TW473944B - Method for forming conducting bump on contact pad - Google Patents

Abstract

The present invention relates a kind of method for manufacturing a bump. A stencil printing method is used in the invented method, in which the variation of positive pressure difference between solder paste and the wafer is used. After solder paste is squeezed downwards from the stencil mask, a much better contact property between the solder paste and the metal under the bump is obtained by combining the ultrasonic oscillation in the horizontal direction, and a smoother flow of solder paste flowing from the mask under the solder paste tank is obtained by combining the ultrasonic oscillation in the vertical direction. In addition, through the cooperation of moving the wafer downward, the solder paste bump can be made to grow up to a predetermined height. At last, solder paste is cut off by the combination of ultrasonic oscillation in horizontal, vertical directions of the stencil plate, and the adjustment of negative pressure difference between solder past tank and the wafer. Therefore, stability of quality can be assured as long as stable values for the pressure difference value and the moving downward speed of wafer are appropriately allocated.

Description

473944 V. Description of the invention (1) |

I Field of invention: '\ The present invention relates to an integrated circuit packaging process, and particularly relates to | a new technology of forming a flip ip chip bump on a bonding pad i, which can increase The height of the bump metal makes the bump formation process stable and lower cost. | |

Background of the Invention: I conductors have been replaced by generations of ultra-large integrated circuit (ULSI) process technology. Half the size, not only increases the component accumulation on the wafer due to the shrinking of the components. I Thin fins therefore reduce costs and create profits. In addition, customers are critical: critical picks are also a driving force for the rapid development of integrated circuits, and how to increase the size of the chip packaging technology has become a key indicator. The chip is thin enough, and the number of chips is one in a package, or how to make the crystal to be packaged. Traditional bump formation is one of the targets of the packaging technology. To complete the integration process, the system first prepares a semiconductor wafer. The semiconductor wafer has been plated, chemically modified, and has reached the stage of protecting the solder pads. Then, a two-phase deposition method or a PECVD method on the sputter layer is used to form a metal under bump (UBM), which is then coated on a laminating pad of the machine. Subsequently, a dry film coating technique was used to dry the film to a thickness of about 1200 ° m. Then, a tin layer was applied to the position of the bump $ on the dry film. A plating process is subsequently applied to form bump metal UBM of the same thickness. After removing the dry film ', it is approximately the same as the dry film'. Reflow (ref low) to grow spherical conductive bumps

Page 4 473944

5. Description of the invention (2) block. In addition to the above-mentioned method of defining the position of the metal bumps with the dry film pattern, Cheng's technology uses a method of forming conductive bumps, and in addition, the conductive bumps are formed on the metal under the bumps by means of electroplating. Square, seed screen printing The wafers that have completed the UBM process are inserted into the net as follows, first. The mesh on the screen matches the position of the metal under the bump. "" The plate printing flat knife scrapes the solder paste over the screen. When the solder paste and the metal under the bumps are connected, then "scrape | stop. After the screen is removed, the metal under each bump will have tin = later." It will stick to i. As long as re-soldering is performed, it can grow into a spherical conductive body and adhere to its ^ block.! Another and the above-mentioned doctor blade screen printing method, ^ i pressure screen printing. This kind of Screen printing has a system with I that can control the upper pressure pi is large and the lower pressure P2 is small, and then 7 printing heads, which makes the solder paste stick to the metal under the bump. So, it will be similar to the knife side The screen printing method is more stable for screen printing. Compared with the blade-type screen, the above-mentioned conventional technology has a thickness that is more concerned by the industry. 5 The thickness of the screen template (stenci 1 to 3) is high. The disadvantage is that 5 First, the schematic diagram of scraping the solder paste above the template height. Figure 5 = c The schematic diagram of the solder paste above the same degree of the template. In addition, = the solder paste is also the joint. No When the hole has a slope The screen is pulled up and the reward is also s. The points are pulled up and the solder paste is lowered and the solder paste is not in contact with the solder paste. 舲 冰 a Another warehouse owner 4 In addition, it is necessary to remove the remaining edges of the mask holes after use. 473944 5. Description of the invention (3) Solder paste, otherwise it cannot be used again. In view of the above problems, the present invention will propose a solution that will not limit the height. And it is more uniform, and the problem of the remaining solder paste on the side of the hole of the solder paste mask can also be solved together. OBJECTS AND SUMMARY OF THE INVENTION The object of the present invention is to provide a method for forming screen printing bumps. Another object of the present invention is to Provided is a method for stably growing screen-printed bumps by using a relative pressure difference between a solder paste tank and a wafer, and combining ultrasonic oscillation and wafer downward. The present invention discloses a method for bump process, and applies the net in the method of the present invention. The method of printing uses the difference in positive pressure difference between the solder paste tank and the wafer to squeeze the solder paste from the screen mask, and combines ultrasonic horizontal oscillation to make the solder paste and the metal under the bumps have better contact. The ultrasonic wave oscillating in the vertical direction makes the solder paste flow more smoothly when it flows down from the mask under the solder paste tank. In addition, it is matched with the downward movement of the wafer to make the solder bumps grow to a predetermined height, and finally Combine the stencil's ultrasonic horizontal and vertical oscillations and adjust the solder paste tank and wafer to a negative pressure difference to cut the solder paste. Therefore, as long as the pressure difference value of the stable value and the downward movement speed of the wafer are appropriately adjusted, It can ensure the stable quality. Detailed description of the invention:

Page 6 473944 V. Description of the invention (4) In view of the bump forming process of traditional screen printing as described in the background of the invention,. Not only is the height of the solder paste formed on the metal under the bump limited, but it must be used after use.

I Remove the remaining solder paste from the edge of the mask hole. The present invention utilizes a method in which the solder paste is extruded on the I side and the wafer is moved vertically downwards during the screen printing process to grow bumps of an expected height. In addition, with the use of ultrasonic waves, the solder paste flows out of the mask j. Holes more smoothly, and because the negative pressure difference is applied when cutting the solder paste, and the "supersonic vibration, the cleaning of the mask can be achieved. Avoid. Please refer to the schematic diagram of Figure 2. First load a wafer 100 on a solder paste 1 screen printing platform. A solder paste tank 110 is on top, and the solder paste tank 110 is matched with the solder mask 120 for screen printing. Solder paste (Of course, it can also be other conductive paste, such as conductive polymer). The wafer 100 has completed the integrated circuit process, protective layer, and the production of contact pads (the contact pads have Form bumps; metal under bump 105 (UBM) or metal under bumps is not required), j bump process to be carried out. The figure shows a schematic diagram of one of UBM 10 5 wafers to be bumped. In addition, The solder paste tank 110 is filled with granular tin alloy balls mixed with a co-solvent (f 1 ux), and each particle has a size of about ten to twenty // m.

I Next, adjust the gap between the solder paste tank 1 1 0 mask 12 on the solder paste screen printer and the metal 105 under the bump and adjust the pressure p 1 from the top to the bottom of the solder mask and the wafer. The pressure P2 from the bottom to the top of the platform is in a state where P1 is greater than P2, so that only a small part of the solder paste 1 2 5 is exposed, in order to more accurately calibrate each solder paste curtain 120 holes.

Page 7 473944 V. Description of the invention (5) and the position of the metal under the bump 105. Generally speaking, the positive pressure difference between the two is about 5-50psi. In order to achieve pressure adjustment, there can be various methods. The wafer platform loading chamber and the solder tank are respectively in different chambers. For example, the height of the solder paste in the solder tank 110 is adjusted to adjust pi, and the gas is introduced into the wafer platform. Enter the room to adjust the ambient pressure, etc. In order to make the solder paste in the solder paste tank 110 flow out more easily, i can selectively use ultrasonic waves to oscillate vertically 1 2 8 at this time. In addition, adjusting the 120 hole size of the mask can also increase its fluidity, and the temperature in the solder paste tank. Proper control can reduce the problem of thermal expansion with a better implementation

