Gold wire ball bonding method

Abstract

The embodiment of the present application discloses a gold wire ball welding bonding method, which comprises the following steps: bonding a first welding point of a gold wire ball welding on a welding pad of a substrate; and bonding a second welding point of the gold wire ball welding on a welding pad of a chip; wherein the height of the substrate is lower than the height of the chip, so that the height of a spherical welding point of the first welding point and the arc starting height are calculated from the surface of the substrate, thereby controlling the arc height of a bonding wire. The technical scheme of the present application solves the problem that the arc of the gold wire in the SIP package is prone to be too high. The first welding point of the ball welding is selected to be punched on the substrate with a lower height, and the second welding point is punched on the chip with a higher height, so that the two inevitable heights of the ball height of the first welding point and the arc starting height are diluted by the substrate with a lower height, thereby controlling the arc height and solving the problem that the arc of the gold wire in the SIP package is prone to be too high.

Description

Technical Field

[0001] This invention relates to the field of gold wire ball bonding technology. More specifically, it relates to a gold wire ball bonding method. Background Technology

[0002] Currently, due to the need for subsequent capping, the bonding arc height of SiP packaging has relatively strict requirements (less than 500μm). If the conventional ball bonding is used to bond the chip with a higher height to the substrate with a lower height (i.e., the first solder joint of the ball bonding falls on the chip), considering the structural height of the ball bonding itself (taking Φ25μm gold wire as an example, the diameter of the bonding joint is about 60μm~80μm, the height of the ball bonding joint is about 35μm~45μm, plus the height of the subsequent arc initiation of 50μm~100μm) and the thickness of the chip itself (150μm~350μm), the arc height is very likely to be too high, which will affect the subsequent capping. Summary of the Invention

[0003] The purpose of this invention is to provide a gold wire ball bonding method to solve at least one of the problems existing in the prior art.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a method for gold wire ball bonding, the method comprising: The first solder joint of the gold wire ball is bonded to the pad on the substrate; The second solder joint of the gold wire ball is bonded to the chip's solder pad; The height of the substrate is lower than the height of the chip, so that the height of the spherical solder joint and the arc starting height of the first solder joint are measured from the surface of the substrate, thereby controlling the arc height of the bonding wire arc.

[0005] Optionally, the step of bonding the second solder joint of the gold wire ball to the pad of the chip includes: Pad balls are pre-formed on the pads of the chip; The second solder joint is bonded to the pad ball.

[0006] Optionally, the bonding pressure and ultrasonic power of the pad ball are both lower than those of the first solder joint.

[0007] Optionally, the substrate pads are gold pads, and the chip pads are aluminum pads.

[0008] Optionally, the bonding of the first solder joint of the gold wire ball to the pad of the substrate includes: A first pressure is applied to the gold ball formed at the end of the gold wire so that the gold ball contacts the pad of the substrate and forms a basic spherical shape; A second pressure and ultrasonic vibration are applied to modify the basic spherical shape; A third pressure is applied to the modified sphere to make the modified sphere fit against the pads of the substrate.

[0009] Optionally, the step of bonding the second solder joint of the gold wire ball to the pad of the chip includes: Under the fourth pressure, the cutting blade moves a first distance in a predetermined direction to unfold the gold wire into a fishtail shape and make contact with the pads of the chip; Under the fifth pressure, the chopping blade moves a second distance in the predetermined direction and applies ultrasonic vibration to further unfold the fishtail-shaped gold wire and promote bonding between the fishtail-shaped gold wire and the chip's pads, wherein the fifth pressure is greater than the fourth pressure and the second distance is less than the first distance. Under the sixth pressure, the cleaver moves a third distance in the opposite direction to the predetermined direction to separate the gold wire from the fishtail-shaped gold wire and complete the cleaving. Ultrasonic vibration is applied to bond the tail wire formed after cleaving to the pads of the chip.

[0010] Optionally, by adjusting the second solder joint position compensation parameter, the actual bonding position can be made to match the preset position, wherein when the second solder joint position compensation parameter is negative, the actual second solder joint is offset away from the first solder joint.

[0011] Optionally, after a pad ball is pre-formed on the pad of the chip, the cleaver moves laterally a predetermined distance to tear off the tail wire of the pad ball laterally.

[0012] Optionally, before bonding, the chips to be bonded are subjected to plasma cleaning to remove the oxide layer and contaminants on the surface of the chip's pads.

