Source: https://patents.justia.com/patent/20060270078
Timestamp: 2020-04-06 15:49:36
Document Index: 585575000

Matched Legal Cases: ['Application No. 2005', 'art 19', 'art 19', 'art 59', 'art 59', 'art 59']

US Patent Application for Method of fabricating light emitting diode package Patent Application (Application #20060270078 issued November 30, 2006) - Justia Patents Search
Justia Patents US Patent Application for Method of fabricating light emitting diode package Patent Application (Application #20060270078)
The invention relates to an LED package and proposes a method of fabricating an LED package including steps of providing a package substrate having a mounting area of an LED and a metal pattern to be connected with the LED, and plasma-treating the package substrate to reform at least a predetermined surface area of the package substrate where a resin-molded part will be formed. The method also includes mounting the LED on the mounting area on the substrate package and electrically connecting the LED with the metal pattern, and forming the resin-molded part in the mounting area of the LED to seal the LED package.
This application claims the benefit of Korean Patent Application No. 2005-44519 filed on May 26, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
Referring to FIG. 1, the LED package 10 includes a lower substrate 11 and an upper substrate 12 having a cavity formed therein. The lower substrate 11 has adequate metal patterns such as lead frames 14a and 14b, conductive vias 15a and 15b, and bonding pads 16a and 16b. An LED 18 is mounted in a mounting area defined by a cavity and can be electrically connected to the lead frames 14a and 14b via connecting means like wires. A resin-molded part 19 is formed in the mounting area with the LED 18 mounted therein. The resin-molded part 19 typically has functions of protecting the LED 18, and with a specific phosphor contained therein, of converting a wavelength.
The present invention has been made to solve the foregoing problems of the prior art and it is therefore an object of the present invention to provide a new method of fabricating a light emitting diode (LED) package in which the surface of a package substrate is reformed to firmly bond a resin-molded part and the package substrate at an interface therebetween.
The package substrate may be a silicon substrate, in which case, the step of plasma-treating is performed in a vacuum state with inert gas as a reactive gas at an output power of 700 W to 1500 W for 1 to 3 hours. Under such plasma treatment conditions, it is preferable that a silicon substrate is kept at a temperature ranging from 80° C. to 120° C.
In another embodiment of the present invention, heat treatment can be performed instead to obtain reforming effect similar to that of the plasma treatment. This method includes steps of: providing a silicon package substrate having a mounting area of an LED and a metal pattern to be connected with the LED; heat-treating the package substrate in an atmosphere of inert gas at a temperature ranging from about 300° C. to 400° C. for 1 to 3 hours in order to reform at least a predetermined surface area of the package substrate where a resin-molded part will be formed; mounting the LED on the mounting area of the LED and electrically connecting the LED with the metal pattern; and forming the resin-molded part in the mounting area of the LED to seal the LED package.
As shown in FIG. 3, the plasma treatment apparatus 30 according to the present invention includes a reactive chamber 31 for forming plasma. The reactive chamber 31 has a pedestal 36 for supporting the package substrate 35. When high power is applied by a power supplier 32, reactive gas forms glow-discharge plasma 34 in the reactive chamber 31 which is then impinged on the substrate to reform the surface of the substrate. For such reactive gas, it is preferable to use inert gas such as N2 or H2 in order to prevent undesired chemical reaction with the package substrate of for example silicon. The plasma treatment is performed at an appropriate level of supplied power and for an appropriate time so that the substrate surface is reformed to improve adhesion strength without damaging the substrate. The appropriate range is preferably 700 W to 1500 W, and more preferably, 800 W to 1000 W. The time for plasma treatment is preferably 1 to 3 hours. In addition, the effect of plasma can be accelerated when the substrate is heated. Here, the preferable temperature range of the substrate can be 80° C. to 120° C.
