A method for chip dipping and tinning

Abstract

The present invention belongs to the technical field of surface assembly of lead frames of semiconductor devices, and specifically relates to a method for chip dipping and mounting. The method provided by the present invention comprises the following steps: heating and melting the solder to obtain a solder melt; placing a chip above the solder melt, and dipping the bottom surface of the chip in contact with the surface of the solder melt to obtain a chip with the bottom surface dipped in the solder melt; placing the chip with the bottom surface dipped in the solder melt just above the base island and in parallel contact with the surface of the base island for mounting. With the method provided by the present invention, the bottom surface of the chip spontaneously absorbs the molten solder, which effectively prevents the solder from overflowing and forming solder slag when it melts directly on the base island; then the chip with the bottom surface dipped in the solder melt is moved to just above the base island and then contacts the base island to bond the chip, which can effectively prevent squeezing and overflowing during contact. The method provided by the present invention can effectively solve the problem of solder overflow during bonding.

Description

Technical Field

[0001] The invention belongs to the technical field of surface assembly of lead frames of semiconductor equipment, and in particular relates to a method for tin-dipping a chip. Background Art

[0002] A chip (Die), also known as a microcircuit, microchip, or integrated circuit, refers to a silicon wafer containing an integrated circuit. It is very small and is often the core part of a computer or other electronic device.

[0003] At present, in the process of surface assembly of semiconductor equipment lead frame, the chip is generally assembled by heating and melting the solder on the base island (pad), and then using a chip bonding machine to transfer the chip to the surface of the base island (pad) with molten solder paste for bonding to complete the chip welding assembly.

[0004] However, in actual operation of the conventional chip assembly method, when the size of the base island and the chip are similar, the solder easily overflows the edge of the base island to form solder slag during chip bonding, and at the same time causes poor chip flatness and generation of bubbles, resulting in poor chip assembly. Summary of the invention

[0005] The object of the present invention is to provide a method for chip tinning and mounting. The method provided by the present invention can effectively solve the problem of solder overflow during chip bonding, and the chip has better flatness and reduces the occurrence of bubbles.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for chip tinning, comprising the following steps:

[0008] The solder is heated and melted to obtain a solder melt;

[0009] Placing a chip above the solder melt, and dipping the bottom surface of the chip in contact with the surface of the solder melt to obtain a chip with the bottom surface dipped in the solder melt;

[0010] The chip with the bottom surface dipped in solder melt is placed just above the base island and in parallel contact with the surface of the base island for chip loading.

[0011] Preferably, the size of the chip is the same as or similar to the size of the base island.

[0012] Preferably, the solder melt is a solder melt droplet, and the tin dipping is that the bottom surface of the chip horizontally contacts the top of the solder melt droplet.

[0013] Preferably, the contact is that the center point of the bottom surface of the chip contacts the apex of the solder melt droplet.

[0014] Preferably, the contact is: the base island is placed horizontally, and the chip with the bottom surface dipped in solder melt is in horizontal contact with the base island.

[0015] Preferably, the melting is performed by heating and melting the solder in a heating container with a horizontal bottom.

[0016] Preferably, placing the chip above the solder melt to dip it in tin is: placing the chip horizontally and moving the chip to above the solder melt in a direction perpendicular to the bottom surface of the solder melt, and the moving speed is 5-15 mm / s.

[0017] Preferably, after the tin dipping, the process further comprises: the chip whose entire bottom surface is dipped in molten solder is placed horizontally, and moved in a direction perpendicular to the bottom surface of the molten solder to separate from the residual molten solder; the chip whose entire bottom surface is dipped in molten solder moves in a direction perpendicular to the bottom surface of the molten solder to separate from the residual molten solder at a speed of 5 to 15 mm / s.

[0018] Preferably, placing the chip with the bottom surface dipped in molten solder just above the base island comprises: placing the chip with the entire bottom surface dipped in molten solder horizontally and moving it to above the base island in a direction perpendicular to the surface of the base island, and the moving speed is 5 to 15 mm / s.

