TWI397967B - Wafer-level reflow apparatuses and fabrication methods for solder balls and flip chip assemblies - Google Patents

Description

Wafer-level reflow soldering apparatus and method of manufacturing solder sphere and flip chip assembly

The present invention relates to a wafer level reflow soldering apparatus and a method of fabricating a semiconductor chip package, and more particularly to a wafer level reflow soldering apparatus and a method of fabricating a solder ball and a flip chip assembly.

The Flip Chip packaging technology flips the wafer and bonds it to the laminated substrate through the metal conductor in a face-down manner. It is widely used in high performance, high speed and high density, and small package size. On the component. The flip chip bonding is to first form a solder bump on the contact pad of the IC wafer, and then reflow the IC wafer on the structure substrate and complete the contact pad alignment, and then reflow heat-treating the solder. The surface tension effect during melting causes the solder to spheroid and complete the bonding of the IC wafer to the substrate. In the flip-chip soldering process, the adhesion between the under bump metal (UBM) and the bump interface, the effect of element diffusion barrier, the wetting ability and the resulting intermetallic compound (IMC) structure all affect long-term reliability. An important factor in testing. Due to the increased wafer area and the use of high-density solder ball connections, the uniformity of solder ball fusion and wafer bonding reflow heat treatment on the wafer becomes very important. When several solder balls that are primarily responsible for transmitting signals fail, they will The electronic components are damaged, so the importance of uniformity in reflow heat treatment cannot be ignored.

General reflow equipment includes hot air reflow furnace, nitrogen reflow furnace, laser reflow furnace, infrared reflow furnace and so on. The single-chip reflow furnace is typically reflowed by SEMIgear's reflow oven in the United States. The solder bumps on the wafer surface are sequentially reflowed by the turntable. On the other hand, the continuous reflow furnace is typical of SIKAMA's reflow oven. The mobile track is used to transport wafers along the conveyor belt with multiple heating/cooling zones. The main engineering objectives of each zone include: a. The preheating zone, the main purpose is to volatilize the solvent in the solder paste. b. The temperature equalization zone, the main purpose is to activate the flux to remove oxides and evaporate excess water. c. The reflow zone, the main purpose is to melt the solder. d. Cooling zone, the main purpose is to join the solder so that the flip chip is integrated with the package substrate.

However, conventional reflow equipment lacks good temperature adjustment and control functions, so when the reflow step is performed, the load of the wafer on the heating plate causes the effect of heating delay. In particular, during the heating and/or cooling process, the wafer experiences a melting point of the solder in the heated region (for example, about 183 ° C), and the surface temperature unevenness of the wafer is particularly remarkable, and the maximum temperature difference across the wafer surface can reach about 30 ° C. The resulting solder melting delay time can be up to about 8-14 seconds, which in turn leads to differences in microstructure of the solder ball array, uneven solder bump height, and bridging of adjacent solder bumps.

In view of this, there is a need in the industry for a wafer-level reflow soldering device that can individually control the temperature on the hot plate to improve the yield of solder bumps on the wafer surface, the reliability of the intermetallic compound (IMC) and solder bumps. degree.

According to an embodiment of the invention, a wafer level reflow soldering apparatus is provided comprising: a plurality of heated regions and a transport belt for transporting a wafer to each heated region. Each heated zone includes: a heating plate having a plurality of heating bodies arranged in a concentric circle; an infrared temperature measuring device; and a controller respectively controlling outputs of the heating bodies, wherein the infrared temperature measuring device monitors a plurality of surfaces of the wafer The temperature of the zone is immediately fed back to the controller to uniformize the solder bumps on the surface of the wafer.

According to another embodiment of the present invention, a method for fabricating a solder ball includes: providing a wafer level substrate structure having a plurality of solder pads on the surface; forming a plurality of solder bumps on the solder pads; The solder bumps are melted into a highly uniform solder sphere by a wafer level reflow device. The wafer level reflow soldering apparatus includes a plurality of heat receiving zones and a conveyor belt for transferring a wafer to each of the heat receiving zones. Each heated zone includes: a heating plate having a plurality of heating bodies arranged in a concentric circle; an infrared temperature measuring device; and a controller respectively controlling outputs of the heating bodies, wherein the infrared temperature measuring device monitors a plurality of surfaces of the wafer The temperature of the zone is immediately fed back to the controller to uniformize the solder bumps on the surface of the wafer.

