Welding method, chip packaging method and chip packaging structure

Abstract

The invention provides a welding method for a power terminal, a chip packaging method and a chip packaging structure. The welding method comprises the following steps: forming a solder layer on a bearing surface of a substrate; placing a terminal on the solder layer; the welding method comprises the steps that a terminal is arranged on a bearing surface, a solder layer is arranged on the bearing surface, laser is adopted to heat the solder layer so as to fix the terminal on the bearing surface, and the welding method further comprises the steps that a plating layer is formed between the solder layer and the terminal or / and formed on the side face of the solder layer, and the plating layer is made of titanium and used for improving the laser absorption rate of the solder layer. The terminal is fixed through laser local heating, the laser absorptivity of the welding flux is improved through the titanium plating layer, the welding efficiency is further improved, the laser heating time is shortened, and therefore the influence of heat energy on the whole structure is reduced.

Description

Technical Field

[0001] The present disclosure relates to the technical field of semiconductor device packaging, and more particularly, to a welding method for power terminals, a packaging method for chips, and a packaging structure thereof. Background Art

[0002] With the rapid development of the new energy industry, semiconductor power modules have been widely used in high-power and high-voltage environments. These modules have higher requirements for the current-carrying capacity, insulation withstand voltage capacity, and efficient heat dissipation capacity of the carrier board. Due to its characteristics of high current-carrying, high voltage withstand, and high heat dissipation, the ceramic insulating substrate has become an ideal choice for power modules.

[0003] There are mainly two types of ceramic insulating substrates. One is the Direct Bond Copper (DBC) substrate, which is widely used in the packaging and heat dissipation of devices such as IGBT power modules, lasers (LD), and photovoltaic (PV). The other is the Active Metal Brazing (AMB) substrate. Since the AMB substrate can achieve better heat dissipation and insulation performance and higher reliability, it can be used to carry high-power chips and is mainly used in electric vehicle power modules.

[0004] When packaging a power module, it is necessary to first fix the power chip on the substrate, and then use brazing or sintering materials to fix the signal terminals on the edge of the substrate. However, this method requires the entire power module structure to be placed above the melting temperature of the welding material to complete the fixing of the signal terminals. Therefore, the entire power module structure has to undergo at least one process temperature cycle uniformly, which will increase the risk of thermal stress loss of the entire power module structure. Summary of the Invention

[0005] In view of the above problems, the purpose of the present disclosure is to provide a welding method for power terminals, a packaging method for chips, and a packaging structure thereof, which achieve the fixing of the terminals by using laser local heating and improve the absorption rate of the solder to the laser through plating.

[0006] According to the first aspect of the embodiments of the present disclosure, a welding method is provided, including:

[0007] Forming a solder layer on the bearing surface of the substrate;

[0008] Placing the terminal on the solder layer; and

[0009] Heating the solder layer by laser to fix the terminal on the bearing surface,

[0010] The welding method further includes: forming a coating layer between the solder layer and the terminal, and / or forming a coating layer on the side surface of the solder layer, wherein the material of the coating layer includes titanium.

[0011] Optionally, the step of forming a coating layer between the solder layer and the terminal includes: coating the coating layer on the solder layer,

[0012] wherein the step of coating the coating layer is performed before the step of placing the terminal on the solder layer.

[0013] Optionally, the step of forming a coating layer between the solder layer and the terminal includes: coating the coating layer on one side surface of the terminal,

[0014] wherein after placing the one side surface of the terminal coated with the coating layer on the solder layer, the coating layer is sandwiched between the solder layer and the terminal.

[0015] Optionally, the step of forming a coating layer between the solder layer and the terminal includes:

[0016] coating the coating layer on one side surface of the terminal,

[0017] placing the one side surface of the terminal coated with the coating layer on the solder layer to complete the step of placing the terminal on the solder layer,

[0018] wherein the coating layer is sandwiched between the solder layer and the terminal.

[0019] Optionally, the step of forming a coating layer on the side surface of the solder layer includes: coating the coating layer on the side surface of the solder layer,

[0020] wherein the step of coating the coating layer is performed before the step of placing the terminal on the solder layer.

[0021] Optionally, the step of forming a coating layer on the side surface of the solder layer includes: coating the coating layer on the side surface of the solder layer,

[0022] wherein the step of coating the coating layer is performed after the step of placing the terminal on the solder layer.

[0023] Optionally, the laser irradiates on the surface of the terminal, and / or the laser directly irradiates on the solder layer.

[0024] Optionally, the material of the terminal includes Cu.

[0025] Optionally, the laser includes blue laser.

