Patent Description:
With development of electronic technologies, an electronic device is continuously developing toward miniaturization, integration, and ultra-thinness. Therefore, an increasingly high requirement is posed to a bonding process for electronic components in the electronic device. A bonding effect between the electronic components in the electronic device is crucial to performance of the electronic device.

When two electronic components are bonded, if a high-temperature solder with a high melting temperature is used for bonding, the electronic components are warped, or performance of the electronic components is changed. As a result, reliability of the electronic components is affected. However, if a low-temperature solder with a low bonding temperature is used for bonding, because the low-temperature solder has high brittleness and a low elongation rate, the low-temperature solder and solder pads on the electronic components form an intermetallic compound (intermetallic compound, IMC) with low strength. As a result, reliability of the bonding between the electronic components is low.

Therefore, how to improve stability of bonding between electronic components without affecting performance of the electronic components becomes an urgent technical issue to be addressed by persons skilled in the art.

<CIT> discloses a method for manufacturing a semiconductor device by mounting a semiconductor element on a circuit board, the semiconductor element having a first electrode made of a first material on a semiconductor substrate, the circuit board having a second electrode made of a second material on an insulating substrate. The method includes forming a connecting member on the first electrode, a melting point of the connecting member being lower than a melting point of the first material, placing the semiconductor element on the circuit board, so as to face the connecting member toward the second electrode, and connecting the first electrode and the second electrode, so as to interpose the connecting member between the first electrode and the second electrode, at a temperature that is lower than the melting point of the first material and higher than the melting point of the connecting member.

<CIT> discloses an electrical interconnect structure, including a first component, a second component, and an electrical interconnect electrically and mechanically interconnecting the first component to the second component, the electrical interconnect including a first solder sphere and a second solder sphere stacked on each other.

<CIT> discloses a method of mounting a semiconductor element, the method includes: attaching a first solder joint material onto a first pad formed on a substrate supplying a second solder joint material onto the first solder joint material, a second melting point of the second solder joint material being lower than a first melting point of the first solder joint material; arranging the semiconductor element so that a second pad formed on the semiconductor element faces the first pad and a joint gap is provided between the semiconductor element and the substrate; and performing reflow at a reflow temperature lower than the first melting point and higher than the second melting point to join the first solder joint material and the second solder joint material.

The invention is defined in the claims.

Embodiments of this application provide an electronic assembly and an electronic device, to resolve low stability of bonding between electronic components.

To achieve the foregoing objective, the following technical solutions are used in the embodiments. According to a first aspect, an electronic assembly is provided, including: a first electronic component, where a first active surface of the first electronic component has at least one first solder pad; a second electronic component, where a second active surface of the second electronic component has at least one second solder pad, and the second active surface faces the first active surface; and at least one first soldering portion, where one first soldering portion is located between one first solder pad and one second solder pad, and the first soldering portion is bonded to the first solder pad and the second solder pad on both sides of the first soldering portion. The first soldering portion includes a high-temperature solder layer and a low-temperature solder layer. The high-temperature solder layer is disposed close to the first solder pad and is bonded to the first solder pad. The low-temperature solder layer is disposed close to the second solder pad and is bonded to the second solder pad. A melting point of the low-temperature solder layer is lower than that of the high-temperature solder layer, and a material constituting the low-temperature solder layer is partially the same as that constituting the high-temperature solder layer, so that the low-temperature solder layer is bonded to the high-temperature solder layer through atomic diffusion. In the electronic assembly provided in this embodiment of this application, the high-temperature solder layer is bonded to the first solder pad, and an IMC with high strength is formed on a bonding interface. In addition, the low-temperature solder layer is bonded to the high-temperature solder layer through atomic diffusion, and no IMC is formed in a bonding process. Stability of bonding between the first electronic component and the first soldering portion can be improved, thereby improving stability of the electronic assembly.

The electronic assembly further includes at least one second soldering portion. The second soldering portion is disposed on a side that is of the first soldering portion and close to the second solder pad, and is bonded to the second solder pad. The melting point of the low-temperature solder layer is lower than that of the second soldering portion, and the material constituting the low-temperature solder layer is partially the same as that constituting the second soldering portion, so that the low-temperature solder layer is bonded to the second soldering portion through atomic diffusion. In the electronic assembly provided in this embodiment of this application, the second soldering portion is bonded to the second solder pad, and an IMC with high strength is formed on a bonding interface. In addition, the low-temperature solder layer is bonded to the second soldering portion through atomic diffusion, and no IMC is formed in a bonding process. Stability of bonding between the second electronic component and the second soldering portion can be improved, thereby improving stability of the electronic assembly.

Optionally, a bonding interface between the high-temperature solder layer and the low-temperature solder layer is a plane, and the material constituting the high-temperature solder layer is a pure metal. The high-temperature solder layer may be formed by using an electroplating process, and the process is simple.

Optionally, a bonding interface between the high-temperature solder layer and the low-temperature solder layer is a curved surface whose center is concave toward a side on which the first solder pad is located, and the material constituting the high-temperature solder layer is a metal alloy. A requirement for the material of the high-temperature solder layer is low, and a high-temperature solder commonly used on the market may be used.

Optionally, an orthographic projection of the first solder pad on the first electronic component falls within an orthographic projection of the second solder pad on the first electronic component. In this structure, the first solder pad and the second solder pad directly face each other with a large area, and a good bonding effect.

Optionally, the low-temperature solder layer has a thickness of <NUM>-<NUM> in a direction perpendicular to the first solder pad. When the low-temperature solder layer is excessively thin, a bonding effect between the low-temperature solder layer and each of the high-temperature solder layer and the second soldering portion is affected. However, when the low-temperature solder layer is excessively thick, this is not conducive to preparation by brushing solder paste over a steel mesh. The high-temperature solder layer or the second soldering portion has a thickness of <NUM>-<NUM> in a direction perpendicular to the first solder pad. With drop simulation analysis on the electronic assembly, the first soldering portion and the second soldering portion are subject to large stress at a location within <NUM> away from the first solder pad and the second solder pad. However, when the first soldering portion and the second soldering portion are excessively thick, this is not conducive to preparation by brushing solder paste over a steel mesh.

Optionally, the second soldering portion is a micro protrusion disposed on the second solder pad. The electronic assembly provided in this embodiment of this application is also applicable to bonding of a BGA device.

