NiPdAu substrate gold wire bonding method

Abstract

The application provides a NiPdAu substrate gold wire bonding method, before bonding, the gold layer on the surface of the NiPdAu is ground by a wedge, the interface adhesion is removed, and the interface activation is realized; a ball is prepositioned at the position of the two solder points (the NiPdAu substrate), then the bonding of the one solder point is completed, finally, the bonding of the two solder points is completed through the wire pressure ball process, the bonding plane of the two solder points is not on the bonding area of the NiPdAu plated board, but on the prepositioned gold ball, the prepositioned gold ball provides a surface with good and consistent state for the following bonding, the crescent and the gold ball form reliable connection, on the other hand, the contact area between the prepositioned gold ball and the bonding area of the substrate is increased, the diffusion between the atoms is promoted, and the interface bonding force is improved; when the bonding of the one and two solder points is carried out, the ultrasonic energy is set in sections, the energy and the pressure are increased in sections, and the mechanical reliability of the bonding interface is enhanced. The application promotes the diffusion between the gold atoms in the interface layer, effectively improves the mechanical reliability of the bonding, and overcomes the difficulties of the bonding wire separation of the NiPdAu substrate and the poor mechanical reliability.

Description

Technical Field

[0001] This invention relates to the field of electrical component technology, and specifically to a method for gold wire bonding of NiPdAu substrates. Background Technology

[0002] Traditional printed circuit board (PCB) micro-assembly processes mainly include soldering and gold wire bonding. In order to meet the process requirements of both soldering and gold wire bonding, the PCB surface treatment method generally adopts a process of nickel layer as base, thin gold plating, and then thick gold plating. This not only increases the process difficulty of PCB surface treatment, but also increases material and labor costs.

[0003] To address the aforementioned issues, the industry has introduced a surface treatment process for chemically plated NiPdAu. However, the gold layer on the NiPdAu substrate is relatively thin, leading to problems such as wire breakage during actual wire bonding, failure of bonding pull force to meet GJB548C requirements, poor gold wire-substrate bonding force, and poor mechanical reliability of gold wire bonding.

[0004] Therefore, a suitable gold wire bonding process for NiPdAu substrates is needed. Summary of the Invention

[0005] This invention addresses the problems of bond detachment and insufficient bonding force during wire bonding on NiPdAu substrates. It provides a gold wire bonding method for NiPdAu substrates. Before bonding, the gold layer on the NiPdAu surface is ground with a cleaver to remove interfacial adhesions, thus activating the interface. Balls are pre-placed at the two bonding points (NiPdAu substrate), followed by bonding of the first bonding point, and finally, bonding of the second bonding point using a wire-pressing ball process. During the bonding of the first and second bonding points, ultrasonic energy is set in stages, with energy and pressure gradually increasing to enhance the mechanical reliability of the bonding interface. This process promotes diffusion between gold atoms in the interfacial layer, effectively improving the mechanical reliability of the bond and overcoming the difficulties of bond detachment and poor mechanical reliability on NiPdAu substrates.

[0006] This invention provides a method for gold wire bonding on a NiPdAu substrate, comprising the following steps:

[0007] S1. Select the cleaving blade, turn on the heating stage, and the cleaving blade pre-polishes the interface layer of the first solder joint and the interface layer of the second solder joint on the NiPdAu substrate to remove the gold layer surface attachments and oxide layer of the first and second solder joints to obtain the pre-polished first solder joint and the pre-polished second solder joint.

[0008] S2. Place a spark rod under the chopping knife to generate instantaneous voltage. Through tip discharge, burn the tail of the gold wire into an air free ball. Under the action of pressure and ultrasound, the chopping knife moves down to the position of the pre-ground two solder pads. The air free ball and the metal layer on the surface of the pre-ground two solder pads rub against each other to connect the air free ball and the pre-ground two solder pads. Then cut off the tail to obtain the pre-placed ball of the two solder points.

