Gold wire ball wedge bonding method and 1.6 T silicon optical module

Abstract

The invention relates to a gold wire ball wedge bonding method, which comprises the following steps of: planting a first gold ball on an RF (Radio Frequency) bonding pad of a PCB (Printed Circuit Board) by adopting a ball bonding process, carrying out wedge bonding on one end of a gold wire on an RF bonding pad of a silicon optical chip by adopting a wedge bonding process, and pulling the other end of the gold wire up and then carrying out wedge bonding on the first gold ball; or, the second gold balls are planted on the RF bonding pad of the silicon optical chip and the first gold balls are planted on the RF bonding pad of the PCB by adopting a ball bonding process, then one end of the gold wire is subjected to wedge bonding on one second gold ball by adopting a wedge bonding process, and the other end of the gold wire is pulled up and then is subjected to wedge bonding on one first gold ball. The 1.6 T silicon optical module comprises the structure formed by bonding through the gold wire ball wedge bonding method. The method has the beneficial effects that the problem that the total length of the gold wire is too long is solved by adopting a gold wire ball wedge bonding method, the problem that the reliability of wedge bonding on a bonding pad in a PCB is unstable is solved, after ball wedge bonding is adopted, the maximum diameter of the gold wire can be 35 microns, the force is strong, the reliability is good, and the high-frequency performance is good.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of optical modules, in particular to a gold wire ball wedge bonding method and a 1.6T silicon optical module. BACKGROUND

[0002] A mainstream scheme of a traditional 1.6T silicon optical module adopts a single-wave 200G design, and there are 8 paths, that is, 8x200G=1.6T. In the 1.6T silicon optical module, a double-gold-wire design is generally adopted between each RF pad of a PCB and each RF pad of a silicon optical chip, so as to reduce the parasitic inductance of the gold wire. The reason is that the parasitic inductance of two gold wires is half of that of one gold wire, and there are two bonding processes of the gold wire and the RF pad on the PCB or the silicon optical chip, which are ball bonding and wedge bonding.

[0003] The working principle of the ball bonding process is as follows: the gold wire passes through the capillary of the hollow clamp, the part of the gold wire that protrudes is melted through arc discharge, and is spheroidized under the action of surface tension, then the ball is pressed and welded to one RF pad of the silicon optical chip through the clamp, and after being pressed, the ball serves as the first welding point, then the bent gold wire is pulled out from the first welding point, is pulled up, and is pressed and welded to one RF pad of the PCB, to form the second welding point. In production and application, the ball bonding is usually repeated once at the second welding point to lock the ball of the gold wire, so that the gold wire is more firm at the second welding point, as shown in FIG. 1. Figure 1 The ball bonding has no direction restriction in the bonding process, the ball bonding process increases the bonding strength of the gold wire, the two gold wires are independent, and are approximately parallel.

[0004] Since the parasitic inductance of the gold wire is required to be as small as possible, and the width size of the currently designed RF pad is generally designed to be 140 μm in length and 70 μm in width due to problems such as parasitic capacitance, the ball bonding is affected by the size of the pad, the ball diameter of the gold wire bonding is generally 2-3 times the diameter of the gold wire, and the diameter of the gold wire is generally 25 μm, so the ball diameter is less than 60 μm, thereby reserving a safety distance of 10 μm. Therefore, the current scheme can only punch two gold wires for each RF pad, and the number of gold wires cannot be increased. In addition, the ball bonding process requires that the gold wire must be pulled up after one welding, and the arc height of the gold wire is generally at least 75 μm, that is, at least 3 times the diameter of the gold wire. In addition, the thickness of the ball after one welding is generally 25 μm, so the overall arc height of the gold wire is more than 100 μm, which leads to a longer total length of the gold wire, a larger parasitic inductance, and a decline in high-frequency performance.

[0005] As shown in FIG. 2, the ball bonding process is not limited in direction, and the two gold wires are independent and approximately parallel. Figure 2As shown, the arc height of the gold wire in wedge soldering can be less than 25μm, which can significantly reduce the total length of the gold wire and improve high-frequency performance. However, wedge soldering uses physical pressure to break the gold wire. At the same time, since the RF pads on the PCB board are hard RF pads, the break point of the wedge soldering gold wire is prone to cracking, which can easily lead to failure during subsequent reliability screening such as temperature cycling. Therefore, the optical module industry does not actually use wedge soldering (because the reliability of wedge soldering is unstable). To avoid failure caused by gold wire breakage, ball soldering is currently the standard process.

