Ultra-low stress welding structure

Abstract

The invention discloses an ultra-low stress welding structure, which comprises a metal frame, a preformed soldering lug and a ceramic substrate, and is characterized in that the metal frame comprises a body part and a welding part, the welding part is arranged at the bottom of the body part, and the width of the welding part is smaller than that of the body part, so that step-shaped groove bodies are formed in the two sides of the welding part; the ceramic substrate comprises a ceramic base body and a brazing pad, and the brazing pad is arranged at the top end of the ceramic base body; the preformed soldering lug is arranged between the welding part and the brazing pad; in the welding process, the preformed soldering lug is melted to form two parts, the filling solder between the brazing pad and the welding part climbs and flows into the groove body to form redundant soldering tin, the soldering tin and the filling solder are physically separated through the step-shaped groove body, and therefore the metal frame is effectively welded to the brazing pad through the filling solder. Therefore, the quality problems of ceramic cracking, plating falling and the like caused by the fact that the accumulated stress exceeds the tensile stress of the substrate in the ceramic airtight packaging process are reduced.

Description

Technical Field

[0001] The present application relates to the field of ceramic hermetic packaging, and in particular to an ultra-low stress welding structure. Background Art

[0002] Ceramic substrate hermetic packaging is widely used in applications requiring high reliability. However, with the gradual miniaturization of products, the thermal stresses of the welding process are becoming increasingly difficult to release through structural deformation. After multiple packaging processes, stress release can easily lead to ceramic cracking and airtightness failure, significantly impacting product yield. Therefore, it is urgent to address welding stresses to improve product yield and reliability.

[0003] Patent: A multi-layer brazing structure of metal and ceramic (201310751752). This structure improves welding quality by improving welding materials, but does not solve the stress problem during welding. It only releases stress through structural deformation, and its applicability to solving the airtightness problem of tiny ceramic hermetic packages is very limited.

[0004] Patent: A metal brazing structure (201911268811) features a pad that is the same width as the metal frame. However, this method does not directly address welding stress, but instead reduces stress through annealing and other methods. This method cannot address issues such as ceramic damage caused by direct welding stress and is not suitable for lower-strength ceramic packaging surfaces such as LTCC. Summary of the Invention

[0005] The purpose of this application is to overcome the problems of the existing technology and disclose an ultra-low stress welding structure. The structure of this application greatly reduces the stress in the brazing process of ceramic hermetic packaging, so as to reduce the quality problems such as ceramic cracking and coating shedding caused by the accumulated stress exceeding the tensile stress of the substrate during the ceramic hermetic packaging process, and improve the yield of ceramic hermetic packaging.

[0006] The purpose of this application is achieved through the following technical solutions: An ultra-low stress welding structure, comprising: a metal frame, a preformed welding sheet and a ceramic substrate, The metal frame includes a main body and a welding portion, wherein the welding portion is provided at the bottom of the main body and has a width smaller than that of the main body, thereby forming a stepped groove on both sides of the welding portion; The ceramic substrate includes a ceramic base and a soldering pad, wherein the soldering pad is arranged on the top of the ceramic base; The preformed solder sheet is arranged between the soldering portion and the soldering pad; During soldering, the preformed solder sheet melts to form two parts: the filler solder between the solder pad and the soldering part, and the excess solder that climbs and flows into the slot body. The solder and the filler solder are physically separated by the stepped slot body, so that the metal frame is effectively soldered to the solder pad through the filler solder.

[0007] According to a preferred embodiment, during welding, a reflow soldering method is used to complete the welding of the metal frame and the ceramic substrate.

[0008] According to a preferred embodiment, during welding, a hot air reflow furnace is used to weld the metal frame and the ceramic substrate, and the reflow welding process includes preheating, temperature equalization, welding, heat preservation and cooling processes.

[0009] According to a preferred embodiment, the preheating process is used to heat the component and activate the flux so that all areas of the component are heated evenly; the welding process melts the solder to form a metallurgical bond with the surface of the pad; and the holding process utilizes the solidified solder to creep and diffuse in this temperature range to release welding stress.

[0010] According to a preferred embodiment, the width of the soldering pad is smaller than the width of the soldering portion by at least 0.1 mm.

[0011] According to a preferred embodiment, the preform and the solder pad have the same size and are aligned with each other.

[0012] According to a preferred embodiment, the thickness of the preformed solder sheet is less than or equal to 100 um.

