Mounting method of led chip and mounting structure of led chip

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

According to the present invention, an LED chip is mounted on a mounting pad formed on the surface of a substrate, particularly a mounting pad formed by laminating a plurality of conductor layers so that the uppermost layer is an Au layer, via a conductive adhesive. Regarding the mounting method of the LED chip to be mounted and the mounting structure of the LED chip.

【0002】

[Conventional technology]

FIG. 7 is a mounting structure of a conventional LED chip, and FIG. 8 is an enlarged cross-sectional view taken along the line VIII-VIII of FIG. The LED chip mounting structure 100 shown in FIG. 7 is applied to, for example, an Infrared Data Association (IrDA) compliant infrared data communication module, and is the LED chip 1 while ensuring the amount of light emitted to the outside. In order to enable miniaturization, the light emitted from the side surface (and the lower surface) as well as the upper surface of the LED chip 1 can be used. Specifically, as shown in FIG. 7, the LED chip 1 is die-bonded on a mounting pad 103 formed on the surface of the substrate 2, and the mounting pad 103 is emitted from the side surface of the LED chip 1. The LED chip 1 is formed so as to be considerably larger than the occupied area in a plan view so that light can be reflected.

【0003】

As shown in FIG. 8, the mounting pad 103 is formed by laminating a plurality of conductor layers 131, 132, 133 on the surface of the substrate 2, and is arranged at an appropriate position in the wiring pattern 21 formed on the surface of the substrate 2. .. The wiring pattern 21 is formed by etching a copper foil provided on the entire surface of the substrate 2, and the lowermost layer 131 of the mounting pad 103 is formed at the same time when the wiring pattern 21 is formed. The uppermost layer 133 of the mounting pad 103 is formed smoothly by Au having a relatively high reflectance, and is configured so that the light from the LED chip 1 can be efficiently used.

【0004】

The lower surface of the LED chip 1 is a full-face electrode, and the LED chip 1 is mounted on the mounting pad 103 with the lower surface facing down via the conductive adhesive 4. The conductive adhesive 4 is a conductive adhesive formed by mixing a large number of conductive fillers having predetermined metal particles into a binder made of a paste-like resin or the like, and is cooled after heating. It solidifies by that.

【0005】

When mounting the LED chip 1, first, the conductive adhesive 4 is applied to a desired portion of the mounting pad 103, and the LED chip 1 is placed on the conductive adhesive 4. The conductive adhesive 4 is then heated. At this time, the binder of the conductive adhesive 4 melts, the conductive fillers come into contact with each other, and these are sandwiched between the lower surface electrode 15 of the LED chip 1 and the uppermost layer (Au layer) 133 of the mounting pad 103. Is done. As a result, electrical conduction between the LED chip 1 and the mounting pad 103 is achieved. Then, when the conductive adhesive 4 is cooled, the binder solidifies while adhering between the LED chip 1, the mounting pad 103, and the conductive filler due to its viscosity. In this way, the LED chip 1 is mounted on the mounting pad 103.

【0006】

[Problems to be Solved by the Invention]

However, as described above, the uppermost layer 133 of the mounting pad 3 is formed of Au, and since Au is a relatively stable metal, it causes a thermochemical reaction when, for example, the conductive adhesive 4 is heated. For example, it does not firmly bond with the conductive adhesive 4. That is, the bonding force is weak between the Au layer 133 of the mounting pad 103 and the conductive adhesive 4. Therefore, when a shearing force acts in the interface direction between the Au layer 133 of the mounting pad 103 and the conductive adhesive 4, the Au layer 133 of the mounting pad 103 and the conductive adhesive 4 are separated from each other. , LED chip 1 sometimes fell off.

【0007】

In particular, in such an LED chip mounting method, when the conductive adhesive 4 is heated to soften the conductive adhesive 4, the conductive adhesive 4 flows on the mounting pad 103 due to the weight of the LED chip 1. When the conductive adhesive 4 is heated, a part of the binder evaporates and the conductive adhesive 4 shrinks slightly, so that the conductive adhesive 4 solidifies. In many cases, residual stress still acts even after this. As a result, the Au layer 133 of the mounting pad 103 and the conductive adhesive 4 are easily peeled off.