I: For example, the size of the 120 holes in the mask is about 12 0 // m. This size allows about 6-7 particles of solder paste to flow out at the same time. The temperature of the solder paste in the solder paste tank is about 10-40 ° C. Please refer to the diagram shown in Figure 3. Raise the wafer platform so that the solder paste and the under bump metal 105 contact the exposed solder paste 125 to stick the solder paste. At this time; | Selectively use ultrasonic waves for horizontal and horizontal oscillations 129 to make the sticky solder paste and the metal under the bump 10 5 better adhesion conditions, and to avoid subsequent crystal | round platform down, Disconnect when the solder paste grows. The horizontal and horizontal oscillation is 12 9 distances only need to reach 1-5 // m.丨 Next, please refer to the schematic diagram shown in Figure 4, and slowly move the wafer platform down to i, while still controlling P1 to be greater than P2, and the pressure difference is about 5-50psi, so that the sticky solder paste 1 2 5 is relatively high Grow upward to a predetermined thickness. The speed of the wafer platform moving slowly downward is about 1-1 0 / z m / s to avoid disconnection; similarly, ultrasonic waves can be selectively used to oscillate vertically 1 2 8 so that

Page 8 473944 V. Description of Invention (6) |

I The solder paste flowing out of the solder paste tank 110 is smoother. Of course, you can also increase the ultrasonic vibration 128 in the horizontal direction to facilitate the smoother flow of solder paste. The height of the solder paste of the metal 105 under the bump is about 100-150 / z m. Finally, please refer to the schematic diagram shown in Figure 5. When the predetermined solder paste height is reached, the pressure states of P1 and P2 are changed so that the pressure P2 is greater than PI.! I · 1 to squeeze back the solder paste, between The negative pressure differential is approximately 10-80 psi. In order to avoid that there is still a small part of the solder paste residue, in conjunction with the ultrasonic vertical vibration direction or / and horizontal vibration, the solder paste residue can be completely avoided. The top of the solder paste on the metal 105 under the bump will shrink and form. Neck 130. Finally, when the wafer is lowered at the same time, it will be disconnected. Figure 5 is a schematic diagram of the neck when it is about to be disconnected. The present invention has been described above with a preferred embodiment, and those skilled in the art are familiar with this field Without deviating from the spirit of the present invention, when some modifications can be made, the scope of patent protection should depend on the scope of the attached patent application and its equivalent fields.

Page 473944 Brief description of the drawings Brief description of the drawings: The preferred embodiment of the present invention will be described in more detail in the following explanatory text supplemented by the following figures: Figures A and B are respectively scraping templates according to traditional methods Schematic diagram of solder paste above and below. FIG. 2 shows a schematic diagram of loading a wafer to prepare a conductive bump for UBM according to the method of the present invention. FIG. 3 is a schematic diagram showing that the conductive bump adheres to the UBM according to the method of the present invention. FIG. 4 is a schematic diagram showing that the conductive bump adhered to the UBM grows as the platform descends according to the method of the present invention. Fig. 5 shows a schematic diagram of the method according to the present invention, in which the pressure is adjusted to a negative pressure difference to disconnect the conductive bumps. Drawing number comparison table: Wafer 100 Solder paste tank 110 Solder paste mask 120 Metal under bump 105CUBM) Neck 130 Solder paste exposed 125 Ultrasonic horizontal oscillation 128 Ultrasonic horizontal oscillation 129

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Claims (1)

