Chip Mounting Method

Abstract

The present invention provides a chip mounting method, which includes: providing a lead frame, the lead frame including a die bonding area; providing a mask, the mask including an opening corresponding to the die bonding area; covering the mask above the lead frame, and the die bonding area is exposed from the opening; providing silver paste, coating the silver paste above the mask, and the silver paste enters the die bonding area from the opening; removing the mask; providing a chip, and attaching the chip to the silver paste in the die bonding area; wherein, the silver content of the silver paste is 80% to 90%, and the viscosity of the silver paste is 40,000 to 80,000 cps; the opening includes a plurality of interconnected side edges, and each side edge is bent or folded towards the inside of the opening.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor packaging, and particularly relates to a chip mounting method. Background Art

[0002] The existing chip mounting methods mainly include: through the dispensing mechanism, vacuum and pressure devices of a chip mounter, dotting or scribing the silver paste in the cartridge onto the mounting area of the lead frame; using the suction nozzle on the soldering head of the chip mounter to pick up the chips one by one from the wafer by internal vacuum adsorption; then releasing the suction nozzle on the soldering head of the chip mounter through internal vacuum, placing the chips adsorbed on the suction nozzle on the silver paste above the mounting area of the frame, and controlling the pressure and time through the soldering head of the chip mounter to make the silver paste spread around the chips, so that the chips and the lead frame are fixedly connected through the silver paste.

[0003] However, the above chip mounting method has at least the following technical problems: 1) Limited by the number of dispensing / scribing pens and the mechanism movement in the chip mounter, the larger the chip size, the smaller the UPH (units per hour) production capacity of the silver paste operation of the chip mounter;

[0004] 2) For silver paste chip mounting products with a chip thickness ≤ 75um, due to the too thin chip thickness, the conventional dotting / scribing operation method will cause, for example, large differences in the silver paste thickness at different positions of single dotting / scribing (before chip mounting), resulting in uneven silver paste climbing height and silver paste coverage after chip mounting; differences in the amount of glue caused by the extrusion air pressure and vacuum fluctuations of the dispensing mechanism will cause abnormal silver paste contamination on the chip surface or insufficient silver paste coverage on the back of the chip after chip mounting.

[0005] In view of this, a new chip mounting method needs to be proposed to overcome the problems of abnormal silver paste coverage on the back of the chip and contamination on the chip surface in the existing chip mounting methods. Summary of the Invention

[0006] The purpose of the present invention is to provide a chip mounting method, which is used to significantly improve the problems of insufficient coverage, insufficient climbing thickness and overflow of silver paste in the mounting area of the lead frame.

[0007] To solve the above problems, the technical solution of the present invention provides a chip mounting method, and the chip mounting method includes:

[0008] Providing a lead frame, where the lead frame includes a mounting area;

[0009] Providing a mask, where the mask includes an opening corresponding to the mounting area;

[0010] Covering the mask above the lead frame, and the mounting area is exposed from the opening;

[0011] Provide silver paste, coat the silver paste above the mask, and the silver paste enters the die bonding area through the opening;

[0012] Remove the mask;

[0013] Provide a chip and attach the chip to the silver paste in the die bonding area;

[0014] Wherein, the silver content of the silver paste is 80% - 90%, and the viscosity of the silver paste is 40000 - 80000 cps; the opening includes a plurality of interconnected side edges, and each side edge is bent or folded towards the inside of the opening.

[0015] As an alternative technical solution, the angle formed by any two of the side edges protrudes towards the outside of the opening.

[0016] As an alternative technical solution, the angle is 45° - 60°.

[0017] As an alternative technical solution, the projection of the chip in the die bonding area coincides with the projection of the opening in the die bonding area.

[0018] As an alternative technical solution, the side edge is a concave arc structure or a concave broken line structure.

[0019] As an alternative technical solution, a plurality of interconnected side edges form a concave rectangular structure.

[0020] As an alternative technical solution, the concave rectangular structure includes a concave arc long side and a concave arc short side. There is a first vertical distance between the two end points of the concave arc long side, and a second vertical distance between the two end points of the concave arc short side; there is a third vertical distance between the lowest positions of two opposite concave arc short sides; there is a fourth vertical distance between the lowest positions of two opposite concave arc long sides; wherein, the ratio of the third vertical distance to the first vertical distance is 0.7 - 0.8; the ratio of the fourth vertical distance to the second vertical distance is 0.7 - 0.8.

