A welding process for DPIM power module

Abstract

The present invention discloses a welding process for a DPIM power module, which includes: an electrode bonding process and a power chip welding process; the electrode bonding process includes: bonding the bottom pin of the frame electrode to the ceramic substrate, and cutting off the transverse connecting ribs of the frame electrode after bonding; the power chip welding process includes: welding the power chip to the ceramic substrate after the electrode is bonded using a multi-stage temperature control process. The present invention provides a welding process for a DPIM power module, which effectively solves the problem of oxidation of the ceramic substrate during the welding process and the problem of dark cracks in the ceramic substrate due to stress generated by heating and cooling, and greatly reduces the area of ​​the voids.

Description

Technical Field

[0001] The invention belongs to the technical field of power semiconductor preparation, and in particular relates to a welding process for a DPIM power module. Background Art

[0002] In the DPIM power module package, the quality of power chip welding directly affects the reliability and service life of the DPIM power module. Therefore, in the DPIM module manufacturing process, one of the key process nodes includes the welding process of the module power chip. The traditional module welding process generally uses flux as a reducing agent to remove the oxide film in the reflow oven, and adopts the traditional degassing method to first melt the solder in atmospheric pressure, and then perform vacuum decompression to discharge the bubbles in the welding part of the DPIM power module. The traditional welding process generally adopts 5 to 7 stage working temperatures, such as Figure 1 or Figure 2 As shown, the void rate of the product is generally difficult to control, which easily leads to a low qualified rate of DPIM module finished products.

[0003] In the steps of vacuuming and passing formic acid, the traditional welding process generally involves vacuuming first, then heating, then reducing by passing formic acid, then vacuuming again, and cooling by passing nitrogen. Since the packaging form of our company's DPIM module is significantly different from that of traditional power packaging modules, during the production process using the above process steps, it was found that the existing process applied to the production of DPIM products has at least the following technical problems:

[0004] 1. The vacuum degree is not enough before the formic acid is introduced. The copper layer on the surface of the ceramic substrate DBC is easily oxidized due to high temperature and cannot be completely reduced after the formic acid is introduced;

[0005] 2. During the process of formic acid reduction and re-vacuum degassing, the bubbles between the power chips cannot be completely discharged, which easily forms voids between the ceramic substrate (ie, DBC) and the power chips (ie, IGBT chips and FDR chips), resulting in a high void rate and a large waste of production costs;

[0006] 3. The overall cooling process of the existing process is too fast, resulting in DBC dark cracks or ruptures, low product manufacturing qualification rate, and significantly reduced production yield and manufacturing efficiency. Summary of the invention

[0007] Based on the above technical problems, the present invention provides a welding process for a DPIM power module, which effectively solves the problem of oxidation of the ceramic substrate during the welding process and the problem of dark cracks in the ceramic substrate due to stress generated by heating and cooling, and greatly reduces the void area and the probability of void generation, thereby improving product production yield and saving manufacturing costs.

[0008] The technical solution adopted by the present invention is specifically:

[0009] The present application discloses a welding process for a DPIM power module, including: an electrode bonding process and a power chip welding process;

[0010] The electrode bonding process includes: bonding the bottom pin of the frame electrode to the ceramic substrate, and cutting off the transverse connecting ribs of the frame electrode after bonding;

[0011] The power chip welding process includes: welding the power chip to the ceramic substrate with bonding electrodes by using a multi-stage temperature control process.

[0012] As an optional technical solution, the multi-stage temperature control process includes: a product preheating stage, a device welding stage, and a cooling stage.

[0013] As an optional technical solution, the product preheating stage includes:

[0014] S1. Place or transfer the product to be welded into the vacuum chamber and slowly evacuate the chamber;

[0015] S2. When the pressure in the chamber is between 4-3 mbar, nitrogen (N2) is filled into the vacuum chamber at a rate of 40-60 SL / min. When the pressure in the chamber reaches 950.0-900.0 mbar, the filling is stopped and heating is started.

