material  202   b  is of the order of several micrometers or more, controlling the heating temperature at a temperature greater than or equal to 1418° C. and less than 1500° C. can cause only the coating material  202   b  to melt. In contrast, forming the coating material  202   b  in nanoscale particles enables the particles of the coating material  202   b  to melt at a temperature lower than the inherent melting point of calcium fluoride, i.e., 1418° C., at a temperature of, for example, several hundreds of degrees Celsius to 1200° C., or, further, several hundreds of degrees Celsius to 1000° C. Therefore, the heat treatment step S 12  can be carried out with a lower heating temperature and/or in a shorter duration. In general, even when the difference in the inherent melting points between the first inorganic compound and the second inorganic compound is small, forming the particles of the coating material  202   b  sufficiently smaller than particles of the base material  202   a  and in nanoscale dimensions extends the difference in the melting point between the base material  202   a  and the coating material  202   b . This facilitates selectively making only the coating material  202   b  melt. Also, this may enable use of a combination of a first inorganic compound and a second inorganic compound inherently having a melting point higher than that of the first inorganic compound. 
     The coating material  202   b  formed in the surface treatment step S 11  is discretely formed on the surface of the base material  202   a  by self-assembling. Making the particles of the coating material  202   b  melt once causes the coating material  202   b  to extend in a melt state, resulting in an increase in the area of the surface of the base material  202   a  coated by the coating material  202   b . Making the particles of the coating material  202   b  melt once also makes the surface of the coating material  202   b  smooth, for example, like a mirror, and thus improves the light reflectivity of the surface of the coating material  202   b.    
     The coating material  202   b  may be arranged such as to coat at least a portion of the surface of the base material  202   a . It is, however, preferable that the coating material  202   b  be arranged such as to coat the entire surface of the base material  202   a . This improves the light reflectivity of the resin composition  20  containing the first filling material  202 . 
     Note that the area of the surface of the base material  202   a  coated by the coating material  202   b  can be made larger by increasing the temperature and the duration of the heat treatment. 
     When, like wollastonite, the particles of the first inorganic compound used as the base material  202   a  contain impurities such as an iron component, the heat treatment is preferably carried out in a reducing atmosphere or an inert gas atmosphere. When the heat treatment is carried out in an oxidizing atmosphere such as the atmosphere, the iron component is converted into an oxide that exhibits greater visual light absorption. This reduces the light reflectivity of the resin composition  20  containing the first filling material  202 . 
     Taking this into account, the heat treatment is preferably carried out in a reducing gas atmosphere or an inert gas atmosphere to reduce oxidation of the iron component, thereby inhibiting the reduction in the light reflectivity of resin composition  20  containing the first filling material  202 . 
     Examples of the reducing atmosphere include a reducing gas atmosphere such as a hydrogen gas and a carbon monoxide gas. Examples of the inert gas atmosphere include an argon gas atmosphere. 
     Carrying out the above steps manufactures the first filling material  202 . 
     Resin Composition Preparation Step 
     The resin composition preparation step S 20  prepares the resin composition  20  containing the resin  201  and the first filling material  202 . The resin composition preparation step S 20  includes the filling material preparation step S 10  and the mixing step S 21 . 
     Mixing Step S 21   
     The mixing step S 21  produces the resin composition  20  by adding the first filling material  202  prepared in the filling material preparation step S 10  to the light-transmissive resin  201  and mixing them. 
     In the mixing step S 21  of the present embodiment, the second filling material  203 , which is for imparting light reflectivity, may be blended into the resin composition  20  in addition to the first filling material  202 . Optionally, the resin composition  20  may be mixed further with the above-mentioned filling materials and additives. Preferably, the first filling material  202  and the second filling material  203  are uniformly dispersed so as to reduce unevenness in the light reflection of the resin-molded body  22  using the resin composition  20 . 
     The mixing step S 21  can be carried out by a known mixing device such as a twin screw extruder. 
     Package Preparation Step 
     The package preparation step S 30  manufactures the package  2  including the resin-molded body  22 . The package preparation step S 30  includes the resin composition preparation step S 20  and the resin-molded body forming step S 31 . 
