Solder presetting and in-situ brazing method for deep-hole three-dimensional welding seam

Abstract

The invention relates to the technical field of electronic packaging and welding, and provides a solder presetting and in-situ brazing method for a deep-hole three-dimensional welding seam, which comprises the following steps of: presetting a bonding pad structure at the edge of a three-dimensional welding seam of a circuit board with an integrally formed or spliced structure, continuously depositing solder balls with different melting points at fixed intervals through laser ball mounting, forming a solder ball array with a mixed solder loading structure; and reflow soldering is conducted, and accurate soft soldering of the deep hole three-dimensional welding seam is completed through supporting and surface tension constraint of the high-melting-point brazing filler metal framework on the molten brazing filler metal. According to the method, accurate connection of the deep hole three-dimensional welding seam can be achieved, and the size and components of the interconnection structure can be accurately controlled.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronic packaging and welding technology, in particular to a brazing material prepositioning and in-situ brazing method for deep-hole three-dimensional welds. BACKGROUND

[0002] With the continuous updating and iteration of electronic communication equipment, the traditional planar circuit structure has gradually failed to meet the needs of miniaturization, high integration and high electronic packaging density. Many new circuit structures have been invented and applied, among which the three-dimensional structure circuit has a larger area to integrate capacitors, inductors and other functional devices, and can achieve higher density packaging, thus having a very broad application prospect in the field of electronic communication. However, due to the formation of a deep-hole three-dimensional weld during splicing and packaging, and the problem of the circuit structure itself, the inner part of the circuit board must be kept vertical during welding. To achieve reliable electrical interconnection of each area to be connected of the circuit, it is very difficult to apply the existing electronic packaging interconnection method to weld such welds. The common electronic packaging interconnection methods at present mainly include wave soldering, induction soldering, hot air reflow soldering, laser reflow soldering, etc. Among these methods, for the welding of deep-hole inner corner welds in a vertical state, the wave soldering and induction soldering methods are limited by the large size of their own welding equipment, and their accessibility cannot meet the needs of this application scenario. While the traditional printed tin paste hot air reflow soldering and laser reflow soldering methods can solve the accessibility requirement, but when the deep-hole inner corner welds are welded in a vertical position, they cannot constrain the phenomenon of molten brazing material flowing downward under gravity when heated, and the control of the shape of the prepositioned brazing material is not accurate enough.

[0003] In summary, the existing technology has the technical problems of being unable to constrain the downward flow of molten brazing material when heated, and the control of the shape of the prepositioned brazing material is not accurate enough. CONTENT

[0004] In view of the above-mentioned deficiencies of the prior art, the present application provides a brazing material prepositioning and in-situ brazing method for deep-hole three-dimensional welds, which constrains the downward flow of molten brazing material when heated, accurately controls the shape of the prepositioned brazing material, and greatly improves the welding yield and reliability of three-dimensional structure circuit boards.

[0005] The brazing material prepositioning and in-situ brazing method for deep-hole three-dimensional welds provided by the present application comprises the following steps: At the welding seam of the circuit board of the integrated molding or splicing structure, the metallized pads are processed along the edge of the butt joint / splicing welding seam, the solder balls with different melting points are continuously deposited on the metallized pads by using the laser ball planting technology, and the solder balls are mutually wetted, spreaded and solidified to form the solder ball array with mixed loading or stacking structure; the pad surface is the metallized layer with good wetting property to the conventional solder, which is formed by plating copper, depositing silver, plating gold, chemical plating nickel and gold, or chemical plating nickel-chemical plating palladium immersion gold process, and the thickness of the metallized layer meets the requirements of the process specifications; The circuit board with the mixed loading or stacking solder structure is spliced to form a three-dimensional deep hole three-dimensional structure, so that the solder structure at the splicing welding seam of the circuit board is in contact with the pad or solder structure of the adjacent circuit board, and a three-dimensional solder pre-setting structure is formed. The deep hole three-dimensional welding seam with the solder pre-setting structure is subjected to reflow soldering to complete the in-situ brazing.