[0009] S3. The gold wire at the bottom of the cleaver is sparked and discharged through a spark rod to perform secondary burning of the ball, resulting in a gold wire with an air free ball. The cleaver is moved down so that the end of the gold wire with the air free ball contacts the pad of the pre-ground solder joint. At the same time, pressure and ultrasonic energy are applied to the cleaver. Under the action of pressure and ultrasound, the air free ball rubs against the metal layer on the surface of the pre-ground solder joint pad to obtain the bonding solder joint.

[0010] S4. Driven by the bonding head, the cleaver bends the other end of the gold wire of the bonded joint into a preset angle and shape in space to obtain a wire arc. Then, the wire arc is stretched to the position of the pre-placed ball of the second bond joint. Under the action of ultrasound and pressure, the end of the wire arc is pressed to the surface of the pre-placed ball of the second bond joint and the pre-placed ball of the second bond joint is bonded to the wire arc.

[0011] S5. After pre-grinding, the cutting tool performs tail welding at the two welding points to cut off the wire arc, and the gold wire bonding of the NiPdAu substrate is completed.

[0012] The cleaver is lifted, the wire clamp closes, and the process returns to step S1 to prepare for the next bonding.

[0013] In the preferred embodiment of the NiPdAu substrate gold wire bonding method of the present invention, in step S3, when welding the pre-polished solder joint to the air free ball, the ultrasonic energy is set in segments.

[0014] The NiPdAu substrate gold wire bonding method described in this invention, as a preferred embodiment, divides the ultrasonic energy of a pre-polished solder joint during welding with an air free sphere into a first stage and a second stage of the solder joint.

[0015] The ultrasonic energy, bonding pressure, and bonding time of the first stage of a solder joint are all less than those of the second stage of a solder joint.

[0016] The NiPdAu substrate gold wire bonding method described in this invention, as a preferred embodiment, has the following characteristics: the ultrasonic energy of a first stage of a solder joint is 60-80 DAC, the bonding pressure is 25-32 g, and the bonding time is 30-35 ms.

[0017] The ultrasonic energy for the second stage of a single solder joint is 120–140 DAC, the bonding pressure is 40–45 g, and the bonding time is 43–50 ms.

[0018] One solder joint undergoes preliminary bonding in the first stage, and another solder joint undergoes final bonding in the second stage.

[0019] In a preferred embodiment of the NiPdAu substrate gold wire bonding method of the present invention, in step S4, when welding the two pre-polished solder joints to the air free ball, the ultrasonic energy is set in segments.

[0020] The NiPdAu substrate gold wire bonding method described in this invention, as a preferred embodiment, divides the ultrasonic energy of the two solder joints during welding with the air free ball after pre-grinding into a first stage and a second stage of the two solder joints.

[0021] The ultrasonic energy, bonding pressure, and bonding time of the first stage of the two-solder joint are all less than those of the second stage of the two-solder joint.

[0022] In the preferred embodiment of the NiPdAu substrate gold wire bonding method described in this invention, the ultrasonic energy of the first stage of the two bonding points is 60-80 DAC, the bonding pressure is 25-32 g, and the bonding time is 30-35 ms.

[0023] The second stage ultrasonic energy for the two-solder joint is 120-140 DAC, the bonding pressure is 40-45 g, and the bonding time is 43-50 ms.

[0024] The two solder joints undergo preliminary bonding in the first stage and final bonding in the second stage.

[0025] In the preferred embodiment of the NiPdAu substrate gold wire bonding method of the present invention, in step S1, the ultrasonic energy of pre-grinding is 100-130 DAC, the bonding pressure is 25-33 g, and the pre-grinding time is 10-15 ms. In step S1, the cleaving tool is a ceramic cleaving tool, and the heating stage temperature is set to 80℃-120℃.

[0026] In the preferred embodiment of the NiPdAu substrate gold wire bonding method of the present invention, in steps S2 and S3, the ignition current of the burning ball is 45-60mA, the ignition time is 600-800μs, and the EFO voltage is 4500-5000V.