Optionally, the electronic assembly further includes an underfill adhesive layer located between the first electronic component and the second electronic component. The underfill adhesive layer is separately bonded to the first active surface and the second active surface, surrounds peripheries of the first soldering portion and the second soldering portion, and is bonded to the first soldering portion and the second soldering portion. The underfill adhesive layer is filled between the first electronic component and the second electronic component, and the underfill adhesive layer is bonded to the first soldering portion and the second soldering portion, so that the first soldering portion and the second soldering portion can be protected and secured, to further improve stability of bonding between the first electronic component and the second electronic component. According to a second aspect, a method for preparing an electronic assembly is provided. The electronic assembly includes a first electronic component and a second electronic component. A first active surface of the first electronic component has at least one first solder pad. A second active surface of the second electronic component has at least one second solder pad. The second active surface faces the first active surface. The method for preparing an electronic assembly includes: forming, on each first solder pad of the first electronic component, a high-temperature solder layer bonded to the first solder pad; placing a low-temperature solder between the high-temperature solder layer and the second solder pad; and separately bonding the low-temperature solder to the high-temperature solder layer and the second solder pad through atomic diffusion, to form a low-temperature solder layer, where the bonded high-temperature solder layer and low-temperature solder layer serve as a first soldering portion to bond the first electronic component to the second electronic component. A melting point of the low-temperature solder layer is lower than that of the high-temperature solder layer, and a material constituting the low-temperature solder layer is partially the same as that constituting the high-temperature solder layer.

Optionally, the material constituting the high-temperature solder layer is a metal alloy, and the forming, on each first solder pad of the first electronic component, a high-temperature solder layer bonded to the first solder pad includes: placing, on each first solder pad of the first electronic component, a first high-temperature solder; and bonding the first high-temperature solder to the first solder pad, to form the high-temperature solder layer bonded to the first solder pad.

Optionally, the material constituting the high-temperature solder layer is a pure metal, and the forming, on each first solder pad of the first electronic component, a high-temperature solder layer bonded to the first solder pad includes: forming, on the first solder pad of the first electronic component by using an electroplating process, the high-temperature solder layer bonded to the first solder pad Optionally, the placing a low-temperature solder between the high-temperature solder layer and the second solder pad includes: placing the low-temperature solder on the high-temperature solder layer.

Optionally, the placing a low-temperature solder between the high-temperature solder layer and the second solder pad includes: placing the low-temperature solder on the second solder pad.

Optionally, before the separately bonding the low-temperature solder to the high-temperature solder layer and the second solder pad through atomic diffusion, the method for preparing an electronic assembly further includes: attaching the first electronic component to the second electronic component in alignment, so that the low-temperature solder separately attached to the high-temperature solder layer and the second solder pad.

Before the separately bonding the low-temperature solder to the high-temperature solder layer and the second solder pad through atomic diffusion, the method for preparing an electronic assembly further includes: forming, on each second solder pad of the second electronic component, a second soldering portion bonded to the second solder pad, where the melting point of the low-temperature solder layer is lower than that of the second soldering portion, and the material constituting the low-temperature solder layer is partially the same as that constituting the second soldering portion. The bonding the low-temperature solder to the second solder pad through atomic diffusion includes: bonding the low-temperature solder to the second soldering portion through atomic diffusion.

Optionally, the material constituting the second soldering portion is a metal alloy, and the forming, on each second solder pad of the second electronic component, a second soldering portion bonded to the second solder pad includes: placing, on each second solder pad of the second electronic component, a second high-temperature solder; and bonding the second high-temperature solder to the second solder pad, to form the second soldering portion bonded to the second solder pad.

Optionally, the material constituting the second soldering portion is a pure metal, and the forming, on each second solder pad of the second electronic component, a second soldering portion bonded to the second solder pad includes: forming, on the second solder pad of the second electronic component by using an electroplating process, the second soldering portion bonded to the second solder pad.

Optionally, the placing a low-temperature solder between the high-temperature solder layer and the second solder pad includes: placing the low-temperature solder on the second soldering portion. Optionally, before the bonding the low-temperature solder to the second soldering portion through atomic diffusion, the method for preparing an electronic assembly further includes: attaching the first electronic component to the second electronic component in alignment, so that the low-temperature solder separately attached to the high-temperature solder layer and the second soldering portion.

According to a third aspect, an electronic device is provided, including the electronic assembly according to any one of the implementations of the first aspect.

<NUM>: electronic device; <NUM>: display module; <NUM>: middle frame; <NUM>: housing; <NUM>: cover plate; <NUM>: electronic assembly; <NUM>: first electronic component; <NUM>: first solder pad; <NUM>: second electronic component; <NUM>: second solder pad; <NUM>: first soldering portion; <NUM>: high-temperature solder layer; <NUM>: low-temperature solder layer; <NUM>: second soldering portion; G1: first high-temperature solder; G2: second high-temperature solder; D: low-temperature solder; <NUM>: steel mesh; <NUM>: opening; <NUM>: shielding portion; and <NUM>: underfill adhesive layer.

Technical terms or scientific terms used in this application should have general meanings understood by persons skilled in the art, unless otherwise defined. Terms "first", "second", and "third", and similar expressions used in the specification and claims of this application do not indicate any order, quantity, or importance, but are merely intended to distinguish between different components. Therefore, a feature limited by "first", "second", or "third" may explicitly or implicitly include one or more features. In the descriptions of the embodiments of this application, "a plurality of" means at least two, unless otherwise specified.

Orientation terms such as "left", "right", "up", and "down" are defined with respect to placement orientations of components shown in the accompanying drawings. It should be understood that these directional terms are relative concepts and are used for relative descriptions and clarifications, and may vary accordingly based on changes of the placement orientations of the components.

An embodiment of this application provides an electronic device. The electronic device may be a terminal device with a display interface, for example, a mobile phone, a television, a display, a tablet computer, or a vehicle-mounted computer, may be an intelligent wearable display device, for example, a smart watch or a smart band, or may be a communications device, for example, a server, a memory, or a base station; or is a smart car or the like. A specific form of the electronic device is not particularly limited in this embodiment of this application. For ease of description, the following embodiments are described by using an example in which the electronic device is a mobile phone.

In this case, as shown in <FIG>, the electronic device <NUM> mainly includes a display module <NUM>, a middle frame <NUM>, a housing (or referred to as a battery cover or a rear housing) <NUM>, and a cover plate <NUM>.

The display module <NUM> has a light exit side on which a displayed image can be seen, and a rear surface opposite to the light exit side. The back surface of the display module <NUM> is close to the middle frame <NUM>. The cover plate <NUM> is disposed on the light exit side of the display module <NUM>.

The display module <NUM> includes a display panel (display panel, DP).

In a possible embodiment of this application, the display module <NUM> is a liquid crystal display module. In this case, the display panel is a liquid crystal display (liquid crystal display, LCD). In view of this, the display module <NUM> further includes a backlight unit (back light unit, BLU) located on a rear surface (away from a surface, of the LCD, that is used to display an image) of the liquid crystal display.

The backlight unit may provide a light source for the liquid crystal display, so that each sub-pixel (sub pixel) in the liquid crystal display can emit light to display an image.

Alternatively, in another possible embodiment of this application, the display module <NUM> is an organic light emitting diode display module. In this case, the display panel is an organic light emitting diode (organic light emitting diode, OLED) display panel. Because an electroluminescent layer is disposed in each sub-pixel of the OLED display panel, the OLED display panel can implement self-illumination after receiving a working voltage. In this case, the backlight unit no longer needs to be disposed in the display module <NUM> with the OLED display panel.