     Resin-Molded Body Forming Step 
     The resin-molded body forming step S 31  forms the resin-molded body  22  using the resin composition  20  prepared in the resin composition preparation step S 20 . As the resin forming method for forming the resin-molded body  22 , a known resin forming method, such as transfer molding, injection molding, compression molding, and extrusion molding can be used. The resin forming method is selected as appropriate according to whether the resin  201  used for the resin composition  20  is a thermosetting resin or a thermoplastic resin and according to the structure of the package  2 . 
     For example, when the resin  201  is a thermoplastic resin and the package  2  is structured such that the lead electrodes  21  are held by the resin-molded body  22 , injection molding may be used. Specifically, the resin-molded body  22  can be formed by clamping lead electrodes  21  between vertically-divided molding dies and injecting melted resin composition  20  into the molding dies. 
     Reducing the pressure applied to the resin composition  20  in forming the resin may make the resin-molded body  22  have isotropic mechanical strength. The resin-molded body  22  having the isotropic mechanical strength may inhibit the occurrence of a separation between the resin-molded body  22  and the sealing member  4  at a bonding interface therebetween. Meanwhile, using particles having an elongated shape, such as a fibrous shape, a needle-like shape, or a stick-like shape as the first filling material  202  and increasing the pressure applied in forming the resin may make the resin-molded body  22  have anisotropic mechanical strength. The resin-molded body  22  having the anisotropic mechanical strength may enhance the mechanical strength of the resin-molded body  22  in a predetermined direction. 
     Light-Emitting Element Mounting Step 
     The light-emitting element mounting step S 40  mounts a light-emitting element  3  in the package  2  manufactured in the package preparation step S 30 . 
     In the present embodiment, the light-emitting element  3  is bonded to a bottom surface  2   b  of the recess  2   a  of the package  2  using a die-bonding member; and pad electrodes of the light-emitting element  3  and the lead electrodes  21  are electrically connected using wiring members such as wires. 
     Sealing Member Forming Step 
     The sealing member forming step S 50  seals the light-emitting element  3  and the lead electrodes  21  arranged in the recess  2   a  by forming the sealing member  4  in the recess  2   a  of the package  2 . 
     Carrying out the package preparation step S 30 , the light-emitting element mounting step S 40 , and the sealing member forming step S 50  as described above manufactures the light-emitting device  1 . 
     Variant Embodiment 
     The light-emitting device  1  is not limited to the side-view type. The light-emitting device  1  may be of the top-view type, in which the light extraction direction is perpendicular to the mounting surface. The light-emitting device  1  may be of the chip scale package type or chip size package (CSP) type, in which the package  2  does not have the recess  2   a  and the light-reflective resin-molded body  22  is provided such as to cover side surfaces of the light-emitting element  3 . Furthermore, the light-emitting device  1  may be of the chip on board (COB) type, in which the light-emitting element  3  is arranged on a plate-shaped board and the light-reflective resin-molded body  22  is formed in a frame shape on the board such as to surround the light-emitting element  3 . 
     The form of the light-emitting device  1  is not limited to those described above so long as the resin-molded body  22  is arranged to surround at least a portion of the light-emitting element  3  such that the resin-molded body  22  is used to reflect the light from the light-emitting element  3 . 
     EXAMPLES 
     Next, examples of light-emitting devices in each of which a light-emitting element is mounted on a package using a resin composition containing a first filling material and comparative examples are described with reference to  FIGS. 5A to 11B . 