[0027] The present invention discloses a method for gold wire bonding on a NiPdAu substrate. In a preferred embodiment, the bonding structure obtained by the NiPdAu substrate gold wire bonding method includes: a NiPdAu substrate, a pre-polished first solder joint disposed on one side of the NiPdAu substrate, a second pre-polished second solder joint connected to the NiPdAu substrate, two solder joint pre-placed balls bonded to the two pre-polished second solder joints, and a gold wire with an air free sphere bonded to the first pre-polished solder joint. The gold wire with the air free sphere comprises a connected air free sphere and a gold wire. The two solder joint pre-placed balls are bonded to the ends of the gold wires that are away from the air free spheres.

[0028] The ball bonding process of this invention is summarized as follows:

[0029] (1) Select ceramic wear-resistant chopping knife

[0030] (2) Pre-grinding the bonding interface layer of the first and second weld points with a cleaving tool;

[0031] (3) Pre-placed ball at the two welding points (see attached diagram for details);

[0032] (4) Segmented ultrasonic bonding of a single weld point;

[0033] (5) Two-point wire-pressed ball segment ultrasonic bonding.

[0034] This invention is applicable to the gold wire bonding process of NiPdAu coated printed circuit boards, and can effectively improve the mechanical reliability of gold wire bonding on thin gold printed circuit boards with NiPdAu coating material as the main material.

[0035] The present invention has the following advantages:

[0036] (1) Before bonding, this method removes the gold layer surface deposits and oxide layer by pre-grinding the interface layer of the first and second bonding points with a wedge. Preheating may cause other metals to be doped, which is beneficial to the tight bonding between gold atoms and increases the mechanical reliability of the bonding interface.

[0037] (2) This method sets the ultrasonic energy of welding at the first and second welding points in segments, which can enhance the inter-diffusion between atoms in the interface layer and improve the interface bonding force.

[0038] (3) In this method, balls are pre-placed at the two solder joints, and then the bonding of the two solder joints is completed by wire pressing the balls. In this bonding mode, the bonding plane of the two solder joints is not on the bonding area of ​​the NiPdAu coated printed circuit board, but on the pre-padded gold balls. The pre-placed gold balls provide a surface with good condition (flatness, smoothness) for the subsequent bonding, so that the crescent and the gold balls form a reliable connection. On the other hand, the contact area between the pre-placed gold balls and the bonding area of ​​the substrate is increased, which promotes the diffusion between atoms and improves the interfacial bonding force.

[0039] (4) This method improves the reliability of bonding process of NiPdAu substrate. By replacing NiAu substrate with NiPdAu substrate, the process difficulty of surface treatment of printed circuit board is reduced, while saving manpower and material costs. Attached Figure Description

[0040] Figure 1 This is a flowchart of a gold wire bonding method for NiPdAu substrates;

[0041] Figure 2 This is a schematic diagram of the structure after bonding using a gold wire bonding method for a NiPdAu substrate.

[0042] Figure label:

[0043] 1. NiPdAu substrate; 2. First solder joint after pre-grinding; 3. Second solder joint after pre-grinding; 4. Pre-placed balls at the second solder joint; 5. Gold wire with air free balls. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0045] Example 1

[0046] like Figures 1-2 As shown, a method for gold wire bonding on a NiPdAu substrate includes the following steps:

[0047] S1. Select the cleaving blade, turn on the heating table, and the cleaving blade pre-polishes the interface layer of the first solder point and the interface layer of the second solder point on the NiPdAu substrate 1 to remove the gold layer surface attachments and oxide layer of the first solder point and the second solder point to obtain the pre-polished first solder point 2 and the pre-polished second solder point 3.

[0048] The ultrasonic energy for pre-grinding is 100-130 DAC, the bonding pressure is 25-33 g, and the pre-grinding time is 10-15 ms. In step S1, the chopping tool is a ceramic chopping tool, and the heating table temperature is set to 80℃-120℃.

[0049] S2. Place an ignition rod below the cleaver to generate an instantaneous voltage. Through tip discharge, burn the tail of the gold wire into an air free ball. The ignition current of the burning ball is 45-60mA, the ignition time is 600-800μs, and the EFO voltage is 4500-5000V. Under the action of pressure and ultrasound, the cleaver moves down to the position of the pad of the pre-ground two solder points 3. The air free ball rubs against the metal layer on the surface of the pad of the pre-ground two solder points 3 to connect the air free ball to the pad of the pre-ground two solder points 3. Then cut off the tail to obtain the pre-placed ball of the two solder points 4.