According to still another embodiment of the present invention, a method for fabricating a flip chip assembly includes: providing a wafer having a solder ball array; and reversing the wafer on a package substrate; The soldering apparatus attaches the reverse-covered wafer to the package substrate, wherein the wafer-level reflow soldering apparatus comprises: a plurality of heat receiving zones and a conveyor belt conveying a wafer to each of the heat receiving zones. Each heated zone includes: a heating plate having a plurality of heating bodies arranged in a concentric circle; an infrared temperature measuring device; and a controller respectively controlling outputs of the heating bodies, wherein the infrared temperature measuring device monitors a plurality of surfaces of the wafer The temperature of the zone is immediately fed back to the controller to uniformize the solder bumps on the surface of the wafer.

In order to make the invention more apparent, the following detailed description of the embodiments and the accompanying drawings are as follows:

The following is a detailed description of the embodiments and examples accompanying the drawings, which are the basis of the present invention. In the drawings or the description of the specification, the same drawing numbers are used for similar or identical parts. In the drawings, the shape or thickness of the embodiment may be expanded and simplified or conveniently indicated. In addition, the components of the drawings will be described separately, and it is noted that the components not shown or described in the drawings are known to those of ordinary skill in the art, and in particular, The examples are merely illustrative of specific ways of using the invention and are not intended to limit the invention.

1 shows a schematic diagram of a wafer level reflow apparatus having multiple heated zones in accordance with an embodiment of the present invention. The wafer level reflow device 10 includes a plurality of heated zones 10a-10l and a conveyor to transport the wafers to the heated zones. The plurality of heat receiving zones include preheating zones 10a-10b, temperature equalizing zones 10c-10e, reflow zones 10f-10i, and cooling zones 10k-10l, wherein the temperature of the reflow zones 10f-10i must be precisely controlled so that The maximum temperature difference in each reflow zone is less than about 1.3 °C.

Figure 2A shows a schematic view of a heating plate in each heated zone in accordance with an embodiment of the present invention. In FIG. 2A, each of the heat receiving regions 20 includes a heating plate 26 having a plurality of heating bodies arranged in a concentric circle, and an infrared temperature measuring device 30a, 30b receiving infrared rays to measure the temperature of each area of the wafer, and a controller 32 controls the output of each heating body, wherein the infrared temperature sensing devices 30a, 30b monitor the temperature of a plurality of regions of the wafer surface and immediately feed back the temperature to the controller 32 to uniformize the surface temperature of the wafer. The heating plate 26 is disposed on the support column 24. A nitrogen gas introduction port 22 introduces nitrogen into the heating pan 26. In one embodiment, the heating plate 26 includes a bottom heating plate 26a, a middle heating plate 26b, and an upper heating plate 26c, wherein each heating plate has a plurality of holes 27 for circulating nitrogen gas 28 to make the temperature in the heated region uniform. . Figure 2A shows a schematic view of a heating plate in each heated zone in accordance with an embodiment of the present invention. The thermocouple 35 is used as the measurement temperature as compared with the conventional heat receiving zone 20', and is placed in the heating plates 26a, 26b, 26c by the elongated heating body, resulting in poor temperature uniformity.

Figure 3 shows a schematic view of a plurality of heating bodies arranged in a concentric circle in accordance with an embodiment of the present invention. In one embodiment, the heating plate 26 has a plurality of heating bodies arranged in a concentric circle, wherein the first group of heating bodies 40a are disposed in a peripheral region of the heating plate 26, and the third group of heating bodies 40c are disposed in a central region of the heating plate. And the second group of heating bodies 40b are disposed between the first group of heating bodies 40a and the third group of heating bodies 40c. For example, the size of the heating plate is, for example, but not limited to, a disk of 8 吋 or 12 ,, wherein the first group of heating bodies 40a are disposed 90 mm from the outer edge of the heating plate, and the second group of heating bodies 40b are disposed at The second group of heating bodies 40c are disposed 150 mm from the outer edge of the heating plate at a distance of 125 mm from the outer edge of the heating plate. In addition, in another embodiment, the first group of heating bodies 40a has three concentric heating bodies, the second group of heating bodies 40b has two concentric heating elements, and the third group of heating bodies 40c has two concentric heatings. body. When the infrared temperature measuring device measures that a certain area of the wafer surface is lower than expected, the controller can be immediately fed back, and the solder bumps on the surface of the wafer are heated to a uniform temperature by increasing the output of the heating body corresponding to the area.