[0016] S3, after the temperature rises, 3 The chamber is vacuumed again at a rate of / min, so that the pressure in the chamber is between 4-3mbar again; when the temperature of the ceramic substrate reaches 75-100℃, the next step is carried out and the temperature is continued to rise;

[0017] S4, charging formic acid (HCOOH), when the pressure in the chamber reaches 610.0-580.0 mbar, stop charging formic acid, and control the charging time to be 1-3 minutes; at this time, wait for the temperature of the ceramic substrate to rise to 145-155°C, and then proceed to the next process;

[0018] S5, filling with nitrogen (N2) for 1-3 minutes, and stopping the filling after the pressure in the chamber reaches 950.0-900.0 mbar;

[0019] S6. After the temperature of the ceramic substrate reaches 175-185°C, the device welding stage begins.

[0020] As an optional technical solution, in the step S4, when formic acid (HCOOH) is charged, the charging rate is 40-60SL / min, and nitrogen is used for carrying; in the step S5, when nitrogen (N2) is charged, the charging rate is 40-60SL / min.

[0021] As an optional technical solution, the device welding stage includes:

[0022] S7, slowly evacuate the chamber until the pressure in the chamber is between 4-3 mbar again, and keep the temperature of the ceramic substrate at 175-185°C;

[0023] S8, charging formic acid (HCOOH) for 2-5 minutes or stopping charging formic acid after the pressure inside the chamber reaches 520.0-490.0 mbar; wherein, the charging rate when charging formic acid (HCOOH) is 40-60 SL / min, and the formic acid is carried by nitrogen.

[0024] S9. Fill with nitrogen (N2) at a rate of 40-60SL / min. When the pressure in the chamber reaches 950.0-900.0mbar, stop filling. When the temperature of the ceramic substrate rises to 195-210°C, keep it at this temperature for 0.5-2 minutes, and then perform a low-temperature solder welding process or a high-temperature solder welding process, wherein the composition of the low-temperature solder is a tin-antimony alloy solder Sn90Sb10 containing 90% tin and 10% antimony, and the composition of the high-temperature solder is an alloy solder PbSn5Ag2.5 containing 92.5% lead, 5% tin and 2.5% silver.

[0025] As an optional technical solution, the high temperature solder welding process includes:

[0026] S10, continue to heat up, wait for the temperature of the ceramic substrate to reach 255-260.0℃, start to slowly evacuate, and keep it at 255-260℃ for 0.5-2 minutes; then heat up to 275-280℃, and the time from 255-260.0℃ to 275-280℃ is controlled within 2-4min;

[0027] S11, continue to evacuate the chamber and make the chamber pressure less than 8.5-6mbar, and wait for the temperature of the ceramic substrate to reach 320-328℃;

[0028] S12, when the temperature of the ceramic substrate reaches 320-328°C, quickly evacuate the chamber to keep the pressure inside the chamber below 3.5 mbar, and wait until the temperature of the ceramic substrate rises to 330.0°C;

[0029] S13, when the temperature of the ceramic substrate rises to 330.0°C, nitrogen is started to be filled in at a rate of 60-90SL / min. After the pressure in the chamber reaches 950.0-900.0mbar, it is maintained at 330°C for 0.5-2 minutes;

[0030] S14, when the pressure in the chamber reaches 950.0-900.0 mbar, it enters the cooling stage.

[0031] As an optional technical solution, the low temperature solder welding process includes:

[0032] S10′, continue to heat up, wait for the temperature of the ceramic substrate to reach 245-260.0°C, start to slowly evacuate, and maintain at 245-260°C for 0.5-2 minutes;

[0033] S11′, continue to evacuate the chamber and make the chamber pressure less than 8.5-6 mbar, and wait for the temperature of the ceramic substrate to reach 265-270°C;

[0034] S12′, when the temperature of the ceramic substrate reaches 265-270°C, quickly evacuate the chamber to keep the pressure inside the chamber below 3.5 mbar, and wait until the temperature of the ceramic substrate rises to 275.0°C;

[0035] S13′, when the temperature of the ceramic substrate rises to 275.0°C, nitrogen is filled in at a rate of 60-90 SL / min, and after the pressure in the chamber reaches 950.0-900.0 mbar, it is maintained at 275°C for 0.5-2 minutes;

[0036] S14′, when the pressure in the chamber reaches 950.0-900.0 mbar, it enters the cooling stage.