[0006] Further, in the stacking structure of the solder balls, the diameters of the solder balls can be different, and the diameters can change with the composition of the solder balls or / and the position of the stacking structure. For example, the diameter of the high-melting-point solder ball is selected as 200 mu m, and the diameter of the low-melting-point solder ball is selected as 500 mu m; or the diameter of the solder ball in the odd-numbered layer / row is selected as 200 mu m, and the diameter of the solder ball in the even-numbered layer / row is selected as 500 mu m, etc.

[0007] Further, for the combination of SAC305 and Sn42Bi58, the reflow temperature is 138℃~217℃; for the combination of Pb95Sn5 and Sn63Pb37, the reflow temperature is 183℃~308℃.

[0008] Further, in the chemical plating nickel-chemical plating palladium immersion gold (ENEPIG), the thickness of the Ni layer is 3~6 mu m, the thickness of the Pd layer is 100~500 nm, and the thickness of the Au layer is 20~100 nm.

[0009] Compared with the prior art, the present application has the following beneficial effects: The application provides a solder prepositioning and in-situ brazing method for deep-hole three-dimensional welds, which comprises the following steps: processing a metallized pad along the edge of a butt joint or a spliced structure of an integrated circuit board, continuously depositing solder balls with different melting points on the metallized pad by using a laser ball planting technology, and forming a solder ball array with a mixed loading or stacked structure by mutual wetting, spreading and solidification; the solder ball array deposited by the method has high solder amount and position accuracy, and the initial shape of the weld can be accurately controlled; when the circuit board is spliced into a three-dimensional structure, the solder ball array can form a solid prepositioned solder structure around the three-dimensional weld, and directly contact or form a small gap fit with the pads and solder ball arrays of adjacent circuit boards, thereby providing a stable material structure basis for subsequent welding processing, avoiding the problems of slippage or splicing deformation of traditional solder paste, and the three-dimensional mounting of welding wires, welding rods and preformed sheets; meanwhile, when the deep-hole three-dimensional weld is reflow soldered, the reflow temperature is between the melting points of the high and low melting point solder balls, the melting state of the prepositioned solder structure can be controlled, the high melting point solder ball remains solid, physical structure support and surface tension constraint are provided for the molten solder, the flow and overflow of the molten solder are inhibited, the welding of vertical or even negative angle welds can be realized, the reflow temperature can be reduced while obtaining a high-temperature interconnection structure, the thermal deformation and damage of the three-dimensional spliced weld are reduced, and the welding yield and reliability are improved. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings, which are not necessarily drawn to scale, like reference numerals describe similar components throughout the several views: Figure 1 FIG. 1 is a flowchart of a solder prepositioning and in-situ brazing method for deep-hole three-dimensional welds according to an embodiment of the application; Figure 2 FIG. 2 is a schematic diagram of a state in which a nozzle of a laser ball planting machine sprays solder balls in a deep-hole pad area of a circuit board according to an embodiment of the application; Figure 3 FIG. 3 is a schematic diagram of a state in which a single-row single-layer stacked structure of high and low melting point mixed loading solder balls is generated at an inner side fillet weld of two plates according to an embodiment of the application; Figure 4 FIG. 4 is a schematic diagram of a state in which a multi-row multi-layer stacked structure of high and low melting point mixed loading solder balls is generated at an inner side fillet weld of two plates according to an embodiment of the application; Figure 5 FIG. 5 is a schematic diagram of a state in which a plurality of circuit boards are spliced into a three-dimensional structure circuit board according to an embodiment of the application; Figure 6 are some schematic diagrams of various solder longitudinal section stacking modes of embodiments of the present application.

[0011] Explanation of reference signs: 1, nozzle of laser ball placement machine; 2, solder ball array; 21, stacking structure of solder balls; 3, circuit board; 30, deep hole; 31, inner fillet; 32, three-dimensional structure circuit board. DETAILED DESCRIPTION

[0012] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments will be described clearly and completely below in combination with the drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should fall within the scope of protection of the present application.