[0026] According to a second aspect of the embodiments of the present disclosure, a method for packaging a chip is provided, including the soldering method as described above.

[0027] According to a third aspect of the embodiments of the present disclosure, a packaging structure is provided, including:

[0028] A substrate;

[0029] A chip located on the substrate;

[0030] A solder layer located on the substrate; and

[0031] Terminals fixed on the solder layer,

[0032] wherein a plating layer is provided between the solder layer and the terminals, and / or a plating layer is formed on the side surface of the solder layer, and the material of the plating layer includes titanium.

[0033] One of the above technical solutions has the following beneficial effects:

[0034] By fixing the terminals on the substrate through laser soldering, since the laser can achieve local heating, the influence of the soldering heat energy on the overall structure is reduced. Further, a titanium plating layer is provided between the terminals and the solder layer, and / or a titanium plating layer is provided on the side surface of the solder layer. During the laser heating process, the titanium plating layer can improve the absorption rate of the solder to the laser energy, improve the soldering efficiency, reduce the laser heating time, and thus further reduce the influence of the heat energy on the overall structure.

[0035] In some embodiments, the material of the terminals is copper, and copper has a good absorption effect on blue laser. Especially for the laser with a wavelength of 400 - 495 nm, the absorption rate can reach 80% or higher. When directly irradiating the copper terminals with laser to indirectly heat the solder, due to the high absorption rate of copper to blue laser, the heat energy transferred to the solder is also very high, thereby improving the soldering efficiency.

[0036] In some embodiments, the laser includes a new generation of solid-state lasers such as diode lasers, hard disk lasers, and fiber lasers. Compared with the lasers generated by gas CO 2 and solid rod-shaped Nd:YAG laser generators, the new generation of solid-state lasers has better focusing performance. Among them, the blue diode laser can produce a top-hat beam, and the top-hat beam has a flat area in the center, which can produce a highly uniform and highly concentrated light spot, thereby ensuring uniform heating of the solder in the predetermined area without affecting the structure of other areas.

[0037] It should be noted that the above general description and the following detailed description are only exemplary and explanatory and cannot limit the present disclosure. Description of the Drawings

[0038] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present disclosure and do not limit the present disclosure.

[0039] Figure 1 Shows the welding schematic diagram of the first embodiment of the present disclosure.

[0040] Figure 2 Shows the welding schematic diagram of the second embodiment of the present disclosure.

[0041] Figure 3 Shows the schematic diagram of the position of the coating in the third embodiment of the present disclosure.

[0042] Figure 4 Shows the curve of the absorption rate of copper material for different light wavelengths. Detailed implementation manners

[0043] The present disclosure will be described in more detail below with reference to the accompanying drawings. In the respective drawings, like elements are denoted by like reference numerals. For clarity, the various parts in the drawings are not drawn to scale. In addition, some well-known parts may not be shown. For the sake of brevity, a semiconductor structure obtained after several steps may be described in one drawing.

[0044] It should be understood that when describing the structure of a device, when a layer or a region is referred to as being "above" or "over" another layer or another region, it may mean directly above the other layer or another region, or there may be other layers or regions between it and the other layer or another region. And if the device is flipped, this layer or region will be "below" or "beneath" the other layer or another region.

[0045] If in order to describe the situation of being directly above another layer or another region, expressions such as "directly on... above" or "above... and adjacent thereto" will be used in this article.

[0046] In the following, many specific details of the present disclosure are described, such as the structure, materials, dimensions, processing techniques and technologies of the device, in order to understand the present disclosure more clearly. But as those skilled in the art can understand, the present disclosure can be implemented without these specific details.

[0047] Figure 1 Shows the welding schematic diagram of the first embodiment of the present disclosure.

[0048] Such as Figure 1As shown, the encapsulation structure at this time is a semi-finished product, including a substrate 1, a solder layer 21, a connection layer 22, a chip 30, a plating layer 41, and terminals 50. In this embodiment, the substrate 1 is a ceramic substrate (DBC substrate or AMB substrate), and the substrate 1 includes a first metal layer 11, a second metal layer 12, and a ceramic layer 10 sandwiched between the two metal layers. Among them, the materials of the first metal layer 11 and the second metal layer 12 can be copper, and the surface of the first metal layer 11 can be used as the bearing surface for the chip 30 and the terminals 50. The solder layer 21 and the connection layer 22 are both located on the first metal layer 11 and are separated from each other. The material of the solder layer 21 is, for example, solder paste, sintered silver powder, etc. The material of the connection layer 22 can be conductive glue or insulating glue, or it can also be solder paste, sintered silver powder, etc. After the chip 30 is fixed on the first metal layer 11 through the connection layer 22, the terminals 50 are then fixed on the first metal layer 11. Among them, the chip 30 is, for example, a power semiconductor device, such as SiC mosfet, SiC JFET, SiC BJT, SiC IGBT, SiC thyristor, SiCSBD, SiC JBS, SiC MPS, superjunction SiC diode, SiC PiN, SiC hybrid diode, etc. The chip 30 is electrically connected to a preset position on the first metal layer 11, for example, through a wire bonding process.