       FIG. 5A  is a photograph of a first filling material before subjected to the surface treatment step.  FIG. 5B  is a photograph enlarging a part of the first filling material shown in  FIG. 5A .  FIG. 6A  is a photograph showing a first filling material that has been subjected to the surface treatment step.  FIG. 6B  is a photograph enlarging a part of the first filling material shown in  FIG. 6A .  FIG. 7A  is a photograph showing a first filling material that has been subjected to the heat treatment step at a temperature of 850° C. in an example.  FIG. 7B  is a photograph enlarging a part of the first filling material shown in  FIG. 7A .  FIG. 8A  is a photograph showing a first filling material that has been subjected to the heat treatment step at a temperature of 900° C. in an example.  FIG. 8B  is a photograph enlarging a part of the first filling material shown in  FIG. 8A .  FIG. 9A  is a photograph showing a first filling material that has been subjected to the heat treatment step at a temperature of 950° C. in an example.  FIG. 9B  is a photograph enlarging a part of the first filling material shown in  FIG. 9A .  FIG. 10A  is a photograph showing a first filling material that has been subjected to the heat treatment step at a temperature of 970° C. in an example.  FIG. 10B  is a photograph enlarging a part of the first filling material shown in  FIG. 10A .  FIG. 11A  is a photograph showing a first filling material that has been subjected to the heat treatment step at a temperature of 1000° C. in an example.  FIG. 11B  is a photograph enlarging a part of the first filling material shown in  FIG. 11A . 
     In  FIGS. 5A, 6A, 7A, 8A, 9A, 10A, and 11A , a reading of 10 divisions in the scale corresponds to 50 μm. In  FIGS. 5B, 6B, 7B, 8B, 9B, 10B, and 11B , a reading of 10 divisions in the scale corresponds to 1 μm, and each figure is a photograph enlarging the surface of one particle of each first filling material. In  FIG. 6B , the oblong, rectangular column-shaped object is a particle of wollastonite serving as base material; and the many small particles formed on the surface of the particle of wollastonite are particles of calcium fluoride serving as coating material. 
     Original Material of Resin composition 
     The following materials were used for the light-emitting devices of the examples and comparative examples.
         Base material of the first filling material: Wollastonite (Manufactured by KINSEI MATEC CO., LTD.; product name: SH1800; average fiber diameter: 3.5 μm; average fiber length: 28 μm)   Agent used in the chemical surface treatment of the first filling material: Aqueous ammonium fluoride solution   Second filling material: Titanium oxide (manufactured by ISHIHARA SANGYO KAISHA, LTD.; product name: CR-90-2; average particle diameter: 0.45 μm)   Resin: Polyamide resin PA6T (manufactured by Mitsui Chemicals, Inc.; product name: ARLEN (R) C2000)   Package: Side-view type (manufactured by NICHIA Corporation; product name: NSSW304D)       

     Examples 
     Packages of the examples were produced by the following procedure: 
     Surface Treatment Step 
     A wollastonite, the base material of the first filling material, was dispersed in a 10% aqueous ammonium fluoride solution with a mass ratio of 1:10. While gently stirring the aqueous ammonium fluoride solution so as not to break the wollastonite, reaction was carried out for three hours at a temperature of 70° C. After the reaction, steps of dehydration, drying, and dry sieving were carried out to obtain wollastonite having a surface on which particles of calcium fluoride were formed. 
     Heat Treatment Step 
     Next, at each of the predetermined temperatures 850° C., 900° C., 950° C., 970° C., and 1000° C., a heat treatment was carried out for two hours in a reducing atmosphere so as to obtain a first filling material containing particles of wollastonite on the surface of which a coating material comprising particles of calcium fluoride is melted and extended. 
     Note that, prior to carrying out the heat treatment at each predetermined temperature, the ambient temperature was increased from a room temperature to the predetermined temperature taking four hours. 
     Now, a description is given of the difference in the shape of the coating material due to the difference in the heating temperature with reference to  FIGS. 5A to 11B . 
     As shown in  FIG. 5B , the first filling material before surface treatment was applied was solely composed of the base material and had a flat surface. 
     As shown in  FIG. 6B , the particles of the coating material self-assembled in the surface treatment step had a diameter of about 30 nm to about 50 nm. 
     As shown in  FIG. 7B , when the heating temperature was 850° C., the particles of the coating material self-assembled in the chemical surface treatment remained in a granular form. The area of the base material coated by each of the particles of the coating material was larger than before the heat treatment was carried out. However, the base material had many regions where the base material was exposed between the particles of the coating material. Note that the particles of the coating material once melted to form a smooth surface. 