[0050] S3. The gold wire at the bottom of the cleaver is sparked by an ignition rod to perform a secondary balling process, resulting in a gold wire 5 with air free balls. The sparking current is 45-60mA, the sparking time is 600-800μs, and the EFO voltage is 4500-5000V. The cleaver is moved down so that the end of the gold wire 5 with air free balls contacts the pad of the pre-ground solder point 2. At the same time, pressure and ultrasonic energy are applied to the cleaver. Under the action of pressure and ultrasound, the air free balls rub against the metal layer on the surface of the pre-ground solder point 2 pad to obtain the bonded solder point.

[0051] When welding a pre-grinding weld point 2 to an air free sphere, the ultrasonic energy is set in segments, divided into a first stage and a second stage of the weld point.

[0052] The ultrasonic energy for the first stage of a single solder joint is 60–80 DAC, the bonding pressure is 25–32 g, and the bonding time is 30–35 ms.

[0053] The ultrasonic energy for the second stage of a single solder joint is 120–140 DAC, the bonding pressure is 40–45 g, and the bonding time is 43–50 ms.

[0054] One solder joint undergoes preliminary bonding in the first stage, and another solder joint undergoes final bonding in the second stage.

[0055] S4. Driven by the bonding head, the cleaver bends the other end of the gold wire of the bonded joint into a preset angle and shape in space to obtain a wire arc. Then, the wire arc is stretched to the position of the pre-placed ball 4 of the second bond joint. Under the action of ultrasound and pressure, the end of the wire arc is pressed to the surface of the pre-placed ball 4 of the second bond joint and the pre-placed ball 4 of the second bond joint is bonded to the wire arc.

[0056] When welding the pre-grinding two weld points 3 to the air free ball, the ultrasonic energy is set in segments, divided into the first stage of the two weld points and the second stage of the two weld points.

[0057] The ultrasonic energy for the first stage of the two-solder joint is 60-80 DAC, the bonding pressure is 25-32 g, and the bonding time is 30-35 ms.

[0058] The second stage ultrasonic energy for the two-solder joint is 120-140 DAC, the bonding pressure is 40-45 g, and the bonding time is 43-50 ms.

[0059] The two solder joints undergo preliminary bonding in the first stage and final bonding in the second stage.

[0060] S5. After pre-grinding, the cutting tool performs tail welding at the second welding point 3 to cut off the wire arc, and the gold wire bonding of the NiPdAu substrate 1 is completed.

[0061] The cleaver is lifted, the wire clamp closes, and the process returns to step S1 to prepare for the next bonding.

[0062] like Figure 2 As shown, the bonding structure obtained by the NiPdAu substrate gold wire bonding method includes: a NiPdAu substrate 1, a pre-polished first solder joint 2 disposed on one side of the NiPdAu substrate 1, a pre-polished second solder joint 3 connected to the NiPdAu substrate 1, a second solder joint pre-placed ball 4 bonded to the pre-polished second solder joint 3, and a gold wire 5 with an air free ball bonded to the pre-polished first solder joint 2. The gold wire 5 with an air free ball includes a connected air free ball and a gold wire. The second solder joint pre-placed ball 4 is bonded to the end of the gold wire away from the air free ball.

[0063] Example 2

[0064] like Figures 1-2 As shown, a method for gold wire bonding on a NiPdAu substrate includes the following specific process steps:

[0065] (1) Select a ceramic wear-resistant chopping knife;

[0066] (2) Turn on the heating table and set the heating table temperature to 80℃~120℃;

[0067] (3) Parameter settings are as follows:

[0068] Cleaver grinding parameters: 100-130 DAC (ultrasonic energy), 25-33 g (bonding pressure), 10-15 ms;

[0069] Burn-in parameters: 45~60mA (ignition current), 600~800μs (ignition time), 4500~5000V (EFO voltage);