[0013] Optionally, the step of bonding the second solder joint of the gold wire ball to the pad of the chip includes: Under the fourth pressure, the cutting blade moves a first distance in a predetermined direction to unfold the gold wire into a fishtail shape and make contact with the pads of the chip; Under the fifth pressure, the chopping blade moves a second distance in the predetermined direction and applies ultrasonic vibration to further unfold the fishtail-shaped gold wire and promote bonding between the fishtail-shaped gold wire and the chip's pads, wherein the fifth pressure is greater than the fourth pressure and the second distance is less than the first distance. Under the sixth pressure, the chopping blade moves a third distance in the opposite direction to the predetermined direction, so that the gold wire separates from the fishtail-shaped gold wire to complete the tangent. Ultrasonic vibration is applied to bond the tail wire formed after the tangent to the pad ball.

[0014] The beneficial effects of this invention are as follows: The technical solution of this invention addresses the problem of excessive arc height in the gold wires inside the packaged SIP by placing the first solder joint of the ball soldering on the substrate with a lower height and the second solder joint on the chip with a higher height. This reduces the unavoidable height of the ball and the arc height of the first solder joint by the substrate at the lower position, thereby controlling the arc height and solving the problem of excessive arc height in the gold wires inside the packaged SIP. Attached Figure Description

[0015] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0016] Figure 1 A flowchart illustrating a gold wire ball bonding method provided in an embodiment of the present invention is shown.

[0017] Figure 2 A flowchart illustrating a gold wire ball bonding method provided by another embodiment of the present invention is shown. Detailed Implementation

[0018] To more clearly illustrate the present invention, the following description, in conjunction with embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0019] Currently, due to the need for subsequent capping, the bonding arc height of SiP packaging has relatively strict requirements (less than 500μm). If the conventional ball bonding is used to bond the chip with a higher height to the substrate with a lower height (i.e., the first solder joint of the ball bonding falls on the chip), considering the structural height of the ball bonding itself (taking Φ25μm gold wire as an example, Φ is the diameter, the diameter of the bonding joint is about 60μm~80μm, the height of the ball bonding joint is about 35μm~45μm, plus the height of the subsequent arc initiation 50μm~100μm) and the thickness of the chip itself (150μm~350μm), the arc height is very likely to be too high, thus affecting the subsequent capping.

[0020] In view of this, such as Figure 1 As shown, one embodiment of the present invention provides a gold wire ball bonding method, the method comprising: bonding a first gold wire ball bonding joint to a pad on a substrate; bonding a second gold wire ball bonding joint to a pad on a chip; wherein the height of the substrate is lower than the height of the chip, so that the height of the spherical bonding joint and the arc starting height of the first bonding joint are measured from the surface of the substrate, thereby controlling the arc height of the bonding arc.

[0021] In a specific example, such as Figure 2As shown, the method includes step ①, a search action: the wedge (a ceramic tube with a gold wire in the middle) moves downward to find the position of the first solder joint and align it with the pad. Step ②, first solder joint bonding: the wedge presses a small gold ball, pre-fired at the end of the gold wire, onto the first solder joint (ball bonding). Step ③, arc pulling: the wedge moves upward, pulling out the gold wire and beginning to form a line arc. Step ④, line arc formation: the wedge moves above the second solder joint, and the shape of the line arc is formed. Step ⑤, second solder joint bonding: the wedge descends, flattening the gold wire onto the second solder joint (fishtail bonding, not ball bonding). Step ⑥, line tail formation: the wedge moves upward, breaking the gold wire, leaving a small tail at the break. Step ⑦, raising to arc height: the wedge is raised to the height of electronic arcing (EFO), preparing to burn the next ball. Step ⑧, gold ball formation: electronic arcing burns the end of the gold wire into a small gold ball, then returns to step ① to begin the next bonding cycle.

[0022] The technical solution of this invention addresses the problem of excessive arc height in the gold wires inside the packaged SIP by placing the first solder joint of the ball soldering on the substrate with a lower height and the second solder joint on the chip with a higher height. This reduces the unavoidable height of the ball and the arc height of the first solder joint by the substrate at the lower position, thereby controlling the arc height and solving the problem of excessive arc height in the gold wires inside the packaged SIP.

[0023] In a specific example, the 100μm ultra-low arc gold wire ball bonding technology includes the following steps: First, optimization of solder joint bonding parameters. The first solder joint bonding parameters are optimized. Since the first solder joint is on the substrate, and the silicon substrate surface is coated with a thick gold layer, the bonding wire and the surface pads have good affinity and can bond well. The factors determining the solder joint quality are mainly four: pressure, oscillation power, welding time, and welding temperature. The experiment primarily focuses on controlling these four aspects.

[0024] Furthermore, the bonding parameters for the second solder joint were optimized. When using gold wire ball bonding, the second bonding point differs from conventional wedge bonding points; it is formed by welding gold wire to half of the circular hole at the front end of the wedge. The other half of the circular hole at the front end of the wedge is suspended at the bottom, making it prone to noticeable indentations or damage to the welding area when the ultrasonic energy and welding pressure are slightly higher. The bonding stability of the second solder joint is more sensitive to changes in parameters; bonding pressure, ultrasonic power, and process time all contribute to determining the bonding effect.

