Package substrate and LED flip chip package structure

A package substrate includes: an insulating substrate, a first and a second soldering pads spacedly disposed on a first surface of the insulating substrate, a first and a second electrodes spacedly disposed on an opposite second surface of the insulting substrate. The first and the second soldering pads are electrically connected to the first and the second electrodes respectively. Moreover, a first and a second grooves are defined on the first surface of the insulating substrate, the first and the second grooves are spaced from each other and disposed between the first and the second soldering pads. The invention further provides a LED flip chip package structure including the package substrate, a LED flip chip and fluorescent glue. The invention adds the grooves in the spacing between the soldering pads as a buffer space for melted solder flowing during reflow soldering process and therefore can relieve short-circuit phenomenon.

FIELD OF THE INVENTION

The invention relates to a flip chip package technical field, and more particularly to a package substrate and a LED flip chip package structure.

BACKGROUND OF THE INVENTION

As a distance between a positive (P) electrode and a negative (N) electrode of a LED flip chip is around 75˜150 micrometers (μm), in a conventional design of ceramic package substrate used in a flip chip technique, when performing reflow soldering after die bonding and/or when the LED flip chip package structure undergoing a second reflow soldering of a back-end surface mounted technology (SMT) process, a short-circuit phenomenon may be easily occurred resulting from solders melting and flowing, which would result in the LED malfunction.

Specifically, referring toFIG. 1, it is a structural view of a conventional LED flip chip package structure. As shown inFIG. 1, a LED flip chip package structure10includes: a ceramic substrate11, soldering pads12a,12b, metal-filled holes13, electrodes14a,14b, a LED flip chip15, a bowl-shaped structure18and a fluorescent glue19. The soldering pads12a,12bare disposed on an upper surface of the ceramic substrate11and spaced from each other, the electrodes14a,14bare disposed on a lower surface of the ceramic substrate11and spaced from each other, the soldering pads12a,12brespectively are electrically connected to the electrodes14a,14bby the metal-filled holes13. The LED flip chip15is disposed with a positive electrode151and a negative electrode153, and the positive electrode151and the negative electrode153respectively are electrically connected to the soldering pads12a,12bby solders16. The bowl-shaped structure18is disposed on the upper surface of the ceramic substrate11and surrounding the LED flip chip15. The fluorescent glue19is disposed in the bowl-shaped structure18and covering the LED flip chip.

Referring toFIG. 2, it is a microscopic photograph showing the soldering pads in the LED flip chip package structure shown inFIG. 1. As seen fromFIG. 1andFIG. 2, it can be found that since a distance between the soldering pads12a,12bis relatively short, during a reflow soldering process, the solders16would be melted and flow into a region between the soldering pad12aand the soldering pad12band thereby cause the soldering pad12aand the soldering pad12bto be electrically connected with each other, as a result, a short-circuit phenomenon as shown inFIG. 2would be occurred.

SUMMARY OF THE INVENTION

Therefore, aiming at the insufficiency in the foregoing related art, the invention provides a package substrate and a LED flip chip package structure.

Specifically, a package substrate according to an embodiment of the invention includes: an insulating substrate, a first soldering pad and a second soldering pad spacedly disposed on a first surface of the insulating substrate, a first electrode and a second electrode spacedly disposed on a second surface opposite to the first surface of the insulting substrate. The first soldering pad and the second soldering pad are electrically connected to the first electrode and the second electrode respectively. Moreover, a first groove and a second groove are defined on the first surface of the insulating substrate, the first groove and the second groove are spaced from each other and located between the first soldering pad and the second soldering pad.

In an embodiment of the invention, a depth of each of the first groove and the second groove is in a range from 20 micrometers to 30 micrometers.

In an embodiment of the invention, each of the first groove and the second groove includes a main part and an extension part laterally protruding from the main part.

In an embodiment of the invention, the extension part is substantially round.

In an embodiment of the invention, the first groove is one of an L shape and a reversed L shape, and the second groove is the other one of the L shape and the reversed L shape.

In an embodiment of the invention, a distance between the first groove and the second groove is 10%˜50% of a distance between the first soldering pad and the second soldering pad.

In an embodiment of the invention, a length of the first groove is approximately 95% of a length of a side of the first soldering pad adjacent to the first groove, and a length of the second groove is approximately 95% of a length of a side of the second soldering pad adjacent to the second groove.

In an embodiment of the invention, a depth of each of the first groove and the second groove is 10%˜15% of a thickness of the insulating substrate.

In an embodiment of the invention, the package substrate further includes a bowl-shaped structure disposed on the first surface of the insulating substrate, and the bowl-shaped structure is disposed surrounding the first soldering pad and the second soldering pad as well as the first groove and the second groove.

In an embodiment of the invention, a material of the bowl-shaped structure is a high reflective plastic such as silicone molding compound or epoxy molding compound.

In an embodiment of the invention, the insulating substrate is a ceramic substrate, the first groove and the second groove are formed by sintering directly, or formed by laser engraving after the ceramic substrate being sintered.

Moreover, a LED flip chip package structure according to an embodiment of the invention includes a LED flip chip, fluorescent glue and the package substrate according to any one of the above described embodiments. A positive electrode and a negative electrode of the LED flip chip respectively are electrically connected to the first soldering pad and the second soldering pad by solder, and the fluorescent glue is disposed covering the LED flip chip.

In an embodiment of the invention, the first soldering pad and the second soldering pad respectively are electrically connected to the first electrode and the second electrode by metal-filled holes respectively disposed rightly below the positive electrode and the negative electrode of the LED flip chip.

Sum up, the above embodiments of the invention define grooves in the spacing between the soldering pads on the surface of the insulating substrate (e.g., a ceramic substrate) as a buffer space for solder flowing after being melted during a reflow soldering process, so that the short-circuit phenomenon can be relieved consequently.