[0013] Referring to Figures 1-6 , the present application provides a solder prepositioning and in-situ brazing method for deep hole three-dimensional fillet, comprising the following steps: S101, on the welding seam of an integrated molded or spliced circuit board, metalized pads are processed along the edge of the butt joint / spliced welding seam, laser ball placement technology is used to continuously deposit solder balls with different melting points on the metalized pads, and the solder balls are mutually wetted, spread and solidified to form a mixed or stacked solder ball array; the pad surface is a metalized layer formed by plating copper, silver deposition, gold plating, chemical nickel plating and gold deposition, or chemical nickel plating-palladium immersion gold process, which has good wettability with conventional solder, and the thickness meets the process specification requirements; S102, the circuit board with the mixed or stacked solder structure is spliced to form a three-dimensional deep hole three-dimensional structure, so that the solder structure at the spliced welding seam is in contact with the pads or solder structure of the adjacent circuit board, forming a three-dimensional solder prepositioning structure; S103, reflow soldering is performed on the deep hole three-dimensional welding seam with the solder prepositioning structure to complete in-situ brazing.

[0014] It should be noted that, in the circuit board welding seam of the integrated molding or splicing structure, the metallized pads are processed along the edge of the butt joint / splicing welding seam, the solder balls of different melting points are continuously deposited on the metallized pads by using the laser ball planting technology, and are mutually wetted, spreaded and solidified to form the solder ball array of mixed loading or stacking structure, the solder ball array deposited by this method has high solder amount and position accuracy, and the initial shape of the welding seam can be accurately controlled; when the circuit boards are spliced into a three-dimensional structure, the solder ball array can form a solid-state pre-solder structure around the three-dimensional welding seam, and directly contacts or forms a small gap fit with the pads and solder ball arrays of adjacent circuit boards, thereby providing a stable material structure basis for subsequent welding processing, avoiding the sliding or splicing deformation of the traditional solder paste and the three-dimensional mounting difficulties of welding wires, welding rods and formed sheets, etc.; at the same time, when the deep hole three-dimensional welding seam is reflow soldered, the reflow temperature is between the melting points of the high and low melting point solder balls, the melting state of the pre-solder structure can be controlled, the high melting point solder ball remains solid, physical structure support and surface tension constraint are provided for the molten solder, the flow and overflow of the molten solder are inhibited, the welding of the vertical or even negative angle welding seam can be realized, the reflow temperature can be reduced while obtaining the high-temperature interconnection structure, the thermal deformation and damage of the three-dimensional splicing welding seam are reduced, and the welding yield and reliability are improved.

[0015] It should be noted that, during reflow soldering, the reflow temperature can be between the melting points of the high and low melting point solder balls, so that the melting state of the low melting point solder ball and the high melting point solder ball in the stacking structure of the solder ball is controlled during reflow soldering, the low melting point solder ball is melted, the high melting point solder ball remains solid, an additional liquid-solid interface is formed on the surface of the high melting point solder ball, support and surface tension constraint are provided for the molten solder, and the sinking of the molten solder under gravity is inhibited; the two solders with different melting points used are SAC305 and Sn42Bi58 or Pb95Sn5 and Sn63Pb37, etc., which are high and low temperature solder combinations with obvious difference in melting point, and the reflow temperature of the high and low temperature solder combination is between the high and low melting points.