[0013] According to a preferred embodiment, flux is provided on the surface of the preform.

[0014] The aforementioned main solution of this application and its further options can be freely combined to form multiple solutions, all of which can be adopted and protected by this application. After understanding the solution of this application, those skilled in the art will understand that there are many combinations based on existing technology and common knowledge, all of which are technical solutions to be protected by this application, and these are not exhaustive here.

[0015] Beneficial effects of this application: This application avoids the formation of a solder meniscus on the welding surface through the dimensional design of the metal frame, preformed solder sheet, and ceramic substrate, as well as the structural design of the groove at the bottom of the metal frame. This significantly reduces the vertical cooling stress caused by the inconsistent vertical shrinkage rates of the solder and the metal frame, and avoids the problems of airtightness failure and ceramic cracking caused by stress release. This allows for an ultra-low stress welding effect with a vertical tensile stress of no more than 8MPa. This significantly reduces the total welding stress during the ceramic packaging process, reducing airtightness failure caused by stress-induced pad detachment, ceramic cracking, and air leakage, thereby reducing product production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the ultra-low stress welded structure of the present application before welding; Figure 2 This is a schematic diagram of the ultra-low stress welded structure after welding of the present application; Figure 3 It is a schematic diagram of reflow profile soldering; Among them, 10 is a metal frame, 101 is a main body, 102 is a welding part, 103 is a trough, 20 is a preformed solder sheet, 201 is a filling solder, 202 is a solder, 30 is a ceramic substrate, 301 is a ceramic base, and 302 is a soldering pad. DETAILED DESCRIPTION

[0017] The following describes the embodiments of the present application through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0018] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0019] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product of this application is typically placed when in use. These terms are intended only to facilitate the description of this application and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0021] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0022] In addition, the present application would like to point out that, in the present application, unless the specific structures, connection relationships, positional relationships, power source relationships, etc. are specifically written out, the structures, connection relationships, positional relationships, power source relationships, etc. involved in the present application are all known to those skilled in the art based on the existing technology without creative work.

[0023] Example refer to Figures 1 to 3 As shown, the present application discloses an ultra-low stress welding structure, which includes: a metal frame 10 , a preformed welding sheet 20 and a ceramic substrate 30 .

[0024] Preferably, the metal frame 10 includes a main body 101 and a welding portion 102 . The welding portion 102 is disposed at the bottom of the main body 101 , and the width of the welding portion 102 is smaller than that of the main body 101 , thereby forming step-shaped grooves 103 on both sides of the welding portion 102 .

[0025] Preferably, the ceramic substrate 30 includes a ceramic base 301 and a soldering pad 302 , and the soldering pad 302 is disposed on the top of the ceramic base 301 .

[0026] Furthermore, the width of the soldering pad 302 is smaller than the width of the soldering portion 102 by at least 0.1 mm.

[0027] Preferably, the preform 20 is disposed between the welding portion 102 and the soldering pad 302. A solder flux is provided on the surface of the preform 20.

[0028] Furthermore, the preform 20 and the solder pad 302 have the same size and are aligned with each other.

[0029] Furthermore, the thickness of the preformed solder sheet 20 is less than or equal to 100 um.

[0030] Preferably, the metal frame 10 is made of a metal material similar to that of the ceramic substrate 30 , and the preform 20 is made of soft solder. The preform's cross-sectional width A is identical to the pad width B. The effective interface width between the metal frame and the solder is equal to or slightly greater than the pad width (dimension difference ≤ 0.2 mm).

[0031] During soldering, the preform 20 melts and forms two parts: the filler solder 201 between the soldering pad 302 and the soldering portion 102 , and the excess solder 202 that rises and flows into the groove 103 . The solder 202 and the filler solder 201 are physically separated by the stepped groove 103 .

[0032] That is, through the structural design of the groove body 103, the structure of the solder wetting upward along the side of the metal frame after welding is eliminated, and the formation of a solder meniscus structure on the welding surface is avoided, which can significantly reduce the vertical cooling stress caused by the inconsistent shrinkage rate of the solder and the metal frame in the vertical direction.

[0033] As a result, during the cooling process, the filler solder, metal frame, and ceramic substrate can achieve uniform cooling and contraction in the vertical direction, eliminating significant cooling stress caused by differential shrinkage rates among the three (if a solder meniscus structure is present, the solder will spread across the sides of the metal frame and ceramic substrate, causing significant cooling stress due to differential shrinkage rates among the three). This significantly reduces brazing stress. The holding zone during the cooling process also allows the solder to anneal in the creep temperature range after solidification, reducing cooling stress caused by mismatched shrinkage rates of the frame, solder, and substrate in the XY directions.