4A-4F are schematic views showing a solder bump reflow process in accordance with an embodiment of the present invention. Referring to FIG. 4A, a substrate 101 is provided with a pad 103. A protective layer 105 is disposed on both ends of the pad 103 to expose a region where the solder ball is disposed in the center. A bump underlayer metal (UBM) layer 107 is formed (e.g., by sputtering), disposed over the substrate 101, covering the regions of the protective layer 105 and the solder balls in the center of the pads.

Referring to FIG. 4B, the steps of applying the photoresist layer 109, mask exposure, and development are sequentially performed to form a patterned photoresist layer 109 to expose the opening region 111 where the solder ball is to be formed. Next, an electroplated bump underlayer metal (UBM) layer 113 (for example, a 5 μm Cu layer and a 3 μm Ni layer) and a solder bump 115 (for example, a 110 μm solder paste) are sequentially deposited in the opening region 111, as shown in FIG. 4C. Shown.

Next, referring to FIG. 4D, the photoresist layer 109 is removed, and then an etching step is performed to remove the under bump metal layer 107, as shown in FIG. 4E. The solder bumps 115 on the wafer level substrate 101 are reflowed by the reflow soldering apparatus with temperature uniform control provided by the embodiment of the present invention to form solder pellets 117 of uniform shape, as shown in FIG. 4F. It should be noted that the solder bump reflow process of the above embodiment is only used to illustrate the application of the wafer level reflow soldering apparatus with multiple heat receiving zones in the embodiment of the present invention, but is not intended to limit the scope of the present invention. It is alternatively applied to the process of other solder bumps.

5A-5D are schematic views showing a reflow process of a flip chip wafer assembly according to another embodiment of the present invention. Referring to FIG. 5A, the wafer 120 on which the array of solder balls 117 have been formed is overturned and infiltrated into the trench 130 containing the flux solution 132 to adhere the flux 122 to the array of solder balls 117, as described in Figure 5B shows.

Referring to FIG. 5C, the flux-attached wafer 120 is attached to a package substrate 140 and aligned with the bond pads 142 of the package substrate. It should be noted that the flux removal and cleaning steps can be selectively applied. The reflow soldering step is performed by the reflow soldering apparatus with uniform temperature control provided by the embodiment of the present invention to form a wafer level flip chip assembly having uniform bonding and goodness, as shown in FIG. 5D. It should be noted that the flip chip wafer reflow process of the above embodiment is only used to illustrate the application of the wafer level reflow soldering apparatus with multiple heat receiving zones in the embodiment of the present invention, and is not intended to limit the scope of the present invention. It can also be applied to the process of other wafer assemblies.

According to an embodiment of the present invention, the reflowing step by the reflow soldering apparatus having uniform temperature control has the advantages of effectively improving the intermetallic compound (IMC) structure and the wafer-free state in the wafer and non-wafer state. The height uniformity of the underlying solder bumps. Moreover, since the ratio of re-reflow is low, the overall height of the wafer is poor. Moreover, since solder bump bridging and irregular bumps are formed less, the solder bump yield can be improved. For example, by using a reflow soldering apparatus having a concentric heating body according to an embodiment of the present invention, solder bumps can be effectively reduced compared to conventional solder bumps having a strip-shaped heating body and a thermocouple controlled reflow furnace. Block shorts, irregular solder bumps, and UBM residue problems, and solder bump yields also significantly increased from 87% to 92%.

The present invention has been disclosed in the above various embodiments, and is not intended to limit the scope of the present invention. Any one of ordinary skill in the art can make a few changes and refinements without departing from the spirit and scope of the invention. . The scope of the invention is defined by the scope of the appended claims.

10. . . Wafer level reflow equipment

10a-10l. . . Multiple heated zones

20. . . Heated area

20’. . . Traditional heated area

twenty two. . . Nitrogen inlet

twenty four. . . Support column

26. . . Heating plate

26a, 26b, 26c. . . Heating plate

27. . . Hole

28. . . Nitrogen

30a, 30b. . . Infrared temperature measuring device

32. . . Controller

35. . . Thermocouple

40a-40c. . . First, second, third group of heating bodies

101. . . Substrate

103. . . Solder pad

105. . . The protective layer

107. . . Bump bottom metal (UBM) layer

109. . . Photoresist layer

111. . . Open area

113. . . Plated bump bottom metal (UBM) layer

115. . . Solder bump

117. . . Solder sphere

120. . . Flip chip

122. . . Flux

130. . . Slot

132. . . Flux solution

140. . . Package substrate

142. . . Mat

1 is a schematic view showing a wafer level reflow soldering apparatus having multiple heat receiving zones according to an embodiment of the present invention.