[0049] In this embodiment, a plating layer 41 needs to be formed between the solder layer 21 and the terminals 50. Among them, the material of the plating layer 41 includes titanium. During welding, the laser 60 is placed above the terminals 50, and the laser beam 61 is emitted vertically downward, so as to irradiate the surface of the terminals 50. The terminals 50 transfer the laser energy to the solder layer 21 below. Among them, the titanium in the plating layer 41 can greatly improve the absorption rate of the solder layer 21 to the laser energy.

[0050] In some specific embodiments, the plating layer 41 is first coated on the solder layer 21, and then the terminals 50 are placed on the solder layer 21, so that the plating layer 41 is sandwiched between the solder layer 21 and the terminals 50.

[0051] In other specific embodiments, the plating layer 41 is first coated on one side surface of the terminals 50, and then the side surface of the terminals 50 coated with the plating layer 41 is placed on the solder layer 21. At this time, the terminals 50 are in contact with the plating layer 41, and the plating layer 41 is sandwiched between the solder layer 21 and the terminals 50.

[0052] See Figure 4 , where the horizontal axis represents the wavelength λ of light, and the unit is nanometer (nm); the vertical axis is the absorption rate of the material to light; the dotted curve represents the absorption curve of commercially pure copper (Cu-ETP) to light of different wavelengths; the solid curve represents the absorption curve of CuSn 6 to light of different wavelengths, CuSn 6It is a compound formed when copper and solder are welded at high temperatures; the cylinder represents the laser wavelength range generated by the blue diode laser, approximately 400 - 495 nm.

[0053] It can be seen from Figure 4 that Cu has a very high laser energy absorption rate for the laser in the blue diode laser band, which can reach 80% or even higher. Therefore, the material of terminal 50 can be Cu, and the laser 60 can be a blue diode laser. In some other embodiments, the laser used for welding can also be a hard disk laser or a fiber laser.

[0054] After terminal 50 is welded, an insulating material is used to wrap structures such as the substrate and chip 30, and the end of terminal 50 is exposed, thereby forming a complete package structure.

[0055] When the above-mentioned power semiconductor device is joined to the copper layer on the ceramic substrate, laser welding can control overheating, internal stress and deformation of materials and structures, as well as the adverse particle growth of second-phase particles (such as carbides or nitrides), ensuring the minimum thermal effect on materials and more accurately controlling heat and process thermal cycles. In addition, since laser welding provides a high power density and the smallest diameter of the laser irradiation point, it shows many advantages, such as high penetration, high welding speed, higher accuracy, and controllable heat input. At the same time, using a laser beam to form a surface protection layer on the outer surface of the solder layer can improve the high wear resistance, corrosion resistance, thermal-mechanical fatigue resistance, and impact load resistance of the solder layer, thereby helping to improve the overall reliability of the product. It is worth mentioning that the functional characteristics of laser welding are of higher quality than the surface protection layer of plasma arc (PTA) or existing arc cladding process methods.

[0056] Figure 2 Shows a welding schematic diagram of the second embodiment of the present disclosure.

[0057] As Figure 2 shown, the second embodiment of the present disclosure is similar to the first embodiment, and the same parts will not be elaborated. The difference is that in the first embodiment, after overlapping terminal 50 with substrate 1, terminal 50 is irradiated for welding. In this embodiment, instead of forming a plating layer 41 between solder layer 21 and terminal 50, plating layer 41 is coated on the side of solder layer 21, and the laser beam 61 is incident from the edge of solder layer 21 and directly irradiates on solder layer 21 for welding. Among them, the step of coating plating layer 41 can be carried out before the step of placing terminal 50 on solder layer 21, or after the step of placing terminal 50 on solder layer 21.

[0058] Among them, the material of the coating layer 41 includes titanium. Titanium can greatly improve the absorption rate of the solder layer 21 to the laser energy. The heat of the laser is transmitted to the solder layer 21 through the coating layer 41, and then the welding of the terminal 50 and the substrate 1 can be quickly realized.

[0059] Figure 3 The schematic diagram of the position of the coating layer in the third embodiment of the present disclosure is shown.