[0019] The present invention provides a method for chip dipping and mounting, comprising the following steps: heating and melting solder to obtain a solder melt; placing a chip above the solder melt, contacting the bottom surface of the chip with the surface of the solder melt for dipping, and obtaining a chip with the bottom surface dipped in the solder melt; placing the chip with the bottom surface dipped in the solder melt directly above the base island and in parallel contact with the surface of the base island for mounting. The method provided by the present invention first contacts the bottom surface of the chip with the molten solder, and the bottom surface of the chip spontaneously absorbs the molten solder, effectively avoiding the problem of excessive solder overflowing to form solder slag when the solder melts directly on the base island; then the chip with the bottom surface dipped in the solder melt is moved to the top of the base island and then contacts the base island for bonding. Since the solder is distributed and coated on the surface of the chip bottom surface, when it contacts the base island, compared with the solder droplets formed by heating and melting on the surface of the base island when the bottom surface of the chip directly contacts, the solder melt of the present invention is already in a dispersed state on the bottom surface of the chip, which can effectively avoid the problem of squeezing and overflowing during contact. Therefore, the method provided by the present invention can effectively solve the problem of solder overflow during chip bonding, so that the chip has better flatness and fewer bubbles between the base island and the chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of a solder heating container of the present invention;

[0021] Figure 2 It is a schematic diagram of the process of the chip moving to the top of the solder melt of the present invention;

[0022] Figure 3 It is a schematic diagram of the bottom surface of the chip of the present invention being in contact with the solder melt and being dipped in tin;

[0023] Figure 4 A schematic diagram of the bottom surface of the chip of the present invention being moved away after being dipped in tin;

[0024] Figure 5 It is a schematic diagram of the process of a chip with solder melt coated on the bottom surface of the present invention moving to the top of the base island;

[0025] Figure 6 It is a schematic diagram of the chip with solder melt on the bottom surface of the present invention contacting and bonding with the base island;

[0026] Figure 7 It is a schematic diagram of the bonding head moving away after the bonding of the sheets is completed in the present invention;

[0027] Among them, 1 is a heating container, 2 is solder melt, 3 is a chip, 4 is a suction nozzle, 5 is a bonding head, and 6 is a base island. DETAILED DESCRIPTION

[0028] The present invention provides a method for chip tinning, comprising the following steps:

[0029] The solder is heated and melted to obtain a solder melt;

[0030] Placing a chip above the solder melt, and dipping the bottom surface of the chip in contact with the surface of the solder melt to obtain a chip with the bottom surface dipped in the solder melt;

[0031] The chip with the bottom surface dipped in solder melt is placed just above the base island and in parallel contact with the surface of the base island for chip loading.

[0032] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0033] The invention heats and melts the solder to obtain a solder melt.

[0034] In the present invention, the melting is preferably performed by heating and melting the solder in a heating container with a horizontal bottom.

[0035] In a specific embodiment of the present invention, the heating container is preferably a heating tank with a horizontal bottom surface.

[0036] The present invention has no special requirements on the shape of the solder, and the cross section of the solder may be circular or in any other shape.

[0037] In a specific embodiment of the present invention, the solder is preferably a solder wire with a circular cross-section.

[0038] The present invention has no special requirements on the specific method of conveying the solder to the heating container.

[0039] As a specific embodiment of the present invention, the present invention adopts a tin wire feeding machine to convey the solder wire to the instant heating container.

[0040] In the present invention, after being heated and melted, the shape of the molten solder is preferably a nearly hemispherical solder droplet.

[0041] After obtaining the solder melt, the present invention places the chip above the solder melt, and makes the bottom surface of the chip contact the surface of the solder melt for tin dipping, thereby obtaining a chip with the bottom surface dipped in the solder melt.

[0042] The present invention has no special requirements on the size of the chip.

[0043] In the present invention, the size of the chip is preferably the same as or similar to the size of the base island.

[0044] In a specific embodiment of the present invention, the size of the chip is preferably 2.8 mm×4.1 mm, and the size of the base island is 3.1 mm×4.5 mm.

[0045] As a specific embodiment of the present invention, the solder melt is a solder melt droplet, and the tin dipping is preferably performed by the bottom surface of the chip horizontally contacting the top of the solder melt droplet.

[0046] As a specific embodiment of the present invention, the contact is preferably that the center point of the bottom surface of the chip contacts the apex of the solder melt droplet.

[0047] In the present invention, placing the chip above the solder melt is preferably: placing the chip horizontally and moving it above the solder melt in a direction perpendicular to the bottom surface of the solder melt, and the moving speed is preferably 5-15 mm / s, more preferably 6-12 mm / s.