[0070] Solder bond parameters:

[0071] Phase 1: 60–80 DAC (ultrasonic energy), 25–32 g (bonding pressure),

[0072] 30–35 ms (bonding time)

[0073] Phase Two: 120–140 DAC (ultrasonic energy), 40–45 g (bonding pressure), 43–50 ms (bonding time)

[0074] Two-solder bonding parameters:

[0075] Phase 1: 40–50 DAC (ultrasonic energy), 20–30 g (bonding pressure),

[0076] 25–30 ms (bonding time)

[0077] Phase Two: 72–85 DAC (ultrasonic energy), 40–45 g (bonding pressure),

[0078] 38–47 ms (bonding time)

[0079] (4) The spark rod below the cleaver generates an instantaneous voltage, which burns the tail of the gold wire into a regular free air ball (FAB) through tip discharge. Under the action of pressure and ultrasound, the cleaver moves down to the position of the second solder pad. The FAB and the metal layer on the surface of the NiPdAu solder pad rub against each other to form a tight connection at the atomic level. After that, the tail is cut off to complete the pre-placed ball of the second solder pad.

[0080] (5) The gold wire at the bottom of the cleaver is ignited by the spark rod to complete the secondary ball burning. The cleaver moves down to contact a solder pad. At the same time, pressure and ultrasonic energy are applied to the cleaver. Under the action of pressure and ultrasound, the FAB and the metal layer on the surface of the solder pad rub against each other, destroying the contamination and oxide layer on the metal surface and forming a tight connection at the atomic level, thereby completing the bonding of a solder point.

[0081] (6) Driven by the bonding head, the cleaver moves along the planned trajectory, bending the gold wire into a certain angle and shape in space to form a line arc. Then it is stretched to the position of the pre-placed ball on the NiPaAu pad. Under the action of ultrasound and pressure, the gold wire is pressed onto the surface of the pre-placed ball to complete the bonding of the two solder points.

[0082] (7) After the second solder joint is formed, the cutter is used to cut off the gold wire at the second solder joint. Then the cutter is lifted and the wire clamp is closed, preparing for the second soldering. At this point, the entire lead wire arc and bonding point are completed.

[0083] Using this ball bonding process, no bonding wire detachment issues occurred on the NiPdAu substrate, achieving a 100% bonding success rate on the first attempt. After wire bonding was completed, destructive tensile tests were performed on the bonding wires, and the tensile strength values ​​all met the requirements of GJB548C. This indicates that the proposed gold wire bonding process is suitable for bonding NiPdAu substrates and can effectively solve problems such as bonding wire detachment on NiPdAu plating pads, thereby improving mechanical reliability.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for gold wire bonding on a NiPdAu substrate, characterized in that: Includes the following steps: S1. Select the cleaver and turn on the heating table. The cleaver pre-polishes the interface layer of the first solder joint and the interface layer of the second solder joint on the NiPdAu substrate (1) to remove the gold layer surface attachments and oxide layer of the first solder joint and the second solder joint to obtain the pre-polished first solder joint (2) and the pre-polished second solder joint (3). S2. A spark rod is placed below the chopping knife to generate an instantaneous voltage. The tail of the gold wire is burned into an air free ball through tip discharge. Under the action of pressure and ultrasound, the chopping knife moves down to the position of the pad of the pre-ground two solder points (3). The air free ball and the metal layer on the surface of the pad of the pre-ground two solder points (3) rub against each other to connect the air free ball with the pad of the pre-ground two solder points (3). Then the tail is cut off to obtain the pre-placed ball of the two solder points (4). S3. The gold wire at the bottom of the cleaver is ignited and discharged by a spark rod to perform secondary burning, resulting in a gold wire (5) with an air free ball. The cleaver is moved down so that the end of the gold wire (5) with the air free ball contacts the pad of the pre-ground solder point (2). At the same time, pressure and ultrasonic energy are applied to the cleaver. Under the action of pressure and ultrasound, the air free ball rubs against the metal layer on the surface of the pre-ground solder point (2) pad to obtain the bonded solder point. S4. Driven by the bonding head, the cleaver bends the other end of the gold wire of the bonded joint into a preset angle and shape in space to obtain a wire arc. Then, the wire arc is stretched to the position of the pre-placed ball (4) of the second bond joint. Under the action of ultrasound and pressure, the end of the wire arc is pressed to the surface of the pre-placed ball (4) of the second bond joint and the pre-placed ball (4) of the second bond joint is bonded to the wire arc. S5. The cutting blade performs tail welding at the two welding points (3) after pre-grinding, cuts off the arc, and the gold wire bonding of the NiPdAu substrate (1) is completed. The cutting tool is lifted, the wire clamp is closed, and the process returns to step S1 to prepare for the next bonding.