【0008】

The present invention has been conceived under the above circumstances, and is a method for mounting an LED chip and mounting of an LED chip that can prevent peeling between the mounting pad and the conductive adhesive. The challenge is to provide the structure.

【0009】

[Disclosure of Invention]

In order to solve the above problems, the present invention takes the following technical measures.

【0010】

That is, the method for mounting an LED chip provided by the first aspect of the present invention is formed by laminating a plurality of conductor layers on the surface of a substrate so that the bottom layer is a Cu layer and the top layer is an Au layer. It is a method of mounting an LED chip on a mounted mounting pad via a conductive adhesive, and a recess having a size capable of accommodating the LED chip is provided in a portion of the mounting pad corresponding to the LED chip. The Cu layer is formed so as to be exposed on the bottom surface thereof, and the LED chip is placed on the Cu layer via a conductive adhesive, and then the conductive adhesive is heated and solidified. There is.

【0011】

Here, it is assumed that the conductive adhesive is of a type that is formed into a paste at room temperature and is solidified by being cooled after heating.

【0012】

In the first aspect of the present invention, the conductive adhesive comes into contact with the Cu layer of the mounting pad, and therefore, when heated, it is common in the Cu layer and the conductive adhesive. The low melting point alloy contained in the above is hydrogen-bonded, whereby they are firmly bonded to each other. Therefore, since the bonding strength between the conductive adhesive and the mounting pad can be improved, it is possible to prevent the conductive adhesive and the mounting pad from peeling off. As a result, it is possible to prevent the LED chip from falling off.

【0013】

The method for mounting an LED chip provided by the second aspect of the present invention is conductive on a mounting pad formed by laminating a plurality of conductor layers on the surface of a substrate so that the uppermost layer is an Au layer. It is a method of mounting an LED chip via a sex adhesive, in which a groove having a predetermined depth is formed in a portion of the mounting pad corresponding to the LED chip, and the conductive adhesive enters the inside of the groove. In this way, the conductive adhesive is applied onto the mounting pad, the LED chip is placed on the conductive adhesive, and then the conductive adhesive is heated and solidified.

【0014】

In a preferred embodiment, a plurality of the grooves may be formed so as to radiate from a portion corresponding to the center of the LED chip in the mounting pad.

【0015】

In a preferred embodiment, the groove may be formed so that the surface of the substrate is exposed on the bottom surface thereof.

【0016】

In the second aspect of the present invention, when the conductive adhesive is solidified, a part of the bottom surface of the LED chip and the Au layer are adhered, and a part of the solidified conductive adhesive is an LED. It becomes a protrusion protruding from the bottom surface of the chip and extends into the groove. Therefore, when a shearing force acts in the surface direction of the mounting pad (direction along the bottom surface of the LED chip), not only the adhesive force between the bottom surface of the LED chip and the Au layer but also the rigidity of the protrusion described above Thereby, it is possible to prevent the conductive adhesive and the mounting pad from shifting in the interface direction thereof, and it is possible to resist the above-mentioned shearing force. Therefore, it is possible to prevent the conductive adhesive and the mounting pad from peeling off, and as a result, it is possible to prevent the LED chip from falling off.

【0017】

The LED chip mounting structure provided by the third aspect of the present invention is characterized in that it is manufactured by the LED chip mounting method according to the first aspect or the second aspect of the present invention. Therefore, the same effect as described above can be obtained with respect to the method of mounting the LED chip according to the first aspect and the second aspect of the present invention.

【0018】

Other features and advantages of the invention of the present application will become clearer from the following description of embodiments of the invention.

【0019】

BEST MODE FOR CARRYING OUT THE INVENTION

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

【0020】

FIG. 1 is a schematic plan view showing an example of the mounting structure of the LED chip according to the present invention, and FIG. 2 is an enlarged cross-sectional view taken along the line II-II of FIG. In these figures, the same reference numerals are given to the members, parts, and the like shown in FIGS. 7 and 8 showing the conventional examples.