[0016] It should be noted that the preset filler-based deep-hole inside fillet welding method provided in the embodiment can systematically solve the key technical problems of the prior art, such as “molten filler flowing under gravity”, “inaccurate control of the shape of the preset filler”, and “scraping deformation of the preset filler during circuit splicing”, and improve the welding reliability and accuracy of the three-dimensional structure circuit board. In step S101, a metallized pad is processed along the edge of the butt joint / splicing weld on the circuit board weld of the integrated structure or the splicing structure, different melting point filler balls are continuously deposited on the metallized pad by using the laser ball planting technology, and the filler balls are mutually wetted, spread, and solidified to form a mixed or stacked structure of the filler ball array; the pad surface is a metallized layer formed by plating copper, silver, gold, chemical nickel plating and gold plating, or chemical nickel plating-palladium immersion gold plating process, which has good wettability with conventional filler, and the thickness meets the requirements of various process specifications, thereby forming a mixed melting point filler ball array with controllable structure and clear composition, solving the problem of insufficient control of the shape and position of the filler in the traditional solder paste printing process, and effectively avoiding abnormal splicing gap or welding defects caused by inaccurate filler stacking. In step S102, the circuit board with the mixed or stacked filler structure is spliced to form a three-dimensional deep-hole structure, so that the filler structure at the splicing weld is in contact with the pad or filler structure of the adjacent circuit board, forming a three-dimensional filler preset structure, which simultaneously contains high-melting-point and low-melting-point filler balls, and is significantly different from the traditional single-melting-point filler layout, which can provide the support framework required for welding formation for the subsequent reflow process, and build a welding environment with a constraint function. In step S103, the deep-hole three-dimensional weld with the filler preset structure is reflow soldered to complete the in-situ brazing. During reflow soldering, the reflow process can be accurately controlled: the low-melting-point filler balls are completely melted to fill the weld, and a liquid-solid interface is formed on the surface of the high-melting-point filler balls. The liquid-solid interface provides multiple support sites and surface tension boundaries, effectively limiting the gravity-driven flow of the molten filler in the vertical direction from a physical mechanism. The high-melting-point filler balls and the liquid-solid interface jointly act as a filler barrier to participate in shape and flow control, significantly improving the uniformity and stability of the weld formation, effectively solving the technical problems of uncontrollable downward flow of molten filler, poor weld accessibility, and low welding formation accuracy, which have long restricted the reliability of three-dimensional circuit interconnection, and have significant technical effects and application value.

[0017] It should be noted that the inside fillet welds of adjacent circuit boards can be in a vertical state, an inclined state, or even a vertical welding position, and the high-melting-point filler balls that do not melt during reflow can provide additional constraints for the flow of molten filler.

[0018] It should be noted that the diameter of the solder ball in the stacked structure of the solder ball can be 50 μm to 2000 μm; the diameter of the solder ball can be the same or different. When the diameter of the solder ball is different, the diameter changes with the composition of the solder ball or / and the position of the stacked structure. For example, the diameter of the high-melting-point solder ball is selected to be 200 μm, and the diameter of the low-melting-point solder ball is selected to be 500 μm; or the diameter of the solder ball in the odd-numbered layer / row is selected to be 200 μm, and the diameter of the solder ball in the even-numbered layer / row is selected to be 500 μm, and the like.

[0019] It should be noted that if the pre-placed solder is prepared by using the conventional method, the high-melting-point solder paste and the low-melting-point solder paste are applied to the circuit board pad, and reflow solidification and setting are performed, then due to the different melting points, the high-temperature solder needs to be solidified before the low-temperature solder, the solder application structure is greatly limited, and during the reflow process, the solder wets and spreads, and the structure and shape are difficult to control; if the reflow solidification and setting are not performed, since the solder itself is in a paste state and has a certain flowability, the structure, shape and composition distribution cannot be accurately controlled, and the pre-placed solder and the pad surface are not metallurgically combined, and when the circuit is assembled or transferred as a whole, the pre-placed solder is easily affected by gravity, collision, scratching and the like, resulting in damage to the pre-placed structure. Therefore, the conventional paste-type solder application pre-placing method has great limitations for the welding of the inside corner fillet of the deep hole.

[0020] It should be noted that if the pre-placed solder is prepared by using the conventional method, the high-melting-point solder paste and the low-melting-point solder paste are applied to the circuit board pad, and reflow solidification and setting are performed, then due to the different melting points, the high-temperature solder needs to be solidified before the low-temperature solder, the solder application structure is greatly limited, and during the reflow process, the solder wets and spreads, and the structure and shape are difficult to control; if the reflow solidification and setting are not performed, since the solder itself is in a paste state and has a certain flowability, the structure, shape and composition distribution cannot be accurately controlled, and the pre-placed solder and the pad surface are not metallurgically combined, and when the circuit is assembled or transferred as a whole, the pre-placed solder is easily affected by gravity, collision, scratching and the like, resulting in damage to the pre-placed structure. Therefore, the conventional paste-type solder application pre-placing method has great limitations for the welding of the inside corner fillet of the deep hole.

[0021] In some preferred embodiments, the metallized pads at the butt joint are structurally continuous, or the non-metallized gap is not greater than 250 microns. The solder ball array on the structurally continuous metallized pad can have a gap with the pad or solder structure of the adjacent circuit board, and the size of the gap is not greater than 250 microns. The solder ball array and the pad or solder structure of the adjacent circuit board can have physical contact.