2. The method for gold wire bonding on a NiPdAu substrate according to claim 1, characterized in that: In step S3, when welding the pre-ground weld point (2) to the air free ball, the ultrasonic energy is set in segments.

3. The method for gold wire bonding on a NiPdAu substrate according to claim 2, characterized in that: The ultrasonic energy of the pre-ground weld point (2) when welding with the air free ball is divided into the first stage of the weld point and the second stage of the weld point. The ultrasonic energy, bonding pressure, and bonding time of the first stage of the solder joint are all less than those of the second stage of the solder joint.

4. The method for gold wire bonding on a NiPdAu substrate according to claim 3, characterized in that: The ultrasonic energy for the first stage of the first solder joint is 60-80 DAC, the bonding pressure is 25-32 g, and the bonding time is 30-35 ms. The ultrasonic energy for the second stage of the first solder joint is 120-140 DAC, the bonding pressure is 40-45 g, and the bonding time is 43-50 ms. The first stage of the solder joint involves preliminary bonding, and the second stage involves final bonding.

5. The method for gold wire bonding on a NiPdAu substrate according to claim 1, characterized in that: In step S4, when welding the pre-ground two weld points (3) to the air free ball, the ultrasonic energy is set in segments.

6. The method for gold wire bonding on a NiPdAu substrate according to claim 5, characterized in that: The ultrasonic energy during the welding of the pre-ground two weld points (3) with the air free ball is divided into the first stage and the second stage of the two weld points; The ultrasonic energy, bonding pressure, and bonding time of the first stage of the two solder joints are all less than those of the second stage of the two solder joints.

7. The method for gold wire bonding on a NiPdAu substrate according to claim 6, characterized in that: The ultrasonic energy for the first stage of the two-solder joint is 60-80 DAC, the bonding pressure is 25-32 g, and the bonding time is 30-35 ms. The ultrasonic energy for the second stage of the two-weld joint is 120-140 DAC, the bonding pressure is 40-45 g, and the bonding time is 43-50 ms. The two solder joints undergo preliminary bonding in the first stage and final bonding in the second stage.

8. The method for gold wire bonding on a NiPdAu substrate according to claim 1, characterized in that: In step S1, the ultrasonic energy for pre-grinding is 100-130 DAC, the bonding pressure is 25-33 g, and the pre-grinding time is 10-15 ms. In step S1, the chopping tool is a ceramic chopping tool, and the heating table temperature is set to 80℃-120℃.

9. The method for gold wire bonding on a NiPdAu substrate according to claim 1, characterized in that: In steps S2 and S3, the ignition current of the burning ball is 45-60mA, the ignition time is 600-800μs, and the EFO voltage is 4500-5000V.

10. A method for gold wire bonding on a NiPdAu substrate according to claim 1, characterized in that: The bonding structure obtained by the NiPdAu substrate gold wire bonding method includes: the NiPdAu substrate (1), a pre-polished first solder joint (2) disposed on one side of the NiPdAu substrate (1), the pre-polished second solder joint (3) connected to the NiPdAu substrate (1), two solder joint pre-placed balls (4) bonded to the pre-polished second solder joint (3), and a gold wire (5) with an air free ball bonded to the pre-polished first solder joint (2). The gold wire (5) with an air free ball includes a connected air free ball and a gold wire. The two solder joint pre-placed balls (4) are bonded to the end of the gold wire away from the air free ball.

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