[0025] Further, the specific steps include: Step 2, arc control. The arc characteristics of the lead are an important factor in wire bonding because they affect the device's performance and reliability. For example, the arc cannot be too high, as an excessively high arc will cause the leads to be exposed after molding. Even if the leads are not exposed, an excessively high arc will result in excessively long and drooping leads, which may be bent by the cover plate during subsequent capping processes, potentially leading to short circuits between leads. Unnecessarily long leads will cause mutual interference between leads, degrading the electrical performance of the device. However, the arc cannot be too low either. A low arc means that the lead is pulled down significantly during the transfer of the lead from the first solder joint to the second solder joint. A low arc usually indicates that the lead is pulled very tightly, and strong tension will accumulate at the neck or root of the first solder joint. If pulled too low, cracks or even breakage can easily occur in these areas. Therefore, optimizing a reliable gold wire ball bonding process suitable for low arc bonding is extremely important for the mass application of adapter boards.

[0026] Further, the specific steps include: Step 3, lead wire pull test. To accurately characterize the influence of gold wire ball bonding strength, the basic pull value of the gold wire is tested as a control to determine the quality of the gold wire bonding strength. The test samples are completed using the same materials, operators, and equipment as the product in its technical specifications, and then tested according to relevant standards.

[0027] In one possible implementation, bonding the second solder joint of the gold wire ball solder to the pad of the chip includes: pre-forming a pad ball on the pad of the chip; and bonding the second solder joint to the pad ball.

[0028] In this embodiment, by pre-forming pads on the chip pads and then bonding the second solder joint to the pads, the second solder joint is changed from being directly bonded to the aluminum pads to being bonded to the gold balls. Utilizing the better affinity between the gold balls and the gold wires, the bonding compatibility between the gold wires and the chip aluminum pads can be improved, thereby increasing the bonding stability of the second solder joint. At the same time, the pads raise the bonding surface of the second solder joint, which can prevent the chip pads from being damaged when the wrench is pressed down directly.

[0029] In one possible implementation, the bonding pressure and ultrasonic power of the pad ball are both lower than those of the first solder joint.

[0030] In this embodiment, the bonding pressure and ultrasonic power of the pad are set to be lower than those of the first solder joint. This can ensure the bonding strength between the pad and the chip pad, while avoiding excessive pressure and ultrasonic power that could cause unnecessary damage to the chip surface, thereby improving the bonding yield and reducing defective products caused by chip damage.

[0031] In one possible implementation, the substrate pads are gold pads, and the chip pads are aluminum pads.

[0032] This embodiment clarifies the application scenario of using gold pads for the substrate and aluminum pads for the chip, enabling the first solder joint to achieve reliable bonding by utilizing the good affinity between the gold wire and the gold pad. At the same time, it specifically addresses the problems of poor compatibility between aluminum pads and gold wires, which can easily lead to poor bonding and pressure damage, making the technical solution applicable to common silicon-based SIP packaging structures.

[0033] In one possible implementation, bonding the first solder joint of the gold wire ball to the pad of the substrate includes: applying a first pressure to the gold ball formed by the end of the gold wire to make the gold ball contact the pad of the substrate and form a basic spherical shape; applying a second pressure and ultrasonic vibration to modify the basic spherical shape; and applying a third pressure to the modified spherical shape to make the modified spherical shape adhere to the pad of the substrate.

[0034] This embodiment employs a three-step process: a first pressure step to punch the gold ball into a basic spherical shape, an ultrasonic friction step to refine the spherical shape to enhance flatness, and a second pressure step to further bond the spherical shape to the pad. This process ensures that the solder ball of the first solder joint has a full shape, good flatness, and tight bonding with the pad, thereby improving the bonding quality and consistency of the first solder joint.

[0035] In a specific example, the parameters of the first solder joint were first optimized. The first solder joint is on the substrate, and the surface of the silicon substrate is coated with a thick gold layer. Therefore, the bonding wire and the surface pad have good affinity and can bond well. The factors that determine the quality of the solder joint are mainly four: pressure, oscillation power, soldering time, and soldering temperature. The experiment also mainly focuses on controlling these four aspects.

[0036] Furthermore, the first solder joint bonding parameter adjustment involves consulting relevant equipment technical manuals and materials to set the first solder joint bonding procedure into three small steps. The first stage, Force mode, uses high pressure to directly strike the gold ball onto the solder pad, forming a basic spherical shape; the second stage, Scrub mode, uses ultrasound to refine the spherical shape and enhance its flatness; the third stage, Force mode, applies additional pressure to make the spherical shape fit the solder pad more closely. Force mode is a pressure mode, and Scrub mode is an ultrasonic mode.