[0006] The flat surface of the wedge: The flat surface of the wedge is generally at the front and is used for its installation and positioning. It is related to the transducer design. Most machines use screws to fix the wedge to the transducer's amplitude rod from the front, with the flat surface of the wedge facing forward. The foot of the wedge: The lower end and bottom of the wedge are the most critical parts, as they are where the bonding occurs. The lower end of the wedge is also called the "foot," with a toe at the front and a heel at the back. The radii of the toe and heel are crucial. The heel must have a relatively large radius to prevent cracks at the root of the first weld point during bonding. However, the radius needs to be smaller for wire pulling after the second weld point bonding to facilitate wire pulling. The bottom structure of the wedge: For strip leads, it is best to use a wedge with a groove between the bottom and the wire feed gap. This groove provides some clearance during wire feeding, preventing cracks from occurring at the heel bend of the first weld point during arc pulling. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a gold wire ball wedge bonding method and a 1.6T silicon photonics module to overcome the shortcomings of the prior art.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for gold wire ball wedge bonding includes the following steps: First, the first gold ball is implanted on the RF pad of the PCB board using ball bonding technology; Then, a wedge soldering process is used to wedge one end of the gold wire onto an RF pad of the silicon photonic chip, and the other end is pulled up and then wedge soldered onto a first gold ball implanted on the RF pad in the PCB board.

[0009] The beneficial effects of this invention are: Because the first gold ball is relatively soft and has a certain thickness, the wedge bonding process can avoid contacting the silicon photonics chip when pressing and pulling the gold wire, and can complete the operation of cutting, pressing and pulling the gold wire to avoid damage to the silicon photonics chip, thus greatly improving reliability. When the gold wire is pulled, the force is applied to the first gold ball, and the first gold ball and the RF pad adopt the ball bonding process. The welding area between the first gold ball and the RF pad is large, so that the gold layer of the RF pad itself on the PCB board will not be lifted and fall off from the body. This solution uses the gold wire ball wedge bonding method to solve the problem of excessive gold wire length and the problem of unstable reliability of wedge bonding on the RF pad in the PCB board. Due to the influence of RF pad size and gold ball, the maximum gold wire diameter for ball soldering is generally 25μm, and the minimum gold ball diameter is 50μm. This is because the gold ball cannot exceed the RF pad and a certain safety distance must be left. However, with ball wedge soldering, the maximum gold wire diameter can be 35μm. The thicker the gold wire diameter, the stronger the force, the better the reliability, and the better the high-frequency performance.

[0010] Based on the above technical solution, the present invention can be further improved as follows.

[0011] Furthermore, after the gold wire completes wedge soldering with the first gold ball, the soldering area between the first gold ball and the RF pad on the PCB board is 50μm to 60μm.

[0012] Furthermore, after the gold wire is wedge-welded with the first gold ball, the thickness of the first gold ball is 25μm to 40μm.

[0013] Furthermore, two first gold balls are implanted on the RF pads of the PCB board; the length of the RF pads on the PCB board is 140μm and the width is 70μm; the maximum diameter of the gold wire is 35μm.

[0014] Furthermore, a second gold ball is first placed on the RF pad of the silicon photonic chip and a first gold ball is placed on the RF pad of the PCB board using a ball bonding process. Then, a wedge bonding process is used to wedge one end of a gold wire onto a second gold ball placed on the RF pad of the silicon photonic chip, and the other end is pulled up and then wedge bonded onto a first gold ball placed on the RF pad of the PCB board.

