Die bonding method for nickel-palladium-gold bonding pad

Abstract

The invention discloses a die bonding method for a nickel-palladium-gold bonding pad. The die bonding method comprises the steps of primary printing, primary reflow soldering, secondary printing, die bonding, secondary reflow soldering, cleaning and the like. Through the method, a firm metal compound layer is generated between the first printing solder paste and the nickel-palladium-gold bonding pad after primary reflow soldering, and the second printing solder paste forms a tin ball shape on the metal compound layer in the steel mesh window, so that the semiconductor FC chip bonding pad and the nickel-palladium-gold bonding pad are tightly connected through the tin layer and the metal compound layer. And reliable mechanical and electrical connection is formed. The problem that the bonding strength of the semiconductor FC chip and the nickel-palladium-gold bonding pad of the substrate is low is solved, and the risk that the solder paste on the nickel-palladium-gold bonding pad and the solder paste on the adjacent bonding pad generate bridge connection is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor packaging, and in particular to a die bonding method for a nickel-palladium-gold pad. Background Art

[0002] The substrate is the basic material for semiconductor packaging. Generally, the substrate is a copper-clad laminate. In manufacturing, the substrate material - copper-clad laminate (CCL) is selectively processed with holes, chemical copper plating, electroplating copper, etching, etc. to obtain the required circuit pattern and form two or more layers of conductive pattern interlayer interconnection. The front of the substrate is processed by copper-clad laminate, electroplating, etching and other processes to obtain metal pads for chip mounting. After long-term mass production verification, the material of the metal pad on the surface of the substrate is preferably nickel-palladium-gold, which is not only easy to print solder paste, but also meets the reliability requirements of bonding wire bonding. However, in the actual operation process, due to the limited opening of the steel mesh, it is easy to cause the nickel-palladium-gold pad to have insufficient bonding force with the surface pad of the FC chip, which is easy to cause the thrust between the FC chip and the substrate pad to be too small, making it easy for the chip to loosen between the pads, affecting the electrical performance. If the opening of the steel mesh is increased and the amount of solder paste printing is increased, there is a risk of solder paste bridging of adjacent pads, causing product short circuit and reducing the yield. Summary of the invention

[0003] The invention provides a die bonding method for a nickel-palladium-gold pad, which is used to solve the problems of low bonding strength between a semiconductor FC chip and a nickel-palladium-gold pad on a substrate, and easy bridging of solder paste on the nickel-palladium-gold pad with solder paste on an adjacent pad.

[0004] The technical solution provided by the present invention is as follows:

[0005] A die bonding method for a nickel-palladium-gold pad comprises the following steps:

[0006] S1. Making a steel mesh, wherein the window size of the steel mesh does not exceed 80% of the size of the nickel-palladium-gold pad;

[0007] S2, printing solder paste on the nickel-palladium-gold pad through the steel mesh;

[0008] S3, melting the solder paste printed on the nickel-palladium-gold pad to form a metal compound layer between the solder paste and the nickel-palladium-gold pad;

[0009] S4, printing solder paste on the surface of the metal compound layer through the steel mesh;

[0010] S5, mounting the FC chip on the surface of the nickel-palladium-gold pad printed with solder paste;

[0011] S6, melting the solder paste printed on the surface of the metal compound layer;

[0012] S7. Cleaning the substrate.

[0013] Furthermore, in step S3, the solder paste printed on the substrate is melted by reflow soldering, and the reflow soldering temperature is 245°C.

[0014] Furthermore, in step S6, the solder paste printed on the surface of the metal compound layer is melted by reflow soldering, and the reflow soldering temperature is 250°C.

[0015] Furthermore, in step S4, when solder paste is printed on the surface of the metal compound layer, the solder paste printed on the metal compound layer must not exceed the edge of the nickel-palladium-gold pad.

[0016] Furthermore, in step S2, printing solder paste on the nickel-palladium-gold pad through the steel mesh is specifically performed by passing the solder paste and flux through the openings of the steel mesh, and evenly coating the solder paste on the nickel-palladium-gold pad under the action of a scraper of a printing machine.

[0017] Furthermore, in step S4, printing solder paste on the surface of the metal compound layer through the steel mesh is specifically as follows: passing the solder paste and flux through the openings on the steel mesh, and evenly coating the solder paste on the nickel-palladium-gold pad under the action of a printing machine scraper.