     As shown in  FIG. 8B , when the heating temperature was 900° C., the particles self-assembled in the chemical surface treatment still remained in a granular form, but the area of the base material coated by the particles of the coating material was larger than when the heating temperature was 850° C. 
     As shown in  FIG. 9B , when the heating temperature was 950° C., the particles self-assembled in the chemical surface treatment still remained in a granular form, but substantially the entire surface of the base material was coated by the coating material. 
     As shown in  FIG. 10B , when the heating temperature was 970° C., substantially the entire surface of the base material was coated by the coating material. In this case, the particles of the coating material self-assembled in the chemical surface treatment had almost no granularity, but had some amount of unevenness on their surface. 
     As shown in  FIG. 11B , when the heating temperature was 1000° C., substantially the entire surface of the base material was coated by the coating material. In this case, the coating material has a surface with no unevenness and is formed in a film having a substantially uniform thickness. 
     Comparison between the  FIGS. 5A, 6A, 7A, 8A, 9A, 10A, and 11A  showed that the each of the first filling materials remained in a fibrous form even after being subjected to the surface treatment and the heat treatment under any of the conditions tested. Therefore, any of those first filling materials can be used as a filler for enhancing the mechanical strength of the resin composition. 
     Mixing Step 
     Next, two kinds of filling materials, i.e., a first filling material having a surface on which the coating material was coated and a second filling material composed of titanium oxide, were mixed with a polyamide resin in the following ratio to obtain a resin composition. 
     The mass ratio of the polyamide resin, the first filling material, and the second filling material in the resin composition was: 45 (polyamide resin): 15 (first filling material): 40 (second filling material). The polyamide resin, the first filling material, and the second filling material were melted and kneaded at a temperature higher than the melting point of the polyamide resin, e.g., 320° C., so as to uniformly disperse the first filling material and the second filling material in the polyamide resin. The kneading operation was carried out to disperse the first filling material and the second filling material into the polyamide resin, so gently as not to break the wollastonite, i.e., the base material of the first filling material. After the kneading operation, pellets of the resin composition were produced by extrusion molding. 
     Resin Molded-Body Forming Step 
     Next, the pellets of the resin composition were melted at a temperature of about 320° C. and injected into an injection molding mold in which lead electrodes are placed, to form a resin-molded body. The injection molded resin-molded body was then cooled to be solidified, to produce a package. This package has a recess having a bottom surface and side walls, wherein at least a portion of a lead frame is exposed on the bottom surface and the side walls are formed of the resin-molded body. 
     Comparative Example 
     A package of the comparative example was produced in the following procedure:
         The same material as the original wollastonite material used as the first filling material in the examples and the same material as the titanium oxide used as the second filling material in the examples were prepared.   The first filling material and the second filling material were kneaded in polyamide resin so as to be dispersed therein, in the same manner as the examples. The mass ratio between the polyamide resin, the first filling material, and the second filling material was 45 (polyamide resin):15 (first filling material):40 (second filling material). Then, a package was produced in the same manner as the resin-molded body forming step of the examples, except the conditions described above.       

     Evaluation 
     Light emitting devices were produced by mounting the same light-emitting element on the packages of one of the examples and the comparative example. An evaluation was carried out as to a total luminous flux of the light emitted from each of those light-emitting devices when the light-emitting element of the light-emitting device is made emit light. For each of the example and the comparative example, the luminous flux of each light-emitting device was measured by an integral total luminous flux measurement apparatus. 
     Note that the light-emitting device of the example was the one produced using the first filling material subjected to the heat treatment step for two hours at a temperature of 1000° C. 
     The evaluation result showed that, if the total luminous flux of the light-emitting device of the comparative example is taken as 100, the total luminous flux of the light-emitting device of the example was 100.5. Namely, it was confirmed that using the first filling material of the example enabled improvement in the light emission output of the light-emitting device. 
     The light-emitting device according to the present disclosure can be used for lighting devices, displays, backlights for liquid crystal display devices of cellular phones, auxiliary light sources for moving picture illumination, and other general light sources for consumer use.