A contact-shaped composite filler metal, a preparation method and application thereof

Abstract

The application belongs to the technical field of brazing, and particularly relates to a contact-shaped composite brazing filler metal and a preparation method and application thereof. The preparation method comprises the following steps: obtaining a sheet made of material A; stamping the sheet by using a stamping die to make the surface of the sheet bent to form a plurality of trapezoidal grooves, so that a honeycomb array structure sheet is obtained; spraying solder paste in the trapezoidal grooves of the honeycomb array structure sheet, wherein the solder paste comprises brazing filler metal B and a flux; and placing the honeycomb array structure sheet with the sprayed solder paste into a reflow oven for heating, so that the brazing filler metal B in each trapezoidal groove is melted to form a protruding contact, and a contact-shaped composite brazing filler metal sheet is obtained. In the heating process, the flux is separated out and flows to cover the outer surface of the contact-shaped composite brazing filler metal sheet. The application can realize preparation of a high-strength composite welding point, and has the characteristics of low-temperature welding and high-temperature application.

Description

Technical Field

[0001] This invention belongs to the field of brazing technology, specifically relating to a contact-shaped composite brazing filler metal, its preparation method, and its application. Background Technology

[0002] Brazing is a precision joining technology that uses molten filler metal to wet, spread, and fill gaps on the surface of a solid base material (the material being joined), forming a metallurgical bond upon cooling. It is widely used in electronics, aerospace, automotive, and medical fields. Its core advantage is the ability to reliably join dissimilar materials (such as metals and ceramics, or different metals) at relatively low temperatures without damaging the properties of the base material.

[0003] Brazing interconnect materials and technologies are the core foundation supporting product structure integration and functional implementation, and their performance directly determines the reliability and service life of products. Especially in the manufacturing and assembly of electronic components, the increasing demands on the upper limit of service temperature for end products, and the trend towards higher integration and more complex heterogeneous product structures, have led to a significant increase in the frequency of welding processes. Against this backdrop, traditional high-temperature brazing alloys are prone to interface cracking or structural deformation due to thermal stress concentration with the base material and adjacent structural components during the welding process; while traditional low-temperature brazing alloys, limited by their low melting point, are unable to withstand the temperature environment during product service and are prone to softening failure. These inherent defects in both types of brazing alloys can no longer meet the dual requirements of current electronic components for stable welding assembly processes and long-term service reliability, becoming a key bottleneck restricting the realization of core product functions and performance breakthroughs.

[0004] During high-temperature brazing, due to the limited high-temperature heat input, some sensitive components and printed circuit boards (PCBs) are prone to significant thermal deformation, which can induce typical defects such as the "head-in-pillow" effect (HIP), pad wettability failure, and component thermal damage, seriously affecting the reliability of the interconnect structure. To solve this problem, low-temperature brazing technology has become a key approach. Its core objective is to reduce the product assembly welding temperature from the melting point range of traditional high-temperature solders to a low-temperature range while ensuring the metallurgical bonding quality and mechanical properties of the solder joints, thus achieving the process characteristics of "low-temperature connection - high-temperature service". This technical approach is both a recognized technical challenge in the field of electronic manufacturing and a core research hotspot in current interconnect technology.

[0005] Currently, the main processes for achieving low-temperature brazing in the industry include low-temperature sintering of nano-metal particles, transient liquid-phase low-temperature sintering, and particle-reinforced low-temperature welding (sintering) processes. All three methods have a certain application foundation in practical engineering, but each also has its own problems. Specifically: the low-temperature sintering process of nano-metal particles has limitations such as high solder paste preparation costs and the immaturity of atmospheric pressure sintering technology, therefore it is currently only applied to some wide-bandgap semiconductor power devices with special requirements; the transient liquid-phase sintering process has problems such as long sintering time (about 20 minutes) and high process temperature (above 200~300℃), and the resulting intermetallic compounds are diverse and unevenly distributed, leading to brittle and hard solder joints, which seriously restricts the widespread application of this process; the particle-reinforced welding (sintering) process has not yet formed a systematic research method and evaluation system, and its applicable scenarios and scope are still relatively limited. Summary of the Invention

[0006] To address the above problems, this invention provides a contact-shaped composite brazing filler metal, its preparation method, and its application.