[0048] In the present invention, the chip is preferably moved by vacuum adsorption on the header by a suction nozzle. The present invention has no special requirements on the vacuum pressure of the chip adsorbed on the header, and it is sufficient to ensure that the chip does not fall off the header during the movement.

[0049] In the present invention, after the tin dipping, the present invention preferably further comprises: the chip whose entire bottom surface is dipped with molten solder is placed horizontally, and moved in a direction perpendicular to the bottom surface of the molten solder to separate from the residual molten solder; the movement speed of the chip whose entire bottom surface is dipped with molten solder to separate from the residual molten solder in a direction perpendicular to the bottom surface of the molten solder is preferably 5 to 15 mm / s, more preferably 6 to 12 mm / s.

[0050] After obtaining the chip with the bottom surface dipped in the molten solder, the present invention places the chip with the bottom surface dipped in the molten solder just above the base island so as to be in parallel contact with the surface of the base island for chip loading.

[0051] In the present invention, the contact is preferably: the base island is placed horizontally, and the chip with the bottom surface dipped in solder melt is in horizontal contact with the base island.

[0052] In the present invention, placing the chip above the solder melt is preferably: placing the chip horizontally and moving it above the solder melt in a direction perpendicular to the bottom surface of the solder melt, and the moving speed is preferably 5-15 mm / s, more preferably 6-12 mm / s.

[0053] The present invention has no special requirements on the amount of solder for chip welding and mounting, and the tin content of chip mounting well known to those skilled in the art can be used.

[0054] In a specific embodiment of the present invention, the solder volume of the chip welding package is preferably 0.58 to 2.88 mm 3 The present invention preferably has a soldering amount of 0.58 to 2.88 mm 3 When loading chips, the technical solution provided by the present invention is adopted to load chips, which can effectively prevent solder from overflowing.

[0055] The present invention has no special requirements on the solder thickness of the chip welding mounting, and the solder thickness of the chip mounting well known to those skilled in the art can be used.

[0056] In a specific embodiment of the present invention, the solder thickness of the chip welding chip is preferably 50-60 μm. The present invention preferably adopts the technical solution provided by the present invention to effectively prevent solder overflow when the solder thickness is 50-60 μm.

[0057] The chip tin dipping method provided by the present invention comprises the following steps: firstly, the solder is heated and melted to obtain a solder melt; and the solder melt is preferably a solder melt droplet, and the tin dipping is that the bottom surface of the chip horizontally contacts the vertex of the solder melt droplet; and the contact is regulated as follows: the base island is horizontally placed, and the chip with the bottom surface dipped in the solder melt is horizontally in contact with the base island; the chip is placed above the solder melt as follows: the chip is horizontally placed and moved in a direction perpendicular to the bottom surface of the solder melt to the top of the solder melt for dipping in the solder, and the moving speed is 5 to 15 mm / s, which can ensure that the bottom surface of the chip is fully in contact with the solder melt and that the entire bottom surface of the chip is evenly dipped in the solder melt; then the chip with the entire bottom surface dipped in the solder melt according to the present invention is horizontally placed, moved in a vertical direction to separate from the residual solder melt, and moved in a vertical direction to the top of the base island to contact the base island; the chip with the entire bottom surface dipped in the solder melt is placed above the base island; The chip with the molten solder moves at a speed of 5-15 mm / s in the vertical direction away from the residual molten solder. The present invention regulates the separation speed of the chip with the entire bottom surface coated with the molten solder to 5-15 mm / s, thereby ensuring that the bottom surface of the chip carries an appropriate amount of molten solder, thereby avoiding overflow of excessive molten solder when the bottom surface of the chip contacts the base island, or insufficient molten solder, thereby failing to achieve effective welding of the chip and reducing the service life of the chip. Finally, the present invention moves the chip with the molten solder on the bottom surface to directly above the base island to contact the base island for chip loading. During chip loading, the base island is placed horizontally, and the chip with the molten solder on the bottom surface contacts the base island horizontally. The chip with the entire bottom surface coated with the molten solder moves at a speed of 5-15 mm / s in the vertical direction. The present invention regulates the speed at which the chip with the entire bottom surface coated with the molten solder contacts the base island to 5-15 mm / s, thereby ensuring that the molten solder coated on the bottom surface of the chip overflows. The preparation method provided by the present invention preferably controls the above-mentioned operation steps and technical parameters, which can not only solve the problem of solder overflow during chip welding and chip mounting, but also solve the flatness problem and chip tilt problem during chip bonding, and effectively reduce the number of bubbles after mounting. The effect is more significant when the base island size is similar to or the same as the chip size.