[0018] Further, in step S5, the FC chip is mounted on the surface of the nickel-palladium-gold pad printed with solder paste. Specifically, the FC chip is mounted on the surface of the nickel-palladium-gold pad printed with solder paste and flux using a die bonding machine, and during die bonding, the die bonding accuracy and whether there is damage caused by ejector pins on the bottom of the FC chip are confirmed, and after die bonding, the FC chip is checked for defects such as reverse sticking, offset, and chip crushing.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a method for bonding nickel-palladium-gold pads, so that a solid metal compound layer is generated between the first printed solder paste and the nickel-palladium-gold pad after a reflow, and the second printed solder paste forms a tin ball on the metal compound layer in the steel mesh window, so that the semiconductor FC chip pad and the nickel-palladium-gold pad are tightly connected through the tin layer and the metal compound layer to form a reliable mechanical and electrical connection. The problem of low bonding strength between the semiconductor FC chip and the nickel-palladium-gold pad of the substrate is solved, and the risk of bridging between the solder paste on the nickel-palladium-gold pad and the solder paste on the adjacent pad is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of a die bonding method for a nickel-palladium-gold pad in an embodiment of the present invention;

[0022] Figure 2Schematic diagram of a nickel-palladium-gold pad on a substrate in an embodiment of the present invention, wherein FIG a is a front view of the nickel-palladium-gold pad, and FIG b is a back view of the nickel-palladium-gold pad;

[0023] Figure 3 It is a schematic diagram of the structure of the steel mesh and the window in an embodiment of the present invention.

[0024] The reference numerals are as follows:

[0025] 1-Nickel-Pd-Au pad, 2-Steel mesh, 3-Window. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the embodiments described below are part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0027] Therefore, the detailed description of the embodiments of the present application provided below in conjunction with the accompanying drawings is intended to represent only selected embodiments of the present application, and is not intended to limit the scope of protection claimed in the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0028] It should be understood that in the description of the embodiments of the present invention, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features.

[0029] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0030] See also Figure 1 The present invention provides a method for bonding a nickel-palladium-gold pad, comprising the following steps:

[0031] S1. Make a steel mesh, the window size of which shall not exceed 80% of the size of the nickel-palladium-gold pad.

[0032] In step S1, the steel mesh 2 is prepared as Figure 3 As shown, the size of the opening 3 of the steel mesh 2 does not exceed 80% of the size of the nickel-palladium-gold pad. The structure of the steel mesh 2 and the opening 3 is shown in Figure 3 .

[0033] S2. Print solder paste on the nickel-palladium-gold pad on the substrate through the steel mesh.

[0034] S3, melting the solder paste printed on the nickel-palladium-gold pad to form a metal compound layer between the solder paste and the nickel-palladium-gold pad.

[0035] S4. Printing solder paste on the surface of the metal compound layer through the steel mesh.

[0036] S5. Mount the FC chip onto the surface of the NiPdAu pad printed with solder paste.

[0037] S6. Melt the solder paste printed on the surface of the metal compound layer.

[0038] S7. Cleaning the substrate.

[0039] Optionally, in step S2, printing solder paste on the nickel-palladium-gold pad through the steel mesh is specifically as follows: passing the solder paste and flux through the window 3 of the steel mesh 2, and evenly coating the solder paste on the nickel-palladium-gold pad under the action of a printing machine scraper.

[0040] Step S2: First printing: Solder paste and flux are mixed through Figure 3 The opening 3 on the steel mesh 2 shown is used to evenly coat the solder paste on the nickel-palladium-gold pad 1 on the surface of the substrate under the action of the printer scraper. The main component of the flux is a mixture with rosin as the main component, which is an auxiliary material to ensure the smooth welding of the solder paste and the nickel-palladium-gold pad 1 of the substrate. The area of ​​the opening 3 of the steel mesh 2 shall not be greater than 80% of the area of ​​the nickel-palladium-gold pad 1 to reduce the risk of solder paste bridging after reflow soldering.

[0041] Optionally, in step S3, the solder paste printed on the substrate is melted by reflow soldering, and the reflow soldering temperature is 245°C.

[0042] Step S3 is the first reflow soldering, and the specific operation is: melt the solder paste pre-printed on the nickel-palladium-gold pad 1 by reflow soldering, and the temperature of the first reflow soldering is controlled at a maximum of 245°C and the track speed is 150cm / min. After reflow soldering, the solder paste is in the shape of a solder ball due to surface tension, and a metal compound layer is formed between the solder paste and the nickel-palladium-gold pad 1, so that the solder ball solder paste is tightly combined with the nickel-palladium-gold pad 1 of the substrate.

[0043] Optionally, in step S4, when solder paste is printed on the surface of the metal compound layer, the solder paste printed on the metal compound layer must not exceed the edge of the nickel-palladium-gold pad.

[0044] Step S4 is secondary printing, and the specific operation is as follows: the solder paste and solder flux pass through the windows at the corresponding positions on the steel mesh, and the solder paste is evenly coated on the tin ball-shaped surface on the nickel-palladium-gold pad 1 under the action of the printer scraper. The secondary printed solder paste has good adhesion to the semiconductor FC chip surface pad and the lower tin ball-shaped solder paste and metal compound. With the help of the secondary printed solder paste, the semiconductor FC chip surface with originally weak bonding force and the nickel-palladium-gold pad 1 are closely connected. Figure 2 Shown is a schematic diagram of the structure of the nickel-palladium-gold pad on the substrate, wherein the left side figure a is a front view of the nickel-palladium-gold pad, and the left side figure b is a back view of the nickel-palladium-gold pad.