[0021] As an alternative technical solution, the chip is a rectangular chip, the first vertical distance is the same as the length of the long side of the rectangular chip, and the second vertical distance is the same as the length of the short side of the rectangular chip.

[0022] As an alternative technical solution, when providing silver paste, coating the silver paste above the mask, the step of the silver paste entering the die bonding area through the opening further includes: coating the silver paste on the shielding part of the mask where there is no opening; providing a squeegee, and moving the squeegee along the surface of the mask to scrape the silver paste into the opening and deposit it in the die bonding area.

[0023] As an alternative technical solution, a chip is provided. The steps of attaching the chip to the mounting area after applying the silver paste include: providing a wafer and a pick-and-place machine. The wafer includes a plurality of chips. The pick-and-place machine includes a soldering head, and the soldering head includes a nozzle. The nozzle vacuum-adsorbs the chip, peels it off the wafer, and moves it above the mounting area. The nozzle releases the vacuum, and the chip is placed on the silver paste in the mounting area. Then, the soldering head presses the chip and the silver paste, and the silver paste cures, and the chip is mounted in the mounting area.

[0024] As an alternative technical solution, the thickness of the chip is less than 75 μm.

[0025] As an alternative technical solution, the thickness of the mask is 50 μm.

[0026] Compared with the prior art, in summary, the present invention provides a chip mounting method. It uses a mask with an opening for silver paste coating, coats the silver paste into the mounting area corresponding to the opening of the lead frame, controls the silver content, viscosity, and shape of the opening of the silver paste, and realizes the rapid mounting of chips, especially chips with a relatively thin thickness. It has the following beneficial effects: 1) Select the silver content of the silver paste to be 80% - 90% and the viscosity to be 40,000 - 80,000 cps. At the same time, design the side of the opening of the mask to be bent or folded towards the inside of the opening. By controlling the silver content and viscosity, the silver paste can be evenly distributed and have stable flow support during the brushing process; 2) By redesigning the shape of the opening of the mask, when used with the above silver paste, the coverage area and thickness of the silver paste entering the opening in the mounting area are consistent and uniform, with small differences; 3) During the chip mounting process, the soldering head of the pick-and-place machine table controls the mounting height so that the silver paste after mounting evenly overflows between the chip and the mounting area, and will not cause problems such as silver paste overflow resulting in chip surface contamination or abnormal gum creep; 4) Using the combination of the mask and the silver paste for glue application can also significantly increase the chip mounting production capacity. Compared with the dot / scribe glue process, the chip mounting production capacity UPH can be increased by 4 - 5 times, improving the mounting process ability of semiconductor packaging; 5) Due to the redesign of the characteristics of the silver paste and the structure of the mask, it can meet the mounting requirements of ultra-thin chips with a chip thickness of 75 μm and below.

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but it is not intended to limit the present invention. Description of the Drawings

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a flowchart of a chip mounting method provided by an embodiment of the present invention.

[0030] Figure 2 It is a top view of a lead frame provided by an embodiment of the present invention.

[0031] Figure 3 It is a top view of a mask provided by an embodiment of the present invention.

[0032] Figure 4 It is a top view of the mask stacked above the lead frame.

[0033] Figure 5 For Figure 4 It is a schematic cross-sectional view of the mask and the lead frame on the gluing platform in

[0034] Figure 6 For Figure 2 It is a partially enlarged schematic view of the lead frame in

[0035] Figure 7 For Figure 3 It is a partially enlarged schematic view of the mask in

[0036] Figure 8 It is a top view after a single lead frame and a single mask unit are stacked.

[0037] Figure 9 It is a top view after silver glue covers the chip mounting area of the lead frame.

