JP2011134920A - Led package mounting structure and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost high-reliability LED package mounting structure improved in solder fatigue life. <P>SOLUTION: An LED package 10 has a light emitting surface 11 in a direction vertical to the mounting surface of a circuit substrate 20 and includes a first connection terminal member 12 on the bottom surface of the package and a second connection terminal member 13 on the back surface of the light emitting surface while the package is soldered and connected with the circuit substrate through the connection terminal members 12, 13. Solder materials used for connection with the circuit substrate 20 are different at the connection terminal members 12, 13. A melting point of solder 31 used for the connection terminal member 13 is lower than that of solder 30 used for the connection terminal member 12 by 30 degrees or higher. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an LED package mounting structure in which an LED package is mounted on a circuit board such as a printed wiring board.

  In recent years, the use of LEDs has been rapidly progressing as a light source for backlight units for liquid crystal display devices such as televisions and monitors. This is a flow corresponding to the demand for improving the performance of the liquid crystal display device, and by using the LED light source, it becomes possible to reduce the power consumption and the thickness of the television as compared with the conventional cold cathode fluorescent tube. . In particular, by dividing the LEDs that make up the backlight into multiple groups and implementing area control that controls the brightness of the LEDs in units of groups according to the content of the video, further lower power consumption and higher image quality are possible. It becomes.

  There are roughly two types of backlight systems for liquid crystal display devices that enable area control: a direct type and a slim block type. In the direct type, a large number of LED light sources are dispersed and arranged in a plane so that the optical axis is perpendicular to the liquid crystal panel, and light is emitted by a diffusion plate arranged at a certain distance from the light source. Mix to equalize the brightness. On the other hand, the slim block type has a configuration in which a plurality of combinations of LEDs and a series of light guide plates are arranged in a plane in a plane, and the LEDs are guided so that their optical axes are parallel to the liquid crystal panel. Located beside the light plate. When the light emitted from the light source is incident from the side surface of the light guide plate, the light is totally reflected and propagates in the light guide plate, and is scattered by reflection dots or the like applied to the lower surface of the light guide plate and taken out to the upper surface of the light guide plate. The slim block method is characterized in that it can be made thinner because it does not require a space for obtaining a uniform in-plane luminance distribution compared to the direct type.

  When using the slim block method, in order to use a general top emission type surface mount LED package (hereinafter referred to as a top view LED package) in which the optical axis is perpendicular to the mounting surface of the LED package After mounting the LED on the relay board, it is necessary to solder the relay board vertically to the circuit board, or to fix the relay board vertically to the chassis and then perform wiring with connectors etc., increasing the number of parts and assembly man-hours Cost. On the other hand, a side-emitting type surface-mounted LED package (hereinafter referred to as a side-view type LED package) whose optical axis is parallel to the mounting surface of the LED package is disclosed (for example, Patent Document 1). . When the side view type LED package is used, since the LED is directly mounted on a circuit board such as a printed wiring board, there is an advantage that the cost can be suppressed.

JP 7-115227 A

  By the way, when a side-view type LED package is mounted on a circuit board by soldering, the solder connection portion under the LED package electrode cracks and progresses due to a temperature change accompanying the ON / OFF of the LED, and finally solder fatigue There was a problem of poor conduction due to breakdown. This is because the linear expansion coefficient of the LED package is smaller than the linear expansion coefficient of the circuit board, and therefore stress due to thermal deformation is generated in the solder portion. Especially for TV applications, from the viewpoint of ensuring the reliability of the LED package, a printed wiring board using a ceramic material as the LED package body and an inexpensive organic resin material as the circuit board from the viewpoint of reducing member costs. Since it is often used and the difference in linear expansion coefficient between the two materials is large, the problem of solder fatigue failure becomes more serious. Furthermore, in the side view type package, it is difficult to increase the electrode area of the package as in the top view type package, and the small connection area with the solder is also a factor for shortening the time until the conduction failure. Yes.

As a solution to the above problem, it is conceivable to increase the solder supply amount to increase the solder thickness of the connection portion. However, when the solder thickness is increased, the mounting accuracy of the LED package on the circuit board is lowered. That is, when the positional displacement of the LED package in the front / rear / left / right direction is increased, or the light emitting surface is inclined or rotated forward / backward, the optical coupling efficiency with the light guide plate is deteriorated. In addition, as an alternative to solder, it is conceivable to employ other connection means such as connection with a heat-effect resin containing solder, but this is not realistic because it leads to an increase in costs such as member costs.

