A solder preform and a method of making the same

Abstract

The application discloses a solder preform and a preparation method thereof. The solder preform comprises a solder body, the solder body has the same thickness and the same alloy composition everywhere; the solder body has at least one predetermined region provided with an activator, so that the solder body melts at the predetermined region first before other regions of the solder body during a welding process. According to the application, the predetermined region is determined on the solder body, and the activator is arranged on the predetermined region, so that the active control of the melting sequence is realized under the premise that the solder alloy composition and the thickness are basically uniform. The melting starts from the predetermined region and orderly spreads to the surrounding, guides the unidirectional advancement of the wetting front, effectively avoids the gas wrapping, and significantly reduces the cavity formation. Meanwhile, the self-alignment of the device is facilitated, and the assembly precision is improved. In addition, the controllable time sequence melting makes the solder collapse process predictable, and the uniformity of the solder layer thickness is improved.

Description

Technical Field

[0001] This application relates to the field of welding materials for electronic packaging, specifically to a solder preform and its preparation method. Background Technology

[0002] Solder preforms are key materials widely used in electronic packaging, commonly found in die attach, integrated heat spreader (IHS) bonding, and heat sink connections. Solder preforms are typically thin sheets of solder with specific shapes and sizes that melt and wet the surface to be soldered during reflow soldering, forming a metallurgical bonding layer upon cooling. Traditional solder preforms exhibit a generally uniform melting behavior during reflow soldering; that is, when the solder preform reaches its melting point, melting occurs almost simultaneously throughout. This uniform melting behavior brings a series of problems in actual processes: First, simultaneous melting in various places causes the wetting front to advance disorderly from multiple directions. When multiple wetting fronts collide during their advancement, they can easily trap the surrounding air or the gas generated by the activator / flux during the solder melting process inside the solder layer, forming voids. Second, uniform melting cannot provide a directional wetting driving force for the soldered device. The device is prone to random displacement or tilting at the moment of solder melting, resulting in a decrease in alignment accuracy. Third, the solder collapse process lacks controllability, and the consistency of the final solder layer thickness is difficult to guarantee.

[0003] To improve welding quality, various methods for introducing flux into solder preforms have been developed in the prior art. For example, Chinese patent CN107433400B discloses a preformed solder containing flux, in which the flux is coated inside the solder body; Chinese patent CN120828234B discloses a preformed solder sheet, in which flux is uniformly coated on the surface of the solder sheet substrate. These methods can control the amount of flux used and reduce flux spatter to a certain extent, but their flux distribution method (overall coating or uniform coating) determines that they cannot affect the melting sequence of the solder preform itself, and therefore cannot solve the many problems caused by uniform melting mentioned above. Summary of the Invention

[0004] This application aims to address one of the technical problems in related technologies to a certain extent. To this end, this application provides a solder preform and a method for its preparation.

[0005] To achieve the above objectives, this application adopts the following technical solution: a solder preform, comprising a solder body, wherein the solder body has the same thickness and the same alloy composition at all locations;

[0006] The solder body has at least one predetermined area provided with an activator, such that the solder body melts in the predetermined area before other areas of the solder body during the soldering process.

[0007] The application of this application has the following beneficial effects: By defining a predetermined region on the solder body and placing an activator on the predetermined region, active control of the melting sequence is achieved while maintaining the basic uniformity of the solder alloy composition and thickness. Melting starts from the predetermined region and spreads orderly to the surrounding areas, guiding the wetting front to advance unidirectionally, effectively avoiding gas encapsulation and significantly reducing void formation. Simultaneously, the preferential start of melting from the predetermined region provides a directional wetting driving force for the soldered components, which is beneficial for component self-alignment and improves assembly accuracy. Furthermore, controllable timing-based melting makes the solder collapse process predictable, improves the uniformity of the solder layer thickness, and results in better bonding quality consistency.

[0008] Optionally, the predetermined area is located at the center of the solder body.