The cover plate <NUM> is located on a side, of the display module <NUM>, that is away from the middle frame <NUM>. For example, the cover plate <NUM> may be cover glass (cover glass, CG), and the cover glass may have specific flexibility.

The middle frame <NUM> is located between the display module <NUM> and the housing <NUM>. A surface, of the middle frame <NUM>, that is away from the display module <NUM> is used to mount internal components, for example, a battery, a printed circuit board (printed circuit board, PCB), a camera (camera), and an antenna. After the housing <NUM> and the middle frame <NUM> are closed, the internal components are located between the housing <NUM> and the middle frame <NUM>.

The electronic device <NUM> further includes a main board disposed on the PCB. The PCB is configured to carry the main board and is bonded to the main board, so that the main board can control each component in the electronic device <NUM>. For example, the main board may be a central processing unit (central processing unit, CPU). Stability of bonding between the main board and the PCB plays a critical role in performance of the electronic device <NUM>. For example, breaking at a bonding location between the main board and the PCB causes signal interruption between the main board and the PCB, thereby causing damage to the electronic device <NUM>.

Certainly, a plurality of electronic components are bonded in the electronic device <NUM>. For example, a fingerprint module used for fingerprint recognition is bonded to a flexible printed circuit (flexible printed circuit, FPC) board, and the FPC is bonded to the PCB, to implement a fingerprint recognition function of the electronic device <NUM>. Alternatively, for example, chips with a plurality of functions in a system on chip (system on chip, SOC) are bonded to complete a system-in-a-package (system in a package, SIP). Alternatively, for example, the SOC is bonded to the PCB, a power module is bonded to the PCB, and a packaging device is bonded to the PCB.

Electronic components may be classified into a land grid array (land grid array, LGA) device and a ball grid array (ball grid array, BGA) device based on different structures, in the electronic components, that are used for bonding to other devices. The LGA device is bonded to another device by using a solder pad. The BGA device is bonded to another device by using a solder ball.

In view of this, to improve stability of bonding between electronic components in the electronic device <NUM>, to ensure performance of the electronic device <NUM>, as shown in <FIG>, an embodiment of this application provides an electronic assembly <NUM>, including: a first electronic component <NUM> and a second electronic component <NUM>.

Herein, the first electronic component <NUM> and the second electronic component <NUM> may be any component with an electrical signal transmission function in the electronic device <NUM>, for example, a connector, an electronic transformer, a relay, a laser device, a PCB, an FPC, an integrated circuit (or referred to as a chip), a packaging device, a biometric authentication module, a processor, a memory, or a power module.

In a possible embodiment, as shown in <FIG>, for example, the first electronic component <NUM> is a PCB, and the second electronic component <NUM> is a processor. In this case, because the PCB has a large area, the first electronic component <NUM> may be bonded to another second electronic component <NUM> in addition to the processor. Certainly, first solder pads <NUM> bonded to different second electronic components <NUM> may have different shapes and sizes. The processor may be an LGA device, that is, is bonded to the PCB by using a solder pad. Alternatively, the processor may be a BGA device, that is, is bonded to the PCB by using a solder ball.

In another possible embodiment, as shown in <FIG>, for example, both the first electronic component <NUM> and the second electronic component <NUM> are dies (die). In this case, the first electronic component <NUM> and the second electronic component <NUM> are equal in size. Therefore, the first electronic component <NUM> and the second electronic component <NUM> are bonded in a one-to-one correspondence.

As shown in <FIG> (a sectional view along an A-A' direction in <FIG>), representing an embodiment not forming part of the invention, a first active surface a of the first electronic component <NUM> has at least one first solder pad <NUM>. In <FIG>, an example in which the first active surface a of the first electronic component <NUM> has a plurality of first solder pads <NUM> is used for description.

An active surface of an electronic component is a surface, of the electronic component, on which a solder pad is disposed and the electronic component is electrically connected to another device by using the solder pad to implement signal interaction.

A second active surface b of the second electronic component <NUM> has at least one second solder pad <NUM>. The second active surface b of the second electronic component <NUM> faces the first active surface a of the first electronic component <NUM>.

For example, a material of the first solder pad <NUM> and the second solder pad <NUM> is a pure metal, for example, copper (Cu).

As shown in <FIG>, the electronic assembly <NUM> further includes at least one first soldering portion <NUM>. One first soldering portion <NUM> is located between one first solder pad <NUM> and one second solder pad <NUM>, and the first soldering portion <NUM> is bonded (bonding) to the first solder pad <NUM> and the second solder pad <NUM> located on both sides of the first soldering portion <NUM>.

Bonding is a process in which two homogeneous or heterogeneous materials undergo surface processing and are directly combined under a specific condition to implement electrical or mechanical interconnection between the two materials. In this embodiment of this application, for example, a bonding effect may be achieved by using a soldering process. A quantity of the first soldering portions <NUM> is related to a quantity of the first solder pads <NUM> and the second solder pads <NUM>. Each group of the first solder pad <NUM> and the second solder pad <NUM> that face each other are bonded by using one first bonding portion <NUM>.

As shown in <FIG>, the first soldering portion <NUM> includes a high-temperature solder layer <NUM> and a low-temperature solder layer <NUM>. The high-temperature solder layer <NUM> is disposed close to the first solder pad <NUM>, and the high-temperature solder layer <NUM> is bonded to the first solder pad <NUM>. The low-temperature solder layer <NUM> is disposed close to the second solder pad <NUM>, and the low-temperature solder layer <NUM> is bonded to the second solder pad <NUM>.

For a bonding process of the low-temperature solder layer <NUM> and the second solder pad <NUM>, in a possible embodiment, the high-temperature solder layer <NUM> bonded to the first solder pad <NUM> is formed on the first solder pad <NUM>, and then a low-temperature solder is placed on the high-temperature solder layer <NUM>. Then the first electronic component <NUM> is attached to the second electronic component <NUM> in alignment, so that the low-temperature solder is located between the high-temperature solder layer <NUM> and the second solder pad <NUM>. Finally, the low-temperature solder is separately bonded to the high-temperature solder layer <NUM> and the second solder pad <NUM> through atomic diffusion, to form the low-temperature solder layer <NUM> separately bonded to the second solder pad <NUM> and the high-temperature solder layer <NUM>. The bonded high-temperature solder layer <NUM> and low-temperature solder layer <NUM> serve as the first soldering portion <NUM> to bond the first electronic component <NUM> to the second electronic component <NUM>.

