JP2012109288A - Wafer for led - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer for LED which holds stabilized heat dissipation and mechanical strength and, at the same time, allows for microfabrication and high reliability even for chemical resistance because extensive studies are conducted about a plating method that allows for microfabrication by using a combined material only in a core material in the center part, and thereby respective metal layers are formed uniformly and integrally with no interlayer exfoliation, and contact thermal resistance with the LED is extremely low.SOLUTION: The wafer for LED is obtained by forming an Au plating surface layer of Au or an Au alloy on both surfaces vertically symmetrically around a thin film core material consisting of Mo, and then forming composite underlying layer consisting at least of a Cu plating layer between the core material and the Au plating surface layer, so as to complement and maintain the core material and the Au plating surface layer.

Description

  The present invention relates to an LED wafer that functions to hold an LED as a semiconductor element and prevent it from storing heat.

  In semiconductor devices such as LEDs (light emitting diodes) and semiconductor integrated circuits, the amount of heat dissipation tends to increase due to the recent increase in density and output, and thus excellent high heat dissipation performance is required for the wafer. At the same time, there is a tendency to demand fineness, fineness, and associated corrosion resistance, impact resistance, and the like. In addition, in relation to high heat dissipation performance, there is also a demand for non-deformable stability or a low coefficient of thermal expansion required to maintain contact with an LED or the like. Conventionally, a sapphire substrate has been used as this LED wafer, but recently there is a lack of thermal conductivity and impact resistance.

  When the semiconductor element is an LED, the LED is mounted on a sapphire substrate, as shown in FIG. 8, but in this case, heat generated from the light emitting part of the LED due to contact resistance is generated by the sapphire substrate. (Refer to the left diagram in FIG. 9). Many semiconductor elements have a reduced function when heat is stored, and particularly LEDs have a negative effect such as a decrease in brightness and damage to the sapphire substrate. A heat radiating substrate (wafer) made of metal having a good thermal conductivity and a relatively low heat resistance is used for the portion receiving it (see the right figure in FIG. 9). For example, a metal called a metal wafer such as copper, molybdenum, tungsten, or titanium. And, it is known that molybdenum (Mo) sandwiched mainly by copper (Cu, Cu) plating (referred to as “DMD”) is good (see the right figure in FIG. 9). . However, these metals still have problems with respect to corrosion resistance, chemical resistance, heat transfer contact with LED, and the like.

  Generally, the properties and performances required for wafers require excellent thermal conductivity. Therefore, not only the thermal conductivity, but also, for example, when mounting with LEDs, there is little thermal contact resistance, distortion In addition, stability without warping and high mechanical strength and machinability are required. In addition, it is required to be suitable for attachment and brazing, and to be excellent in chemical resistance. Conventionally, development has been progressed so that these properties are comprehensively exhibited by layer bonding of a plurality of metal materials (grad materials) (Patent Documents 1 and 2). As means for taking this multilayer structure, conventionally, a rolling method in which a grad material is pressure-bonded and polymerized or a hot uniaxial processing method has been used. However, it has been difficult to obtain uniformity of the layer thickness especially by the rolling method.

  FIG. 10 shows an apparatus based on a conventional hot uniaxial processing method. An LED wafer 54 is made of a laminated material 52, 52 made of either Cu or Ti on both surfaces of a substrate 50 made of W or Mo metal. However, there were problems as described below.

JP-A-6-268115 Japanese Patent No. 3862737

  In the rolling method and the hot uniaxial processing method, a plurality of laminated metal materials (also referred to as grad materials and grad metals) are overlapped and compressed to flatten due to thermoplasticity, and the laminated materials are thermocompression bonded to each other. Although it forms a layer (this structure is called “CMC”), it is difficult to match conditions such as heating temperature, time, and compressive strength for adhesion, and it is not reliable and does not peel. When it occurs, mechanical strength and heat dissipation performance are hindered (heat is stored in the peeled portion), and the coupling with the package substrate and the LED element becomes unstable due to the rise.

  In particular, since there is a limit to minimizing the thickness of the grad metal, there is a problem that cannot be avoided in terms of miniaturization of the LED wafer. Furthermore, as a method to prevent warping due to the joining of different metals, the laminated metal materials are arranged so as to be symmetrical on both the upper and lower surfaces around the base material as the center, but still different metals with different thermal deformation are heated simultaneously. Due to the compression, the thickness of the grad layer is unevenly distributed, and in particular, the rolling method tends to cause undulations and colonies in the layer. These occurrences also cause overall warpage, and also hinder the mechanical strength and heat dissipation performance. There was also a problem of becoming a factor inviting.