[0009] Optionally, the activator includes one or more of the following: organic acids, organic acid derivatives, amine activators, and halogen-free activators.

[0010] Optionally, there are multiple predetermined regions, and the activator components and / or contents provided in the multiple predetermined regions are different, so that the solder body melts sequentially in different predetermined regions during the welding process.

[0011] Furthermore, this application also provides a method for preparing a solder preform, the method comprising:

[0012] A solder body is provided, wherein the solder body has the same thickness and the same alloy composition throughout;

[0013] At least one predetermined area is defined on the solder body;

[0014] An activator is applied to the predetermined area so that the solder body melts in the predetermined area before other areas of the solder body during the soldering process.

[0015] The preparation method provided in this application is similar to the reasoning process of the beneficial effects of the aforementioned solder preforms, and will not be repeated here.

[0016] Optionally, defining at least one predetermined region on the solder body includes:

[0017] The predetermined area is defined at the center of the solder body.

[0018] Optionally, defining at least one predetermined region on the solder body includes:

[0019] A mask is covered on the solder body, the mask having an opening corresponding to the predetermined area.

[0020] Optionally, applying the activator at the predetermined region includes:

[0021] The activator is applied to a predetermined area using one or more of the following processes: dispensing, selective deposition, and coating.

[0022] Optionally, the preparation method further includes: before applying an activator to the predetermined region, performing a surface texturing treatment on the predetermined region, the surface texturing treatment including:

[0023] The predetermined area is subjected to one or more of the following treatments: plasma treatment, ultraviolet ozone treatment, and laser etching treatment.

[0024] Optionally, applying the activator at the predetermined area includes applying the activator in a liquid or semi-liquid form;

[0025] The preparation method further includes: applying an activator to the predetermined area to obtain an intermediate product, and drying the intermediate product to make the solder preform finished product a dry, non-sticky form.

[0026] Optionally, defining at least one predetermined region on the solder body includes defining a plurality of predetermined regions on the solder body;

[0027] Furthermore, applying the activator at the predetermined area includes applying activators of different components and / or different amounts to the multiple predetermined areas respectively.

[0028] Optionally, the activator includes one or more of the following: organic acids, organic acid derivatives, amine activators, and halogen-free activators.

[0029] These features and advantages of this application will be disclosed in detail in the following specific embodiments and accompanying drawings. Preferred embodiments or means of this application will be illustrated in detail with reference to the accompanying drawings, but are not intended to limit the technical solutions of this application. Furthermore, each of these features, elements, and components appearing in the following text and drawings is a plurality, and different symbols or numbers are used for convenience of representation, but all represent components with the same or similar structure or function. Attached Figure Description

[0030] The following description, in conjunction with the accompanying drawings, further illustrates this application:

[0031] Figure 1 This is a schematic diagram of the structure of a solder preform provided in an embodiment of this application;

[0032] Figure 2 A flowchart illustrating the method for preparing the solder preform provided in the embodiments of this application;

[0033] Figure 3 This is a schematic diagram of the structure of a solder preform in one optional embodiment.

[0034] Among them, 1 is the solder body; 10 is the predetermined area; 100 is the first area; 101 is the second area; 102 is the third area; and 11 is the activator. Detailed Implementation

[0035] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain this application and should not be construed as limiting it.

[0036] The terms "an embodiment," "example," or "example" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this application. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0037] In the description of this application, it should be understood that the terms "upper," "lower," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In the description of this application, "a plurality of" means two or more, unless otherwise precisely specified.