[0022] In some preferred embodiments, the solder ball array is composed of two or more kinds of solder selected from SAC305, Sn42Bi58, Pb95Sn5, Au80Sn20 and Sn63Pb37, which have a significant difference in melting point.

[0023] In some preferred embodiments, the solder ball array is a single row or multiple rows of solder balls, and is a single layer or multiple layers of stacked structure, and the diameter of the solder ball is 50 μm to 2000 μm; when the diameter of the solder ball is different, the diameter changes with the composition of the solder ball or / and the position of the stacked structure.

[0024] In some preferred embodiments, the solder ball array has a mixed structure of high-temperature solder balls and low-temperature solder balls arranged alternately in any number of layers or in any number of rows.

[0025] In some preferred embodiments, the low-temperature solder balls and the high-temperature solder balls are arranged alternately, with a single low-temperature solder ball adjacent to a single high-temperature solder ball or a random number of low-temperature solder balls adjacent to a random number of high-temperature solder balls.

[0026] In some preferred embodiments, the stack structure of the solder balls includes a densely stacked solder ball stack structure and / or a non-densely stacked solder ball stack structure in the horizontal and vertical cross sections.

[0027] In some preferred embodiments, the reflow temperature of the reflow soldering is between the melting points of the high-temperature solder balls and the low-temperature solder balls, and the melting states of the low-temperature solder balls and the high-temperature solder balls in the stack structure of the solder balls can be controlled so that the surface of the high-temperature solder ball forms an additional liquid-solid interface to provide support and surface tension constraint for the molten solder and inhibit the molten solder from overflowing due to gravity.

[0028] Further, the melting states of the low-temperature solder balls and the high-temperature solder balls in the stack structure of the solder balls can be controlled so that the low-temperature solder balls are completely melted and the high-temperature solder balls are partially melted, and the surface of the partially melted high-temperature solder ball forms the additional liquid-solid interface to provide support and surface tension constraint for the molten solder and inhibit the molten solder from sinking due to gravity. It should be noted that in this embodiment, the low-temperature solder balls are required to be completely melted to form a stable liquid-solid interface with the surface of the high-temperature solder ball during the reflow soldering. The liquid-solid interface has a dual function: on the one hand, the partially melted region can be wetted and connected with the surrounding molten low-temperature solder to form a continuous solder network structure, thereby improving the overall consistency and metallurgical bonding quality of the weld; on the other hand, the core of the high-temperature solder that is not completely melted remains rigid to form the skeleton of the stack structure of the solder balls, thereby enhancing the forming stability and anti-gravity sagging ability of the molten solder during the welding process. Through the scheme proposed in this embodiment, the flow control, shape control, and structural support ability of the molten solder can be further enhanced, and the controllability of the solder spreading in the vertical deep hole weld and the consistency of the welding product can be significantly improved, thereby achieving a better technical effect.

[0029] It should be noted that in this embodiment, the solder balls used are not limited to two types of solder balls with the same diameter and different melting points, and multiple diameters of solder balls can be used for the high-temperature solder balls and the low-temperature solder balls to form a more complex stack structure of the solder balls.

[0030] It should be noted that the soldered circuit board pad surface uses copper plating, silver plating (ImAg), gold plating, electroless nickel immersion gold (ENIG), or electroless nickel- electroless palladium immersion gold (ENEPIG) process to form a surface material with good wettability to conventional solder. The thickness of each metal layer meets the process specification requirements, for example, in ENEPIG, the thickness of the Ni layer is 3-6 μm, the thickness of the Pd layer is 100-500 nm, and the thickness of the Au layer is 20-100 nm. The metal plating layer (such as Ag, Ni / Au) can significantly improve the wettability between the solder and the pad, so that the solder rapidly spreads and forms after contacting the pad, effectively improving the stability and uniformity of the solder ball in the ball placement process and the reflow process. Good wettability helps to form a continuous and dense intermetallic compound (IMC) layer, which enhances the mechanical bonding force and thermal fatigue resistance of the solder joint without being too thick, thereby improving the electrical and structural reliability of the weld.