For a bonding process of the low-temperature solder layer <NUM> and the second solder pad <NUM>, in another possible embodiment, the high-temperature solder layer <NUM> bonded to the first solder pad <NUM> is formed on the first solder pad <NUM>, and then a low-temperature solder is placed on the second solder pad <NUM>. Then the first electronic component <NUM> is attached to the second electronic component <NUM> in alignment, so that the low-temperature solder is located between the high-temperature solder layer <NUM> and the second solder pad <NUM>. Finally, the low-temperature solder is separately bonded to the high-temperature solder layer <NUM> and the second solder pad <NUM> through atomic diffusion, to form the low-temperature solder layer <NUM> separately bonded to the second solder pad <NUM> and the high-temperature solder layer <NUM>. The bonded high-temperature solder layer <NUM> and low-temperature solder layer <NUM> serve as the first soldering portion <NUM> to bond the first electronic component <NUM> to the second electronic component <NUM>. A difference from the bonding process of the low-temperature solder layer <NUM> and the second solder pad <NUM> in the foregoing embodiment lies in that the low-temperature solder is placed on the second solder pad <NUM>.

The low-temperature solder layer <NUM> may be bonded to the second solder pad <NUM> through direct contact or by using another component.

A melting point of the low-temperature solder layer <NUM> is lower than that of the high-temperature solder layer <NUM>, and a material constituting the low-temperature solder layer <NUM> is partially the same as that constituting the high-temperature solder layer <NUM>, so that the low-temperature solder layer <NUM> is bonded to the high-temperature solder layer <NUM> through atomic diffusion.

In this embodiment of this application, the melting point of the low-temperature solder layer <NUM> is lower than that of the high-temperature solder layer <NUM>, but a range of the melting point of the low-temperature solder layer <NUM> is not limited. During selection of the material of the low-temperature solder layer <NUM>, the melting point of the low-temperature solder layer <NUM> should be as low as possible while it is ensured that bonding reliability meets a requirement.

The material of the high-temperature solder layer <NUM> may be a metal alloy, or the material of the high-temperature solder layer <NUM> may be a pure metal.

The material constituting the low-temperature solder layer <NUM> being partially the same as that constituting the high-temperature solder layer <NUM> may be understood as that, when the material of the high-temperature solder layer <NUM> is a metal alloy, the material constituting the low-temperature solder layer <NUM> and the material constituting the high-temperature solder layer <NUM> include a same main material but different dopant materials.

For example, in a possible embodiment, the material of the high-temperature solder layer <NUM> is a tin alloy. The material of the high-temperature solder layer <NUM> is obtained by doping metals such as silver (Ag), antimony (Sb), and lead (Pb) in a main material tin (Sn). The material of the low-temperature solder layer <NUM> is obtained by doping metals such as bismuth (Bi), indium (In), and cadmium (Cd) in the main material tin. The material of the high-temperature solder layer <NUM> and the material of the low-temperature solder layer <NUM> include the same main material but different dopant materials.

The material constituting the low-temperature solder layer <NUM> being partially the same as that constituting the high-temperature solder layer <NUM> may also be understood as that, when the material of the high-temperature solder layer <NUM> is a pure metal, a main material in the material of the low-temperature solder layer <NUM> is the pure metal constituting the high-temperature material layer <NUM>, and another metal material is further doped in the main material.

For example, in another possible embodiment, the material of the high-temperature solder layer <NUM> is a silver element, and the material of the low-temperature solder layer <NUM> is obtained by doping copper, tin, nickel (Ni), zinc (Zn), or boron (B) in a main material silver (for example, BAg40CuZnSnNi).

In this way, because the material constituting the low-temperature solder layer <NUM> is partially the same as that constituting the high-temperature solder layer <NUM>, a coefficient of thermal expansion (coefficient of thermal expansion, CTE) and an elasticity modulus (modulus) of the material of the high-temperature solder layer <NUM> are close to those of the material of the low-temperature solder layer <NUM>. In a bonding process, atoms included in both the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> are diffused, so that the high-temperature solder layer <NUM> is bonded to the low-temperature solder layer <NUM> through atomic diffusion.

Based on the electronic assembly <NUM> provided in this embodiment of this application, the high-temperature solder layer <NUM> is disposed between the low-temperature solder layer <NUM> and the first solder pad <NUM>, so that the high-temperature solder layer <NUM> is directly bonded to the first solder pad <NUM>. Because an elongation rate of the high-temperature solder is higher than that of the low-temperature solder, the high-temperature solder is less brittle than the low-temperature solder, and is not easy to break. In view of this, strength of an intermetallic compound (intermetallic compound, IMC) formed when the high-temperature solder layer <NUM> is bonded to the first solder pad <NUM> is higher than that of an IMC formed when the low-temperature solder layer <NUM> is directly bonded to the first solder pad <NUM> in <FIG>, representing an embodiment not forming part of the invention.

In view of this, because the material constituting the low-temperature solder layer <NUM> is partially the same as that constituting the high-temperature solder layer <NUM>, in the bonding process of the low-temperature solder layer <NUM> and the high-temperature solder layer <NUM>, the low-temperature solder layer <NUM> is bonded to the high-temperature solder layer <NUM> through atomic diffusion. Therefore, no IMC is formed in the bonding process of the low-temperature solder layer <NUM> and the high-temperature solder layer <NUM>, and stability of the bonding between the low-temperature solder layer <NUM> and the high-temperature solder layer <NUM> is high.

When the first electronic component <NUM> is bonded to the second electronic component <NUM>, in <FIG>, the low-temperature solder layer <NUM> is directly bonded to the first solder pad <NUM>, and an IMC with low strength is formed on a bonding interface. However, in the electronic assembly <NUM> provided in this embodiment of this application, the high-temperature solder layer <NUM> is bonded to the first solder pad <NUM>, and an IMC with high strength is formed on a bonding interface. In addition, the low-temperature solder layer <NUM> is bonded to the high-temperature solder layer <NUM> through atomic diffusion, and no IMC is formed in a bonding process. Therefore, stability of bonding between the first electronic component <NUM> and the first soldering portion <NUM> can be improved, thereby improving stability of the electronic assembly <NUM>.

In addition, as shown in <FIG>, which represents an embodiment not forming part of the invention, it can be learned through stress analysis that, when the electronic assembly <NUM> is subject to an external force (for example, impact, drop, or vibration), edge locations (indicated by black blocks in <FIG>) on a contact surface between the first soldering portion <NUM> and the first solder pad <NUM> and the second solder pad <NUM> are subject to a large force. In this embodiment of this application, after the high-temperature solder layer <NUM> is disposed, the high-temperature solder layer <NUM> is at a location subject to large stress. Reliability of the high-temperature solder is higher than that of the low-temperature solder. Therefore, compared with directly placing the low-temperature solder layer <NUM> at a location subject to large stress in <FIG>, a structure of the first soldering portion <NUM> provided in this embodiment of this application can further improve stability of bonding between the first electronic component <NUM> and the first soldering portion <NUM>.

