Method of increasing solder bump volume and height

Abstract

To provide a method for increasing the volume and height of a solder bump existing on a contact pad of a substrate.SOLUTION: The method includes: a) a step of positioning a solder ball (2) having a predetermined volume in a capillary (1) positioned above a solder bump; b) a step of liquefying the solder ball (2) by applying laser energy from a laser source to the solder ball (2) via the capillary (1); c) a step of ejecting the liquefied solder ball (2) from the capillary (1) onto the solder bump by applying pressurized gas to the liquefied solder ball (2) via the capillary (1); and d) a step of transferring thermal energy and kinetic energy from the ejected liquefied solder ball (2) to the solder bump to melt the solder bump and fuse the liquefied solder ball (2) with the melted solder bump.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE

[0001] This disclosure relates to a method for increasing the volume and height of solder bumps present on contact pads of a substrate.

[0002]

[0002] U.S. Patent No. 6,468,893 discloses a method for forming solder bumps by: (a) forming a first solder paste layer on each electrode / pad of a substrate by printing solder paste on the electrodes / pads using a first mask; (b) forming a first solder bump on each electrode / pad by melting the first solder paste layer and solidifying the first solder paste layer after removing the first mask; (c) forming a second solder paste layer on each first solder bump by printing solder paste on the first solder bump using a second mask; and (d) forming a second solder bump on each electrode / pad by melting the first solder bump and the second solder paste layer together and solidifying the first solder bump and the second solder paste layer after removing the second mask. The above method allows solder bumps of a desired volume or height to be formed or printed on a substrate.

[0003]

[0003] Generally, when solder bumps have different heights, it is known in the prior art to use a mask with openings and apply solder paste through the openings to uniformize the heights of multiple solder bumps present on a substrate. Solder bumps with different heights can cause problems in certain joining applications, such as connecting a specific electronic component, such as a chip or another substrate, to a substrate via the solder bumps. In particular, when attaching an electronic component or another substrate, a high compressive force must be applied to avoid contact defects such as openings after attachment. Therefore, the openings in the mask may be individually sized so that all solder bumps have a uniform size after applying solder paste through the mask to the solder bumps with different heights. The solder bumps may be heated in a reflow oven to achieve reliable bonding.

[0004] In view of the above problems, it is an object of the present invention to provide a method for increasing the volume and height of solder bumps present on contact pads of a substrate, which method allows the volume and height of the solder bumps to be easily adjusted without a mask, and a solder ball ejection device for carrying out such a method.

[0005]

[0005] This object is solved by the methods according to independent claims 1 and 10. Preferred embodiments are the subject matter of the dependent claims.

[0006]

[0006] The present disclosure discloses a method for increasing the volume and height of a solder bump present on a contact pad of a substrate, which may include the steps of: a) positioning a solder ball having a predetermined volume in a capillary positioned above the solder bump; b) liquefying the solder ball by applying laser energy from a laser source to the solder ball through the capillary; c) ejecting the liquefied solder ball from the capillary onto the solder bump by applying pressurized gas to the liquefied solder ball through the capillary; and d) melting the solder bump by transferring thermal energy and kinetic energy from the ejected liquefied solder ball to the solder bump, causing the liquefied solder ball to fuse with the molten solder bump.

[0007]

[0007] In the above-described method, the energy of the liquefied solder balls, particularly in the form of kinetic and thermal energy, can be used to melt the solder bumps in contact with the liquefied solder balls, allowing the liquefied solder balls to fully penetrate and fuse with the solder bumps. This method allows the volume and height of the solder bumps to be easily increased without the use of a mask. It should be noted that the term "solder ball" does not limit the shape of the solder balls to perfect spheres, but includes any solder preform that is substantially spherical. The material of the solder balls may be different from the material of the solder bumps. For example, the solder balls may be made of the solder alloy SAC305, and the solder bumps may be made of a SnBi alloy.

[0008] In a further embodiment, during step d), laser energy, preferably from a laser source, is further applied to the solder bumps.

[0009]

[0009] Specifically, a laser source can be operated during steps a) to d) to ensure that the solder balls are liquefied in step b) and that the liquefied solder balls fully penetrate and fuse with the solder bumps in step d).

[0010] In a further embodiment, prior to step a), laser energy, preferably from a laser source, is applied to the solder bumps.