  In view of the above situation, the present invention has been intensively researched on a plating method capable of miniaturization by using a laminated material only as a core material at the center of each layer. Is formed uniformly and inseparably, does not cause delamination between layers, and has very little contact thermal resistance with the LED, so it can maintain stable heat dissipation and mechanical strength, and at the same time can be miniaturized and has chemical resistance Also, it was an object to provide a highly reliable LED wafer.

  In order to solve the above problems, the present invention has the following configuration.

  (1) That is, this invention forms Au plating surface layers of Au or Au alloy on both sides so as to be vertically symmetrical about a thin plate-like core material made of Mo, and the core material and the Au plating surface layer (1) (Embodiments 1 to 4 correspond respectively), characterized in that a composite underlayer composed of at least a Cu plating layer that complements and maintains it is formed. ).

  According to the above configuration, not only the heat conduction between layers is good, but the Cu plating layer is provided on the upper and lower sides of the Mo core material, and Mo is sandwiched between Cu (thermal conductivity 420 W / (m.k)). Unlike so-called “DMD”, the upper and lower surfaces are Au-plated surface layers with good wettability, so that the LEDs can be tightly bonded via an adhesive and contact with heat conduction. Resistance is extremely low.

  Also, due to the nature of the Au-plated surface layer, LED adhesion stability and surface corrosion resistance can be obtained for the attachment of delicate LEDs. In addition, the noble metal Au with this property should be used only on the surface. This is advantageous in terms of cost.

Au has a thermal conductivity of 320 W / (mk), a density of 19300 kg / m ³ , and a hardness of 2.5, and heat can be radiated without delay through itself and Cu. Further, together with Cu (hardness 3.0), a fine cushioning property for softly attaching the LED can be obtained due to the low hardness.

  (2) Further, as described in claim 2, the composite underlayer has a sandwich structure having thin Ni plating layers on both upper and lower surfaces of the Cu plating layer, and the Cu plating layer is made of the Ni plating layer as an underlayer. The Au plating surface layer is formed on the Cu plating layer with the Ni plating layer as a base (Examples 1 and 2 correspond).

  Ni is a stable metal and has good compatibility as a base for other plating, contributing to the formation of a Cu plating layer on the core material and the formation of an Au plating surface layer on the Cu plating layer. The strong bonding of the plating surface layer is maintained, and the characteristics of the Au plating surface layer are easily exhibited. Note that Ni has a thermal conductivity of 90 W / (mk), but high heat dissipation performance is exerted on the LED wafer as a whole by thinly plating.

  (3) In addition, as in claim 3, the Au plating surface layer may be Au—Sn alloy plating containing 20 to 30% of Sn (corresponding to Example 2).

  In this case, the mechanical strength of Au is improved, and the LED mounting is stably held.

  (4) In addition, as described in claim 4, an Au plating layer and an Sn plating layer are sequentially formed on the sandwich structure, and the Au plating surface layer is formed on the Sn plating layer. Thus, a sandwich Au composite layer in which Sn plating is sandwiched between Au plating is formed on the upper and lower surface portions (Example 3 corresponds).

  In this case, since the hardness of Sn is as small as 1.5, a softer layer than Au (hardness 2.5) is formed on the surface, which is particularly suitable for mounting delicate LEDs. Moreover, the thermal conductivity of this Au composite layer is also good.

  (5) Further, as described in claims 8 and 9, when a barrier layer of a Pd plating layer is provided between the Au surface plating layer and the Ni plating layer, Au-Ni interdiffusion can be suppressed. The plating thickness can be reduced.

  As described above, according to the present invention, the laminated material is used only for the core material at the center of the layer, and the layers are formed symmetrically by plating up and down around this, so that each metal layer is uniformly and non-isolated. It is formed and has no warpage stability, and no delamination occurs between the layers. For this reason, the LED can be securely mounted and safely held. In addition, since the contact thermal resistance with the LED is extremely low, stable heat dissipation and mechanical strength are maintained, and at the same time, miniaturization is possible and the chemical resistance is also highly reliable. Is efficiently reflected and heat dissipation is enhanced, and at the same time, the luminous efficiency is improved. Furthermore, there is an excellent effect that the use of Au, which is a noble metal, is rationally saved and advantageous in terms of cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory sectional view schematically showing a layer structure of an LED wafer according to a first embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view showing a part of the LED wafer replaced with an actual thickness ratio as much as possible. It is explanatory drawing which shows typically the use condition of the wafer for LED. It is explanatory drawing which shows the light reflection effect in the attachment state of LED about use of the wafer for LED. It is sectional explanatory drawing which shows typically the layer structure of the wafer for LED which shows 2nd Example. It is sectional explanatory drawing which shows typically the layer structure of the wafer for LED which shows 3rd Example. It is sectional explanatory drawing which shows typically the layer structure of the wafer for LED which shows 4th Example. It is explanatory drawing which shows a prior art example by the comparison of a left-right view in the use condition of the wafer for LED. It is explanatory drawing which shows a prior art example by the comparison of a left-right view in the use condition of the wafer for LED. It is another explanatory drawing of a prior art example.