[0037] As an optional technical solution, the cooling stage includes:

[0038] S15, cooling with cooling circulating water, when the temperature of the ceramic substrate drops to 240-225°C, turn off the cooling water, keep the temperature of the ceramic substrate at about 240-225°C for 1-4 minutes, and then turn on the cooling water again to continue cooling;

[0039] S16. When the temperature of the ceramic substrate drops to 185-175°C, the cooling water is turned off again, and the temperature of the ceramic substrate is kept at 185-175°C for 1-2 minutes, and then the cooling water is turned on to continue cooling;

[0040] S17, when the temperature of the ceramic substrate drops to 125-120°C, the equipment starts to cool down naturally;

[0041] S18, after waiting for the temperature of the ceramic substrate to reach 35-25°C, open the equipment chamber door, take out the welded product, and end.

[0042] As an optional technical solution, the ceramic substrate is a DBC ceramic substrate, and the DBC ceramic substrate is doped with metal zirconium with a doping concentration of 2%-8%.

[0043] As an optional technical solution, the power chip includes an IGBT and an FRD chip, or the power chip includes at least one of a SiC, a GaN, and a MOSFET power chip.

[0044] The beneficial effects of the present invention are:

[0045] In the present invention, the product enters the welding furnace from room temperature, and the heating process is designed with multiple steps to prevent the product from being overheated and the ceramic substrate from being insufficiently reduced, causing oxidation of the ceramic substrate; the cooling process is designed with a buffer to avoid the product from being suddenly overcooled during cooling and the internal stress of the ceramic substrate cannot be released during the change from high temperature to low temperature, causing the ceramic substrate to crack. In addition, formic acid and / or nitrogen are filled at different stages during the heating process, which has a significant effect on the protection and welding effect of the product, can prevent the product from being oxidized during welding in the atmosphere and reduce the problem of product degassing solder splashing during vacuum welding, making the product cavity very large and the cavity rate exceeding the standard, greatly improving the production yield, reducing the output of defective products and waste products, and saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the basic process temperature curve of the prior art.

[0047] Figure 2 It is a schematic diagram of a conventional process temperature curve in the prior art.

[0048] Figure 3 Schematic diagram of the temperature curve of the improved high-temperature solder welding process.

[0049] Figure 4 This is a schematic diagram of the temperature curve of another improved high-temperature solder welding process.

[0050] Figure 5 This is a schematic diagram of the entire process of the traditional DPIM packaging process.

[0051] Figure 6 It is a schematic diagram of various semiconductor structures formed in the traditional DPIM packaging process.

[0052] Figure 7 FIG. 4 is a schematic diagram of the entire process of the DPIM packaging process of this embodiment.

[0053] Figure 8 It is a schematic diagram of various semiconductor structures formed in the DPIM packaging process of this embodiment.

[0054] Fig. 9 FIG. 4 is a flow chart of the welding process of the DPIM power module of this embodiment.

[0055] Fig.10Schematic diagram of the semiconductor structure used in the welding process of the DPIM power module according to this embodiment.

[0056] Fig.11 Schematic diagram of the improved low-temperature solder welding process temperature curve.

[0057] Fig.12 This is a schematic diagram of the temperature curve of another improved low-temperature solder welding process. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The steps and components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0059] Example 1

[0060] like Fig. 9 As shown, the present application discloses a welding process for a DPIM power module, including: an electrode bonding process and a power chip welding process. The power chip in the present invention is preferably an IGBT chip and a FDR chip, and power chips such as SiC, GaN, and MOSFET may also be selected.

[0061] Specifically, the electrode bonding process includes: bonding the bottom pin of the frame electrode to the ceramic substrate through a bonding jig and a bonding device (see Chinese invention patents CN202410669171.7 and CN202411328364.2), and further cutting off the transverse connecting ribs of the frame electrode after bonding. Furthermore, the frame electrode includes pins for realizing internal and external electrical connections of the DPIM module (see Chinese utility model patent application number CN202422421886.9).