[0011]

[0011] Before step a), laser energy, preferably laser energy from a laser source, can be transmitted to the solder bumps to preheat or premelt the solder bumps so that in step d), the solder balls can easily penetrate completely into the solder bumps and easily fuse with them.

[0012]

[0012] In a further embodiment, the thermal energy and kinetic energy of the liquefied solder balls and / or the laser energy required for the step of melting the solder bumps can be adjusted by setting the gas pressure to 25 mbar to 130 mbar and / or setting the laser energy to 2 mJ to 150 mJ.

[0013]

[0013] In a further embodiment, the substrate has at least two solder bumps of different heights, and steps a) to d) are performed on a first solder bump having a lower height than a second solder bump having a higher height to adjust the height of the first solder bump to the height of the second solder bump.

[0014]

[0014] The above-described method allows the height of a first solder bump to be easily adjusted to the height of a second solder bump. In particular, the method can be used to adjust the height of all solder bumps present on a substrate to the height of the tallest solder bump, thereby creating a coplanar connection plane on the substrate. Electronic components, such as chips or other substrates, can then be securely connected to the substrate without contact defects, such as solder bridges.

[0015]

[0015] In a further embodiment, the method further includes steps e) measuring the difference in height between the first solder bump and the second solder bump; and f) calculating the total volume of solder material required to add to the first solder bump so as to increase the volume and height of the first solder bump until it reaches the height of the second solder bump, wherein steps e) and f) are performed before steps a) to d), and if the predetermined volume of the solder ball is smaller than the calculated total volume of solder material, steps a) to d) are repeated.

[0016]

[0016] Thus, by carrying out the above-described method, the height of the first solder bump can be easily and reliably increased to the height of the second solder bump. Measuring the height difference between the first and second solder bumps may be performed in any manner. However, optical measurement, for example using a camera or laser, is preferred. By calculating the total volume of solder material required to be added to the first solder bump so as to increase its volume and height to the height of the second solder bump, processing speed can be increased because there is no need to compare the height of the second solder bump with the height of the first solder bump after each liquefied solder ball is added to the first solder bump.

[0017]

[0017] In a further embodiment, the method further includes steps g) measuring the actual height of the solder bump; and h) calculating the total volume of solder material to be added to the solder bump so as to increase the volume and height of the solder bump until it reaches a predetermined target height, wherein steps g) and h) are performed before steps a) to d), and if the predetermined volume of the solder ball is smaller than the calculated total volume of solder material, steps a) to d) are repeated.

[0018]

[0018] By carrying out the above-described method, the height of the solder bump can be easily and reliably increased to a target height. By calculating the total volume of solder material required to be added to the solder bump so as to increase the volume and height of the solder bump until it reaches a predetermined target height, processing speed can be increased because there is no need to perform solder bump height measurements after each liquefied solder ball is added to the solder bump.

[0019] In a further embodiment, the step of measuring the actual height of the solder bumps is performed optically.

[0020] Optical measurement of the solder bump height is preferred, for example using a camera or a laser.

[0021] In a further embodiment, the predetermined volume of the solder balls is 1.4e -5 mm 3 ~0.015mm 3 , preferably 3,3e -5 mm 3 is.

[0022]

[0022] That is, 1,4e -5 mm 3 ~0.015mm 3By applying solder balls with a relatively small, predetermined volume, the volume and height of the solder bumps can be adjusted very precisely. Even small height differences of the solder bumps in the micrometer range can be compensated for, resulting in a coplanar connection plane on the substrate.

[0023]

[0023] The present disclosure discloses a solder ball ejection apparatus including a capillary, a laser source, a pressurized gas source, and a controller, and the controller can be configured to control the capillary, the laser source, and the pressurized gas source to perform a method according to any of the above aspects. Specifically, the solder ball ejection apparatus can be configured to perform a method including: a) positioning a solder ball having a predetermined volume in a capillary positioned above a solder bump present on a contact pad of a substrate, b) liquefying the solder ball by applying laser energy from a laser source to the solder ball through the capillary, c) applying pressurized gas from a pressurized gas source to the liquefied solder ball through the capillary, thereby ejecting the liquefied solder ball from the capillary onto the solder bump, and d) transferring thermal energy and kinetic energy from the ejected liquefied solder ball to the solder bump, thereby melting the solder bump and fusing the liquefied solder ball with the molten solder bump.