  In view of the above problems, the present invention improves the fatigue life of the solder that electrically connects the LED package and the circuit board when there is a difference in linear expansion coefficient between the LED package and the circuit board, thereby reducing the conduction failure. An object of the present invention is to provide an LED package mounting structure that can be prevented with high reliability at low cost.

  The object is to provide a mounting structure in which an LED package and a circuit board for mounting the LED package are electrically connected by solder, and a first connection terminal portion is provided on the bottom surface of the package and a second connection terminal is provided on the back surface. And an LED package mounting structure characterized by being soldered to the circuit board via the first and second connection terminal portions.

  According to the LED package mounting structure according to the present invention, since the solder connection area between the LED package and the circuit board on which the LED package is mounted can be increased, the linear expansion coefficient difference between the LED package and the circuit board can be increased. Even when there is, it is possible to improve the fatigue life of the solder that electrically connects the LED package and the circuit board, and to prevent conduction failure.

It is a schematic side sectional view of the LED package mounting structure according to the first embodiment of the present invention. It is a schematic front sectional drawing of the LED package mounting structure which is 1st Embodiment of this invention. 1 is a schematic rear cross-sectional view of an LED package mounting structure according to a first embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a schematic side cross-sectional view of an LED package mounting structure according to the first embodiment of the present invention.

  The LED package mounting structure is obtained by electrically connecting a surface mounting type LED package 10 to a circuit board 20 via solder. Here, the LED package 10 has a case made of a ceramic sintered body obtained by laminating and firing a plurality of green sheets mainly composed of alumina, and an LED element (not shown) is mounted inside the case. . As the ceramic material, aluminum nitride, silicon carbide, beryllium oxide or the like is used in addition to alumina. A resin package such as polyamide may be used instead of the ceramic package.

  As a material of the circuit board 20 on which the LED package 10 is mounted, an organic resin substrate such as a relatively inexpensive glass epoxy substrate is used, and a ceramic substrate having excellent reliability and a metal base substrate having excellent heat conductivity can also be used. It is possible and not particularly limited.

  The LED package 10 is mounted so that the light emitting surface 11 is substantially perpendicular to the mounting surface with the circuit board 20, and is placed on the bottom surface of the package perpendicular to the light emitting surface 11 in the mounted state. The connection terminal portion 12 has a second connection terminal portion 13 on a surface (back surface of the light emitting surface) that is perpendicular to the mounting surface and opposite to the light emitting surface 11. In the first and second connection terminal portions 12 and 13, for example, a metallized layer made of W or Mo is covered with Ni plating and Au plating or Ni plating and Ag plating. The first connection terminal portion and the second connection terminal portion each have two pads of an anode electrode and a cathode electrode corresponding to the p-side electrode and the n-side electrode of the LED element. The anode electrode pads of the second connection terminal portion and the cathode electrode pads of the first connection terminal portion and the second connection terminal portion are electrically connected. In this case, the same polarity of the first connection terminal portion and the second connection terminal portion (121 in FIG. 2 and 131 in FIG. 3, 122 in FIG. 2 and 132 in FIG. 3) are separated on the surface of the package. However, it is preferable that the surface of the package is separated and independent and is electrically connected by the internal wiring of the package. The anode electrode pad 132 and the cathode electrode pad 131 of the second connection terminal portion can be installed in any size as long as they can be laid out without contacting both electrodes within the range of the package size.

  The first connection terminal portion 12 and the second connection terminal portion 13 are connected to component mounting pads 21 on the circuit board 20 via solders 30 and 31 having different compositions. The component mounting pads on the circuit board side that are connected to the first connection terminal portion and the second connection terminal portion of the package are independent and independent pads, and may be electrically connected within the circuit board. In addition, the same pad may be separated by the opening of the solder resist 22. In any case, the surface of the circuit board 20 needs to be independent so that solder materials of different compositions used in the first connection terminal portion and the second connection terminal portion do not mix on the pad.

  The diameter of the side perpendicular to the light emitting surface 11 of the package of the component mounting pad 21 (or solder resist opening) on the circuit board side connected to the second connection terminal portion of the package (hereinafter referred to as A). The dimension) is preferably 0.5 to 2 times the pad diameter in the height direction of the second connection terminal portion (hereinafter referred to as dimension B). This is because when the A dimension is smaller than 0.5 times the B dimension or larger than 2 times, the solder fillet does not have an appropriate shape and does not lead to an improvement in the solder fatigue life. If the solder fillet has an appropriate shape, solder breakage occurs first in the first connection terminal portion, and then solder breakage occurs in the second connection terminal portion.