[0037] Furthermore, experiments revealed that the ultrasonic current (USG Current) parameter in the third-stage Force mode has a significant impact on the solder joint diameter. When the ultrasonic current was reduced from 110A to 80A, the diameter of the first solder ball decreased from 77μm to 65μm. This 65μm solder ball diameter is a better match for the pad size (90μm~100μm) of the chip used in this experiment, leaving a 30% pad allowance for equipment alignment and bonding position errors, thus better preventing solder joints from encroaching on the pads. Measurements showed that after optimizing the first solder joint bonding parameters, the solder ball height was approximately 30μm and the solder joint diameter was approximately 65μm. This meets the requirement that the complete gold wire ball bonding ball size is 2.5 to 3.5 times the wire diameter, and that the first solder joint ball diameter after bonding is full, with a microscopic observation showing a ball thickness of approximately 1.5 to 2 times the wire diameter.

[0038] Furthermore, the optimized parameters are shown in Table 1. Here, USG Current represents the ultrasonic current, Time represents the step duration, Force represents the applied pressure, Scrub Cycles represents the number of ultrasonic cycles, Scrub XAmplitude represents the ultrasonic vibration amplitude along the X direction, Scrub Frequency represents the ultrasonic frequency, and Scrub Phase represents the ultrasonic mode (Perp represents a straight trajectory, Circular represents a circular trajectory).

[0039] Table 1 Gold Sphere Bonding Parameters

[0040] In one possible implementation, bonding the second solder joint of the gold wire ball to the chip pad includes: under a fourth pressure, moving a cleaver a first distance in a predetermined direction to unfold the gold wire into a fishtail shape and contact the chip pad; under a fifth pressure, moving the cleaver a second distance in the predetermined direction and applying ultrasonic vibration to further unfold the fishtail-shaped gold wire and promote bonding between the fishtail-shaped gold wire and the chip pad, wherein the fifth pressure is greater than the fourth pressure and the second distance is less than the first distance; under a sixth pressure, moving the cleaver a third distance in the opposite direction to the predetermined direction to separate the gold wire from the fishtail-shaped gold wire to complete the tangencing, and applying ultrasonic vibration to bond the tail wire formed after tangencing to the chip pad.

[0041] This embodiment employs a three-step process: a first unfolding step where light pressure spreads the gold wire into a fishtail shape; a second unfolding step where heavy pressure and ultrasound further unfold the fishtail and promote bonding; and a bonding tangent step where reverse movement completes the tangent and bonds the tail wire to the pad. This process ensures that the fishtail of the second solder joint is fully unfolded and firmly bonded to the pad. Simultaneously, the reverse movement of the tangent position, which moves the tangent away from the main body of the fishtail, prevents the wire clamp pull from peeling the fishtail off the pad during tangent cutting, thereby improving the bonding stability and reliability of the second solder joint.

[0042] In a specific example, the second bonding parameter adjustment includes: when using gold wire ball bonding, the second bonding point differs from the conventional wedge bonding point; it is formed by welding gold wire to half of the circular hole at the front end of the wedge. The bottom of the other half of the circular hole at the front end of the wedge is suspended, which can easily cause obvious indentations or damage to the welding area when the ultrasonic energy and welding pressure are slightly higher.

[0043] Furthermore, the solder bonding process is divided into three sub-steps. The first stage, Scrub mode, involves the cutting tool moving a certain distance in the negative XY direction under pressure to unfold the solder wire into a fishtail shape and create effective contact area with the frame. The second stage, Scrub mode, operates under significantly higher pressure than the first stage, moving the cutting tool a shorter distance in the negative XY direction with more friction cycles, further unfolding the fishtail. The third stage, Force stage, involves bonding and tangencing. Under even greater pressure, the cutting tool moves a certain distance in a square XY direction, causing the gold wire to detach from the fishtail, moving the tangencing position away from the fishtail, and simultaneously, under ultrasonic action, the tail wire is anchored to the pad to prevent the wire clamp from breaking the gold wire and simultaneously detaching the fishtail from the pad during tangencing.

[0044] Furthermore, initial testing revealed three main problems when the second solder joint was directly bonded to the chip: pressure marks around the second solder joint pad, failure to bond the second solder joint resulting in cratering on the pad, and deviation between the actual solder joint position and the programmed solder joint position. Among these, the failure to bond the second solder joint was more likely to occur on the aluminum pads of the U4 to U5 chips. In this case, the device displayed "Not Wedged in the Second Solder Joint (NSOL)" and "The Tail End of the Bond Line Formed After the Second Solder Joint is Too Short (SHTL)". The deviation between the actual solder joint position and the programmed solder joint position was a common problem.