[0038] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected," "linked," and "connected" should be interpreted broadly. For example, they can refer to a fixed connection, a connection through an intermediary, the internal connection of two elements, or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0039] Traditional solder preforms exhibit a generally uniform melting behavior during reflow soldering, meaning that melting occurs almost simultaneously at all points when the preform reaches its melting point. This uniform melting behavior leads to a series of problems in actual processes: First, simultaneous melting at all points causes the wetting front (specifically, the three-phase line where the liquid edge of the molten solder contacts the solid surface as it spreads on the soldering surface, or what can be understood as the outer edge of the molten solder's spread) to advance randomly from multiple directions. Multiple wetting fronts colliding during this advancement can easily trap surrounding air or gases generated during solder melting within the solder layer, creating voids. Second, uniform melting cannot provide a directional wetting driving force (the physicochemical force that drives the spontaneous spread of molten solder on the solid surface) for the soldered components. Components are prone to random displacement or tilting at the moment of solder melting, leading to decreased alignment accuracy. Third, the solder collapse process lacks controllability, making it difficult to guarantee the consistency of the final solder layer thickness.

[0040] In existing technologies, two main approaches are generally used to actively control the melting sequence at different locations on the solder: One approach is compositional variation, which uses different alloy compositions in different areas of the solder preform. For example, a lower melting point alloy (such as a high-indium alloy) is used in areas where preferential melting is desired, while a higher melting point alloy (such as a conventional tin-silver-copper alloy) is used in surrounding areas. Sequential melting is achieved by artificially creating a melting point gradient throughout the solder body. However, this approach suffers from complex processes and high costs. Specifically, the metallurgical compatibility of different alloys needs to be carefully matched, and the interface between dissimilar alloys can become a weak point in reliability. Secondly, the manufacturing process is extremely complex, requiring specialized equipment for multi-step casting, splicing, or multi-material co-extrusion, resulting in high costs and low yields. The other approach is geometrical variation, which involves creating localized protrusions, steps, or thinned areas on the solder preform. During soldering and mounting, these thinner areas heat up faster due to their lower heat capacity, or reach their melting point earlier because the localized protrusions preferentially contact the heat source or soldering surface, thus melting before other areas. The drawback of this approach is that the geometrical differences in the structure limit the precision of controlling the melting sequence. Once the entire preform is heated uniformly in the reflow oven, the thermal difference caused by the geometrical differences quickly disappears, and the preferential melting effect is lost. In addition, the raised or thinned structure alters the surface smoothness of the preform, making it prone to deformation and failure due to impacts during storage and transportation.

[0041] To address the aforementioned problems, this embodiment provides a solder preform, such as... Figure 1As shown, the solder preform includes a solder body 1, which has the same thickness and the same alloy composition throughout. The solder body 1 has a predetermined region 10 provided with an activator 11, so that the solder body 1 melts in the predetermined region 10 before other regions of the solder body 1 during the soldering process.

[0042] By defining a predetermined region 10 on the solder body 1 and placing an activator 11 on the predetermined region 10, active control of the melting sequence is achieved while maintaining the basic uniformity of the solder alloy composition and thickness. Melting begins in the predetermined region 10 and propagates orderly to the surrounding areas, guiding the wetting front to advance unidirectionally, effectively avoiding gas encapsulation and significantly reducing void formation. The preferential start of melting from the predetermined region 10 provides a directional wetting driving force for the soldered components, which is beneficial for device self-alignment and improves assembly accuracy. Furthermore, controllable timing of melting makes the solder collapse process predictable, improves the uniformity of the solder layer thickness, and results in better bonding quality consistency.

[0043] Meanwhile, in this embodiment, the solder body 1 has the same thickness and alloy composition throughout, meaning that the alloy composition is consistent across all parts of the solder body 1, and there is no situation where the melting point differs from that of another location. Furthermore, the thickness of the solder body 1 is also consistent throughout, without intentionally creating protrusions or grooves in localized areas. Therefore, the solder preform provided in this embodiment differs from traditional solders that rely on compositional gradients or geometric differences. This embodiment, while maintaining a substantially consistent thickness and uniform alloy composition throughout the solder body 1, achieves control over the melting sequence solely through surface chemical engineering by setting an activator 11 in a predetermined area 10. This makes the solder preform more feasible in terms of manufacturing process, maintaining the same body strength and reliability as uniformly composed solder in terms of performance, without concerns about interfacial compatibility or reliability issues related to dissimilar materials.