Figure 2A shows a schematic view of a heating plate in each heated zone in accordance with an embodiment of the present invention.

Figure 2B shows a schematic view of the heating plate in the heated zone of a conventional reflow soldering apparatus.

Figure 3 shows a schematic view of a plurality of concentrically arranged heating bodies in accordance with an embodiment of the present invention.

4A-4F are schematic views showing a solder bump reflow process in accordance with an embodiment of the present invention.

5A-5D are schematic views showing a reflow process of a flip chip wafer assembly according to another embodiment of the present invention.

20. . . Heated area

20’. . . Traditional heated area

twenty two. . . Nitrogen inlet

twenty four. . . Support column

26. . . Heating plate

26a, 26b, 26c. . . Heating plate

27. . . Hole

28. . . Nitrogen

30a, 30b. . . Infrared temperature measuring device

32. . . Controller

Claims (9)

A wafer level reflow soldering apparatus comprises: a plurality of heated regions, each heated region comprising: a heating plate having a plurality of heating bodies arranged in a concentric circle; an infrared temperature measuring device; and a controller respectively controlling the output of each heating body; And a conveyor belt transporting a wafer to each of the heated zones, wherein the temperature of the infrared temperature measuring device measures a plurality of regions of the surface of the wafer, and instantaneously returns the temperature to the controller to cause solder bumps on the surface of the wafer The heating temperature is uniform. The wafer level reflow soldering apparatus of claim 1, wherein the plurality of heat receiving zones comprise a preheating zone, a temperature equalization zone, a reflow zone, and a cooling zone. The wafer level reflow soldering apparatus of claim 1, wherein the infrared temperature measuring device comprises a plurality of buried infrared temperature sensors. The wafer level reflow soldering apparatus according to claim 1, wherein the heating plate comprises an upper heating plate, a middle heating plate, and a bottom heating plate, wherein each heating plate has a plurality of holes for circulating nitrogen gas. The temperature in the heated zone is uniform. The wafer level reflow soldering apparatus according to claim 1, wherein the plurality of heating bodies arranged in the concentric circle comprise a first group of heating bodies disposed in a peripheral region of the heating plate, and a third group of heating bodies disposed. In a central region of the heating plate, and a second group of heating bodies are disposed between the first group of heating bodies and the third group of heating bodies. The wafer level reflow soldering apparatus of claim 5, wherein the heating plate is a 12-inch disk, wherein the first group of heating bodies is disposed 90 mm from the outer edge of the heating plate, the second group The heating body is disposed at a distance of 125 mm from the outer edge of the heating plate, and the third group of heating bodies is disposed 150 mm from the outer edge of the heating plate. The wafer level reflow soldering apparatus of claim 5, wherein the first group of heating bodies has three concentric heating bodies, the second group of heating bodies has two concentric heating bodies, and the third The group heating body has two concentric heating bodies. A method of fabricating a solder ball, comprising: providing a wafer level substrate structure having a plurality of solder pads on a surface of the substrate; forming a plurality of solder bumps on the solder pads; and using a wafer level reflow soldering device The solder bumps are melted into a highly uniform solder ball, wherein the wafer level reflow soldering apparatus comprises: a plurality of heated regions, each of the heated regions includes: a heating plate having a plurality of heating bodies arranged in a concentric circle; and an infrared temperature measurement a controller for controlling the output of each heating body; and a conveyor for conveying a wafer to each of the heated zones, wherein the infrared temperature sensing device monitors temperatures of the plurality of regions on the surface of the wafer and immediately returns the temperature To the controller, the solder bumps on the surface of the wafer are heated to a uniform temperature. A method for fabricating a flip chip wafer assembly, comprising: providing a wafer having a solder ball array; reversing the wafer on a package substrate; and reversing the reverse layer by a wafer level reflow soldering device Wafer soldering is attached to the package substrate, wherein the wafer level reflow soldering apparatus comprises: a plurality of heated regions, each of the heated regions comprises: a heating plate having a plurality of heating bodies arranged in a concentric circle; an infrared temperature measuring device; The controller separately controls the output of each heating body; and a conveyor belt transmits a wafer to each of the heated regions, wherein the infrared temperature measuring device monitors temperatures of the plurality of regions on the surface of the wafer and immediately returns the temperature to the control The solder bumps on the surface of the wafer are heated to a uniform temperature.