[0007] In a first aspect, the present invention provides a method for preparing a contact-shaped composite solder, comprising:

[0008] S1. Obtain a thin sheet made of material A; wherein material A is a high-temperature metal or a brazing alloy;

[0009] S2. A thin sheet is stamped using a stamping die to bend its surface and form multiple trapezoidal grooves, resulting in a honeycomb array structure thin sheet; solder paste is sprayed into the trapezoidal grooves of the honeycomb array structure thin sheet, wherein the solder paste includes solder B and flux;

[0010] S3. The honeycomb array structure sheet printed with solder paste is placed in a reflow oven for heating. The solder B melts and forms raised contacts in each trapezoidal groove, resulting in a contact-shaped composite solder sheet. During the heating process, the flux is separated and flows to cover the outer surface of the contact-shaped composite solder sheet.

[0011] In a second aspect, the present invention provides a contact-shaped composite solder, which is prepared using the method for preparing a contact-shaped composite solder as described in the first aspect.

[0012] In a third aspect, the present invention provides an application of a contact-shaped composite solder, comprising the following steps:

[0013] A contact-shaped composite solder sheet is prepared using the method for preparing contact-shaped composite solder mentioned in the first aspect;

[0014] The contact-shaped composite solder sheet is fully contacted and pressed onto the PCB board pads. The contact-shaped composite solder sheet is then cold-cut using a laser, retaining the pad pattern and removing excess contact-shaped composite solder sheet to obtain a PCB board with the pre-placed contact-shaped composite solder sheet. In this process, the contact-shaped composite solder sheet is locally melted at the laser-cut location, and the molten material automatically adheres to the PCB board pads to fix the contact-shaped composite solder sheet.

[0015] Component mounting and reflow soldering are performed on a PCB board with pre-placed contact-shaped composite solder sheets. The reflow soldering temperature is higher than the melting point of solder B but lower than the melting point of solder A. After reflow soldering is completed, material A is completely consumed or a very small amount remains. The product formed by mixing material A and solder B is distributed in a honeycomb pattern, and the melting point of the product formed by mixing solder A and solder B is higher than the melting point of solder B.

[0016] The beneficial effects of this invention are:

[0017] The composite solder sheet designed in this invention has a simple preparation process and its surface is covered with flux.

[0018] This invention uses a punching die to press and print thin sheets to obtain honeycomb array structure sheets, so that the solder joints are distributed in a honeycomb pattern, which can realize low-temperature welding and high-temperature brazing technology. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of stamping a thin sheet according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of a honeycomb array structure sheet printed with solder paste, as shown in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of a contact-shaped composite solder sheet as shown in an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram illustrating the pressing and bonding of a contact-shaped composite solder sheet to a PCB board pad, as shown in an embodiment of the invention.

[0023] Figure 5 This is a schematic diagram of a PCB board with pre-formed contact-shaped composite solder sheets, as shown in an embodiment of the present invention.

[0024] Figure 6 This is a schematic diagram illustrating component mounting on a PCB board with pre-placed contact-shaped composite solder sheets, as shown in an embodiment of the present invention.

[0025] Figure 7 This is a schematic diagram illustrating the completion of brazing according to an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Some embodiments of the present invention provide a method for preparing a contact-shaped composite solder, such as... Figure 1-3 As shown, it includes:

[0028] S1. Obtain a thin sheet made of material A; wherein material A is a high-temperature metal or a brazing alloy;

[0029] S2. A thin sheet is stamped using a stamping die to bend its surface and form multiple trapezoidal grooves, resulting in a honeycomb array structure thin sheet; solder paste is sprayed into the trapezoidal grooves of the honeycomb array structure thin sheet, wherein the solder paste includes solder B and flux;

[0030] S3. The honeycomb array structure sheet printed with solder paste is placed in a reflow oven for heating. The solder B melts and forms raised contacts in each trapezoidal groove, resulting in a contact-shaped composite solder sheet. During the heating process, the flux is separated and flows to cover the outer surface of the contact-shaped composite solder sheet.

[0031] In some embodiments, the sheet made of material A should have a certain degree of ductility. If material A is a high-temperature metal, it should preferably be a metal with the same composition as the upper and lower substrates to be welded or Au, so as to ensure the matching effect of the solder joint and reduce the difference in the coefficient of thermal expansion between the solder joint and the upper and lower substrates to be welded. If material A is a brazing alloy, it should be ensured that the melting point of material A is higher than that of brazing alloy B and that it has metallurgical compatibility with brazing alloy B, so as to realize the application of low temperature to high temperature.