The following describes in detail a structure of the electronic assembly <NUM> provided in this embodiment of this application by using several detailed embodiments, which are embodiments of the invention.

An example in which the first electronic component <NUM> is a PCB and the second electronic component <NUM> is an LGA device is used for description.

As shown in <FIG> (a sectional view along an A-A' direction in <FIG>), the electronic assembly <NUM> includes a first electronic component <NUM>, a second electronic component <NUM>, at least one first soldering portion <NUM>, and at least one second soldering portion <NUM>.

A first active surface a of the first electronic component <NUM> faces a second active surface b of the second electronic component <NUM>. In addition, an orthographic projection, on the first electronic component <NUM>, of a first solder pad <NUM> on the first electronic component <NUM> overlaps an orthographic projection, on the first electronic component <NUM>, of a second solder pad <NUM> on the second electronic component <NUM>.

The overlapping herein may be that, as shown in <FIG>, the first solder pad <NUM> and the second solder pad <NUM> have a same size and directly face each other. As shown in <FIG>, from a perspective of a top view, the orthographic projection of the first solder pad <NUM> coincides with the orthographic projection of the second solder pad <NUM>.

Alternatively, the overlapping herein may be that, as shown in <FIG>, the first solder pad <NUM> and the second solder pad <NUM> have a same size but are disposed in a staggered manner. As shown in <FIG>, from a perspective of a top view, the orthographic projection of the first solder pad <NUM> intersects with the orthographic projection of the second solder pad <NUM>, and the first solder pad <NUM> and the second solder pad <NUM> are in a one-to-one correspondence.

Alternatively, the overlapping herein may be that, as shown in <FIG>, a size of the first solder pad <NUM> is less than that of the second solder pad <NUM>. As shown in <FIG>, from a perspective of a top view, the orthographic projection of the first solder pad <NUM> falls within the orthographic projection of the second solder pad <NUM>.

Alternatively, the overlapping herein may be that, as shown in <FIG>, a size of the first solder pad <NUM> is greater than that of the second solder pad <NUM>. As shown in <FIG>, from a perspective of a top view, the orthographic projection of the second solder pad <NUM> falls within the orthographic projection of the first solder pad <NUM>.

In addition, shapes of the first solder pad <NUM> and the second solder pad <NUM> are not limited, and may be closed patterns of any shapes. The shapes of the first solder pad <NUM> and the second solder pad <NUM> may be the same or different.

The first solder pad <NUM> is used as an example. For example, in some possible embodiments, a shape of the first solder pad <NUM> may be a regular pattern, for example, a circular shape in <FIG>, an elliptic shape in <FIG>, a triangular shape in <FIG>, a rectangular shape in <FIG>, a square shape in <FIG>, or a pentagonal shape in <FIG>. In some other possible embodiments, a shape of the first solder pad <NUM> may be an irregular pattern in <FIG>.

As shown in <FIG>, a first soldering portion <NUM> and a second soldering portion <NUM> are disposed between the first solder pad <NUM> and the second solder pad <NUM> that face each other. The first soldering portion <NUM> is disposed close to the first solder pad <NUM>, and the second soldering portion <NUM> is disposed close to the second solder pad <NUM>.

The first soldering portion <NUM> includes a high-temperature solder layer <NUM> and a low-temperature solder layer <NUM>. The high-temperature solder layer <NUM> is disposed close to the first solder pad <NUM>, and is bonded to the first solder pad <NUM>. The low-temperature solder layer <NUM> is disposed close to the second soldering portion <NUM>, and is bonded to the second soldering portion <NUM>. The second soldering portion <NUM> is further bonded to the second solder pad <NUM>.

A melting point of the low-temperature solder layer <NUM> is lower than those of the high-temperature solder layer <NUM> and the second soldering portion <NUM>. A material constituting the low-temperature solder layer is partially the same as that constituting the high-temperature solder layer <NUM>, so that the low-temperature solder layer <NUM> is bonded to the high-temperature solder layer <NUM> through atomic diffusion. In addition, the material constituting the low-temperature solder layer is partially the same as that constituting the second soldering portion <NUM>, so that the low-temperature solder layer <NUM> is bonded to the second soldering portion <NUM> through atomic diffusion. The material constituting the high-temperature solder layer <NUM> and the material constituting the second soldering portion <NUM> may be the same or different.

It can be understood that, based on different materials selected for the high-temperature solder layer <NUM>, processes for preparing the high-temperature solder layer <NUM> vary, processes for bonding the high-temperature solder layer <NUM> to the first solder pad <NUM> also vary, and shapes of a soldering interface between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> also vary. Similarly, different materials form different second soldering portions <NUM>.

The following describes examples of a bonding process of the first electronic component <NUM> and the second electronic component <NUM> based on different materials selected for the high-temperature solder layer <NUM> and the second soldering portion <NUM>.

In a possible embodiment, materials of the high-temperature solder layer <NUM> and the second soldering portion <NUM> are metal alloys. As shown in <FIG>, a bonding process of the first electronic component <NUM> and the second electronic component <NUM> is as follows.

S10: As shown in <FIG>, place a first high-temperature solder G1 on each first solder pad <NUM> of the first electronic component <NUM>.

For example, first, a steel mesh <NUM> is placed on the first electronic component <NUM>. An opening <NUM> of the steel mesh <NUM> corresponds to the first solder pad <NUM>, and a shielding portion <NUM> of the steel mesh <NUM> corresponds to a part between adjacent first solder pads <NUM>. Then solder paste is brushed, so that the solder paste is filled in the opening <NUM> of the steel mesh <NUM>. Then the steel mesh <NUM> is removed to form the first high-temperature solder G1 on the first solder pad <NUM>.

S11: As shown in <FIG>, bond the first high-temperature solder G1 to the first solder pad <NUM> to form the high-temperature solder layer <NUM>. As shown in <FIG>, step S11 is performed after step S10.

For example, the first high-temperature solder G1 is bonded to the first solder pad <NUM> by using a reflow soldering process based on a temperature corresponding to a reflow temperature curve of the first high-temperature solder G1, to form the first high-temperature solder layer <NUM> bonded to the first solder pad <NUM>.

When a main material of the first high-temperature solder G1 is different from a material of the first solder pad <NUM>, for example, the main material of the first high-temperature solder G1 is tin and the material of the first solder pad <NUM> is copper, an IMC is formed on a bonding interface between the first high-temperature solder G1 and the first solder pad <NUM>.

S12: As shown in <FIG>, place a second high-temperature solder G2 on each second solder pad <NUM> of the second electronic component <NUM>.

A method for placing the second high-temperature solder G2 on the second solder pad <NUM> may be the same as that for placing the first high-temperature solder G1 on the first solder pad <NUM>. Refer to step S10.

S13: As shown in <FIG>, bond the second high-temperature solder G2 to the second solder pad <NUM> to form the second soldering portion <NUM>. As shown in <FIG>, step S13 is performed after step S12.