[0045] Furthermore, the first step is to address the discrepancy between the actual solder joint position and the programmed solder joint position. Parameter optimization revealed that adjusting the second solder joint position compensation (Cap-bond offset) parameter effectively solves this problem. A positive value represents proximity to the first solder joint, while a negative value represents distance from it. When the Cap-bond offset is adjusted from 0 to -2 mils, the actual second solder joint gradually aligns with the programmed solder joint, ultimately achieving a match between the bonded solder joint and the programmed solder joint position.

[0046] Furthermore, the chip's second solder pad exhibited pressure damage. Experiments revealed that reducing the ultrasonic current and pressure did not completely resolve this issue; in fact, it exacerbated the problem of poor bonding at the second solder joint. Analysis suggests that the pressure damage and the resulting cratering at the second solder joint are caused by the same reason: the gold wire in the second solder joint is flattened into a fishtail shape under ultrasonic and pressure conditions. Since the gold wire has poor compatibility with the aluminum pad, bonding failure is highly likely. Due to the poor bonding stability, higher ultrasonic power and pressure were chosen, further contributing to the pressure damage. To address the poor bonding stability of the aluminum pad, the experiment first involved plasma cleaning the chip before bonding to remove the oxide layer, excess material, and contaminants, preventing interference with welding and improving bonding strength and reliability. Experimental results showed that 300W, 180s plasma cleaning of the SIP sample improved welding stability but did not completely resolve the issue of poor aluminum pad bonding.

[0047] Furthermore, to address the issue of poor bonding stability of aluminum pads as the second bonding point for gold ball bonding, this experiment selected Bond Stitch on Ball (BSOB) technology. This method involves first bonding a gold ball onto the chip pad before bonding. The purpose of this method is to pre-bond a gold ball onto the aluminum pad, so that the second bonding point falls on the pre-bonded gold ball instead of directly onto the aluminum pad. Compared to the aluminum pad, the gold ball has better affinity with the gold wire, and the fact that the second bonding point is raised by the solder ball also prevents the chip from being damaged by pressure.

[0048] Furthermore, considering the bonding machine used, the line-arc mode was changed from STANDARD LOOP to SSB-PSALOOP. STANDARD LOOP is the standard line-arc mode, while SSB-PSA LOOP is a low-arc mode specifically designed for pressing the arc. This switches from direct bonding to a ball-pad-before-bonding mode, which adds a set of ball-pad parameters. The optimized ball-pad parameters are basically consistent with the parameters of the first solder joint. Reducing the pressure and ultrasonic power aims to avoid unnecessary pressure damage to the chip caused by high pressure and high ultrasonic power. The before-and-after bonding effect diagrams show that there is no pressure damage to the solder pads after bonding, and the bonding stability is greatly improved, with almost no problems of the second solder joint failing to bond.

[0049] Furthermore, during the process of using a ball-filling followed by bonding, an abnormal shape of the second bonding point was observed. Specifically, a horn-shaped gold wire would protrude from the center of the second bonding point, suspended above the pad. Analysis suggests this was due to incomplete breakage of the gold wire during ball filling, causing the cutting tool to misalign the gold wire on the ball when the second bonding point was pressed down, resulting in the protruding horn. Adjusting the Smooth Distance parameter from 0 to a value between 0.4 and 1 effectively suppressed this issue. The principle is that the Smooth Distance setting indicates a small lateral movement of the cutting tool after the gold ball is pressed down, effectively causing the gold wire to be broken laterally.

[0050] Furthermore, the optimized pad parameters and second bonding point parameters are shown in Tables 2 and 3. The study found that the bonding stability of the second bonding point is more sensitive to parameter changes compared to the first bonding point. Bonding pressure, ultrasonic power, and process time jointly determine the bonding effect. If poor bonding occurs, appropriately increasing the bonding pressure and ultrasonic power, and appropriately extending the process time can effectively solve this problem. However, these three types of parameters should not be blindly increased. If the Force parameter in step one of the second bonding point is too large, it will reduce the width of the wire tail, affecting the effective contact between the bonding wire and the pad. If the Force and Scrub X Amplitude parameters in step two are too large, it will cause the wire tail to break. In step three, USG Current and Scrub X Amplitude are directly related to the wire breakage effect; excessive power and offset will result in an excessively short wire tail after the second bonding point. At the same time, to prevent the pad from damaging the chip surface pads, the ultrasonic power and pressure should be reduced as much as possible without affecting the bonding strength when setting the pad parameters.