  Since this invention forms a layer structure by plating, the core material 1 of a metal thin plate is required as the base material. For this purpose, a thin plate material made by thinly stretching Mo metal to about 50 to 200 μm is used, and after applying each plating layer to this, a large number of LED wafers P, P,. Is done. Note that W can be used instead of Mo. However, it is generally expensive.

  For plating, electrolysis, electroless, ion plating (IP) method or the like is desirable, but there is no particular limitation as long as it is plating. In any case, the thickness of each metal layer is formed into a uniform layer with vertical symmetry by plating, and the layers are tightly coupled. For forming the Cu plating layers 5 and 5, besides the Cu plating, a Cu ion plating method can be optimally used.

  In each embodiment, the plating thicknesses of the core material 1, the first and second Ni plating layers 3 and 7, the Cu plating layer 5, the Au plating surface layer 9, and the Sn plating layer 13 are determined for each LED wafer. Each of the examples showing the P layer (FIGS. 1, 5 and 6) is displayed in the appropriate range on the right side. For example, in FIG. 1, Cu plating layers 5 and 5 have a display range of 3.0 to 20.0 μm.

  Explaining each illustrated thickness range in each example, the core member 1 can effectively maintain the central mechanical strength of the sandwich structure in the display range. Further, if the first and second Ni plating layers 3 and 7 are below the display range, they cannot function as a base, and if they are more than that, they are excessive, and the Cu plating layer 5 is below the display range. If it is, it is difficult to obtain the desired conductivity, and if it is the above, it is difficult to obtain a cushioning property (softness) that holds the LED 10 safely. Furthermore, when the Au plating layer or the Au plating surface layer 9 is within the range, it is difficult to obtain desired cushioning properties (softness). The Sn plating layer 13 effectively performs the Au plating increasing function in the display range, and is suitable for saving Au.

  1 to 3 show an embodiment. First, Cu plating layers 5 and 5 are formed on both surfaces of a core material 1 made of a Mo metal plate via thin first Ni plating layers 3 and 3, respectively. The structure having the Cu plating layers 5 and 5 on both surfaces of the core material 1 is referred to as “DMD” in this specification. Further, Au plating surface layers 9 and 9 are formed on both Cu plating layers 5 and 5 through second Ni plating layers 7 and 7 respectively. In the figure, 2 indicates a composite underlayer.

  In the conventional “CMC” structure (see FIG. 9), it is difficult to adjust the material by cutting it to, for example, about 1 μm, and peeling between the materials is likely to occur. In this case, uniform thickness is formed by plating. Became possible. Moreover, as shown in FIG. 2, since the Cu plating layer 5 is formed on the core material 1 and the Au plating surface layer 9 is formed on the Cu plating layer 5 with the Ni plating layers 3 and 7 as the foundation, Since the bonding strength is extremely strong and peeling does not occur, heat dissipation is stably maintained, and attachment of the LED 10 is also stably maintained.

  FIG. 3 schematically shows a state in which the LED 10 is mounted on the package 14 via the LED wafer P, and the package 14 and the LED 10 are attached by the adhesive 16. For the adhesive 16, an Ag or AuSn alloy paste can be used effectively. Since the surface is the Au plating surface layer 9, 9, even if the LED 10 is epitaxially delicate, the mounting strength and safety are effectively ensured.

  This is because, as shown in the figure, since the surface is a soft Au plating surface layer 9, 9 with good adhesion of the adhesive, this enhances the mounting strength of the LED and reduces the impact on the LED 10. . In addition, when the semiconductor element is an LED in particular, light or radiant heat is reflected by the Au plating surface layer 9 (FIG. 4), and not only heat dissipation is obtained, but also the luminous efficiency of the LED is improved.

  Next, it extends to the second to fourth embodiments, and has the same characteristics as described above.

  As shown in FIG. 5, in the LED wafer, Cu plating layers 5 and 5 are formed on both surfaces of a core material 1 made of a Mo metal plate via first Ni plating layers 3 and 3, and both Cu plating layers are formed. Au surface platings 9 and 9 are formed on the 5 and 5 through the second Ni plating layers 7 and 7 respectively. The process so far is the same as in Example 1, but the Au plating surface layers 9 and 9 are formed as Au—Sn alloy plating.