A method for bonding the second high-temperature solder G2 to the second solder pad <NUM> to form the second soldering portion <NUM> bonded to the second solder pad <NUM> may be the same as that for bonding the first high-temperature solder G1 to the first solder pad <NUM>. Refer to step S11.

It should be understood that, there is no sequence between step S10 and step S12, and the two steps may be simultaneously performed in a same time period, or step S12 may be performed after step S10, or step S10 may be performed after step S12.

S14: As shown in <FIG>, place a low-temperature solder D on the high-temperature solder layer <NUM>. As shown in <FIG>, step S14 is performed after step S11.

A method for placing the low-temperature solder D on the high-temperature solder layer <NUM> may be the same as that for placing the first high-temperature solder G1 on the first solder pad <NUM> in step S10.

Alternatively, S14' is performed: As shown in <FIG>, form a low-temperature solder D on the second soldering portion <NUM>. As shown in <FIG>, step S14' is performed after step S13.

S15: As shown in <FIG>, attach the first electronic component <NUM> to the second electronic component <NUM> in alignment, so that the low-temperature solder D is separately attached to the high-temperature solder layer <NUM> and the second soldering portion <NUM>.

If the low-temperature solder D is placed on the high-temperature solder layer <NUM> after step S14 is performed, as shown in <FIG>, when the first electronic component <NUM> is attached to the second electronic component <NUM> in alignment, the first electronic component <NUM> is placed with a front side up, and the second electronic component <NUM> is attached to the front side of the first electronic component <NUM> in alignment.

If the low-temperature solder D is placed on the second soldering portion <NUM> after step S14' is performed, as shown in <FIG>, when the first electronic component <NUM> is attached to the second electronic component <NUM> in alignment, the second electronic component <NUM> is placed with a front side up, and the first electronic component <NUM> is attached to the front side of the second electronic component <NUM> in alignment.

Herein, regardless of whether step S14 or step S14' is performed, the low-temperature solder D is located between the high-temperature solder layer <NUM> and the second soldering portion <NUM> after step S15 is performed.

The low-temperature solder D is placed on the high-temperature solder layer <NUM> and is not bonded thereto. Therefore, a structure shown in <FIG> is used as an example, the second electronic component <NUM> on which the low-temperature solder D is placed is placed with a front side up as a reference, and the first electronic component <NUM> on which no low-temperature solder D is placed is attached to the front side of the second electronic component <NUM> in alignment. This can prevent the low-temperature solder D from detaching from the second soldering portion <NUM> due to gravity, thereby ensuring reliability of bonding.

S16: As shown in <FIG>, separately bond the low-temperature solder D to the high-temperature solder layer <NUM> and the second soldering portion <NUM> through atomic diffusion, to form the low-temperature solder layer <NUM>.

In this case, the bonded high-temperature solder layer <NUM> and low-temperature solder layer <NUM> serve as the first soldering portion <NUM>, and the first soldering portion <NUM> is bonded to the second soldering portion <NUM> through atomic diffusion, so that the first electronic component <NUM> is bonded to the second electronic component <NUM>.

It can be understood that, because a melting point of the low-temperature solder D is lower than those of the high-temperature solder layer <NUM> and the second soldering portion <NUM>, when the low-temperature solder D is bonded to the high-temperature solder layer <NUM> and the second soldering portion <NUM>, a heating temperature is lower than a temperature at which the first high-temperature solder G1 is bonded to the first solder pad <NUM> in step S11. To be specific, when the low-temperature solder D is bonded to the high-temperature solder layer <NUM> and the second soldering portion <NUM>, the low-temperature solder D is melted, but neither the high-temperature solder layer <NUM> nor the second soldering portion <NUM> is melted.

It should be noted: First, in a conventional technology, when the first electronic component <NUM> is bonded to the second electronic component <NUM> by using a high-temperature solder, the first electronic component <NUM> and the second electronic component <NUM> are deformed to varying extents due to heat in a high-temperature environment. In addition, because the first electronic component <NUM> is bonded to the second electronic component <NUM>, the first electronic component <NUM> and the second electronic component <NUM> are subject to deformation tension from each other, thereby causing warpage and deformation of the first electronic component <NUM> and the second electronic component <NUM>.

In this embodiment of this application, the first high-temperature solder G1 is bonded to the first solder pad <NUM> at a high temperature, and the second high-temperature solder G2 is also bonded to the second solder pad <NUM> at a high temperature. However, the bonding between the first high-temperature solder G1 and the first solder pad <NUM> is used as an example. When the first high-temperature solder G1 is bonded to the first solder pad <NUM>, bonding is performed on a surface of the first electronic component <NUM>, and the first electronic component <NUM> is deformed within an acceptable range only due to heat, without being subject to a force from the second electronic component <NUM>. Therefore, a probability of warpage and deformation is significantly reduced.

In addition, the first electronic component <NUM> is used as an example. When an inactive surface of the first electronic component <NUM> has a component or a film layer not resistant to a high temperature, the component or the film layer not resistant to a high temperature may be formed after the high-temperature solder layer <NUM> is formed on the first solder pad <NUM>. For example, when the first electronic component <NUM> is a fingerprint module that has undergone high-gloss surface processing, because a light film is not resistant to a high temperature, the light film may be formed after the high-temperature solder layer <NUM> is formed on the first solder pad <NUM>.

Second, due to process factors such as a proportion difference, a reflow curve difference, and a wettability difference between the three solders: the first high-temperature solder G1, the second high-temperature solder G2, and the low-temperature solder D, a shape of a bonding interface between the second soldering portion <NUM> and the first soldering portion <NUM>, and a shape of a bonding interface between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> in the first soldering portion <NUM> may have a plurality of forms. Therefore, shapes of longitudinal cross sections of the first soldering portion <NUM> and the second soldering portion <NUM>, and the shape of the bonding interface between the first soldering portion <NUM> and the second soldering portion <NUM> are not limited in this embodiment of this application.

A principle for forming a shape of a bonding interface between the second soldering portion <NUM> and the low-temperature solder layer <NUM> is the same as that for forming the bonding interface between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> in the first soldering portion <NUM>. The shape of the bonding interface between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> in the first soldering portion <NUM> is used as an example for description. It can be understood that, because the high-temperature solder layer <NUM> is bonded to the low-temperature solder layer <NUM> through atomic diffusion, the shape of the bonding interface between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> is a shape of the bonded high-temperature solder layer <NUM> and first solder pad <NUM>.

In view of this, in a possible implementation, the high-temperature solder layer <NUM> is bonded to the first solder pad <NUM> by using a soldering process. In this case, as shown in <FIG>, the bonding interface c between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> is a curved surface whose center is concave toward a side on which the first solder pad <NUM> is located.