[0058] In order to further illustrate the present invention, the technical solution provided by the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0059] Example 1

[0060] according to Figure 1 As shown, a tin wire feeding device is used to feed a round solder wire to the bottom surface of a heating tank 1, and the solder wire is heated until it melts to form a solder melt droplet 2 that is approximately hemispherical;

[0061] according to Figure 2As shown in the figure, the chip size is: 2.8mm×4.1mm. The bonding head 5, which has sucked the horizontally placed chip 3 at the bottom, is moved vertically to the top of the solder melt 2 at a moving speed of 12mm / s, and then the bottom surface of the horizontally placed chip is brought into contact with the approximately hemispherical solder melt droplet 2 in the vertical direction at a moving speed of 12mm / s until the bottom surface of the chip is completely in contact with the solder melt droplet 2, as shown in FIG. Figure 3 As shown, a chip with the bottom surface dipped in molten solder is obtained; then the bonding head is moved vertically at a moving speed of 12 mm / s to keep the chip with the bottom surface dipped in molten solder away from the heating tank 2, as shown in FIG. Figure 4 As shown;

[0062] Move the bonding head that sucks the chip with the bottom surface dipped in solder melt to the top of the base island. The size of the base island is 3.1mm×4.5mm. By adjusting the relative XY position of the chip and the base island, the chip is placed directly above the base island. Figure 5 As shown in the figure, the bonding head is lowered vertically to the surface of the base island, and the solder melt on the bottom surface of the chip contacts the base island from point to surface, and finally completely occupies the space between the bottom surface of the chip and the surface of the base island, as shown in the figure. Figure 6 As shown; then the bonding head turns off the vacuum and moves upward in the vertical direction, and the chip welding and mounting is completed, as shown Figure 7 As shown, the solder volume of the chip welding chip is: 0.58mm 3 ; Solder thickness is 50μm.

[0063] Comparative Example 1

[0064] A solder wire feeding device is used to convey a round solder wire to the bottom surface of the base island, and the solder wire is heated until it melts to form a solder melt droplet that is approximately hemispherical;

[0065] The chip size is: 2.8mm×4.1mm. The bonding head 5, which has sucked the horizontally placed chip 3 at the bottom, is moved vertically to the top of the base island at a moving speed of 12mm / s. The base island size is 3.1mm×4.5mm. The relative XY position of the chip and the base island is adjusted by the bonding head position. The chip is located just above the base island, and the bonding head is lowered to the surface of the base island along the vertical direction. The solder melt droplets on the chip and the surface of the base island change from point contact to surface contact, and finally completely occupy the space between the bottom surface of the chip and the surface of the base island; then the bonding head closes the vacuum and moves upward along the vertical direction, and the chip welding and chip loading is completed; The solder amount of the chip welding and chip loading: 0.58mm 3 ; Solder thickness is 50μm.

[0066] A comparative test was performed on the chip soldering method provided in Example 1 and the chip soldering method provided in Comparative Example 1, and the methods of Example 1 and Comparative Example 1 were repeated 100 times respectively;

[0067] Compared with the method provided in Comparative Example 1, the test results of Example 1 are shown in Table 1:

[0068] Table 1 Comparative results of test of Example 1 and Comparative Example 1

[0069]

[0070] It can be concluded from Table 1 that in the chip soldering method provided in Example 1 of the present invention, all the solder is within the range of the pad without overflow; the flatness is significantly improved, and the proportion of bubble area is significantly reduced.