[0051] Table 2 Solder Bonding Parameters

[0052] Table 3. Parameters of Gold Wire Tail

[0053] Furthermore, regardless of whether it's on gold or aluminum pads, the bonding process after ball padding exhibits excellent stability, without causing chip damage. The bonding points are relatively full, and the gold balls provide excellent wetting, significantly mitigating poor bonding between the aluminum pads and gold wires. According to relevant regulations, ball padding bonding meets one type of bonding requirement. This standard requires that the contact area of ​​the second bond in a composite bond must be greater than 75% of the area of ​​the underlying bond. This can be seen from the actual bonding micrographs, which demonstrate that it well meets the requirements for composite bonding in the relevant standards.

[0054] In one possible implementation, the actual bonding position is made to match a preset position by adjusting the second solder joint position compensation parameter, wherein when the second solder joint position compensation parameter is negative, the actual second solder joint is offset away from the first solder joint.

[0055] This embodiment corrects the deviation between the actual landing point and the programmed setting point by adjusting the second solder joint position compensation parameter, which can make the actual bonding position of the second solder joint match the setting position, improve the bonding position accuracy, and avoid bonding problems such as failure to bond or solder joint encroachment on the pad caused by position deviation.

[0056] In one possible implementation, after pads are pre-formed on the pads of the chip, the cleaver moves laterally a predetermined distance to tear the tail wires of the pads laterally.

[0057] In this embodiment, the cleaver moves laterally a predetermined distance after the ball is placed to break the tail wire of the ball laterally. This avoids the tail wire of the ball not being broken cleanly, which would cause the cleaver to scrape the gold wire on the ball crookedly when the second solder joint is pressed down, resulting in an abnormal horn-shaped suspension. This improves the appearance consistency and bonding quality of the ball bonding.

[0058] In one possible implementation, the chips to be bonded are subjected to plasma cleaning before bonding to remove oxide layers and contaminants from the surface of the chip's pads.

[0059] This embodiment performs plasma cleaning on the chip to be bonded before bonding to remove the oxide layer and excess contaminants on the surface of the chip pads, which can improve the surface condition of the pads, increase the bonding force and welding stability of the second solder joint, and reduce bonding defects caused by pad oxidation or contamination.

[0060] In one possible implementation, the bonding of the second solder joint of the gold wire ball to the chip pad includes: under a fourth pressure, a cutting tool moves a first distance in a predetermined direction to unfold the gold wire into a fishtail shape and contact the chip pad; under a fifth pressure, the cutting tool moves a second distance in the predetermined direction and applies ultrasonic vibration to further unfold the fishtail-shaped gold wire and promote bonding between the fishtail-shaped gold wire and the chip pad, wherein the fifth pressure is greater than the fourth pressure and the second distance is less than the first distance; under a sixth pressure, the cutting tool moves a third distance in the opposite direction to the predetermined direction to separate the gold wire from the fishtail-shaped gold wire to complete the tangent, and applies ultrasonic vibration to bond the tail wire formed after the tangent to the pad ball.

[0061] In a specific example, gold wire ball bonding is formed by the combined influence of multiple factors. In actual research and production, after a large number of experiments, it was finally determined that the bonding effect is best when the ball is pre-padded at the second solder joint before bonding. The bonding pressure and ultrasonic power of the second solder joint should not be too high. After repeated experiments and verification, the bonding quality of gold wire ball bonding can be improved, and the reliability and finished product qualification rate can be increased.

[0062] This embodiment employs a three-step process to bond the second solder joint to the pad ball, building upon the existing pad ball bonding. This process leverages the excellent affinity between the gold ball and the gold wire to enhance the bonding stability of the second solder joint and prevent damage to the chip pads. Furthermore, the three-step unfolding, compaction, and tangenting process ensures that the "fishtail" is fully unfolded, the bonding is firm, and the tangenting does not result in peeling. This achieves the optimal bonding effect of low arc, high bonding strength, and high reliability, making it the best implementation method verified in the disclosure document.

[0063] In a specific example, the arc shape of the bond wire arc is controlled by adjusting at least one of the following parameters: twist height, reverse motion, arc factor, arc height, and twist distance.

[0064] This embodiment achieves precise control over the arc shape of the bonding wire arc by comprehensively adjusting five parameters that play a decisive role in the arc height: twist height, reverse motion, arc factor, arc height, and twist distance. This results in a low arc with excellent shape and satisfactory arc height, avoiding both excessively high arcs that could cause the lead wires to bend or short-circuit during capping and excessively low arcs that could cause excessive gold wire tension, leading to cracks or even breakage at the solder joint neck.