The present invention can be applied to various forms of LED packages which require heterogeneous bonding of a resin-molded part with a substrate. Particularly, the package substrate can be a structure in which a predetermined depth of cavity is formed in a single substrate, capable of reflecting. It can also be a structure with an upper substrate with a cavity formed therein stacked on a lower substrate with metal patterns formed thereon as shown in FIGS. 4(a) and 4(b).
FIGS. 4(a) and 4(b) are perspective views illustrating an upper substrate and a lower substrate at wafer level adopted in the LED package according to one embodiment of the invention.
As shown in FIG. 4(a), a wafer 41 for the lower substrate has metal patterns formed on a mounting area 41a in each individual package unit. The metal patterns are illustrated as lead frames 44a and 44b on an upper surface thereof, but can be understood that vias electrically connecting bonding pads are formed on an undersurface thereof and the lead frames as shown in FIG. 1. The wafer 41 for the lower substrate can be inserted into a reactive chamber shown in FIG. 3 and plasma-treated before it is cut into individual packages. Surface-reforming is required for only the mounting area 41a where the resin-molded part will be formed thereon later, but since the plasma treatment according to the present invention is performed in a degree that does not damage the substrate, it is more advantageous in terms of the process to perform the plasma treatment at wafer level.
As shown in FIG. 4b, plasma treatment can also be performed on a wafer 42 for an upper substrate before it is cut into individual packages. The wafer 42 for the upper substrate has a cavity C defined as a mounting area in each individual package unit, and the cavity C has a side wall 42a that is a sloped surface faced upward to reflect. Therefore, the sloped side wall 42a of the wafer for the upper substrate can be surface-reformed as well during the plasma treatment without being adjusted in its angle.
With reference to FIG. 5, the LED package 50 includes the lower substrate 51 with metal patterns formed thereon and the upper substrate 52 with a cavity formed therein. The upper substrate 52 and the lower substrate 51 can be a silicon substrate, respectively. The metal patterns formed on the lower substrate 51 can be composed of lead frames 54a and 54b, bonding pads 56a and 56b, and conductive vias 55a and 55b electrically connecting each of the lead frames 54a and 54b with each of the bonding pads 56a and 56b. The upper substrate 52 has the cavity defining the mounting area of the LED. The side wall of the cavity is a sloped surface facing upward, which can be utilized as a reflective surface.
In addition, as shown in FIGS. 4a and 4b, plasma treatment (or heat treatment) can be performed on the upper substrate 52 and the lower substrate 51 at wafer level to reform the surface of the upper and lower substrates 52 and 51. The surface becomes finely roughened after plasma-treated, having a larger contact area.
The LED 58 is mounted in the mounting area defined by the cavity and electrically connected to the lead frames 54a and 54b. A resin-molded part 59 is formed in the mounting area with the LED 58 mounted therein. The resin-molded part 59 is formed on the reformed substrate surface, and thus has high adhesion strength to the substrate and high thermal stability. Such a resin-molded part 59 may be made of epoxy resin, silicone resin, urethane resin, or a compound thereof, and specific phosphors can be added thereto depending on the needs.
First, as shown in FIGS. 4(a) and 4(b), the upper substrate and the lower substrate for the LED package were fabricated using silicon wafers and plasma treatment was performed on the substrates. For the reactive gas used in the plasma treatment, H2 and N2 were used at a ratio of 1:1.5. The plasma treatment was performed with vacuum pressure of 10−5 Torr to 10−6 Torr, and supply power of 800 W to 1000 W for 2 hours. The temperature of the substrate was maintained at about 100° C.
In this example, as shown in FIGS. 4(a) and 4(b), the upper and lower substrates were fabricated using silicon wafers, and disposed in a heating furnace to be heat-treated. The heat treatment was performed with the reactive gas of H2 and N2 mixed at a ratio of 1:1.5, at a temperature of 350° C. to 370° C. for about 2 hours.