[0038] Figure 10 For the chip to be mounted to Figure 9 It is a top view on the silver glue in the chip mounting area in

[0039] Figure 11 For Figure 10 It is a schematic cross-sectional view after the chip is mounted to the lead frame in Specific embodiments

[0040] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0042] As Figure 1 shown, in an embodiment of the present invention, a chip mounting method is provided, which includes:

[0043] Providing a lead frame, the lead frame including a die bonding area;

[0044] Providing a mask, the mask including an opening corresponding to the die bonding area;

[0045] Covering the mask above the lead frame, the die bonding area being exposed from the opening;

[0046] Providing silver paste, coating the silver paste above the mask, and the silver paste entering the die bonding area from the opening;

[0047] Removing the mask;

[0048] Providing a chip, and attaching the chip to the silver paste in the die bonding area;

[0049] Wherein, the silver content of the silver paste is 80% - 90%, and the viscosity of the silver paste is 40000 - 80000 cps; the opening includes a plurality of interconnected side edges, and each side edge is bent or folded towards the inside of the opening.

[0050] In the chip mounting method provided by the present invention, the silver content of the silver paste is selected to be 80% - 90%, and the viscosity is 40000 - 80000 cps. At the same time, the side edges of the opening of the mask are designed to be bent or folded towards the inside of the opening. Among them, by controlling the silver content and viscosity, the silver paste can be evenly distributed and have stable flow support during the glue brushing process; and by redesigning the shape of the opening of the mask, when used in combination with the above silver paste, the silver paste entering the opening has a consistent coverage area and uniform thickness in the die bonding area, with little difference. During the chip mounting process, the height of the chip mounting is controlled by the bonding head of the chip mounter so that the silver paste after chip mounting evenly overflows between the chip and the die bonding area, and will not cause problems such as chip surface contamination or abnormal glue creeping caused by silver paste overflow.

[0051] In addition, using the combination of a mask and silver paste for glue coating can also significantly increase the chip mounting production capacity. Compared with the dot / scribe glue process, the production capacity UPH of chip mounting can be increased by 4 - 5 times, improving the die bonding process ability of semiconductor packaging.

[0052] Furthermore, due to the redesigned characteristics of the silver paste and the structure of the mask, the mounting requirements of ultra-thin chips with a chip thickness of 75 μm or less can be met.

[0053] The following will be combined with Figures 2 to 11 described in detail Figure 1 the manufacturing process of each step of the chip mounting method in

[0054] As Figure 2 shown, a number of lead frames 1 arranged in a matrix, and a number of lead frames 1 can be fixed on a carrier board (not shown). Each lead frame 1 includes a die bonding area 2, and the die bonding area 2 is used for die bonding a chip 9 (as Figure 10 and Figure 11 shown).

[0055] As Figure 3 shown, a mask 3 is provided. The mask 3 has a number of openings 4, and the periphery of each opening 4 includes a shielding portion 5.

[0056] As Figures 2 to 4 shown, the openings 4 and the die bonding areas 2 are in one-to-one correspondence, and the die bonding areas 2 are exposed from the openings 4. The shielding portion 5 is used to shield other areas of the lead frame 1 that do not need to be coated with silver paste.

[0057] As Figures 6 to 8 shown, the area of the orthographic projection of the opening 4 within the die bonding area 2 is smaller than the area of the die bonding area 2, that is, the size of the opening 4 is smaller than the size of the die bonding area 2. This is mainly to provide an overflow space for the silver paste when pressing the chip and the silver paste.

[0058] As Figure 5 shown, after the lead frame 1 and the mask 3 are stacked, they are placed on a gluing platform 10. At the same time, silver paste 7 and a squeegee 8 are provided, and the silver paste 7 is coated on the surface of the shielding portion 5. The squeegee 8 is inclined relative to the mask 3 and moves along the surface of the shielding portion 5 to scrape the silver paste 7 into the opening 4 and deposit it in the corresponding die bonding area 2.

[0059] As Figure 5 and Figure 9 shown, during the above process of coating the silver paste 7, the squeegee 8 can repeat the above movement multiple times until the height of the silver paste 7 in the opening 4 is consistent with the depth of the opening 4, so that the coverage area and thickness of the silver paste 7 coated in the die bonding areas 2 of a number of lead frames 1 are consistent and have little difference.

[0060] In a preferred embodiment, the thickness of the mask 3 is 50 μm, that is, the depth of the opening 4 is 50 μm.