[0044] The working principle of activator 11 is explained as follows: During the manufacturing, storage, and transportation of solder body 1, its surface inevitably reacts with oxygen in the air, naturally forming a dense oxide film. The main component of this oxide film is the oxide of the main metallic element (such as tin) in the solder, and its melting point is much higher than that of the solder alloy itself. During the soldering process, it constitutes a physicochemical barrier that hinders the melting, wetting, and flow of the solder. For areas on solder body 1 where activator 11 is not applied, during the reflow soldering heating process, only when the temperature approaches or reaches the melting point of the solder alloy will the volume change and surface tension change generated by the melting process of solder body 1 itself, as well as the interfacial stress generated by the difference between the thermal expansion coefficients of solder body 1 and oxide film, work together to cause the oxide film to break. Only then can melting begin. This means that the actual melting and wetting of these areas occurs near the theoretical melting point or even after slight overheating. For the predetermined region 10 containing the activator 11, the active component in the activator 11 (e.g., the carboxyl group of an organic acid) has a specific chemical reactivity activation temperature, which is lower than the melting point of the solder body 1. During the soldering heating process, when the temperature reaches the activation temperature range of the activator 11 (typically 150°C to 200°C, depending on the specific activator 11 formulation), the activator 11 begins to chemically react with the oxide film in the predetermined region 10, causing the oxide film to dissolve, loosen, or crack, thus losing its ability to act as a melting and wetting barrier. When the temperature continues to rise to the melting point of the solder body 1, the solder in the predetermined region 10 can immediately and unimpededly melt and wet because the oxide film has been destroyed. In other regions, melting and wetting are inhibited because the oxide film remains intact, exhibiting delayed melting.

[0045] like Figure 1 As shown, in this embodiment, the predetermined region 10 is located in the center of the solder body 1. Setting the predetermined region 10 in the center of the solder body 1 allows the melting to spread evenly from the center to the edge, which is suitable for most symmetrical welding structures and can effectively ensure the uniform advancement of the melting front.

[0046] The activator 11 in this embodiment includes one or more of the following: organic acids, organic acid derivatives, amine activators, and halogen-free activators. As mentioned above, the working principle of the activator 11 in this embodiment is to effectively react chemically with the oxide film on the surface of the solder body 1 within a specific temperature range, thereby reducing the effective activation energy required for melting and wetting in that area, and thus enabling the predetermined area 10 to melt preferentially. The various activators 11 listed above are all mature products already available in the prior art, with good stability and process compatibility. For example, organic acids such as succinic acid, adipic acid, and DL-malic acid; organic acid derivatives such as succinic anhydride or maleic anhydride; and amine activators such as triethanolamine or cyclohexylamine. Halogen-free activators are fluxes that have emerged in recent years and do not contain halogen elements such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Examples of commercially available halogen-free fluxes include STANNOL EF250, Kester 951, Interflux IF2005C, or the HF-9000 series.

[0047] Combination Figure 3 As shown, in some optional embodiments, there are multiple predetermined regions 10, and the composition and / or content of the activator 11 in the multiple predetermined regions 10 are different, so that the solder body 1 melts sequentially at different predetermined regions 10 during the soldering process. By setting multiple predetermined regions 10 with different activation levels, more complex timing melting patterns can be constructed to meet the precise timing control of different device geometries and specific process requirements. Figure 3 Taking the embodiment shown as an example, the predetermined region 10 in this embodiment includes a first region 100, a second region 101, and a third region 102. The activator 11 provided in the first region 100, the second region 101, and the third region 102 has the same composition but the content decreases sequentially. During soldering, the solder body 1 preferentially melts at the first region 100, then melts at the second region 101, then melts at the third region 102, and then melts at non-predetermined regions. It is easy to understand that the specific locations of the multiple predetermined regions 10 are determined according to the application requirements and process objectives.