[0015] The further beneficial effects of adopting the above are as follows: First, a first gold ball is placed on the RF pad of the PCB board, and a second gold ball is placed on the RF pad of the silicon photonic chip. Then, gold wire wedge soldering is performed on the first and second gold balls. Since the first and second gold balls are relatively soft and have a certain thickness, the wedge soldering process can avoid contacting the hard RF pad or silicon photonic chip on the PCB board when pressing and pulling the gold wire, and complete the operation of cutting, pressing and pulling the gold wire, which greatly improves reliability. When the gold wire is pulled, the force is applied to the first and second gold balls. The first and second gold balls are bonded to the RF pads using ball bonding technology. The bonding area between the first and second gold balls and the RF pads is large, which prevents the gold layer of the RF pads on the PCB board or silicon photonics chip from being lifted and detached from the body. The existing wedge bonding process directly bonds to the RF pads on the PCB board and silicon photonics chip. When the gold wire is broken, the contact area between the gold wire and the RF pads on the PCB board and silicon photonics chip is very small, generally less than 10μm. Moreover, the breaking is a gradual lifting process, which easily leads to the gold layer of the RF pads on the PCB board or silicon photonics chip being lifted and detached from the body. This solution uses a gold wire ball wedge bonding method to solve both the problem of excessive gold wire length and the problem of unstable reliability of wedge bonding to RF pads on the PCB board. Due to the influence of RF pad size and gold ball, the maximum gold wire diameter for ball soldering is generally 25μm, and the minimum gold ball diameter is 50μm. This is because the gold ball cannot exceed the RF pad and a certain safety distance must be left. However, with ball wedge soldering, the maximum gold wire diameter can be 35μm. The thicker the gold wire diameter, the stronger the force, the better the reliability, and the better the high-frequency performance.

[0016] Furthermore, after the gold wire completes wedge bonding with the first gold ball, the bonding area between the first gold ball and the RF pad on the PCB board is 50μm to 60μm, and after the gold wire completes wedge bonding with the second gold ball, the bonding area between the second gold ball and the RF pad on the silicon photonic chip is 50μm to 60μm.

[0017] Furthermore, after the gold wire is wedge-welded with the first gold ball, the thickness of the first gold ball is 25μm to 40μm, and after the gold wire is wedge-welded with the second gold ball, the thickness of the second gold ball is 25μm to 40μm.

[0018] Furthermore, two first gold balls are implanted on the RF pads of the PCB board; the length of the RF pads on the PCB board is 140μm and the width is 70μm; the maximum diameter of the gold wire is 35μm. Two second gold balls are implanted on the RF pads of the silicon photonics chip; the length of the RF pads on the silicon photonics chip is 140μm and the width is 70μm.

[0019] Based on the above technical solution, the present invention also provides a 1.6T silicon photonics module, comprising a structure bonded by the gold wire ball wedge bonding method described above.

[0020] The further beneficial effects of adopting the above are: it solves the problem of excessive gold wire length and the problem of unstable reliability when wedge soldered on RF pads in PCB board. Since the maximum diameter of gold wire can be 35μm, the thicker the gold wire diameter, the stronger the force, the better the reliability, and the better the high frequency performance.

[0021] Based on the above technical solution, the present invention also provides a 1.6T silicon photonics module, comprising a structure bonded by the gold wire ball wedge bonding method described above.

[0022] The further beneficial effects of adopting the above are: it solves the problem of excessive gold wire length and the problem of unstable reliability when wedge soldered on RF pads in PCB board. Since the maximum diameter of gold wire can be 35μm, the thicker the gold wire diameter, the stronger the force, the better the reliability, and the better the high frequency performance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the ball welding process in the prior art; Figure 2 This is a schematic diagram of the wedge welding process in the prior art; Figure 3 This is a structural diagram of a 1.6T silicon optical module using the first bonding structure; Figure 4 A flowchart of the first type of bonding structure; Figure 5 This is a structural diagram of a 1.6T silicon photonics module using the second bonding structure; Figure 6 A flowchart for the second type of bonding structure; Figure 7 This is a top view of a 1.6T silicon photonics module using the second bonding structure.

[0024] The attached diagram lists the components represented by each number as follows: 1. PCB board, 2. First gold ball, 3. Gold wire, 4. Silicon photonic chip, 5. Second gold ball. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] Example 1 like Figure 3 , Figure 4 As shown, a gold wire ball wedge bonding method includes the following steps: First, the first gold ball 2 is implanted on the RF pad of PCB board 1 using ball bonding process; Then, a wedge soldering process is used to wedge one end of the gold wire 3 onto an RF pad of the silicon photonic chip 4, and the other end is pulled up and then wedge soldered onto a first gold ball 2 implanted on the RF pad in the PCB board 1.