[0032] Specifically, in this embodiment of the invention, the upper and lower substrates to be soldered refer to PCB board pads and component pads.

[0033] Specifically, the solder paste printed on the honeycomb array structure sheet is generally in paste form, with the solder B in microspheres. After a short heating time in step S3, the solder B melts and solidifies, and the flux is discharged and accumulates on the outer surface.

[0034] Specifically, if material A is a solder alloy, then material A should be a Sn-based alloy, with additional elements such as Pb, Cu, and Zn added to the Sn-based alloy; at the same time, solder B should also be a Sn-based alloy, with additional elements such as In, Bi, and Ag added to the Sn-based alloy.

[0035] In some embodiments, such as Figure 1As shown, a stamping die is used to stamp a thin sheet. The stamping die includes an upper die and a lower die. The upper die is a plate with multiple trapezoidal structural blocks protruding at fixed intervals on its lower surface, and each trapezoidal structural block has a through hole in its center. The lower die is a plate with multiple trapezoidal structural blocks protruding at fixed intervals on its upper surface, and each trapezoidal structural block has a through hole in its center. Step S2 specifically includes:

[0036] S21. A thin sheet is placed between the upper and lower punches, wherein the trapezoidal structural blocks of the upper and lower punches are staggered; pressure is applied to the stamping die, and the thin sheet is then stamped in an array to bend its surface and form multiple trapezoidal grooves, thereby obtaining a honeycomb array structure thin sheet.

[0037] S22. Connect the upper punch die to the solder paste storage device and open the solder paste storage device. Spray solder paste onto each trapezoidal groove on the upper surface of the sheet through the through hole in the trapezoidal structure block. Then connect the lower punch die to the solder paste storage device and open the solder paste storage device. Spray solder paste onto each trapezoidal groove on the lower surface of the sheet through the through hole in the trapezoidal structure block.

[0038] Specifically, the upper punch is made of high-hardness alloy material, which has excellent durability and resistance to deformation; the lower punch is also made of high-hardness metal material to ensure its long-term stability and reliability.

[0039] Figure 2 This is a schematic diagram of a honeycomb array structure sheet printed with solder paste according to some embodiments of the present invention.

[0040] In some embodiments, the contact at each trapezoidal groove in the contact-shaped composite solder sheet is 0.01~0.02mm higher than the opening plane of the trapezoidal groove.

[0041] In some embodiments, the sheet thickness is preferably 0.03~0.05mm; after the sheet is stamped using a stamping die, the surface of the sheet is bent to form multiple trapezoidal grooves, and the overall thickness of the honeycomb array structure sheet (i.e., including the height of the trapezoidal grooves) is 0.08~0.10mm.

[0042] In some embodiments, the higher the density of the trapezoidal grooves (i.e., the smaller the opening diameter of the trapezoidal grooves), the better the uniformity of the contact points. Preferably, the opening diameter of the trapezoidal grooves is 0.1~0.2mm.

[0043] Figure 3 This is a schematic diagram of a contact-shaped composite solder sheet according to some embodiments of the present invention.

[0044] In some embodiments, a honeycomb array structure sheet printed with solder paste is placed in a reflow oven and heated simultaneously from both top and bottom. The heating time must be properly controlled, ensuring the flux is completely melted, avoiding excessive heating. After reflow, the flux should fully cover and evenly distribute on the surface of the contact-shaped composite solder sheet, such as... Figure 3 The green area is shown. If the coverage is insufficient, it can be supplemented by spraying or dipping.

[0045] Because the trapezoidal groove opening plane of the contact-shaped composite solder sheet has raised contacts, and the groove structure between the contacts can also store flux, compared with conventional solder sheets, the contact-shaped composite solder sheet prepared by the present invention not only has a larger flux dosage, but also a larger contact area between the flux and the solder, thereby more effectively removing the oxide film and improving the solder joint quality.

[0046] In some embodiments, the thickness of the contact-shaped composite solder sheet is 0.10~0.15mm.