【0021】

In the LED chip mounting structure A shown in FIGS. 1 and 2, the LED chip 1 is mounted on a mounting pad 3 formed on the surface of the substrate 2 via a conductive adhesive 4. The mounting structure A of the LED chip is applied to, for example, an IrDA-compliant infrared data communication module, so that the mounting pad 3 can reflect the light emitted from the side surface of the LED chip 1. It is formed so as to be considerably wider than the occupied area of the LED chip 1 in a plan view (about twice or more in terms of area ratio).

【0022】

The LED chip 1 has a substantially rectangular shape in a plan view and has a predetermined thickness. As shown in FIG. 2, the LED chip 1 has an n-type (or p-type) semiconductor layer 11 and a p-type (or n-type) semiconductor layer 11. ) A semiconductor layer 12 and a light emitting layer 13 interposed between them are provided. The upper surface and the lower surface of the LED chip 1 are provided with an upper surface partial electrode 14 and a lower surface full surface electrode 15 formed by, for example, vapor deposition of a conductor metal, and when energized, the light emitted by the light emitting layer 13 is emitted. It is configured to emit from the top and side surfaces. As the LED chip 1, in the present embodiment, a LED chip 1 having a rectangular bottom surface having a side of about 0.35 mm is used.

【0023】

The substrate 2 is formed of an insulator such as a glass epoxy resin, and a wiring pattern 21 is formed on the surface of the substrate 2 as shown in FIG. The wiring pattern 21 is formed by etching a copper foil provided on the entire surface of the substrate 2.

【0024】

The mounting pad 3 is formed by laminating a plurality of conductor layers on the surface of the substrate 2. In the mounting structure A of the LED chip, as shown in FIG. 2, the bottom layer 31, the intermediate layer 32, and the maximum are formed. It has a three-layer structure consisting of the upper layer 33. The bottom layer 31 is arranged at an appropriate position when forming the wiring pattern 21, and is formed of Cu. The uppermost layer 33 is smoothly formed by Au having excellent reflection, and is configured so that the light from the side surface of the LED chip 1 can be efficiently used. The intermediate layer 32 is formed of Ni. In the present embodiment, the thicknesses of the Cu layer 31, the Ni layer 32, and the Au layer 33 are about 30 μm to 50 μm, about 3 μm to 8 μm, and about 0.5 μm to 2.0 μm, respectively. Further, the mounting pad 3 is formed so as to have a substantially circular shape with a diameter of about 1 mm so that the cross-sectional shape of the light flux emitted above the mounting structure A of the LED chip is circular.

【0025】

As shown in FIG. 1, the mounting pad 3 has a recess 30 formed in a portion corresponding to the LED chip 1, that is, a central portion in a plan view. The recess 30 is formed so as to be large enough to accommodate the LED chip 1 and to expose the Cu layer 31 on the bottom surface as shown in FIG. Such a recess 30 is, for example, removed by a laser beam so as to hollow out a part of the Ni layer 32 and the Au layer 33, or pattern etching when the Ni layer 32 and the Au layer 33 are formed on the Cu layer 31. It is formed by etching.

【0026】

The conductive adhesive 4 is formed by, for example, mixing a large number of conductive fillers having predetermined metal particles and a low melting point alloy, a binder made of a paste-like epoxy resin, and various additives. It is a thing. Such a conductive adhesive 4 is in the form of a paste at room temperature, but solidifies when cooled after heating. In the present embodiment, as the conductive adhesive 4, an Ag paste in which the predetermined metal particles are Ag particles having excellent electrical conductivity is used.

【0027】

Next, a method of mounting the LED chip 1 on the mounting pad 3 will be described.

【0028】

To mount the LED chip 1 on the mounting pad 3, first, the conductive adhesive 4 is applied to the bottom surface of the recess 30 of the mounting pad 3, that is, on the Cu layer 31.

【0029】

Next, the LED chip 1 is placed on the conductive adhesive 4 so as to be housed in the recess 30 with the bottom surface electrode 15 facing down. At this time, the LED chip 1 is temporarily fixed so as not to be easily displaced due to the viscosity of the conductive adhesive 4.