VI. Application scope of patent 1. A method for forming bumps on contact pads, including at least the following steps: Load a wafer on a solder paste screen printer, and the wafer has completed the integrated circuit manufacturing process, protective layer and Contact pad (bonding pad); Adjust the gap between the solder mask of the solder paste screen printer and the metal under the bumps, while aligning the holes of the solder mask of the solder mask with the contact pad; The pressure P1 from top to bottom and the pressure P 2 from bottom to top of the wafer platform under a positive pressure difference of P 1 greater than P 2 make the solder paste stick to the contact pad and the pressure still maintains a positive pressure difference; The wafer is moved downwards so that the height of the solder paste is relatively increased to a predetermined thickness and the pressure still maintains a positive pressure difference; the pressure difference between P1 and P 2 is adjusted so that the negative pressure difference between P1 and P 2 is used to intercept the solder paste, The wafer is moved downward to separate the mask from the solder paste on the contact pad. 2. The method according to item 1 of the patent application range, wherein the above-mentioned P 1 and P 2 belong to different chambers. 3. As the method of applying for the first item in the scope of patent application, the method further includes using ultrasonic waves to oscillate vertically in order to adjust the gap between the solder paste screen of the solder paste screen printer and the metal under the bump to make the solder paste in the solder paste tank. Partial outflow. 4. If the method of the first item of the scope of patent application, the method further comprises: when the wafer platform is in contact with the solder paste flowing out of the hole of the mask, the ultrasonic wave is used to vibrate horizontally to obtain the solder paste sticking to the metal under the bump Better contact. Page 11 473944 VI. Patent application scope 5. The method of the first patent application scope further includes the step of moving the wafer downward k so that the height of the solder paste relatively grows up to a predetermined thickness. The sound wave vibrates vertically to make the solder paste flowing out of the solder paste tank more smoothly. 6. As for the method of the first item of patent application scope, the method further includes the step of moving the wafer downward I i so that the height of the solder paste relatively grows up to a predetermined thickness. At the same time, combined with ultrasonic waves for vertical and horizontal vibration to Make the solder paste flowing out of the solder paste tank more smoothly.丨 | ：! I 7. The method of item 1 of the patent application scope further includes adjusting the pressure difference between P1 and P2 so that when P1 is smaller than P2, the ultrasonic wave is combined with vertical and horizontal vibration to make the solder paste neck. To prevent solder paste from remaining in the mask holes. j! 8. The method according to item 1 of the scope of patent application, in which the pressure difference between P1 and P2 above is to cause the solder paste to generate a neck to facilitate truncation. 9. The method according to item 1 of the scope of patent application, wherein the speed of the downward movement of the wafer stage | downward movement step described above is about 1-10 // m / s to avoid breaking. < 1 0. The method according to item 1 of the scope of patent application, further comprising subjecting the wafer to a reflow (Ref low) process after separation of the mask from the solder paste to form a spherical conductive bump. 0 · Page 12 7. Gynecological materials, supplementary only 6. Application for patent scope 1 1. The method of applying for item 1 of the patent scope, where the above-mentioned positive pressure difference is about 5-50 psi and the negative pressure difference is about 10-80 psi . 1 2. The method according to item 1 of the patent application range, wherein the above-mentioned contact pad further comprises a metal under bump (UBM), so that the above-mentioned conductive bump is formed on the metal under bump. 1 3. —A method for forming bumps on a contact pad includes at least the following steps: Load a wafer into a solder paste screen printer station, which has completed the integrated circuit process, protective layer, and contact pads; adjust the gap between the solder paste screen and the contact pad of the solder paste screen printer station, and at the same time Align the mask hole of the solder paste curtain with the contact pad, and cooperate with the pressure P1 from top to bottom and the pressure P2 from the bottom of the wafer platform to a positive pressure difference to make the mask of the solder mask A small part of the solder paste is exposed in the holes; the contact pads of the wafer are brought into contact with the solder paste on the holes in the mask, and ultrasonic waves are combined in the horizontal direction to increase the adhesion of the solder paste to the contact pads while maintaining the pressure P1 is greater than the positive pressure difference of P 2; Move the wafer downward so that the height of the solder paste is relatively increased to a predetermined thickness, combined with ultrasonic waves to vibrate in a vertical direction and the pressure still maintains a positive pressure difference between P1 and P2; With a negative pressure difference of P1 less than P 2 and combined with ultrasonic waves for vertical and horizontal vibrations to intercept the tin deficiency and move the wafer downward, the solder paste on the contact pad and the holes in the mask are separated. Page 13 473944 VI. The scope of patent application is off. 14. The method of claim 13 in the scope of patent application, wherein P1 and P2 mentioned above belong to different chambers. 15. The method according to item 13 of the scope of patent application, further comprising the step of moving the wafer downward to increase the height of the solder paste to a predetermined thickness, and simultaneously combining ultrasonic waves to make the solder paste groove horizontal The solder paste flows out more smoothly. 16. The method according to item 13 of the scope of patent application, wherein the downward movement speed of the above-mentioned downward movement step of the wafer is about 1-1 0 // m / s to avoid breakage. 1 7. The method according to item 13 of the scope of patent application, further comprising subjecting the wafer to a reflow process after the mask is separated from the solder paste to form a spherical conductive bump. 18. The method according to item 13 of the patent application range, wherein the positive pressure difference is about 5-50 psi and the negative pressure difference is about 10-80 psi. 19. The method according to item 13 of the scope of patent application, wherein the above-mentioned contact pad further comprises a metal under bump (UBM), so that the above-mentioned conductive bump is formed on the metal under bump. Page 14