[0061] As Figure 9 , Figure 10 and Figure 11As shown, the mask 3 is removed; a wafer (not shown) and a mounter (not shown) are provided. The wafer (not shown) includes a plurality of chips 9, and the mounter includes a soldering head (not shown). The soldering head (not shown) includes a nozzle. Among them, the nozzle vacuum-adsorbs the chip 9, peels it off from the wafer, and moves it above the loading area 2. The nozzle releases the vacuum, and the chip 9 is placed on the silver paste 7 on the surface of the loading area 2. The soldering head presses the chip 9 and the silver paste 7, and the silver paste 7 overflows between the chip 9 and the loading area 2. After the soldering head is heated, the silver paste 7 cures, and the chip 9 is mounted in the loading area 2.

[0062] As Figure 10 and Figure 11 shown, during the pressing process of the soldering head, the overflow and climbing thickness of the silver paste 7 (lower on both sides and higher in the middle) are uniform, completely covering the back of the chip 9, and at the same time not overflowing towards the surface of the chip 9, avoiding the contamination of the silver paste on the surface of the chip 9.

[0063] In a preferred embodiment, the opening 4 includes a plurality of interconnected side edges, and each side edge bends or folds towards the inside of the opening. For example, the side edge can be a concave arc structure or a concave broken line structure.

[0064] Among them, the included angle formed by any two side edges of the opening 4 protrudes towards the outside of the opening, and the angle of the included angle is 45° - 60°.

[0065] As Figure 7 shown, the plurality of interconnected side edges of the opening 4 form a concave rectangular structure. The concave rectangular structure includes a concave arc long side 4a and a concave arc short side 4b. There is a first vertical distance A1 between the two end points of the concave arc long side 4a, and there is a second vertical distance B1 between the two end points of the concave arc short side 4b. There is a third vertical distance a1 between the lowest positions of the two opposite concave arc short sides 4b, and there is a fourth vertical distance b1 between the lowest positions of the two opposite concave arc long sides 4a. Among them, the ratio of the third vertical distance a1 to the first vertical distance A1 is 0.7 - 0.8; the ratio of the fourth vertical distance b1 to the second vertical distance B1 is 0.7 - 0.8.

[0066] In a preferred embodiment, if the chip 9 is a rectangular structure, the first vertical distance A1 is the same as the length of the long side of the chip 9, and the second vertical distance B1 is the same as the length of the short side of the chip 9. That is, the vertical connection lines between the four corner end points of the concave rectangular structure form a pattern whose projection on the loading area 2 coincides with the orthographic projection of the rectangular chip 9 in the loading area 2.

[0067] In other words, the orthographic projection of the chip 9 within the die bonding area 2 coincides with the orthographic projection of the opening 4 within the die bonding area 2. "Coincidence" includes "complete coincidence" and "partial coincidence". Preferably, the orthographic projection of the chip 9 within the die bonding area 2 completely covers the orthographic projection of the opening 4 within the die bonding area 2. Further, the size of the orthographic projection of the chip 9 within the die bonding area 2 is slightly larger than the size of the orthographic projection of the opening 4 within the die bonding area 2.

[0068] As Figure 7 shown, for the opening 4 of the concave rectangular structure, the angle 6 between the concave arc long side 4a and the concave arc short side 4b protrudes towards the outside of the opening, and the angle of the angle 6 is 45° - 60°.

[0069] As Figures 6 to 10 shown, multiple sides of the opening 4 are bent or recessed towards the inside of the opening. The silver paste 7 forms a similar concave edge in the die bonding area 2 through the opening 4. There is a reserved gap between the concave edge and the edge of the chip 9. When the chip 9 and the silver paste 7 are pressed together, the silver content and viscosity of the silver paste 7 are controlled so that the silver paste 7 overflows outward while filling the reserved gap, and stays at the edge of the chip 9 without further overflowing, achieving a uniform effect for both the height of the creeping paste and the coverage area.