[0031] It should be noted that the two kinds of solder with different melting points used can be SAC305\ Sn42Bi58 or Pb95Sn5\Sn63Pb37, etc. high and low temperature solder combinations with obvious difference in melting point. The reflow temperature is between the high and low melting points, for example, for SAC305\ Sn42Bi58 combination, the reflow temperature is 138℃-217℃; for Pb95Sn5\Sn63Pb37 combination, the reflow temperature is 183℃-308℃. The high melting point solder ball (such as SAC305, Pb95Sn5) remains partially or completely solid, serving as a welding framework and structural support; the low melting point solder ball (such as Sn42Bi58, Sn63Pb37) completely melts and fills the gap in reflow, achieving dominant connection and wettability.

[0032] It should be noted that the pre-placed solder ball array can include a single row of single layer solder balls with different high and low melting points. The pre-placed solder ball array can also include multiple rows of single layer solder balls with different high and low melting points. The pre-placed solder ball array can also include a single row of multiple layers of solder balls with different high and low melting points. The stack structure of the solder balls can include a stack structure of multiple rows and multiple layers of high and low melting point mixed solder balls.

[0033] Preferably, in one circuit board, the pre-placed solder ball array includes two rows of single layer solder balls with different high and low melting points. In another circuit board spliced with the circuit board, the pre-placed solder ball array includes a single row of two layers of solder balls with different high and low melting points.

[0034] Preferably, the stack structure of the solder balls includes a stack structure of two rows and two layers of high and low melting point mixed solder balls.

[0035] Preferably, referring to Figure 6, the high and low melting point solder balls are arranged in an up-and-down separated manner. When the high and low melting point solder balls are arranged in an up-and-down separated manner, the multiple layers of low melting point solder balls are arranged on the single layer of high melting point solder balls, or the random number of layers of low melting point solder balls are arranged on the random number of layers of high melting point solder balls.

[0036] Preferably, referring to Figure 6 , the stacked structure of the solder balls comprises a stacked structure of the solder balls in which the low melting point solder balls and the high melting point solder balls are alternately arranged and mixed. When the low melting point solder balls and the high melting point solder balls are alternately arranged, a single low melting point solder ball is adjacent to a single high melting point solder ball, or a random number of low melting point solder balls are adjacent to a random number of high melting point solder balls.

[0037] Further, in the process of alternately arranging the high and low melting point solder balls, the high melting point solder balls are sprayed from the nozzle of the ball placer in a molten state, and when reaching the solid interface of the lower circuit board, the diameter of the high melting point solder balls is increased due to wetting and spreading, and the high melting point solder balls are in contact with the surrounding solidified high melting point solder balls, and after solidification, a high melting point solder skeleton is formed to avoid the low melting point solder balls from being molten and the upper high melting point solder balls from being in a free state. It should be noted that in the alternate ball placement, if the high melting point solder balls are not effectively connected with the surrounding structure (for example, simply stacked or floating on the low melting point solder), the upper high melting point solder balls are prone to be free to slide or fall during the reflow process due to the melting of the low melting point solder. The present embodiment provides a scheme in which the high melting point solder balls are pre-melted and sprayed, and before the three-dimensional structure is connected, the wetting contact and solidification with the surrounding high melting point solder balls are completed, so that the high melting point solder balls are actually physically connected to form a continuous rigid support network, thereby more effectively restraining the flow of molten low melting point solder in the subsequent reflow stage. After the formation of the continuous high melting point skeleton, it acts as a three-dimensional skeleton template in the weld area. When the low melting point solder balls are molten in the reflow process, they are locally wrapped in the skeleton structure, and under the action of capillary guidance and liquid-solid interfacial tension provided by the skeleton, the comprehensive effects of local filling, shape control, and flow suppression are achieved, which is helpful to form a high-quality weld with a neat geometric profile and uniform material distribution. The high melting point solder skeleton not only provides flow control and support in the first welding, but also has high thermal cycle stability and fatigue resistance, which can maintain the stability of the weld geometric appearance during subsequent environmental temperature changes or stress loading, thereby prolonging the service life of the device. At the same time, since the scheme provided by the present embodiment is realized by the laser ball placement process, the process is highly controllable, which is conducive to the consistency and repeatability control of the welding quality in batch processing.