[0048] Figure 2 This embodiment illustrates a method for preparing the solder preform, which includes the following steps:

[0049] S100: Provide a solder body 1, wherein the solder body 1 has the same thickness and the same alloy composition in all parts;

[0050] S200: Determine at least one predetermined region 10 on the solder body 1;

[0051] S300: An activator 11 is applied to a predetermined area 10 so that the solder body 1 melts in the predetermined area 10 before other areas of the solder body 1 during the soldering process.

[0052] The preparation method is simple and the process is highly operable. It does not require any modification to the existing equipment for manufacturing solder preforms, such as stamping and cutting. It only requires the addition of equipment for applying activator 11 to the solder body 1 produced.

[0053] In step S200, defining at least one predetermined region 10 on the solder body 1 includes defining the predetermined region 10 at the center of the solder body 1. As previously described, setting the predetermined region 10 at the center of the solder body 1 allows the melt to diffuse uniformly from the center to the edge, which is suitable for most symmetrical soldering structures.

[0054] In step S200, defining at least one predetermined region 10 on the solder body 1 includes covering the solder body 1 with a mask having an opening corresponding to the predetermined region 10. By covering a non-predetermined region with the mask before applying the activator 11, and then applying the activator 11 to the predetermined region 10 through the opening, it is ensured that the activator 11 is precisely applied to the predetermined region 10. Therefore, by utilizing mature masking technology, the activator 11 can be confined within the predetermined region 10 with high precision and repeatability, which is particularly advantageous when the predetermined region 10 has an irregular shape.

[0055] In step S300, applying the activator 11 to the predetermined area includes applying the activator 11 to the predetermined area 10 through one or more of the following processes: dispensing, selective deposition, and coating. All of these processes are industrially mature material deposition methods that can be flexibly selected according to production volume requirements, precision requirements, and cost constraints, and have good mass production adaptability.

[0056] Furthermore, the preparation method further includes: before applying activator 11 to the predetermined region 10 (that is, after step S200 and before step S300), performing surface texturing treatment on the predetermined region 10, the surface texturing treatment including one or more of plasma treatment, ultraviolet ozone treatment and laser etching treatment on the predetermined region 10.

[0057] Surface texturing of the predetermined area 10 can enhance the affinity and physical anchoring ability of the predetermined area 10 to the activator 11, which helps the activator 11 to remain stably in the predetermined area 10 and prevents the activator 11 from falling off relative to the solder body 1.

[0058] Furthermore, in step S300, applying the activator 11 to the predetermined region 10 includes applying the activator 11 in a liquid or semi-liquid form. The preparation method also includes: obtaining an intermediate product after applying the activator 11 to the predetermined region 10, and then drying the intermediate product to make the solder preform finished product a dry, non-sticky form. Drying the activator 11 ensures that it is in a stable solid or semi-solid state, non-sticky and non-flowing, fundamentally preventing its migration to non-determined regions.

[0059] In step S300, defining at least one predetermined region 10 on the solder body 1 includes defining multiple predetermined regions 10 on the solder body 1; and applying an activator 11 to the predetermined regions 10 includes applying activators 11 with different compositions and / or different contents to the multiple predetermined regions 10 respectively. As mentioned above, by applying activators 11 with different compositions and / or different contents to the multiple predetermined regions 10 respectively, multiple predetermined regions 10 with different activation degrees can be obtained, and more complex timing melting patterns can be constructed to meet the precise timing control of different device geometries and specific process requirements.

[0060] The activator 11 includes one or more of the following: organic acids, organic acid derivatives, amine activators, and halogen-free activators.

[0061] The following solder preform is provided as an example in this embodiment for further illustration:

[0062] Using SAC305 solder alloy (Sn 96.5%, Ag 3.0%, Cu 0.5%), a thin, square solder body with dimensions of 10mm × 10mm and a thickness of 0.1mm was prepared through casting, extrusion, rolling, and punching processes. The thickness of the solder body was basically uniform throughout, and the alloy composition was homogeneous. A square pre-defined area with a side length of 1.5mm was defined at the center of the solder body. Using a micro-dispensing device, a solution containing adipic acid (an organic acid activator) was precisely applied to this pre-defined area, with the adipic acid loading being 0.05% of the total mass of the solder body. After application, the solder preform was dried at 80℃ for 10 minutes to obtain a dry, non-sticky finished product.