【0030】

The conductive adhesive 4 between the LED chip 1 and the mounting pad 3 is then heated. At this time, the binder of the conductive adhesive 4 melts and a part of it evaporates, and the low melting point alloy of the conductive filler melts. As a result, the conductive adhesive 4 is compressed by the weight of the LED chip 1, the conductive fillers come into contact with each other, and these are sandwiched between the lower surface electrode 15 of the LED chip 1 and the Cu layer 31. , Electrical conduction between the LED chip 1 and the mounting pad 3 is achieved. Then, when the conductive binder 4 is cooled, the binder solidifies while adhering between the LED chip 1, the mounting pad 3, and the conductive filler due to its viscosity, and the LED chip 1 is die-bonded onto the mounting pad 3. LED.

【0031】

Here, the melted low melting point alloy causes a hydrogen bond with the Cu layer 31, and is firmly bonded to the Cu layer 31. As a result, the bonding strength between the conductive adhesive 4 and the mounting pad 3 can be improved. Therefore, even if a shearing force acts in the interface direction between the conductive adhesive 4 and the mounting pad 3, it can be resisted. As a result, peeling between the conductive adhesive 4 and the mounting pad 3 can be prevented, and the LED chip 1 can be prevented from falling off.

【0032】

Further, the conductive adhesive 4 softened by melting the low melting point alloy and the binder stays in the recess 30 of the mounting pad 3 and is prevented from spreading so as to flow on the mounting pad as in the conventional example. As a result, the conductive adhesive 4 has a relatively large thickness when solidified, so that it is possible to prevent residual stress from being generated inside the conductive adhesive 4. Therefore, it is possible to more reliably prevent the conductive adhesive 4 and the mounting pad 3 from peeling off. In this case, as described above, the conductive adhesive 4 has a relatively large thickness between the LED chip 1 and the mounting pad 3, but the LED chip 1 is located in the recess 30 of the mounting pad 3. Since it is in the housed state, it is possible to prevent the thickness of the mounting structure A of the LED chip from becoming large as a whole.

【0033】

FIG. 3 is a schematic plan view showing another example of the mounting structure of the LED chip according to the present invention, and FIG. 4 is an enlarged cross-sectional view taken along the line IV-IV of FIG. Further, FIG. 5 is a schematic plan view showing another example of the mounting structure of the LED chip according to the present invention, and FIG. 6 is an enlarged cross-sectional view taken along the line VI-VI of FIG. In the following, elements that are the same as or similar to those of the previous embodiment (LED chip mounting structure A) are designated by the same reference numerals as those of the previous embodiment.

【0034】

The LED chip mounting structure B shown in FIGS. 3 and 4 is different from the LED chip mounting structure A in that the mounting pad 3B is provided in place of the mounting pad 3 above.

【0035】

As shown in FIG. 3, the mounting pad 3B has a groove portion 30B having a predetermined depth formed in a portion corresponding to the LED chip 1. Specifically, four grooves 30B extend radially from the portion of the mounting pad 3B corresponding to the center of the LED chip 1 (that is, the center of the mounting pad 3B) toward the four corners of the LED chip. It is formed. Further, as shown in FIG. 4, each groove portion 30B is formed so that the surface of the substrate 2 is exposed on the bottom surface thereof, and the depth thereof is equal to the thickness of the mounting pad 3B. The mounting structure B of this LED chip has a configuration in which the groove portions 30B are separated from each other at the center of the mounting pad 3B, but as shown in FIGS. 5 and 6, the four groove portions 30B'are the mounting pads. It may be configured to be connected to each other at the center of 3B. However, the area corresponding to the LED chip 1 in the mounting pad 3B should not be the groove portion 30B', and the LED chip 1 should be placed on the Au layer 33.

【0036】

Such groove portions 30B and 30B'are removed so as to hollow out a part of Cu layer 31, Ni layer 32 and Au layer 33 by, for example, laser light, similarly to the recess 30 in the mounting structure A of the LED chip. It is formed by pattern etching when forming the Cu layer 31, Ni layer 32, and Au layer 33 on the substrate 2.