[0027] When the RF pads of the silicon photonic chip 4 are slightly higher than those of the PCB board 1 (due to the thickness tolerance of the PCB board 1), and the RF pads of the selected silicon photonic chip 4 have a strong direct gold wire wedge bonding force, the RF pads of the silicon photonic chip 4 do not need to be ball-mounted (some chips can also be directly wedge-bonded using a special process). First, the first gold ball 2 is placed on the RF pads of the PCB board 1, and then gold wire wedge bonding is performed on the first gold ball 2. Since the first gold ball 2 is relatively soft and has a certain thickness, the wedge bonding process can avoid contacting the silicon photonic chip 4 when pressing and pulling off the gold wire 3, and can complete the operation of cutting, pressing and pulling off the gold wire 3, so as to avoid damage to the silicon photonic chip 4 and significantly improve reliability. When the gold wire is pulled, the force is applied to the first gold ball 2. The first gold ball 2 and the RF pad adopt the ball bonding process. The welding area between the first gold ball 2 and the RF pad is large. This will not cause the gold layer of the RF pad itself on the PCB board 1 to be lifted and fall off from the body. The solution adopts the gold wire ball wedge bonding method to solve the problem of excessive gold wire length and the problem of unstable reliability of wedge bonding on the RF pad in the PCB board 1. Due to the influence of RF pad size and gold ball, the maximum diameter of gold wire 3 in ball bonding is generally 25μm, and the minimum diameter of gold ball is 50μm. The reason is that the gold ball cannot exceed the RF pad and a certain safety distance must be left. However, with ball wedge bonding, the maximum diameter of gold wire 3 can be 35μm. The thicker the diameter of gold wire 3, the stronger the force, the better the reliability, and the better the high-frequency performance.

[0028] Example 2 like Figure 3 As shown, this embodiment is a further improvement on embodiment 1, as detailed below: After the gold wire 3 is wedge-welded with the first gold ball 2, the welding area between the first gold ball 2 and the RF pad on the PCB board 1 is 50μm to 60μm, and the thickness of the first gold ball 2 is 25μm to 40μm.

[0029] Furthermore, two first gold balls 2 are implanted on the RF pads of PCB board 1; the length of the RF pads on PCB board 1 is 140μm, the width is 70μm, and the maximum diameter of the gold wire 3 is 35μm.

[0030] Example 3 like Figure 5 , Figure 6 , Figure 7 As shown, a gold wire ball wedge bonding method includes the following steps: First, a second gold ball 5 is placed on the RF pad of the silicon photonic chip 4 and a first gold ball 2 is placed on the RF pad of the PCB board 1 using a ball bonding process. Then, a wedge bonding process is used to wedge one end of the gold wire 3 onto a second gold ball 5 placed on the RF pad of the silicon photonic chip 4, and the other end is pulled up and then wedge bonded onto a first gold ball 2 placed on the RF pad of the PCB board 1.

[0031] First, a first gold ball 2 is placed on the RF pad of the PCB board 1, and a second gold ball 5 is placed on the RF pad of the silicon photonic chip 4. Then, gold wire wedge soldering is performed on the first gold ball 2 and the second gold ball 5. Since the first gold ball 2 and the second gold ball 5 are relatively soft and have a certain thickness, the wedge soldering process can avoid contacting the hard RF pad or silicon photonic chip 4 on the PCB board 1 when pressing and pulling off the gold wire 3, and complete the operation of cutting, pressing and pulling off the gold wire 3, which greatly improves reliability. When the gold wire is pulled, the force is applied to the first gold ball 2 and the second gold ball 5. The first gold ball 2 and the second gold ball 5 are bonded to the RF pad using ball bonding technology. The bonding area between the first gold ball 2 and the RF pad is large, and the bonding area between the second gold ball 5 and the RF pad is also large. This prevents the gold layer of the RF pad itself on the PCB board 1 or the silicon photonics chip 4 from being lifted and detached from the body. The existing wedge bonding process directly bonds to the RF pads on the PCB board 1 and the silicon photonics chip 4. When the gold wire is pulled off, the contact area between the gold wire and the RF pads on the PCB board 1 and the silicon photonics chip 4 is very small, generally less than 10μm. Moreover, the pulling off is a gradual lifting process, which easily leads to the gold layer of the RF pad itself on the PCB board 1 or the silicon photonics chip 4 being lifted and detached from the body. The proposed solution uses a gold wire ball wedge bonding method to solve both the problem of excessively long gold wires and the problem of unstable reliability of wedge bonding on the RF pads in the PCB board 1. Due to the influence of RF pad size and gold ball, the maximum diameter of gold wire 3 in ball bonding is generally 25μm, and the minimum diameter of gold ball is 50μm. The reason is that the gold ball cannot exceed the RF pad and a certain safety distance must be left. However, with ball wedge bonding, the maximum diameter of gold wire 3 can be 35μm. The thicker the diameter of gold wire 3, the stronger the force, the better the reliability, and the better the high-frequency performance.