  Here, as long as an appropriate solder fillet shape is formed, the area (or solder resist opening area) of the component mounting pad 21 on the circuit board side connected to the second connection terminal portion 13 of the package is as much as possible. Larger is preferable. The large pad area also increases the solder connection area. As a result, the heat dissipation characteristics can be improved to reduce the thermal stress associated with the ON / OFF of the LED, and the total length until the solder reaches full breakage is long. Because it becomes.

  As described above, the solder connection area between the package 10 and the circuit board 20 is increased by soldering to the circuit board 20 via the first connection terminal portion 12 and the second connection terminal portion 13 of the package. Even if solder breakage due to thermal stress occurs in the first connection terminal portion 12, conduction failure can be avoided in the second connection terminal portion 13, and it is possible to prevent the LED from becoming unlit.

  Here, the material of the solder 30 used in the first connection terminal portion is preferably a tin-silver binary eutectic solder, a tin-silver-copper ternary eutectic solder or a tin-zinc solder excellent in thermal fatigue characteristics. Specifically, Sn-3.5Ag (melting point: about 221 ° C.), Sn-3Ag-0.5Cu (melting point: about 217 ° C.), Sn-9Zn (melting point: about 199 ° C.), etc. are used in the first connection terminal portion. It is given as solder. For the solder 31 used in the second connection terminal portion, it is necessary to select a material having a lower melting point than the melting point of the solder used in the first connection terminal portion. For this reason, the material of the solder used in the second connection terminal is preferably a solder whose temperature is lowered by adding 3% or more of bismuth to a tin-silver binary eutectic alloy or tin-zinc alloy. Note that bismuth is a hard and brittle metal, and when a small amount of bismuth is added, the melting point of the solder is lowered while the connection reliability of the solder is also lowered. Therefore, as the solder used in the second connection terminal portion, for example, a tin / silver binary eutectic alloy or tin / zinc alloy added with 50 to 60% bismuth to lower the melting point is more preferable. In this case, since bismuth is refined by the eutectic reaction, a decrease in reliability can be avoided. Specifically, Sn-1Ag-57Bi (melting point: about 140 ° C.), Sn-4Zn-56Bi (melting point: about 130 ° C.), and the like are listed as the solder used in the second connection terminal portion. Although not preferable in terms of environmental impact, it goes without saying that tin-lead eutectic alloys that have been used in the past and have excellent bondability and fatigue life characteristics can also be used in the first or second connection terminal portions. Yes.

  Next, a method for producing an LED package structure will be described. When the LED package 10 is connected to the circuit board 20, solder is supplied in advance to the component mounting pads 21 on the circuit board by means such as paste printing, dispenser application, or plating. It is necessary to supply the circuit board 20 with different solders for the pads connected to the first connection terminal portions 12 and the pads connected to the second connection terminal portions 13 of the LED package 10. Therefore, for example, after supplying the first solder 30 to the pad connected to the first connection terminal portion 12 by paste printing, the second solder is applied to the pad connected to the second connection terminal portion 13 by applying a dispenser. 31 supply. Alternatively, an LED package in which solder balls are formed in advance on the second connection terminal portion 13 of the LED package after the first solder 30 is supplied by paste printing to the pad connected to the first connection terminal portion 12 is mounted. By doing so, the second solder 31 may be supplied.

The LED package 10 is carried by a component mounting machine or the like with the first connection terminal portion 12 facing downward, and is mounted on the circuit board 20 so as to contact the component mounting pad 21 coated with solder. Put. The circuit board 20 on which the LED package 10 is placed is conveyed by a belt into the reflow furnace. In the reflow furnace, the circuit board 20
Is heated at a temperature equal to or higher than the melting point of the solder for a certain period of time to melt the solder once, and then the circuit board 20 is taken out of the reflow furnace by belt conveyance. There are several heating zones with different set temperatures in the reflow furnace, and the circuit board 20 is gradually cooled after passing through the heating zone set to the maximum temperature. In this cooling process, as described above, the melting point of the solder 31 used in the second connection terminal portion 13 is lower than the melting point of the solder 30 used in the first connection terminal portion 12, First, the solder 30 of the first connecting terminal portion 12 is solidified again. At this time, the solder 31 of the second connection terminal portion 13 on the back surface of the package is still in a molten state. Thereafter, the solder of the second connection terminal portion is re-solidified. Along with the solder condensation at that time, a force for inclining the light emitting surface 11 of the package in the front-rear direction acts on the second connection terminal portion 13. However, since the solder 30 at the bottom of the package is already hardened, the package 10 can be kept upright without being inclined.