[0047] Figure 4 This is a schematic diagram of the contact-shaped composite solder sheet being pressed and bonded to the PCB board pads, according to some embodiments of the present invention. Figure 5 This is a schematic diagram of a PCB board with pre-formed contact-shaped composite solder sheets, as shown in some embodiments of the present invention.

[0048] In some embodiments, the present invention proposes an application of a contact-shaped composite solder, such as... Figure 4-7 As shown, it includes the following steps:

[0049] A contact-shaped composite solder sheet is prepared using the method for preparing a contact-shaped composite solder proposed in this invention;

[0050] The contact-shaped composite solder sheet is fully contacted and pressed onto the PCB board pads. The contact-shaped composite solder sheet is then cut, retaining the pad pattern, and removing excess contact-shaped composite solder sheet to obtain a PCB board with the contact-shaped composite solder sheet pre-installed. The contact-shaped composite solder sheet undergoes localized melting at the laser-cut location, and the molten material, along with flux, automatically adheres to the PCB board pads, thus fixing the contact-shaped composite solder sheet and preventing displacement during subsequent component mounting.

[0051] Component mounting and reflow soldering are performed on a PCB board with pre-placed contact-shaped composite solder sheets. The reflow soldering temperature is higher than the melting point of solder B but lower than the melting point of solder A. After reflow soldering is completed, material A is completely consumed or a very small amount remains. The product formed by mixing material A and solder B is distributed in a honeycomb pattern, and the melting point of the product formed by mixing solder A and solder B is higher than the melting point of solder B.

[0052] Specifically, to avoid an excessively large heat-affected zone, laser cold cutting is used, aligned with the PCB board pads (such as...). Figure 4 The position and size of the contact-shaped composite solder pieces (shown in red) are determined by cutting them to be slightly smaller than or equal to the pad pattern. The pad pattern is retained, and excess contact-shaped composite solder pieces are removed to obtain a PCB board with pre-placed contact-shaped composite solder pieces. Besides laser cold cutting, other methods can also achieve the same effect.

[0053] Figure 6 This is a schematic diagram of component mounting on a PCB board with pre-placed contact-shaped composite solder sheets, according to some embodiments of the present invention. Figure 7 This is a schematic diagram illustrating the completion of brazing according to some embodiments of the present invention.

[0054] In some embodiments, the reflow soldering temperature is 40-60°C higher than the melting point of solder B, and the reflow soldering time is 200-250 seconds.

[0055] In some embodiments, during reflow soldering, the contact surface flows and collapses. Simultaneously, under the weight of the component, the component solder tip contacts the sheet, preventing further downward collapse of the solder joint, maintaining its height, and enhancing stress buffering. Simultaneously, under the action of solder B, the component solder tip undergoes a metallurgical mixing reaction with material A, generating a high-temperature intermetallic compound containing three components, exhibiting high strength, such as... Figure 7 The dark blue section is shown. Similarly, the PCB board solder pads contact the thin sheet. Under the action of solder B, the PCB board solder pads undergo a metallurgical mixing reaction with material A, generating a high-temperature intermetallic compound containing three components, such as... Figure 7 The yellow section is shown.

[0056] Specifically, during reflow soldering, material A reacts fully with solder B, material A is completely consumed, and the product generated by the mixture of A and B (such as...) Figure 7 The light blue portion (shown here) exhibits a honeycomb-like diffuse distribution at the solder joint (i.e., solder B), thereby strengthening the solder joint structure and increasing its service temperature (melting point), strength, and flexibility (which helps with stress buffering). The product formed by mixing material A and solder B has a higher melting point than solder B.

[0057] By utilizing the contact points of intermetallic compounds and the melting point characteristics of the components in the AB mixture, the service temperature of the solder joints can be significantly increased. Furthermore, the intermetallic compounds form a solid-phase bond at high temperatures; if a solder joint (solder B) cracks, placing the PCB assembly in a temperature environment above its melting point allows the solder joint to self-repair, thus not affecting its functionality.