[0060] Such as Figure 3 As shown, in this embodiment, the settings of the coating layer 41 in the first and second embodiments are combined. The coating layer 41 is not only provided between the solder layer 21 and the terminal 50, but also on the side surface of the solder layer 21. During the process of welding the terminal 50, the edge of the solder and the surface of the terminal can be irradiated with laser at the same time. Among them, the material of the coating layer 41 includes titanium.

[0061] In this embodiment, that is, the energy of the laser is absorbed by the terminal 50, and then the heat is transmitted to the solder layer 21. Also, the energy of the laser is absorbed by the coating layer 41, and then the heat is transmitted to the solder layer 21. The absorption rate of the laser energy is improved through the heat transfer in two aspects, and the welding of the terminal 50 and the substrate 1 is quickly realized.

[0062] One of the above technical solutions has the following beneficial effects:

[0063] The terminal is fixed on the substrate by laser welding. Since the laser can realize local heating, the influence of the welding heat energy on the overall structure is reduced. Further, a titanium coating layer is provided between the terminal and the solder layer, and / or a titanium coating layer is provided on the side surface of the solder layer. During the laser heating process, the titanium coating layer can improve the absorption rate of the solder to the laser energy, improve the welding efficiency, reduce the laser heating time, and thus further reduce the influence of the heat energy on the overall structure.

[0064] In some embodiments, the material of the terminal is copper, and copper has a good absorption effect on blue laser. Especially for the laser with a wavelength of 400 - 495 nm, the absorption rate can reach 80% or higher. When the copper terminal is directly irradiated with laser to indirectly heat the solder, due to the high absorption rate of copper to blue laser, the heat energy transmitted to the solder is also very high, thus improving the welding efficiency.

[0065] In some embodiments, the laser includes at least one of a diode laser, a hard disk laser, and a fiber laser, which is a new generation of solid laser. Compared with the gas CO 2Compared with the laser generated by a solid rod-shaped Nd:YAG laser generator, the new generation of solid lasers has better focusing properties, with a square or rectangular beam spot and a very uniform energy distribution, which is beneficial for surface treatment. The melting temperature of the solder layer is lower than that of copper. When heated by laser irradiation, the heat acts on the target geometry through the adjusted laser spot. The blue diode laser ensures uniform heating with its uniform top-hat configuration, only melting the solder layer to fill the brazing gap and joining the terminals to the substrate without affecting the structure of other areas.

[0066] The above describes the embodiments of the present disclosure. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A welding method, comprising: forming a solder layer on the bearing surface of the substrate; placing a terminal on the solder layer; as well as Heating the solder layer with a laser to fix the terminal on the bearing surface; The welding method further includes: forming a plating layer between the solder layer and the terminal, or / and forming a plating layer on the side of the solder layer, wherein the material of the plating layer includes titanium.

2. The welding method according to claim 1, wherein: The step of forming a plating layer between the solder layer and the terminal comprises: coating the plating layer on the solder layer, The step of applying the plating layer is performed before the step of placing the terminal on the solder layer.

3. The welding method according to claim 1, wherein: The step of forming a plating layer between the solder layer and the terminal comprises: The plating layer is applied on one side surface of the terminal, Placing the terminal on the solder layer by placing the surface of one side of the terminal coated with the plating layer on the solder layer, completing the step of placing the terminal on the solder layer, Wherein, the plating layer is sandwiched between the solder layer and the terminal.

4. The welding method according to claim 1, wherein: The step of forming a plating layer on the side of the solder layer comprises: coating the plating layer on the side of the solder layer, The step of applying the plating layer is performed before the step of placing the terminal on the solder layer.

5. The welding method according to claim 1, wherein: The step of forming a plating layer on the side of the solder layer comprises: coating the plating layer on the side of the solder layer, The step of applying the plating layer is performed after the step of placing the terminal on the solder layer.

6. The welding method according to any one of claims 1 to 5, wherein: The laser is irradiated on the surface of the terminal, or / and the laser is irradiated directly on the solder layer.

7. The welding method according to claim 6, wherein: The material of the terminal includes Cu.

8. The welding method according to claim 6, wherein: The laser includes a blue laser.

9. A chip packaging method, comprising the welding method according to any one of claims 1 to 8.

10. A packaging structure, comprising: substrate; A chip, located on the substrate; A solder layer, located on the substrate; as well as A terminal, fixed on the solder layer, Wherein, a plating layer is arranged between the solder layer and the terminal, or / and a plating layer is formed on the side of the solder layer, and the material of the plating layer includes titanium.

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