[0063] The solder preform obtained in this embodiment was placed on a hot plate and heated from room temperature to 250°C at a heating rate of approximately 5°C / s. High-speed imaging revealed that melting initially began in a predetermined area (a distinct wetting front was observed at approximately 218°C), and then the melting front advanced outwards, with the entire solder preform melting completely after approximately 2 to 3 seconds. X-ray inspection showed that the void ratio within the solder layer was significantly lower than that of the control sample using a uniform solder preform without an activator under the same conditions.

[0064] As a control, a paste-like activator containing adipic acid can also be printed onto a predetermined area in the center of the solder body using a patterned screen printing process. After printing, it is dried at 120°C for 5 minutes to obtain a dry, non-sticky solder preform. The welding test results are similar to those of the above process, both exhibiting stable center-preferential melting behavior.

[0065] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Those skilled in the art will understand that this application includes, but is not limited to, the content described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of this application will be included within the scope of the claims.

Claims

1. A solder preform, characterized in that, Includes a solder body, wherein the solder body has the same thickness and the same alloy composition throughout; The solder body has at least one predetermined area provided with an activator, such that the solder body melts in the predetermined area before other areas of the solder body during the soldering process.

2. The solder preform as described in claim 1, characterized in that, The predetermined area is located in the center of the solder body.

3. The solder preform as described in claim 1, characterized in that, The activator includes one or more of the following: organic acids, organic acid derivatives, amine activators, and halogen-free activators.

4. The solder preform as described in any one of claims 1 to 3, characterized in that, There are multiple predetermined regions, and the activator components and / or contents in the multiple predetermined regions are different, so that the solder body melts sequentially in different predetermined regions during the welding process.

5. A method for preparing a solder preform, characterized in that, The preparation method includes: A solder body is provided, wherein the solder body has the same thickness and the same alloy composition throughout; At least one predetermined area is defined on the solder body; An activator is applied to the predetermined area so that the solder body melts in the predetermined area before other areas of the solder body during the soldering process.

6. The method for preparing a solder preform as described in claim 5, characterized in that, Determining at least one predetermined region on the solder body includes: The predetermined area is defined at the center of the solder body.

7. The method for preparing a solder preform as described in claim 5, characterized in that, Determining at least one predetermined region on the solder body includes: A mask is covered on the solder body, the mask having an opening corresponding to the predetermined area.

8. The method for preparing a solder preform as described in claim 5, characterized in that, The application of the activator at the predetermined region includes: The activator is applied to a predetermined area using one or more of the following processes: dispensing, selective deposition, and coating.

9. The method for preparing a solder preform as described in claim 5, characterized in that, The preparation method further includes: before applying an activator to the predetermined region, performing a surface texturing treatment on the predetermined region, the surface texturing treatment including: The predetermined area is subjected to one or more of the following treatments: plasma treatment, ultraviolet ozone treatment, and laser etching treatment.

10. The method for preparing a solder preform as described in claim 5, characterized in that, The application of the activator at the predetermined area includes: the activator being applied in a liquid or semi-liquid form; The preparation method further includes: applying an activator to the predetermined area to obtain an intermediate product, and drying the intermediate product to make the solder preform finished product a dry, non-sticky form.

11. The method for preparing a solder preform as described in claim 5, characterized in that, Determining at least one predetermined region on the solder body includes: determining multiple predetermined regions on the solder body; Furthermore, applying the activator at the predetermined area includes applying activators of different components and / or different amounts to the multiple predetermined areas respectively.

12. The method for preparing a solder preform as described in claim 5, characterized in that, The activator includes one or more of the following: organic acids, organic acid derivatives, amine activators, and halogen-free activators.

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