By the following detailed description with reference to accompanying drawings, other aspects and features of the invention will become apparent. However, it should be understood that, the drawings only are for the purpose of explanation and not as limiting the scope of the invention, and the scope of the invention should refer to the appended claims. It also be appreciated that, unless otherwise indicated, the drawings are not necessarily drawn to scale, they are merely trying to conceptually illustrate the structures and procedures described herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention are described in detail with reference to the accompanying drawings as follows to better understand the objectives, features and advantages of the invention.

Referring toFIG. 3andFIG. 4together, a LED flip chip package structure30according to an embodiment of the invention includes: an insulating substrate31, soldering pads32a,32b, metal-filled holes33, electrodes34a,34b, a LED flip chip35, a bowl-shaped structure38and a fluorescent glue39. The insulating substrate31, the soldering pads32a,32b, the metal-filled holes33and the electrodes34a,34band even the bowl-shaped structure38together form a package substrate of the embodiment.

A material of the insulating substrate31is ceramic such as aluminum oxide (Al2O3), but the invention is not limited to this, other ceramic material can be adopted instead. The soldering pads32a,32bare disposed on an upper surface of the insulating substrate31and spaced from each other, and further the soldering pads32a,32bfor example are made of copper. The electrodes34a,34bare disposed on a lower surface of the insulating substrate31and spaced from each other, and further the electrodes34a,34bfor example are made of copper. Furthermore, the soldering pad32ais electrically connected to the electrode34aby the metal-filled hole33, the soldering pad32bis electrically connected to the electrode34bby the other metal-filled hole33, and each of the metal-filled holes33penetrates through the insulating substrate31. A positive electrode351and a negative electrode353of the LED flip chip35respectively are electrically connected to the soldering pad32aand the soldering pad32bdisposed on the upper surface of the insulating substrate31by solders36, and each of the metal-filled holes33is preferably disposed rightly below the positive electrode351and the negative electrode353of the LED flip chip35. The bowl-shaped structure38is disposed around the soldering pads32a,32bas well as the LED flip chip35, a material of the bowl-shaped structure38for example is a material with high reflectivity such as silicone molding compound (SMC) or epoxy molding compound (EMC), but the invention is not limited to this. The fluorescent glue39is disposed in the bowl-shaped structure38and covering the LED flip chip35. The fluorescent glue39can be prepared by dispersing fluorescent powers in resin or by coating an inner surface of a resin layer with a fluorescent layer.

In addition, a groove311and a groove313are spacedly formed in a region (also referred to as spacing between the soldering pad32aand the soldering pad32b) between the soldering pad32aand the soldering pad32bon the upper surface of the insulating substrate31, so that during a reflow soldering process, if the solders36being melted flow towards the region between the soldering pads32a,32b, the grooves311,313would act as spatial buffers so as to prevent the occurrence of short-circuit phenomenon. In the illustrated embodiment, the groove311and the groove313can be formed during sintering the insulating substrate31such as ceramic substrate, or formed by laser engraving after sintering the ceramic substrate.

To be more specific, a depth H of each of the groove311and the groove313preferably is 10%˜15% of a thickness T of the insulating substrate31. Typically, the depth H of each of the groove311and the groove313is in a range from 20 micrometers to 30 micrometers. A distance D2between the groove311and the groove313preferably is 10%˜50% of a distance between the soldering pad32aand the soldering pad32b.

Moreover, referring toFIG. 4, with regard to each of the groove311and the groove313, the groove311is taken as an example, it includes a main part311aand an extension part311blaterally protruding from the main part311a. The distance D2between the groove311and the groove313is defined as a transverse distance between respective main parts of the grooves311,313. Preferably, the groove311and the groove313respectively are L-shaped and reversed L-shaped, the groove311is taken as an example, the extension part311bof which is formed by laterally extending from an end of the main part311a. Moreover, it is noted that extension parts of the grooves311,313are not restricted to be formed by laterally protruding from the ends of the respective main parts as shown inFIG. 4, and can be like grooves511,513as shown inFIG. 5that extension parts of which are formed by laterally protruding from middle portions between two ends of respective main parts, the groove511is taken as an example, which includes a main part511aand an extension part511blaterally protruding from the main part511a. Additionally, it can be found fromFIG. 4that the extension part311bof the groove311and the extension part (not labeled inFIG. 4) of the groove313are staggeredly disposed in the longitudinal direction (i.e., the extending direction of the main part). Similarly, the extension part511bof the groove511and the extension part (not labeled inFIG. 5) of the groove513are staggeredly disposed in the longitudinal direction. Furthermore, shapes of the extension parts of the grooves are not limited to those shown inFIG. 4andFIG. 5, and can be other shape such as substantially a round shape shown inFIG. 6instead, i.e., a round shape or an oval shape similar to the round shape.

Referring toFIG. 4again, preferably, a length of the groove311for example is a length L2of its main part311aand is approximately 95% of a length L1of a side of the soldering pad32aadjacent to the groove311; similarly, a length of the groove313for example is a length of its main part and is approximately 95% of a length of a side of the soldering pad32badjacent to the groove313.

In summary, the above embodiments of the invention define grooves in the spacing between the soldering pads on the surface of the insulating substrate such as ceramic substrate as a buffer space for solder flowing after being melted during a reflow soldering process, so that the short-circuit phenomenon can be relieved consequently.

The above description illustrates various exemplary embodiments to explain the invention, and the foregoing exemplary embodiments only are used to help understand the solution of the invention and its core idea. For those skilled persons in the art, various modifications and variations can be made according to the concept of the invention, and therefore the invention needs not be limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.