[0038] Preferably, referring to Figure 6The stack structure of the solder balls comprises densely stacked solder ball stack structure and / or non-densely stacked solder ball stack structure in the transverse and longitudinal cross sections; the densely stacked solder ball stack structure has a high-melting-point solder ball stack slope. When the high-melting-point densely stacked region forms a slope, compared with the vertical stack, the gravity component direction and the solder spreading direction have an included angle, which is beneficial to the controlled flow of the molten solder in the slope direction instead of directly falling, thereby realizing the deflection type flow control and effectively relieving the problem of uncontrolled falling of the molten solder in the vertical weld. The slope stack structure makes the melting rate of the solder in different regions naturally different during the reflow process, thereby reducing the violent wetting fluctuation caused by the large-area simultaneous melting, improving the solder melting stability and the interfacial tension distribution balance, and further improving the weld forming consistency.

[0039] Preferably, in the stack structure of the solder balls, the diameter of the solder balls is 50-2000 μm.

[0040] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for pre-positioning and in-situ brazing of brazing filler metal in deep-hole three-dimensional welds, characterized in that, Includes the following steps: At the weld seams of integrated or spliced ​​circuit boards, metallized pads are processed along the edges of the butt / spliced ​​weld seams. Laser ball-planting technology is used to continuously deposit solder balls with different melting points on the metallized pads, which then wet, spread, and solidify to form a mixed or stacked array of solder balls. The surface of the pads is a metallized layer with good wettability to conventional solders, formed by copper plating, immersion silver plating, gold plating, electroless nickel plating, or electroless nickel-electroless palladium plating. The thickness of the metallized layer meets the requirements of each process specification. Circuit boards with the aforementioned mixed or stacked solder structures are spliced ​​together to form a three-dimensional deep hole structure, so that the solder structure at the splicing weld seam comes into contact with the solder pads or solder structure of the adjacent circuit board to form a three-dimensional solder pre-placed structure. Reflow welding is performed on the deep-hole three-dimensional weld with the aforementioned brazing filler metal pre-set structure to complete in-situ brazing.

2. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, The metallized pads at the butt weld are structurally continuous, or the non-metallized gaps are no more than 250 micrometers.

3. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 2, characterized in that, There is a gap between the solder ball array on the continuous metallized pad and the pad or solder structure of the adjacent circuit board, and the gap size is no more than 250 micrometers.

4. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, The solder ball array is in physical contact with the solder pads or solder structure of the adjacent circuit board.

5. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, The solder ball array is composed of two or more solders selected from SAC305, Sn42Bi58, Pb95Sn5, Au80Sn20 and Sn63Pb37, which have significantly different melting points.

6. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, The solder ball array consists of a single row or multiple rows of solder balls and is a single-layer or multi-layer stacked structure. The diameter of the solder balls ranges from 50 μm to 2000 μm. When the diameter of the solder balls is different, its diameter varies with the composition of the solder balls and / or their position in the stacked structure.

7. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, The brazing ball array has a mixed brazing ball structure in which high and low temperature brazing balls are arranged alternately in layers, either vertically or horizontally, with the bottom layer being a high melting point brazing ball.

8. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, When low-melting-point solder balls and high-melting-point solder balls are arranged alternately, a single low-melting-point solder ball is adjacent to a single high-melting-point solder ball, or a random number of low-melting-point solder balls are adjacent to a random number of high-melting-point solder balls.

9. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 1, characterized in that, The stacking structure of the solder ball array includes a densely stacked solder ball stacking structure and / or a non-densely stacked solder ball stacking structure in the transverse and longitudinal sections.

10. The method for pre-positioning and in-situ brazing of brazing filler metal for deep-hole three-dimensional welds as described in claim 9, characterized in that, The reflow temperature of the reflow soldering is between the melting points of the high and low melting point solder balls, and the melting state of the low melting point solder balls and the high melting point solder balls in the stacked structure of the solder balls can be controlled, so that an additional liquid-solid interface is formed on the surface of the high melting point solder balls, which provides support and surface tension constraint for the molten solder and suppresses the molten solder from overflowing due to gravity.

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