[0062] like Figure 5 and Figure 6As shown in the figure, the traditional DPIM packaging process, after wafer dicing, firstly transfers the soldering pad and chip to the DBC board through the patch equipment (such as M18 Pro, YAMAHAYSM10, CPM FS-10, etc.), and then passes through the vacuum welding furnace for welding, and then completes the internal electrical connection through pressure welding, and then passes through the vacuum furnace to put the fixture with the DBC ceramic substrate and electrode pins into the vacuum welding furnace for secondary welding, and then fills the glue to complete the packaging. The electrodes welded by this traditional process are very easy to fall off during use, and the DBC ceramic substrate is prone to dark cracks due to the stress caused by temperature changes after two furnace welding, resulting in failure of the production process.

[0063] Further, such as Figure 7 , Figure 8 , Fig.10 As shown, in order to reduce the number of welding times, reduce costs and solve the problem that the electrode pins are easy to fall off, the present embodiment directly changes the electrode pins into a frame electrode 2 of a frame structure, and the frame electrode 2 includes a lateral electrode pin 201 and a transverse connecting rib 202. Further, after the bottom pin of the frame electrode 2 is directly bonded to the DBC board 1, the transverse connecting rib 202 is cut off and only the lateral electrode pin 201 is retained. Since the lateral electrode pin 201 is directly bonded to the DBC board 1, the process flow of the present embodiment has only one welding process. Compared with the two welding processes of the traditional DPIM packaging process, the process steps of the present embodiment reduce the impact of thermal stress on the DBC ceramic substrate during welding, further reduce the labor and time required for secondary welding of the assembly electrode pins, shorten the product production cycle, and improve production efficiency. Since the electrode pins are directly bonded, the lateral electrode pins 201 and the DBC board 1 are tightly and firmly combined by atomic force and are not easy to fall off. Therefore, the DPIM module product produced in the present embodiment has good electrical performance and high reliability.

[0064] Furthermore, in order to further prevent the DBC ceramic substrate from having dark cracks during the electrode pin bonding process, the present embodiment may dope a small amount of zirconium metal into the DBC ceramic substrate, and the doping concentration is preferably 2%-8%, so as to further improve the toughness and strength of the DBC ceramic substrate and reduce the occurrence of DBC dark cracks and / or cracks during the bonding process. It should be noted that in the present embodiment, if Figure 8 The solder shown in the figure adopts high temperature solder, and the composition of the high temperature solder is an alloy solder PbSn5Ag2.5 containing 92.5% lead, 5% tin and 2.5% silver.

[0065] like Figure 3 or Figure 4As shown in the process curve, in order to further solve the problem of DBC dark cracks caused by too fast cooling process in the traditional welding process and the easy formation of voids between DBC and the chip, this embodiment adopts a multi-stage temperature control process during the power chip welding process. Specifically, in the process of this embodiment, by increasing the number of formic acid injections, constant temperature steps and vacuum pumping times, the problem of easy oxidation of the DBC ceramic substrate during welding and the dark cracks of the DBC ceramic substrate due to stress caused by temperature rise and fall are further effectively solved, thereby improving the product production yield.

[0066] Furthermore, the multi-stage process temperature curve adopted in this embodiment can be used for welding using both off-line equipment and on-line equipment.

[0067] Specifically, the welding using the offline equipment is as follows: the power chip is manually placed into a welding jig, and then the welding jig is placed into an offline vacuum welding furnace for welding.

[0068] Specifically, the welding using online equipment is as follows: the DBC ceramic substrate is placed on the heating tray and arranged in a certain order, and the bonding machine is used according to the programmed program, and the welding pieces of the same specifications cut by the cutter are adsorbed by the bonding machine nozzle by the manipulator and transferred to the position predetermined by the program for DBC, and then the IGBT chip and FDR chip and the thermistor used in conjunction, such as NTC Remington resistor, are adsorbed and transferred to the welding piece set by the DBC program directly above the welding piece with the welding piece placed, and the power chip is loaded. After the loading is completed, the heating tray (the bearing component of the welding fixture, generally a component of the welding equipment itself) enters the vacuum welding furnace through the track, and the DBC ceramic substrate and the power chip are welded in a vacuum environment and formic acid atmosphere according to different heating and cooling curves, vacuuming and formic acid passing timing and time.