[0024] The solder balls may be stored in a reservoir and separated by a rotating singulation disk, which also transfers the solder balls to the capillary. The solder balls may fall into the capillary and block the capillary opening by having a diameter slightly larger than the diameter of the capillary opening. A laser source may apply short near-infrared laser pulses interacting in the millisecond range to liquefy the solder balls. A pressurized gas source may add pressurized gas, such as N2, into the capillary so that the liquefied solder balls can be ejected from the capillary onto the solder bumps. The energy of the liquefied solder balls is directly related to the speed at which they are ejected from the capillary. The speed of the liquefied solder balls, in turn, depends on the pressure of the pressurized gas source, which is controlled by a controller. The solder ball ejection device or capillary described above may be controlled by a controller to be movable along three axes so as to be positioned over any solder bump on the substrate whose volume and height are to be increased. The controller may be further configured to calculate a total volume of solder material needed to add to the solder bump to increase the volume and height of the solder bump until a further solder bump height is reached or a predetermined height is reached.

[0025]

[0025] In the above-described apparatus, the energy of the liquefied solder balls, particularly in the form of kinetic energy and thermal energy, can be used to melt the solder bumps in contact with the liquefied solder balls, so that the liquefied solder balls can completely penetrate and fuse with the solder bumps. This apparatus makes it possible to easily increase the volume and height of the solder bumps without using a mask.

[0026]

[0026] Furthermore, during step d), laser energy, preferably laser energy from a laser source, can be further applied to the solder bumps, i.e., the laser source can be activated during steps a) to d) to ensure that the solder balls are liquefied in step b) and the liquefied solder balls fully penetrate and fuse with the solder bumps in step d).

[0027]

[0027] The present disclosure discloses a controller for a solder ball ejection apparatus including a capillary, a laser source, and a pressurized gas source, and the controller can be configured to control the capillary, the laser source, and the pressurized gas source to perform a method according to any of the above aspects. Specifically, the controller for the solder ball ejection apparatus can be configured to perform a method including: a) positioning a solder ball having a predetermined volume in a capillary positioned above a solder bump present on a contact pad of a substrate, b) applying laser energy from a laser source to the solder ball through the capillary to liquefy the solder ball, c) applying pressurized gas to the liquefied solder ball through the capillary to eject the liquefied solder ball from the capillary onto the solder bump, and d) transferring thermal energy and kinetic energy from the ejected liquefied solder ball to the solder bump to melt the solder bump and fuse the liquefied solder ball with the molten solder bump. The solder ball ejection device or capillary may be controlled by a controller to be movable along three axes to be positioned over any solder bump on the substrate whose volume and height are to be increased, and the controller may be further configured to calculate the total volume of solder material needed to add to the solder bump to increase the volume and height of the solder bump until a further solder bump height is reached or a predetermined height is reached.

[0028] A pressurized gas source may add pressurized gas, such as N2, into the capillary so that the liquefied solder ball can be ejected from the capillary onto the solder bump. The energy of the liquefied solder ball is directly related to the velocity at which the liquefied solder ball is ejected from the capillary. The velocity of the liquefied solder ball in turn depends on the pressure of the pressurized gas source, which is controlled by a controller.

[0029]

[0029] The controller described above can melt the solder bumps in contact with the liquefied solder balls by controlling and using the energy of the liquefied solder balls, particularly in the form of kinetic and thermal energy, so that the liquefied solder balls can fully penetrate and fuse with the solder bumps. The controller allows for easy increase in the volume and height of the solder bumps without the use of a mask.

[0030]

[0030] Furthermore, during step d), laser energy, preferably laser energy from a laser source, can be further applied to the solder bumps, i.e., the laser source can be activated during steps a) to d) to ensure that the solder balls are liquefied in step b) and the liquefied solder balls fully penetrate and fuse with the solder bumps in step d). [Brief explanation of the drawings]

[0031]

[0031] In the following, an embodiment of the present disclosure will be described with reference to several figures. [Figure 1] 1 illustrates a front view of a solder ball ejection apparatus according to one embodiment for adding solder balls to solder bumps present on a substrate. [Figure 2] 2 shows an enlarged front view of the solder ball ejection device and solder bumps of FIG. 1. [Figure 3] 1 illustrates the application of a solder ball ejection device to achieve uniform height solder bumps on an uneven substrate.