[0045] Optionally, in step S5, the FC chip is mounted on the surface of the nickel-palladium-gold pad printed with solder paste, specifically: the FC chip is mounted on the surface of the nickel-palladium-gold pad printed with solder paste and flux using a die bonding machine, during die bonding, the die bonding accuracy and whether there is damage caused by ejector pins on the bottom of the FC chip are confirmed, and after die bonding, the FC chip is checked for defects such as reverse sticking, offset, and chip crushing.

[0046] Step S5 is die bonding. The specific operation is: use a die bonding machine to mount the FC chip on the surface of the nickel-palladium-gold pad 1 printed with solder paste and flux. During die bonding, the die bonding accuracy and whether there is damage caused by ejector pins on the bottom of the semiconductor FC chip should be confirmed. After die bonding, the semiconductor FC chip needs to be checked for defects such as reverse sticking, offset, and chip crushing.

[0047] Optionally, in step S6, the solder paste printed on the surface of the metal compound layer is melted by reflow soldering, and the reflow soldering temperature is 250°C.

[0048] Step S6 is a secondary reflow soldering, and the specific operation is: melt the solder paste printed on the surface of the metal compound layer by reflow soldering to achieve mechanical and electrical connection between the pad 1 of the FC chip and the nickel-palladium-gold pad 1. During the process, the secondary reflow soldering temperature should be controlled to be maintained at 250°C and the track speed should be 85cm / min. Ensure that the secondary printed solder paste is tightly combined with the metal compound layer and the tin ball solder paste formed after the primary reflow soldering. After the secondary reflow soldering, ensure that the solder paste and metal compound layer of the nickel-palladium-gold pad 1 do not bridge with the solder paste and metal compound layer on the adjacent pad.

[0049] Step S7 is cleaning, and the specific operation is: cleaning the residual flux on the surface of the substrate to make the soldering points uniform, the assembly is beautiful, and the reliability is improved.

[0050] The present invention provides a method for bonding nickel-palladium-gold pads, so that a solid metal compound layer is generated between the first printed solder paste and the nickel-palladium-gold pad after a reflow, and the second printed solder paste forms a tin ball on the metal compound layer in the steel mesh window, so that the semiconductor FC chip pad and the nickel-palladium-gold pad are tightly connected through the tin layer and the metal compound layer to form a reliable mechanical and electrical connection. The problem of low bonding strength between the semiconductor FC chip and the nickel-palladium-gold pad of the substrate is solved, and the risk of bridging between the solder paste on the nickel-palladium-gold pad and the solder paste on the adjacent pad is reduced.

[0051] The above is only the best specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A die bonding method for a nickel-palladium-gold pad, characterized in that: The following steps are involved: S1. Making a steel mesh, wherein the window size of the steel mesh does not exceed 80% of the size of the nickel-palladium-gold pad; S2, printing solder paste on the nickel-palladium-gold pad on the substrate through the steel mesh; S3, melting the solder paste printed on the nickel-palladium-gold pad to form a metal compound layer between the solder paste and the nickel-palladium-gold pad; S4, printing solder paste on the surface of the metal compound layer through the steel mesh; S5, mounting the FC chip on the surface of the nickel-palladium-gold pad printed with solder paste; S6, melting the solder paste printed on the surface of the metal compound layer; S7. Cleaning the substrate.

2. The method for bonding nickel-palladium-gold pads according to claim 1, characterized in that: In step S3, the solder paste printed on the substrate is melted by reflow soldering, and the reflow soldering temperature is 245°C.

3. The die bonding method for a nickel-palladium-gold pad according to claim 1, characterized in that: In step S6, the solder paste printed on the surface of the metal compound layer is melted by reflow soldering, and the reflow soldering temperature is 250°C.

4. The die bonding method for a nickel-palladium-gold pad according to any one of claims 1 to 3, characterized in that: In step S4, when solder paste is printed on the surface of the metal compound layer, the solder paste printed on the metal compound layer shall not exceed the edge of the nickel-palladium-gold pad.

5. The die bonding method for a nickel-palladium-gold pad according to claim 4, characterized in that: In step S2, the solder paste is printed on the nickel-palladium-gold pad on the substrate through the steel mesh, specifically: the solder paste and flux are passed through the windows of the steel mesh, and the solder paste is evenly coated on the nickel-palladium-gold pad under the action of the scraper of the printing machine.

6. The die bonding method for a nickel-palladium-gold pad according to claim 4, characterized in that: In step S4, the solder paste is printed on the surface of the metal compound layer through the steel mesh, specifically: the solder paste and flux are passed through the windows on the steel mesh, and the solder paste is evenly coated on the nickel-palladium-gold pad under the action of a printing machine scraper.

7. The die bonding method for a nickel-palladium-gold pad according to claim 4, characterized in that: In step S5, the FC chip is mounted on the surface of the nickel-palladium-gold pad printed with solder paste. Specifically, the FC chip is mounted on the surface of the nickel-palladium-gold pad printed with solder paste and flux using a die bonding machine. During die bonding, the die bonding accuracy and whether there is damage caused by ejector pins on the bottom of the FC chip are confirmed. After die bonding, the FC chip is checked for defects such as reverse sticking, offset, and chip crushing.

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