  As shown in FIG. 6, in the LED wafer, Cu plating layers 5 and 5 are formed on both surfaces of a core material 1 made of a Mo metal plate via first Ni plating layers 3 and 3, and both Cu plating layers 5 are formed. , 5, Au plating layers 11, 11 and Sn plating layers 13, 13 are sequentially formed through second Ni plating layers 7, 7, respectively, and Au plating surface layers 9, 9 are formed thereon. It is formed. In this upper layer portion, an Au composite layer 15 having a sandwich structure in which the Sn plating layer 13 is sandwiched between the Au plating layers 9 and 11 is formed.

  Sn is also soft together with Au, and its properties are very familiar to each other. The Au composite layer 15 is a layer having strong Au properties due to Au on both sides. In the LED wafer P, stability without warping is obtained by the Au composite layers 15 and 15 on both sides, and the safety of mounting the LED 10 is further ensured by the property of Au.

  As shown in FIG. 7, in the LED wafer, Cu plating layers 5 and 5 are formed on both surfaces of a core material 1 made of a Mo metal plate via first Ni plating layers 3 and 3, and both Cu plating layers 5 are formed. , 5 are respectively formed with Pd plating layers 17, 17 via second Ni plating layers 7, 7, respectively, and Au plating surface layers 9, 9 are formed thereon.

  In the above configuration, by providing a barrier layer of the Pd plating layer 17 between the Au plating surface layer 9 and the second Ni plating layer 7, Au-Ni interdiffusion can be suppressed and Au plating can be performed. The thickness can be reduced.

P LED wafer 1 Core material 2 Composite underlayer 3 First Ni plating layer 5 Cu plating layer 7 Second Ni plating layer 9 Au plating surface layer 11 Au plating layer 13 Sn plating layer 15 Au-based composite layer 17 Pd plating layer

Claims (9)

  An Au plated surface layer of Au or an Au alloy is formed on both sides so as to be vertically symmetric about a thin plate core material made of Mo, and this is complemented and maintained between the core material and the Au plated surface layer. An LED wafer comprising a composite underlayer comprising at least a Cu plating layer.   The composite underlayer has a sandwich structure having thin Ni plating layers on both the upper and lower surfaces of the Cu plating layer, the Cu plating layer is formed on the core material with the Ni plating layer as an underlayer, and the Au plating surface layer is the Cu plating layer The LED wafer according to claim 1, wherein a Ni plating layer is formed on the substrate as a base.   The LED wafer according to claim 2, wherein the Au plating surface layer is Au—Sn alloy plating containing 20 to 30% of Sn.   An Au plating layer and an Sn plating layer are sequentially formed on the sandwich structure, and the Au plating surface layer is formed on the Sn plating layer, thereby sandwiching the Sn plating between the upper and lower surface portions with the Au plating. The LED wafer according to claim 2, wherein the Au composite layer is formed.   Mo core material is 50-200 μm, lower Ni plating layer is 0.1-3.0 μm, Cu plating layer is 3.0-20.0 μm, upper Ni plating layer is 0.5-5.0 μm, Au plating surface The LED wafer according to claim 2, wherein the layer is 0.1 to 2.0 μm.   Mo core material is 50 to 200 μm, lower Ni plating layer is 0.1 to 3.0 μm, Cu plating layer is 3.0 to 20.0 μm, upper Ni plating layer is 0.5 to 5.0 μm, Au plating layer 4. The LED wafer according to claim 3, wherein the surface is 0.1 to 3.0 [mu] m.   Mo core material is 50 to 200 μm, lower Ni plating layer is 0.1 to 3.0 μm, Cu plating layer is 3.0 to 20.0 μm, upper Ni plating layer is 0.5 to 5.0 μm, Sn plating layer 5. The LED wafer according to claim 4, wherein 0.5 to 5.0 μm, and the Au plating layer or the Au plating surface layer is 0.5 to 3.0 μm.   The composite underlayer has a sandwich structure having thin Ni plating layers on both upper and lower surfaces of the Cu plating layer, the Cu plating layer being formed on the core material with the first Ni plating layer as an underlayer, and an Au plating surface layer 2. The LED wafer according to claim 1, wherein a Pd plating layer is formed on the Cu plating layer with a Pd plating layer as a base via a second Ni plating layer.   The core material of Mo is 50 to 200 μm, the upper and lower first Ni plating layers of the core material are 0.1 to 3.0 μm, and the upper and lower Cu plating layers of the Ni plating layer are 3.0 to 20 μm. 0.0 μm, the upper and lower second Ni plating layers of the Cu plating layer are 0.5 to 5.0 μm, and the Pd plating layer constituting the upper and lower portions of the second Ni plating layer is 0.02 to 0 9. The LED wafer according to claim 8, wherein the Au plating surface layer constituting the upper and lower portions of the Pd plating layer is 0.03 to 1.0 μm.

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