[0032]

[0032] The figures are merely schematic in nature and are intended solely for the purpose of understanding the present disclosure. The proportions of the elements shown in the figures have been appropriately adjusted to facilitate a better understanding of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0033]

[0033] Figure 1 discloses a solder ball ejection apparatus 10 according to one embodiment, comprising a movable capillary 1, a laser source (not shown), a pressurized gas source (not shown), and a controller (not shown) configured to control the capillary 1, the laser source, and the pressurized gas source.

[0034] As shown in FIG. 1, capillary 1 is positioned a fixed distance above solder bump 5a, which resides on contact pad 3 of substrate 4. An additional solder bump 5b resides on contact pad 3 on substrate 4, with solder bump 5a having a height that is smaller than solder bump 5b, which each have the same height. Although not shown in FIG. 1, the difference in height between solder bump 5a and solder bump 5b is optically measured, and the total volume of solder material required to add to solder bump 5a to increase the volume and height of solder bump 5a to reach the height of solder bump 5b is calculated. Furthermore, the number of solder balls having a predetermined volume corresponding to the total volume of solder material is calculated.

[0035] Furthermore, a solder ball 2 having a predetermined volume, which is positioned within the capillary 1 and liquefied by applying laser energy from a laser source through the capillary 1, is ejected from the capillary 1 onto the solder bump 5a. Specifically, pressurized gas from a pressurized gas source is applied to the liquefied solder ball 2 through the capillary 1, causing the liquefied solder ball 2 having a specific temperature to be ejected from the capillary 1 at a specific speed. That is, the liquefied solder ball 2 being ejected from the capillary 1 has a certain kinetic energy and a certain thermal energy depending on the temperature and speed of the solder ball 2. The speed of the liquefied solder ball 2, in turn, depends on the pressure of the pressurized gas, which is controlled by a controller.

[0036]

[0036] The kinetic and thermal energy of the liquefied solder balls 2 are used to melt the solder bumps 5a in contact with the liquefied solder balls 2, allowing the liquefied solder balls 2 to completely penetrate and fuse with the solder bumps 5a. Furthermore, laser energy from a laser source can be transmitted to the solder bumps 5a to ensure that the liquefied solder balls 2 completely penetrate and fuse with the solder bumps 5a. The above method is then repeated until the calculated number of solder balls 2 have been added to the solder bumps 5a, i.e., until the total volume of solder material has been added to the solder bumps 5a. As shown by the dashed lines in FIG. 2, the volume and height of the solder bumps 5a are increased with each solder ball 2 added within the solder bumps 5a. It is further noted that when the solder balls 2 contact the solder bumps 5a, they penetrate completely into the solder bumps 5a and fuse with the solder bumps 5a, thereby giving the solder bumps 5a a uniform structure. According to the above-described solder ball injection apparatus 10 and method, the volume and height of the solder bumps 5a can be easily increased without using a mask.

[0037] Additionally, as shown on the left side of FIG. 3, a contoured substrate 4 is provided with a plurality of solder bumps disposed thereon. Note that contact pads are not depicted in FIG. 3. The solder bumps are the same size. However, due to the contours of the substrate 4, the solder bumps designated 5b are the highest relative to the underside of the substrate 4. The solder bumps 5a can be enlarged using the solder ball injection apparatus 10 and method described above to create a coplanar connection plane, shown by the dashed lines on the right side of FIG. 3.

[0038] In particular, the solder ball injection apparatus 10 and method can be used to create a coplanar connection plane on the substrate 4 by adjusting the heights of all solder bumps present on the substrate 4 that have a height lower than the height of the tallest solder bump, regardless of whether the different heights of the solder bumps result from solder bumps having different sizes as shown in FIG. 1 or from an uneven substrate 4 as shown in FIG. 3. Electronic components, such as chips or other substrates, can then be securely connected to the substrate 4 without contact defects, such as solder bridges. In general, the above-described method allows each individual solder bump present on the substrate to be easily adjusted to a desired height. [Explanation of symbols]

[0039]

[0039] 1...capillary, 2...solder ball, 3...contact pad, 4...substrate, 5a...solder bump, 5b...solder bump, 10...solder ball injection device