[0071] Example 2

[0072] according to Figure 1 As shown, a tin wire feeding device is used to feed a round solder wire to the bottom surface of a heating tank 1, and the solder wire is heated until it melts to form a solder melt droplet 2 that is approximately hemispherical;

[0073] according to Figure 2 As shown in the figure, the chip size is: 6.0mm×8.0mm. The bonding head 5, which has sucked the horizontally placed chip 3 at the bottom, is moved vertically to the top of the solder melt 2 at a moving speed of 6mm / s, and then the bottom surface of the horizontally placed chip is brought into contact with the approximately hemispherical solder melt droplet 2 in the vertical direction at a moving speed of 6mm / s until the bottom surface of the chip is completely in contact with the solder melt droplet 2. Figure 3 As shown, a chip with the bottom surface dipped in molten solder is obtained; then the bonding head is moved vertically at a moving speed of 6 mm / s to keep the chip with the bottom surface dipped in molten solder away from the heating tank 2, as shown in FIG. Figure 4 As shown;

[0074] Move the bonding head that sucks the chip with the bottom surface dipped in solder melt to the top of the base island. The size of the base island is 6.5mm×8.5mm. By adjusting the relative XY position of the chip and the base island, the chip is placed directly above the base island. Figure 5 As shown in the figure, the bonding head is lowered vertically to the surface of the base island, and the solder melt on the bottom surface of the chip contacts the base island from point to surface, and finally completely occupies the space between the bottom surface of the chip and the surface of the base island, as shown in the figure. Figure 6 As shown; then the bonding head turns off the vacuum and moves upward in the vertical direction, and the chip welding and mounting is completed, as shown Figure 7 As shown; the solder volume of the chip welding chip: 2.88mm 3 ; Solder thickness is 60μm.

[0075] Comparative Example 2

[0076] A solder wire feeding device is used to convey a round solder wire to the bottom surface of the base island, and the solder wire is heated until it melts to form a solder melt droplet that is approximately hemispherical;

[0077] The chip size is: 6.0mm×8.0mm. The bonding head 5, which has sucked the horizontally placed chip 3 at the bottom, is moved vertically at a moving speed of 6mm / s to the top of the base island. The base island size is 6.5mm×8.5mm. The relative XY position of the chip and the base island is adjusted by the bonding head position. The chip is located just above the base island, and the bonding head is lowered to the surface of the base island in the vertical direction. The solder melt droplets on the chip and the surface of the base island change from point contact to surface contact, and finally completely occupy the space between the bottom surface of the chip and the surface of the base island; then the bonding head closes the vacuum and moves upward in the vertical direction, and the chip welding and chip loading is completed; The solder amount of the chip welding and chip loading: 2.88mm 3 ; Solder thickness is 60μm.

[0078] A comparative test was performed on the chip soldering method provided in Example 2 and the chip soldering method provided in Comparative Example 2, and the methods of Example 2 and Comparative Example 2 were repeated 100 times respectively;

[0079] Compared with the method provided in Comparative Example 2, the test results of Example 2 are shown in Table 2:

[0080] Table 2 Comparative results of Example 2 and Comparative Example 2

[0081]

[0082] It can be concluded from Table 2 that in the chip soldering method provided in Example 2 of the present invention, all the solder is within the range of the pad without overflow; the flatness is significantly improved, and the proportion of bubble area is significantly reduced.

[0083] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for chip tinning, characterized in that: The following steps are involved: The solder is heated and melted to obtain a solder melt, wherein the solder melt is a solder melt droplet; The chip is placed horizontally and moved in a direction perpendicular to the bottom surface of the solder melt to the top of the solder melt for dipping in tin, the moving speed is 5-15 mm / s, and the dipping in tin is that the bottom surface of the chip horizontally contacts the top of the solder melt droplet; a chip with the entire bottom surface dipped in solder melt is obtained; The chip with the entire bottom surface coated with molten solder is placed horizontally, and moved in a direction perpendicular to the bottom surface of the molten solder to separate from the residual molten solder; the chip with the entire bottom surface coated with molten solder moves in a direction perpendicular to the bottom surface of the molten solder to separate from the residual molten solder at a speed of 5 to 15 mm / s; The base island is placed horizontally, and the chip with the entire bottom surface dipped in molten solder is placed horizontally and moved to the top of the base island in a direction perpendicular to the surface of the base island. The moving speed is 5 to 15 mm / s. The chip with the bottom surface dipped in molten solder is placed directly above the base island and in parallel contact with the surface of the base island for chip loading.

2. The method for chip tinning according to claim 1, characterized in that: The size of the chip is the same as or similar to that of the base island.

3. The method for chip tinning according to claim 1, characterized in that: The contact is that the center point of the bottom surface of the chip contacts the top point of the solder melt droplet.

4. The method for chip tinning according to claim 1, characterized in that: The melting step is: heating and melting the solder in a heating container with a horizontal bottom.

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