[0034] Preferably, during welding, the metal frame 10 and the ceramic substrate 30 are welded together using a reflow soldering method.

[0035] Furthermore, during welding, a hot air reflow furnace is used to weld the metal frame 10 and the ceramic substrate 30 . The reflow welding process includes preheating, temperature equalization, welding, heat preservation and cooling processes.

[0036] The preheating process heats the component and activates the flux, ensuring uniform heating across the component. The soldering process melts the solder and forms a metallurgical bond with the pad surface. The holding process utilizes the creep and diffusion of the solidified solder within this temperature range to release solder stress. Thus, the holding process partially eliminates cooling shrinkage stress through thermal diffusion and creep.

[0037] The present application avoids the formation of a solder meniscus structure on the welding surface through the dimensional design of the metal frame 10, the preformed solder sheet 20 and the ceramic substrate 30, as well as the structural design of the groove body 103 at the bottom of the metal frame 10, thereby significantly reducing the vertical cooling stress caused by the inconsistent shrinkage rate of the solder and the metal frame in the vertical direction, and avoiding the airtightness failure problem and ceramic cracking problem caused by stress release.

[0038] This enables the overall ultra-low stress welding effect with a vertical tensile stress of no more than 8MPa to be achieved; it can significantly reduce the total welding stress in the ceramic packaging process, reduce airtightness failure caused by problems such as pad detachment, ceramic cracking, and air leakage caused by stress problems, and reduce product production costs.

[0039] Conventional soldering thinking holds that the quality of the solder meniscus directly impacts the strength and reliability of the solder joint. A well-formed meniscus ensures that the solder joint is less susceptible to breakage under mechanical stress and provides a more stable and reliable electrical connection. However, in the field of miniaturized structural products, the solder meniscus can cause uneven stress release, leading to ceramic cracking and airtightness failure.

[0040] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. An ultra-low stress welded structure, characterized in that: The ultra-low stress welding structure comprises: a metal frame (10), a preformed welding sheet (20) and a ceramic substrate (30). The metal frame (10) comprises a main body (101) and a welding portion (102), wherein the welding portion (102) is arranged at the bottom of the main body (101), and the width of the welding portion (102) is smaller than the width of the main body (101), thereby forming step-shaped grooves (103) on both sides of the welding portion (102); The ceramic substrate (30) comprises a ceramic base (301) and a soldering pad (302), wherein the soldering pad (302) is arranged on the top of the ceramic base (301); The preformed solder sheet (20) is arranged between the soldering portion (102) and the soldering pad (302); During welding, the preformed solder sheet (20) melts to form two parts: the filling solder (201) between the soldering pad (302) and the welding portion (102), and the excess solder (202) that rises and flows into the groove body (103), and the solder (202) and the filling solder (201) are physically separated by the stepped groove body (103). Thus, the metal frame (10) is effectively welded onto the solder pad (302) by filling the solder (201).

2. The ultra-low stress welded structure according to claim 1, wherein: During welding, a reflow welding method is used to complete the welding of the metal frame (10) and the ceramic substrate (30).

3. The ultra-low stress welded structure according to claim 2, wherein: During welding, a hot air reflow furnace is used to weld the metal frame (10) and the ceramic substrate (30), and the reflow welding process includes preheating, temperature equalization, welding, heat preservation and cooling processes.

4. The ultra-low stress welded structure according to claim 3, wherein: The preheating process is used to heat the component and activate the flux so that all areas of the component are heated evenly; the soldering process melts the solder and forms a metallurgical bond with the pad surface; The holding process utilizes the solidified solder to creep and diffuse in this temperature range to release welding stress.

5. The ultra-low stress welded structure according to claim 1, wherein: The width of the soldering pad (302) is smaller than the width of the welding portion (102) by more than 0.1 mm.

6. The ultra-low stress welded structure according to claim 5, wherein: The preformed solder sheet (20) and the soldering pad (302) are of the same size and are aligned.

7. The ultra-low stress welded structure according to claim 1, wherein: The preformed solder sheet (20) has a thickness less than or equal to 100 μm.

8. The ultra-low stress welded structure according to claim 1, wherein: The surface of the preformed solder sheet (20) is provided with soldering flux.

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