[0065] In a specific example, the lead arc characteristics are a crucial factor in wire bonding because they affect device performance and reliability. For instance, the arc cannot be too high, as this will cause the leads to be exposed after molding. Even if the leads are not exposed, an excessively high arc will result in overly long and drooping leads, which may be bent by the cover plate during subsequent capping processes, potentially leading to short circuits between leads. Unnecessarily long leads can cause mutual interference between leads, degrading the electrical performance of the device. However, the arc cannot be too low either. A low arc means that the lead is pulled down significantly by the solder pins as it moves from the first solder joint to the second. A low arc usually indicates that the lead is pulled very tightly, and strong tension will accumulate at the neck or root of the first solder joint. If pulled too low, cracks or even breakage can easily occur in these areas. Therefore, optimizing a reliable gold wire ball bonding process suitable for low arc bonding is extremely important for the mass application of adapter boards.

[0066] Furthermore, the formation of different types of arcs is achieved through setting the wiring parameters. The wiring parameters mainly include kink height, reverse motion, reverse motion angle, loop factor, flat length, shape factor, loop height, and kink distance.

[0067] Furthermore, experiments revealed that Kink Height, Reverse Motion, Loop Factor, Loop Height, and Kink Distance play a decisive role in controlling the arc height. These parameters need to be adjusted comprehensively to obtain a high-quality arc shape that meets the arc height requirements.

[0068] Furthermore, based on the thickness of the chips and capacitors themselves, as well as the adhesive thickness, the arc to be bonded can be divided into the following categories: chips U1~U3, 100μm high; chips U4 and U7, 300μm high; chips U5 and U6, 150μm high; capacitors C1~C3, 350μm high; and capacitors C4~C9, 250μm high. Therefore, at least five sets of parameters with different arc heights need to be established when creating the arc program. The initial arc mode selected for the experiment was SSB-PSA LOOP. In this arc mode, the arc height is the most fundamental parameter affecting the arc height and should be adjusted according to the height of the chips to be bonded. The experiment found that if the arc height does not match the chip height, especially when the Loop Height is set too small and the ratio is set too large, the leads are easily stretched very tightly, and the arc is extremely close to the chip edge. In some cases, two solder joints may even break off completely due to wire tension during the bonding process under the pressure of the bonding tool. At this time, the equipment will show NSOP and SHTL, and the wire needs to be re-threaded.

[0069] Furthermore, the relationship between Loop Height and chip thickness was verified through experiments, as shown in Table 4. The larger the Loop Height, the higher the arc height, but the arc shape cannot be kept consistent. The arc shape may have the problem of excessive warping at the top of the first solder joint. In this case, adjusting the Loop Factor can change its arc shape. The larger the negative Loop Factor, the gentler the arc shape, and vice versa. When Loop Height > 14, Loop Factor should be changed to > -10. When Loop Height < 14, Loop Factor should be within the range of -5 to -10.

[0070] Table 4 Relationship between chip thickness and arc height

[0071] Furthermore, another commonly used wire arc mode with ball padding followed by bonding is the SSB-KL4 mode. Its advantage lies in its ability to improve the consistency of the wire arc, with the arc shape primarily controlled by Kink Distance and Loop Factor. In this mode, to better and more precisely adjust the arc shape, the original 5 groups of wire arcs are subdivided into 10 groups based on different bonding positions: U1, U2, U4, U5, U6, C1~C3, C4~C9, substrate capacitor group, capacitor capacitor group, and substrate substrate group. The specific corresponding parameters are shown in Table 5. The substrate capacitor group represents the bonding between the two thickest positions, therefore its Kink Distance setting is the largest. The measured vertical distance between the highest point of the lead and the substrate is 420μm, meeting the requirement of <500μm. Therefore, when the Kink Distance of the other groups is less than 15, the wire arc will not exceed the required height. The relationship between the wire group and the measured arc height is shown in Table 6.

[0072] Table 5 Relationship between line groups and reversal distance and ratio

[0073] Table 6 Relationship between line group and measured arc height

[0074] In one possible implementation, the SSB-PSA LOOP mode or the SSB-KL4 mode is used for line arc control; in the SSB-PSA LOOP mode, the line arc height is controlled by the arc height parameter and the arc steepness is controlled by the arc factor parameter; in the SSB-KL4 mode, the arc is controlled by the twist distance and the arc factor.

[0075] This embodiment allows for line arc control by selecting either the SSB-PSA LOOP mode or the SSB-KL4 mode. This enables flexible selection of the appropriate line arc mode based on different bonding locations and chip thicknesses. The SSB-PSA LOOP mode directly controls the line arc height through the arc height parameter and the arc steepness through the arc factor, providing direct control. The SSB-KL4 mode, through the combined control of the twist distance and arc factor, achieves better line arc consistency, thereby meeting the ultra-low line arc requirements at different locations.

[0076] In one possible implementation, the highest arc height of the bonding line arc is less than 500 μm.