【0037】

Next, a method of mounting the LED chip 1 on the mounting pad 3B will be described.

【0038】

To mount the LED chip 1 on the mounting pad 3B, first apply the conductive adhesive 4 to the central portion of the mounting pad 3B. At this time, the conductive adhesive 4 is made to enter the inside of each groove portion 30B, 30B'of the mounting pad 3B.

【0039】

Next, the LED chip 1 is placed on the conductive adhesive 4 at the center of the mounting pad 3B with the bottom surface electrode 15 facing down.

【0040】

Then, the conductive adhesive 4 between the LED chip 1 and the mounting pad 3 is heated and then cooled to solidify it. At this time, when the conductive adhesive 4 is heated to melt the low melting point alloy of the binder and the conductive filler, the conductive fillers come into contact with each other and these are the lower surface electrode 15 of the LED chip 1 and the Au layer. Intervening between 33, this achieves electrical conduction between LED chip 1 and mounting pad 3B.

【0041】

Further, the melted binder and the low melting point alloy of the conductive filler are fused and firmly bonded to the bottom surface of each groove portion 30B, 30B', that is, the surface of the substrate 2. Then, the conductive adhesive 4 solidifies in each of the groove portions 30B and 30B', so that a protrusion having rigidity in the cross-sectional direction is formed on the bottom surface of the LED chip 1. Therefore, when a shearing force acts in the interface direction between the conductive adhesive 4 and the mounting pad 3B (the surface direction of the mounting pad 3B), the adhesive force between the conductive adhesive 4 and the Au layer 33 Not only that, the rigidity of the protrusions described above can prevent the conductive adhesive 4 from shifting in the interface direction with respect to the mounting pad 3B, and can resist the shearing force. As a result, peeling between the conductive adhesive 4 and the mounting pad 3B can be prevented, and the LED chip 1 can be prevented from falling off.

【0042】

Further, in the mounting structure of the LED chip, a resin package is generally formed on the substrate 2 so as to cover the LED chip. However, in the mounting structure B of the LED chip, the groove portions 30B and 30B are formed on the mounting pad 3B. Since the is formed, when the resin package is formed, the molten resin flows into the grooves 30B and 30B and is firmly bonded to the conductive adhesive 4 in the grooves 30B and 30B . Thereby, the adhesion between the resin package and the mounting pad 3B can be improved. Therefore, it is possible to prevent the light from the LED chip 1 reflected by the mounting pad 3B from being diffusely reflected at the interface between the mounting pad 3B and the resin package, and the light emitted by the LED chip 1 can be efficiently emitted. It can be used.

【0043】

Of course, the scope of the present invention is not limited to the above-described embodiment. For example, in the mounting structure B of the LED chip, four groove portions 30B and 30B'are formed so as to extend radially from the portion corresponding to the center of the LED chip 1 in the mounting pad 3B, but the present invention is limited to this. However, as long as the protrusions having a certain degree of rigidity in the cross-sectional direction can be formed on the bottom surface of the LED chip 1 by these groove portions 30B and 30B', the shape and the number thereof can be arbitrary.

[Simple explanation of drawings]

[Figure 1]

It is a schematic plan view which shows an example of the mounting structure of the LED chip which concerns on this invention.

[Figure 2]

It is an enlarged cross-sectional view along the line II-II of FIG.

[Fig. 3]

It is a schematic plan view which shows another example of the mounting structure of the LED chip which concerns on this invention.

[Fig. 4]

It is an enlarged cross-sectional view along the IV-IV line of FIG.

[Fig. 5]

It is a schematic plan view which shows another example of the mounting structure of the LED chip which concerns on this invention.

[Fig. 6]

It is an enlarged sectional view along the VI-VI line of FIG.

[Fig. 7]

It is a schematic plan view which shows an example of the mounting structure of the conventional LED chip.

[Fig. 8]

It is an enlarged cross-sectional view along the line VIII-VIII of FIG.

[Explanation of symbols]

1 LED chip 2 board 3, 3B mounting pad 4 Conductive adhesive 30 recess 30B, 30B'groove 31 Cu layer 33 Au layer A, B LED chip mounting structure