[0070] In summary, the present invention provides a chip bonding method, which uses a mask with an opening for silver paste coating, coats the silver paste into the die bonding area corresponding to the opening of the lead frame, and controls the silver content, viscosity of the silver paste and the shape of the opening to achieve rapid bonding of the chip, especially a chip with a relatively thin thickness. It has the following beneficial effects: 1) Select the silver content of the silver paste to be 80% - 90% and the viscosity to be 40000 - 80000 cps. At the same time, design the side edges of the opening of the mask to be bent or folded towards the inside of the opening. By controlling the silver content and viscosity, the silver paste can be evenly distributed and have stable flow support during the brushing process; 2) By redesigning the shape of the opening of the mask, when used in combination with the above silver paste, the silver paste entering the opening has a consistent coverage area and uniform thickness within the die bonding area, with small differences; 3) During the chip bonding process, the bonding head of the chip mounter controls the bonding height so that the silver paste after bonding evenly overflows between the chip and the die bonding area, and does not cause problems such as chip surface contamination or abnormal creeping due to silver paste overflow; 4) Using the combination of the mask and the silver paste for coating can also significantly increase the chip bonding production capacity. Compared with the dot / scribe coating process, the production capacity UPH of chip bonding can be increased by 4 - 5 times, improving the die bonding process ability of semiconductor packaging; 5) Due to the redesign of the characteristics of the silver paste and the structure of the mask, it can meet the bonding requirements of ultra-thin chips with a chip thickness of 75μm or less.

[0071] The present invention has been described by the above related embodiments. However, the above embodiments are only examples for implementing the present invention. In addition, the technical features involved in different embodiments of the present invention described above can be combined with each other as long as they do not conflict with each other. It must be pointed out that the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A chip mounting method, characterized in that, The chip mounting method includes: Providing a lead frame, the lead frame including a die bonding area; Providing a mask, the mask including an opening corresponding to the die bonding area; Covering the mask above the lead frame, with the die bonding area exposed from the opening; Providing silver paste, coating the silver paste above the mask, and the silver paste enters the die bonding area from the opening; Removing the mask; Providing a chip, and attaching the chip to the silver paste in the die bonding area; Wherein, the silver content of the silver paste is 80% - 90%, and the viscosity of the silver paste is 40000 - 80000 cps; the opening includes a plurality of interconnected side edges, and each side edge bends or folds towards the inside of the opening; the plurality of interconnected side edges form a concave rectangular structure; The concave rectangular structure includes a concave arc long side and a concave arc short side. There is a first vertical distance between the two end points of the concave arc long side, and a second vertical distance between the two end points of the concave arc short side; there is a third vertical distance between the lowest positions of two opposite concave arc short sides; there is a fourth vertical distance between the lowest positions of two opposite concave arc long sides; Wherein, the ratio of the third vertical distance to the first vertical distance is 0.7 - 0.8; the ratio of the fourth vertical distance to the second vertical distance is 0.7 - 0.8; The chip is a rectangular chip, the first vertical distance is the same as the length of the long side of the rectangular chip, and the second vertical distance is the same as the length of the short side of the rectangular chip; The orthographic projection of the chip in the die bonding area completely covers the orthographic projection of the opening in the die bonding area, and the size of the orthographic projection of the chip in the die bonding area is larger than the size of the orthographic projection of the opening in the die bonding area.

2. The chip mounting method according to claim 1, wherein The included angle formed by any two of the side edges protrudes towards the outside of the opening.

3. The chip mounting method according to claim 2, wherein, The angle of the included angle is 45° - 60°.

4. The chip mounting method according to claim 1, wherein, The side edge is a concave arc structure or a concave broken line structure.

5. The chip mounting method according to claim 1, characterized in that, The step of providing silver paste, coating the silver paste above the mask, and the silver paste enters the die bonding area from the opening further includes: Coating the silver paste on the shielding part of the mask where there is no opening; Providing a squeegee, moving the squeegee along the surface of the mask to scrape the silver paste into the opening and deposit it in the die bonding area.

6. The chip mounting method according to claim 1, wherein The step of providing a chip and attaching the chip to the die bonding area after coating the silver paste includes: Providing a wafer and a chip mounter, the wafer including a plurality of chips, the chip mounter including a bonding head, and the bonding head including a suction nozzle; The suction nozzle vacuum-adsorbs the chip, peels it off from the wafer, and moves it above the die bonding area. The suction nozzle releases the vacuum, and the chip is placed on the silver paste in the die bonding area; and The bonding head presses the chip and the silver paste, the silver paste cures, and the chip is mounted in the die bonding area.

7. The chip mounting method according to claim 1, characterized in that, The thickness of the chip is less than 75 μm.

8. The chip mounting method according to claim 1, characterized in that, The thickness of the mask is 50 μm.

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