Claims

1. A method for increasing the volume and height of solder bumps present on contact pads (3) of a substrate (4), comprising: a) positioning a solder ball (2) having a predetermined volume in a capillary (1) positioned above the solder bump; b) applying laser energy from a laser source to the solder balls (2) through the capillary (1) to liquefy the solder balls (2); c) discharging the liquefied solder ball (2) from the capillary (1) onto the solder bump by applying pressurized gas to the liquefied solder ball (2) through the capillary (1); d) transferring thermal energy and kinetic energy from the discharged liquefied solder balls (2) to the solder bumps to melt the solder bumps and fuse the liquefied solder balls (2) with the molten solder bumps; A method comprising:

2. The method of claim 1 , wherein during step d), laser energy from the laser source is further applied to the solder bumps.

3. The method of claim 1 , wherein prior to step a), laser energy from the laser source is applied to the solder bumps.

4. 2. The method of claim 1, wherein the thermal energy and the kinetic energy of the liquefied solder balls (2) and / or the laser energy required for the step of melting the solder bumps can be adjusted by setting the gas pressure to 25 mbar to 130 mbar and / or setting the laser energy to 2 mJ to 150 mJ.

5. 2. The method of claim 1, wherein the substrate (4) comprises at least two solder bumps of different heights, and wherein steps a) to d) are performed on a first solder bump (5a) having a lower height than a second solder bump (5b) having a higher height, such that the height of the first solder bump (5a) is adjusted to the height of the second solder bump (5b).

6. e) measuring the height difference between the first solder bump (5a) and the second solder bump (5b); f) calculating the total volume of solder material required to be added to the first solder bump (5a) so as to increase the volume and the height of the first solder bump (5a) until it reaches the height of the second solder bump (5b); further comprising Steps e) and f) are performed before steps a) to d); 6. The method of claim 5, wherein if the predetermined volume of the solder ball (2) is smaller than the calculated total volume of solder material, steps a) to d) are repeated.

7. g) measuring the actual height of the solder bump; h) calculating a total volume of solder material to be added to the solder bump to increase the volume and height of the solder bump until it reaches a predetermined target height; further comprising Steps g) and h) are performed before steps a) to d), 2. The method of claim 1, wherein if the predetermined volume of the solder ball (2) is smaller than the calculated total volume of solder material, steps a) to d) are repeated.

8. The method of claim 7 , wherein the step of measuring the actual height of the solder bump is performed optically.

9. The predetermined volume of the solder ball (2) is 1.4e －５ mm ３ ~0.015mm ３ , or 3, 3e －５ mm ３ The method according to any one of claims 1 to 8, wherein

10. A solder ball ejection device (10) comprising a capillary (1), a laser source, a pressurized gas source, and a controller, the controller: a) positioning a solder ball (2) having a predetermined volume in said capillary (1) positioned above a solder bump present on a contact pad (3) of a substrate (4); b) applying laser energy from the laser source to the solder balls (2) through the capillary (1) to liquefy the solder balls (2); c) applying pressurized gas from the pressurized gas source to the liquefied solder ball (2) through the capillary (1), thereby discharging the liquefied solder ball (2) from the capillary (1) onto the solder bump; d) transferring thermal energy and kinetic energy from the discharged liquefied solder balls (2) to the solder bumps to melt the solder bumps and fuse the liquefied solder balls (2) with the molten solder bumps; a solder ball ejection device (10) configured to control the capillary (1), the laser source, and the pressurized gas source to perform a method comprising:

11. A controller for a solder ball ejection device (10) comprising a capillary (1), a laser source, and a pressurized gas source, the controller comprising: a) positioning a solder ball (2) having a predetermined volume in said capillary (1) positioned above a solder bump present on a contact pad (3) of a substrate (4); b) applying laser energy from the laser source to the solder balls (2) through the capillary (1) to liquefy the solder balls (2); c) discharging the liquefied solder ball (2) from the capillary (1) onto the solder bump by applying pressurized gas to the liquefied solder ball (2) through the capillary (1); d) transferring thermal energy and kinetic energy from the discharged liquefied solder balls (2) to the solder bumps to melt the solder bumps and fuse the liquefied solder balls (2) with the molten solder bumps; a controller configured to control the capillary (1), the laser source, and the pressurized gas source to perform a method comprising:

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