  Here, the melting point of the solder 31 used in the second connection terminal portion 13 is desirably lower by 30 degrees or more than the melting point of the solder 30 used in the first connection terminal portion 12. This is due to the following reason. That is, when the difference between the melting points of the two solders is smaller than 30 degrees, when the solidification point of the solder 30 of the first connecting terminal portion 12 becomes lower than the original melting point due to overcooling, the first connecting terminal portion 12 is used. This is because the re-solidification of the solder 31 of the second connection terminal portion 13 may start before the solder 30 of the second re-solidification is completely re-solidified, and the inclination suppressing effect of the LED package 10 is diminished.

  In addition, the solder fillet shape and the inclination suppression of the LED package 10 in the first embodiment of the present invention described above are the supply amounts and supply amounts of the solders 30 and 31 used in the first and second connection terminal portions 12 and 13. This can be achieved by optimizing the ratio, solder resist opening diameter, circuit board pad diameter, and the like.

  According to the first embodiment, since the solder connection area between the LED package 10 and the circuit board 20 can be increased, the LED package even when there is a difference in linear expansion coefficient between the LED package and the circuit board. It is possible to improve the fatigue life of the solder that electrically connects the circuit board and the circuit board and to prevent poor conduction. In addition, since solder materials having different melting points are used in the first and second connection terminal portions, there is no inclination of the package when the LED package is mounted, and an LED package mounting structure having excellent light coupling efficiency with the light guide plate. It becomes possible to provide.

DESCRIPTION OF SYMBOLS 10 Surface mount type LED package 11 LED light emission surface 12 1st connection terminal part 121 1st connection terminal part (cathode electrode pad)
122 First connection terminal (anode electrode pad)
13 Second connection terminal portion 131 Second connection terminal portion (cathode electrode pad)
132 Second connection terminal (anode electrode pad)
20 Circuit Board 21 Circuit Board Component Mounting Pad 22 Solder Resist 30 Solder 1
31 Solder 2

Claims (11)

In a mounting structure in which an LED package and a circuit board for mounting the LED package are electrically connected by solder,
A first solder connecting the circuit board and a first surface of the LED package facing the circuit board;
An LED package mounting structure comprising: a second solder for connecting the second surface of the LED package different from the first surface and the circuit board. The LED package mounting structure according to claim 1,
The LED package mounting structure, wherein the melting point of the second solder is lower than the melting point of the first solder. The LED package mounting structure according to claim 2,
The LED package mounting structure, wherein the difference between the melting points of the first and second solders is 30 degrees or more. In the LED package mounting structure according to any one of claims 1 to 3,
The LED package mounting structure, wherein the first solder and the second solder connect an electrode formed on the circuit board and an electrode formed on the LED package. The LED package mounting structure according to claim 4,
The electrode formed on the LED package includes a first electrode provided on the first surface and connected to the first solder, and an electrode provided on the second surface and connected to the second solder. An LED package mounting structure comprising a second electrode separately provided. In claim 5,
Both said 1st electrode and said 2nd electrode are electrically connected to the electrode of the LED element which the said LED package has, The LED package mounting structure characterized by the above-mentioned. In the LED package mounting structure according to claim 4,
The electrode formed on the LED package includes a first electrode provided on the first surface and connected to the first solder, and an electrode provided on the second surface and connected to the second solder. And a second electrode
2. The LED package mounting structure according to claim 1, wherein an area of the second electrode is larger than an area of the first electrode. In the LED package mounting structure according to any one of claims 1 to 7,
The LED package mounting structure according to claim 1, wherein an area of the second surface is larger than an area of the first surface. The LED package mounting structure according to any one of claims 1 to 8,
The LED package mounting structure, wherein the LED package has a light emitting surface on a surface opposite to the second surface. In a manufacturing method of a mounting structure in which an LED package and a circuit board on which the LED package is mounted are electrically connected by solder,
A first solder forming step of forming a first solder between the circuit board and a first surface of the LED package facing the circuit board;
A second solder forming step of forming a second solder having a melting point lower than that of the first solder, between the second surface of the LED package different from the first surface and the circuit board;
A reflow process of heating the LED package provided with the first solder and the second solder, and connecting the LED package and the circuit board by the first solder and the second solder. A method for manufacturing an LED package mounting structure, comprising: In the manufacturing method of the LED package mounting structure of Claim 10,
In the reflow process, the first and second solders are melted by heating, and the second solder is solidified after the first solder is solidified.

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