[0077] In a specific example, through the process research of ball bonding of packaged SIP with an arc height of 100μm, a ball bonding wire with low arc height and high bonding strength that meets the structural characteristics of packaged SIP was finally obtained. This embodiment controls the maximum arc height of the bonding wire arc to within 500μm, which can meet the arc height requirements of subsequent capping of SIP packaging, avoid the lead wires being bent by the cover plate during capping and causing short circuits between the lead wires, and ensure the electrical reliability of the packaged device and the yield of finished products.

[0078] In a specific example, the tensile test results are shown in Table 7.

[0079] Table 7 Tensile Test Results

[0080] Furthermore, the test results showed that the gold wire fractures all occurred at the necking point, and did not occur at the first or second solder joint, indicating that the gold wire formed a good metallurgical bond with the chip and substrate, and the bonding quality was good.

[0081] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0082] It should also be noted that in the description of this invention, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for gold wire ball bonding, characterized in that, The method includes: The first solder joint of the gold wire ball is bonded to the pad of the substrate; The second solder joint of the gold wire ball is bonded to the chip's solder pad; The height of the substrate is lower than the height of the chip, so that the height of the spherical solder joint and the arc starting height of the first solder joint are measured from the surface of the substrate, thereby controlling the arc height of the bonding wire arc.

2. The gold wire ball bonding method according to claim 1, characterized in that, The step of bonding the second solder joint of the gold wire ball solder to the chip pad includes: Pad balls are pre-formed on the pads of the chip; The second solder joint is bonded to the pad ball.

3. The gold wire ball bonding method according to claim 2, characterized in that, The bonding pressure and ultrasonic power of the pad ball are both lower than those of the first solder joint.

4. The gold wire ball bonding method according to claim 1 or 2, characterized in that, The substrate has gold pads, and the chip has aluminum pads.

5. The gold wire ball bonding method according to claim 1, characterized in that, The process of bonding the first solder joint of the gold wire ball soldering to the pad of the substrate includes: A first pressure is applied to the gold ball formed at the end of the gold wire so that the gold ball contacts the pad of the substrate and forms a basic spherical shape; A second pressure and ultrasonic vibration are applied to modify the basic spherical shape; A third pressure is applied to the modified sphere to make the modified sphere fit against the pads of the substrate.

6. The gold wire ball bonding method according to claim 1, characterized in that, The step of bonding the second solder joint of the gold wire ball solder to the chip pad includes: Under the fourth pressure, the cutting tool moves a first distance in a predetermined direction to unfold the gold wire into a fishtail shape and make contact with the pads of the chip; Under the fifth pressure, the chopping blade moves a second distance in the predetermined direction and applies ultrasonic vibration to further unfold the fishtail-shaped gold wire and promote bonding between the fishtail-shaped gold wire and the chip's pads, wherein the fifth pressure is greater than the fourth pressure and the second distance is less than the first distance. Under the sixth pressure, the cleaver moves a third distance in the opposite direction to the predetermined direction to separate the gold wire from the fishtail-shaped gold wire and complete the cleaving. Ultrasonic vibration is applied to bond the tail wire formed after cleaving to the pads of the chip.

7. The gold wire ball bonding method according to claim 1, characterized in that, By adjusting the second solder joint position compensation parameter, the actual bonding position is made to match the preset position. When the second solder joint position compensation parameter is negative, the actual second solder joint is shifted away from the first solder joint.

8. The gold wire ball bonding method according to claim 2, characterized in that, After a pad ball is pre-formed on the pad of the chip, the cleaver moves laterally a predetermined distance to break the tail wire of the pad ball laterally.

9. The gold wire ball bonding method according to claim 1, characterized in that, Before bonding, the chips to be bonded are subjected to plasma cleaning to remove the oxide layer and contaminants on the surface of the chip's pads.

10. The gold wire ball bonding method according to claim 2, characterized in that, The step of bonding the second solder joint of the gold wire ball solder to the chip pad includes: Under the fourth pressure, the cutting tool moves a first distance in a predetermined direction to unfold the gold wire into a fishtail shape and make contact with the pads of the chip; Under the fifth pressure, the chopping blade moves a second distance in the predetermined direction and applies ultrasonic vibration to further unfold the fishtail-shaped gold wire and promote bonding between the fishtail-shaped gold wire and the chip's pads, wherein the fifth pressure is greater than the fourth pressure and the second distance is less than the first distance. Under the sixth pressure, the chopping blade moves a third distance in the opposite direction to the predetermined direction, so that the gold wire separates from the fishtail-shaped gold wire to complete the tangent. Ultrasonic vibration is applied to bond the tail wire formed after the tangent to the pad ball.

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