[0032] Example 4 like Figure 5 , Figure 7 As shown, this embodiment is a further improvement on embodiment 3, as detailed below: After the gold wire 3 is wedge-welded with the first gold ball 2, the welding area between the first gold ball 2 and the RF pad on the PCB board 1 is 50μm to 60μm, and the thickness of the first gold ball 2 is 25μm to 40μm. After the gold wire 3 is wedge-welded with the second gold ball 5, the welding area of ​​the second gold ball 5 and the RF pad on the silicon photonic chip 4 is 50μm to 60μm, and the thickness of the second gold ball 5 is 25μm to 40μm.

[0033] Two first gold balls 2 are placed on the RF pads of PCB board 1. The length of the RF pads on PCB board 1 is 140μm and the width is 70μm. The maximum diameter of the gold wire 3 is 35μm. Two second gold balls 5 are placed on the RF pads of silicon photonic chip 4. The length of the RF pads on silicon photonic chip 4 is 140μm and the width is 70μm.

[0034] Example 5 like Figure 3 As shown, a 1.6T silicon photonics module is bonded using the gold wire ball wedge bonding method described in Example 1 or 2.

[0035] Example 6 like Figure 5 , Figure 7 As shown, a 1.6T silicon photonics module is bonded using the gold wire ball wedge bonding method described in Examples 3 or 4.

[0036] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for gold wire ball wedge bonding, characterized in that, Includes the following steps: First, the first gold ball (2) is implanted on the RF pad of the PCB board (1) using ball bonding process; Then, a wedge welding process is used to wedge one end of the gold wire (3) onto an RF pad of the silicon photonic chip (4), and the other end is pulled up and then wedge welded onto a first gold ball (2) implanted on the RF pad in the PCB board (1). After the gold wire (3) is wedge welded with the first gold ball (2), the welding area between the first gold ball (2) and the RF pad on the PCB board (1) is 50μm to 60μm. After the gold wire (3) is wedge welded with the first gold ball (2), the thickness of the first gold ball (2) is 25μm to 40μm. The maximum diameter of the gold wire (3) is 35μm.

2. The gold wire ball wedge bonding method according to claim 1, characterized in that, Two first gold balls (2) are implanted on the RF pad of the PCB board (1); the length of the RF pad on the PCB board (1) is 140μm and the width is 70μm.

3. The gold wire ball wedge bonding method according to claim 1, characterized in that, First, a second gold ball (5) is placed on the RF pad of the silicon photonic chip (4) and a first gold ball (2) is placed on the RF pad of the PCB board (1) using ball bonding process. Then, a wedge bonding process is used to wedge one end of the gold wire (3) onto a second gold ball (5) placed on the RF pad of the silicon photonic chip (4), and the other end is pulled up and then wedge bonded onto a first gold ball (2) placed on the RF pad of the PCB board (1).

4. The gold wire ball wedge bonding method according to claim 3, characterized in that, After the gold wire (3) is wedge-welded with the second gold ball (5), the welding area of ​​the second gold ball (5) and the RF pad on the silicon photonic chip (4) is 50μm to 60μm.

5. The gold wire ball wedge bonding method according to claim 4, characterized in that, After the gold wire (3) is wedge-welded with the second gold ball (5), the thickness of the second gold ball (5) is 25μm to 40μm.

6. The gold wire ball wedge bonding method according to claim 4, characterized in that, Two first gold balls (2) are placed on the RF pad of the PCB board (1); the length of the RF pad on the PCB board (1) is 140μm and the width is 70μm; two second gold balls (5) are placed on the RF pad of the silicon photonic chip (4); the length of the RF pad on the silicon photonic chip (4) is 140μm and the width is 70μm.

7. A 1.6T silicon photonics module, characterized in that, The structure includes those bonded by the gold wire ball wedge bonding method as described in claim 1 or 2.

8. A 1.6T silicon photonics module, characterized in that, The structure includes those bonded by the gold wire ball wedge bonding method as described in any one of claims 3 to 6.

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