In another possible implementation, the high-temperature solder layer <NUM> is bonded to the first solder pad <NUM> by using another process. In this case, as shown in <FIG>, the bonding interface c between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> is a curved surface whose center is convex away from the side on which the first solder pad <NUM> is located. Alternatively, as shown in <FIG>, the bonding interface c between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> is a plane parallel to the first solder pad <NUM>.

In addition, a shape of a side surface d, of the low-temperature solder layer <NUM>, that intersects with the bonding interface c also has a plurality of forms due to process errors and different placement amounts of the low-temperature solder D. That is, a cross section, of the low-temperature solder layer <NUM>, in a direction perpendicular to the first electronic component <NUM> (a longitudinal direction) has a plurality of forms. Therefore, the shape of the side surface d of the low-temperature solder layer <NUM> is not limited in this embodiment of this application.

The following describes examples of the shape of the side surface d, of the low-temperature solder layer <NUM>, that intersects with the bonding interface c.

In a possible implementation, as shown in <FIG>, the side surface d of the low-temperature solder layer <NUM> is a plane.

An included angle between the side surface d of the low-temperature solder layer <NUM> and the first solder pad <NUM> varies based on different relative sizes of the first solder pad <NUM> and the second solder pad <NUM>. As shown in <FIG>, when the first solder pad <NUM> and the second solder pad <NUM> are equal in size, the side surface d of the low-temperature solder layer <NUM> is a plane perpendicular to the first solder pad <NUM>. As shown in <FIG>, when the first solder pad <NUM> is smaller than the second solder pad <NUM>, the side surface d of the low-temperature solder layer <NUM> is a plane that has an included angle of greater than <NUM>° with the first solder pad <NUM>. As shown in <FIG>, when the first solder pad <NUM> is larger than the second solder pad <NUM>, the side surface d of the low-temperature solder layer <NUM> is a plane that has an included angle of less than <NUM>° with the first solder pad <NUM>. In another possible implementation, if a placement amount of the low-temperature solder D is small, as shown in <FIG>, the side surface d of the low-temperature solder layer <NUM> is a curved surface that is concave inward.

In another possible implementation, if a placement amount of the low-temperature solder D is large, as shown in <FIG>, the side surface d of the low-temperature solder layer <NUM> is a curved surface that is convex outward.

In another possible embodiment, the material of the high-temperature solder layer <NUM> is a pure metal. As shown in <FIG>, a bonding process of the first electronic component <NUM> and the second electronic component <NUM> is as follows.

S20: As shown in <FIG>, form, on the first solder pad <NUM> of the first electronic component <NUM> by using an electroplating process, the high-temperature solder layer <NUM> bonded to the first solder pad <NUM>.

A surface, of the high-temperature solder layer <NUM> formed by using the electroplating process, that is away from the first solder pad <NUM> (a bonding interface c between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM>) is a plane parallel to the first solder pad <NUM>. S21: As shown in <FIG>, form, on the second solder pad <NUM> of the second electronic component <NUM> by using an electroplating process, the second soldering portion <NUM> bonded to the second solder pad <NUM>.

Similarly, a surface, of the second soldering portion <NUM> formed by using the plating process, that is away from the second solder pad <NUM> is a plane parallel to the second solder pad <NUM>.

S22: Place a low-temperature solder D on the high-temperature solder layer <NUM> or the second soldering portion <NUM>. In <FIG>, an example in which the low-temperature solder D is placed on the high-temperature solder layer <NUM> is used for description.

A method for placing the low-temperature solder D on the high-temperature solder layer <NUM> or the second soldering portion <NUM> may be the same as that for placing the first high-temperature solder G1 on the first solder pad <NUM> in step S10.

S23: Attach the first electronic component <NUM> to the second electronic component <NUM> in alignment. S24: As shown in <FIG>, separately bond the low-temperature solder D to the high-temperature solder layer <NUM> and the second soldering portion <NUM> through atomic diffusion, to form the low-temperature solder layer <NUM>. The bonded high-temperature solder layer <NUM> and low-temperature solder layer <NUM> serve as the first soldering portion <NUM>, and the first soldering portion <NUM> is bonded to the second soldering portion <NUM> through atomic diffusion, so that the first electronic component <NUM> is bonded to the second electronic component <NUM>.

In this case, as shown in <FIG>, after the first electronic component <NUM> is bonded to the second electronic component <NUM>, the bonding interface c between the high-temperature solder layer <NUM> and the low-temperature solder layer <NUM> is a plane parallel to the first solder pad <NUM>. A bonding interface between the second soldering portion <NUM> and the low-temperature solder layer <NUM> is also a plane parallel to the first solder pad <NUM>.

For a shape of a side surface d of the low-temperature solder layer <NUM>, refer to the foregoing descriptions of <FIG>.

Based on the foregoing structure, as shown in <FIG>, when the electronic assembly is subject to an external force (for example, impact, drop, or vibration), edge locations on a contact surface between the first soldering portion <NUM> and the first solder pad <NUM> and edge locations (indicated by black blocks in <FIG>) on a contact surface between the second soldering portion <NUM> and the second solder pad <NUM> are subject to a large force and are a stress concentration region, and a middle region is a low-stress region. Brittleness of the high-temperature solder is lower than that of the low-temperature solder, that is, reliability of the high-temperature solder is higher than that of the low-temperature solder. Therefore, in this embodiment of this application, a thickness of the high-temperature solder layer <NUM> is adjusted, so that the high-temperature solder layer <NUM> is located in the stress concentration region, and the low-temperature solder layer <NUM> is not disposed in the stress concentration region, to improve stability of bonding between the first electronic component <NUM> and the second electronic component <NUM>.

With drop simulation analysis on the electronic assembly <NUM>, the first soldering portion <NUM> and the second soldering portion <NUM> are subject to large stress at a location within <NUM> away from the first solder pad <NUM> and the second solder pad <NUM>. However, when the first soldering portion <NUM> and the second soldering portion <NUM> are excessively thick, this is not conducive to preparation by brushing solder paste over a steel mesh. In view of this, in some embodiments of this application, thicknesses of the high-temperature solder layer <NUM> and the second soldering portion <NUM> are <NUM>-<NUM>. For example, the thicknesses of the high-temperature solder layer <NUM> and the second soldering portion <NUM> are <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. In this embodiment of this application, a thickness of a component is a size of the component in a direction perpendicular to the first solder pad.

In addition, when the low-temperature solder layer <NUM> is excessively thin, a bonding effect between the low-temperature solder layer <NUM> and each of the high-temperature solder layer <NUM> and the second soldering portion <NUM> is affected. However, when the low-temperature solder layer <NUM> is excessively thick, this is not conducive to preparation by brushing solder paste over a steel mesh. In view of this, in some embodiments of this application, a thickness of the low-temperature solder layer <NUM> is <NUM>-<NUM>. For example, the thickness of the low-temperature solder layer <NUM> is <NUM>, <NUM>, <NUM>, or <NUM>.