[0058] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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 of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a contact-shaped composite solder, characterized in that, include: S1. Obtain a thin sheet made of material A; wherein material A is a high-temperature metal or a brazing alloy; S2. A thin sheet is stamped using a stamping die to bend its surface and form multiple trapezoidal grooves, resulting in a honeycomb array structure thin sheet; solder paste is sprayed into the trapezoidal grooves of the honeycomb array structure thin sheet, wherein the solder paste includes solder B and flux; S3. The honeycomb array structure sheet printed with solder paste is heated for a short time. The solder B melts and forms raised contacts in the trapezoidal groove, resulting in a contact-shaped composite solder sheet. The flux is separated during the heating process and flows to cover the outer surface of the contact-shaped composite solder sheet. The contacts at each trapezoidal groove in the contact-shaped composite solder sheet are 0.01~0.02mm higher than the opening plane of the trapezoidal groove. If material A is a high-temperature metal, then a metal with the same composition as the upper and lower substrates to be welded or Au should be selected; if material A is a brazing alloy, its melting point is higher than that of brazing alloy B, and it has metallurgical compatibility with brazing alloy B.

2. The method for preparing a contact-shaped composite solder according to claim 1, characterized in that, The stamping die includes an upper die and a lower die; the upper die is a plate with multiple trapezoidal structural blocks protruding at fixed intervals on its lower surface, and each trapezoidal structural block has a through hole in its center; the lower die is a plate with multiple trapezoidal structural blocks protruding at fixed intervals on its upper surface, and each trapezoidal structural block has a through hole in its center; step S2 specifically includes: S21. A thin sheet is placed between the upper and lower punches, wherein the trapezoidal structural blocks of the upper and lower punches are staggered; pressure is applied to the stamping die, and the thin sheet is then stamped in an array to bend its surface and form multiple trapezoidal grooves, thereby obtaining a honeycomb array structure thin sheet. S22. Connect the upper punch die to the solder paste storage device and open the solder paste storage device. Spray solder paste onto each trapezoidal groove on the upper surface of the sheet through the through hole in the trapezoidal structure block. Then connect the lower punch die to the solder paste storage device and open the solder paste storage device. Spray solder paste onto each trapezoidal groove on the lower surface of the sheet through the through hole in the trapezoidal structure block.

3. The method for preparing a contact-shaped composite solder according to claim 2, characterized in that, The thickness of the sheet is 0.03~0.05mm, the thickness of the honeycomb array structure sheet is 0.08~0.10mm, and the diameter of the opening on the trapezoidal groove is 0.1~0.2mm.

4. The method for preparing a contact-shaped composite solder according to claim 1, characterized in that, The thickness of the contact-shaped composite solder sheet is 0.10~0.15mm.

5. A contact-shaped composite brazing filler metal, characterized in that, It is prepared using the method for preparing a contact-shaped composite solder as described in any one of claims 1 to 4.

6. An application of a contact-shaped composite brazing filler metal, characterized in that, Includes the following steps: A contact-shaped composite solder sheet is prepared using the method for preparing a contact-shaped composite solder as described in any one of claims 1 to 4. The contact-shaped composite solder sheet is fully contacted and pressed onto the PCB board pads. The contact-shaped composite solder sheet is then cold-cut using a laser, retaining the pad pattern and removing excess contact-shaped composite solder sheet to obtain a PCB board with the pre-placed contact-shaped composite solder sheet. In this process, the contact-shaped composite solder sheet is locally melted at the laser-cut location, and the molten material automatically adheres to the PCB board pads to fix the contact-shaped composite solder sheet. Component mounting and reflow soldering are performed on a PCB board with pre-placed contact-shaped composite solder sheets. The reflow soldering temperature is higher than the melting point of solder B but lower than the melting point of solder A. After reflow soldering is completed, material A is completely consumed or a very small amount remains. The product formed by mixing material A and solder B is distributed in a honeycomb pattern, and the melting point of the product formed by mixing solder A and solder B is higher than the melting point of solder B.

7. The application of the contact-shaped composite brazing filler metal according to claim 6, characterized in that, The reflow soldering temperature is 40-60°C higher than the melting point of solder B, and the reflow soldering time is extended to 200-250 seconds to ensure that material A and solder B react fully.

8. The application of the contact-shaped composite brazing filler metal according to claim 6, characterized in that, During reflow soldering, the contact surface flows and collapses. Under the gravity of the components, the component solder ends and PCB board pads come into contact with the thin sheet material A, preventing the solder joints from collapsing further downwards. At the same time, the component solder ends and PCB board pads undergo a metallurgical mixing reaction with material A under the action of solder B, generating a high-temperature intermetallic compound containing three components.

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