In this comparative example, the upper substrate and the lower substrate were fabricated using the silicon wafers as shown in FIGS. 4 (a) and 4(b). Thirty LED packages were fabricated as illustrated in FIG. 4(a), but without the heat treatment or the plasma treatment being performed on the substrates. In the same fashion as in Example 1 and Example 2, resin with epoxy and silicone mixed at a ratio of 40 wt %:60 wt % was used for the resin-molded part.
The thirty samples obtained from Example 1, Example 2 and Comparative Example were evaluated in the adhesion strength of the resin-molded part (Table 1), the thermal stress generated at 100° C./min, and the amount of moisture absorption (Table 3) inside the package (Ten packages from each Example were evaluated for each of the above evaluation items).
TABLE 1 Comparative Example 1 Example 2 Example (N/cm2) (N/cm2) (N/cm2)
1 223 620 367 2 225 618 370 3 223 622 372 4 238 619 373 5 234 623 369 6 229 623 371 7 230 618 369 8 232 620 372 9 227 621 375 10 225 618 371 Mean 228.6 620.2 370.9
Table 2 below shows the effect due to the differences in thermal expansion coefficients between the resin-molded part and the substrate. In this experiment, the thermal stress generated at the interface at 100° C./min was measured. As shown in Table 2, Examples 1 and 2 exhibit excellent thermal stability compared with Comparative Example. Example 2 with heat treatment exhibits 21% less thermal stress on average than Comparative Example. Particularly, Example 1 with plasma treatment exhibits 30% less thermal stress on average than Comparative Example, which is an even more improved result from the case of heat treatment.
TABLE 2 Comparative Example 1 Example 2 Example(N/cm2) (N/cm2) (N/cm2)
1 360 252 285 2 368 255 280 3 362 253 282 4 369 258 283 5 363 254 289 6 363 259 281 7 368 250 289 8 360 252 282 9 361 257 285 10 368 255 281 Mean 364.2 254.5 283.7
Table 3 below shows the measurement results of the level of adhesion between the resin-molded part and the package substrate. In this experiment, each sample was maintained in an environment of relative humidity of 90%, and 35° C. for 7 days, and the moisture amount was measured in the mounting area of the LED. As shown in Table 3, Examples 1 and 2 show superior levels of adhesion compared with Comparative Example. In Example 2 with heat treatment, the moisture was 0.062 wt % less on average than the Comparative Example. Particularly, in Example 1 with plasma treatment, the moisture was 0.096% less on average than Comparative Example, which is an even more improved result from the case of heat treatment.
TABLE 3 Comparative Example 1 Example 2 Example(wt %) (wt %) (wt %)
1 0.13 0.04 0.08 2 0.11 0.05 0.09 3 0.14 0.06 0.08 4 0.15 0.05 0.09 5 0.17 0.04 0.08 6 0.14 0.05 0.10 7 0.15 0.06 0.09 8 0.16 0.07 0.08 9 0.18 0.07 0.10 10 0.17 0.05 0.09 Mean 0.150 0.054 0.088
As the results from the experiments indicate, plasma treatment allows significantly improved adhesion strength, thermal stability and level of adhesion. Heat treatment also yields similar effects. To obtain a desired level of effects with the heat treatment, however, it is required that the heat treatment is performed in an inert gas atmosphere, at about 300 to 400° C. for 1 to 3 hours.
7. The method according to claim 6, wherein the step of plasma-treating is performed with a silicon substrate kept at a temperature ranging from 80° C. to 120° C.
heat-treating the package substrate in an atmosphere of inert gas at a temperature ranging from about 300° C. to 400° C. for 1 to 3 hours in order to reform at least a predetermined surface area of the package substrate where a resin-molded part will be formed;
Publication number: 20060270078
Patent Grant number: 7371603
Inventors: Yong Kim (Suwon), Seog Choi (Seoul), Hyoung Kim (Suwon), Yong Kim (Seoul)
Application Number: 11/439,189