It can be learned from drop simulation analysis on the electronic assembly <NUM> that a force applied to the first soldering portion <NUM> and the second soldering portion <NUM> in the stress concentration region shown in <FIG> is approximately <NUM>% greater than a force applied in the low-stress region. That is, with the structure provided in this embodiment of this application, stress applied to the low-temperature solder layer <NUM> can be reduced by approximately <NUM>%. Therefore, stability of bonding between the first electronic component <NUM> and the second electronic component <NUM> can be ensured, to extend a service life of the electronic device <NUM>.

Based on the electronic assembly shown in <FIG>, as shown in <FIG> (a sectional view along an A-A' direction in <FIG>), the electronic assembly further includes an underfill (underfill) adhesive layer <NUM> located between the first electronic component <NUM> and the second electronic component <NUM>. The underfill adhesive layer <NUM> is separately bonded to the first active surface a of the first electronic component <NUM> and the second active surface b of the second electronic component <NUM>. In addition, the underfill adhesive layer <NUM> surrounds peripheries of the first soldering portion <NUM> and the second soldering portion <NUM>, and is bonded to the first soldering portion <NUM> and the second soldering portion <NUM>.

A material of the underfill adhesive layer <NUM> may be a thermal cured adhesive.

In addition, the underfill adhesive layer <NUM> is filled between the first electronic component <NUM> and the second electronic component <NUM>, and the underfill adhesive layer <NUM> is bonded to the first soldering portion <NUM> and the second soldering portion <NUM>, so that the first soldering portion <NUM> and the second soldering portion <NUM> can be protected and secured, to further improve stability of bonding between the first electronic component <NUM> and the second electronic component <NUM>.

In addition, in this embodiment, the first soldering portion <NUM> and the second soldering portion <NUM> include three solder layers, and the three solder layers are not too thin, so that a gap between the first electronic component <NUM> and the second electronic component <NUM> is large. In this way, when the underfill adhesive layer <NUM> is formed, an adhesive is subject to small resistance, and the adhesive has good fluidity. This can ensure that the adhesive fully cover each solder joint including a first soldering portion <NUM> and a second soldering portion <NUM>, thereby further improving stability of bonding between the first electronic component <NUM> and the second electronic component <NUM>.

A difference between Embodiment <NUM> and Embodiment <NUM> lies in that the first electronic component <NUM> is a PCB and the second electronic component <NUM> is a BGA device.

As shown in <FIG> (a sectional view along an A-A' direction in <FIG>), the second soldering portion <NUM> is a micro protrusion disposed on the second solder pad <NUM>. In this case, the second soldering portion <NUM> is a component in the second electronic component <NUM>, and no step of forming the second soldering portion <NUM> is performed when the first electronic component <NUM> is bonded to the second electronic component <NUM>.

The micro protrusion may be a solder ball (ball), or may be a bump (bump) or the like. In this embodiment of this application, an example in which the second soldering portion <NUM> is a solder ball is used for description.

In view of this, as shown in <FIG>, a bonding process of the first electronic component <NUM> and the second electronic component <NUM> is as follows.

S30: Form, on each first solder pad <NUM> of the first electronic component <NUM>, a high-temperature solder layer <NUM> bonded to the first solder pad <NUM>.

In an example, step S30 may include: as shown in <FIG>, placing a first high-temperature solder G1 on each first solder pad <NUM> of the first electronic component <NUM>; and as shown in <FIG>, bonding the first high-temperature solder G1 to the first solder pad <NUM> to form the high-temperature solder layer <NUM>.

In another example, step S30 may include: as shown in <FIG>, forming, on the first solder pad <NUM> of the first electronic component <NUM> by using an electroplating process, the high-temperature solder layer <NUM> bonded to the first solder pad <NUM>.

S31: As shown in <FIG> and <FIG>, place a low-temperature solder D on the high-temperature solder layer <NUM>.

S32: As shown in <FIG>, attach the first electronic component <NUM> to the second electronic component <NUM> in alignment.

S33: As shown in <FIG> and <FIG> (sectional views along an A-A' direction in <FIG>), separately bond the low-temperature solder D to the high-temperature solder layer <NUM> and the second soldering portion <NUM> through atomic diffusion, to form the low-temperature solder layer <NUM>, so that the first electronic component <NUM> is bonded to the second electronic component <NUM>. Based on the structure of the electronic assembly shown in <FIG>, as shown in <FIG> (a sectional view along an A-A' direction in <FIG>), the electronic assembly further includes an underfill adhesive layer <NUM> located between the first electronic component <NUM> and the second electronic component <NUM>. The underfill adhesive layer <NUM> is separately bonded to the first active surface a of the first electronic component <NUM> and the second active surface b of the second electronic component <NUM>, surrounds peripheries of the first soldering portion <NUM> and the second soldering portion <NUM>, and is bonded to the first soldering portion <NUM> and the second soldering portion <NUM>.

Claim 1:
An electronic assembly (<NUM>), comprising:
a first electronic component (<NUM>), wherein a first active surface (a) of the first electronic component (<NUM>) has at least one first solder pad (<NUM>);
a second electronic component (<NUM>), wherein a second active surface (b) of the second electronic component (<NUM>) has at least one second solder pad (<NUM>), and the second active surface faces the first active surface; and
at least one first soldering portion (<NUM>), wherein one first soldering portion (<NUM>) is located between one first solder pad (<NUM>) and one second solder pad (<NUM>), and the first soldering portion (<NUM>) is bonded to the first solder pad (<NUM>) and the second solder pad (<NUM>) on both sides of the first soldering portion (<NUM>), wherein
the first soldering portion (<NUM>) comprises a high-temperature solder layer (<NUM>) and a low-temperature solder layer (<NUM>), the high-temperature solder layer (<NUM>) is disposed close to the first solder pad (<NUM>) and is bonded to the first solder pad (<NUM>), and the low-temperature solder layer (<NUM>) is disposed close to the second solder pad (<NUM>) and is bonded to the second solder pad (<NUM>); and
the electronic assembly (<NUM>) further comprising:
at least one second soldering portion (<NUM>), wherein the second soldering portion (<NUM>) is disposed on a side of the first soldering portion (<NUM>) close to the second solder pad (<NUM>), and is bonded to the second solder pad (<NUM>); and
a melting point of the low-temperature solder layer (<NUM>) is lower than that of the high-temperature solder layer (<NUM>) and than that of the second soldering portion (<NUM>), and a material constituting the low-temperature solder layer (<NUM>) is partially the same as that constituting the high-temperature solder layer (<NUM>) and the second soldering portion (<NUM>), so that the low-temperature solder layer (<NUM>) is bonded to the high-temperature solder layer (<NUM>) and the second soldering portion (<NUM>) through atomic diffusion,
characterised in that
the high-temperature solder layer (<NUM>) or the second soldering portion (<NUM>) has a thickness of <NUM>-<NUM> in a direction perpendicular to the first solder pad (<NUM>).