[0069] In this embodiment, multi-stage temperature rise and fall, multi-stage vacuuming and formic acid are mainly used to avoid welding voids on the welding surface. Furthermore, this embodiment can control the total area of ​​a single void of the power chip in the DPIM module within 1% of the welding area, and the total area of ​​multiple voids within 3% of the welding area, which greatly reduces the defect rate of DPIM using traditional processes and improves the reliability of the DPIM module.

[0070] Specifically, in the process of welding the power chip and the DBC after the bonding electrode, the multi-stage temperature control process includes: product preheating stage, device welding stage and cooling stage. Figure 4 Taking the process curve in as an example, these three stages are explained in detail.

[0071] (1) Product preheating stage: including steps S1-S6.

[0072] S1. Place or transfer the product to be welded into the vacuum chamber and slowly evacuate the chamber at a rate of 5-15L / S. Figure 8 The product shown in 8-A;

[0073] S2. When the pressure in the chamber is between 4-3mbar, the vacuum pump of the system reaches its vacuum limit. The gas molecule density in the chamber is very thin, and the oxygen content is reduced to the minimum. At this time, the vacuum environment in the vacuum chamber reaches the optimal state. The subsequent processes are carried out in the chamber at this time, so that the products to be welded are least affected by oxidation.

[0074] Furthermore, nitrogen (N2) is filled into the vacuum chamber at a filling rate of 40-60SL / min until the pressure in the chamber reaches 950.0-900.0mbar. While filling the gas space that has been evacuated and driving away other gases and water vapor inside the chamber, ensure that the nitrogen continues to evenly fill the vacuum chamber. In addition, when the pressure in the vacuum chamber reaches 950.0-900.0mbar, the vacuum chamber basically reaches one atmospheric pressure. After the nitrogen is filled, 99% of the chamber is nitrogen, which further reduces the oxidation probability of the device during heating and provides the most basic guarantee for product reliability. Then stop filling and start heating;

[0075] S3, use vacuum pump to extract air at 15-20m 3 / min, the pressure in the chamber is again between 4-3mbar. This further ensures that the oxygen molecule content in the chamber reaches the minimum and the vacuum state of the chamber is guaranteed, so that the inside of the vacuum chamber remains in an oxygen-free or oxygen-reduced state;

[0076] Furthermore, when the substrate temperature reaches 75-100°C, formic acid (HCOOH) is charged; charging HCOOH when the substrate reaches 75-100°C is conducive to a better reaction between formic acid and oxide on the substrate surface, while increasing the reaction speed;

[0077] S4. When the pressure in the vacuum chamber reaches 610.0-580.0 mbar, fill formic acid (HCOOH) for 1-3 minutes, and then stop filling formic acid. At this time, the space in the vacuum chamber is basically in a formic acid atmosphere, and the formic acid concentration meets the process requirements. Specifically, the formic acid concentration in the chamber can better play a reducing role and reduce the soldering void rate; after the substrate temperature rises to 145-155°C, enter the next process;

[0078] S5, filling nitrogen (N2) to dilute the residual formic acid gas after the initial reaction; further, the filling time of nitrogen (N2) is 1-3min so that the pressure in the chamber reaches 950.0-900.0mbar, the nitrogen fills the entire chamber to reach a saturated state, and the pressure is close to one atmosphere, and then the filling is stopped;

[0079] S6. After the substrate temperature reaches 175-185°C, the device welding stage begins.

[0080] Specifically, in step S4, when formic acid (HCOOH) is charged, the charging rate is 40-60 SL / min, and nitrogen is used for carrying.

[0081] Specifically, since formic acid is generally a liquid, directly passing the liquid into the chamber is not conducive to the subsequent power chip welding, so nitrogen is used to carry it. This embodiment preferably adopts a bubbling method to pass nitrogen into the formic acid source bottle. After the nitrogen passes through the formic acid solution, it carries the formic acid molecules into the chamber. Since gas molecules have better fluidity than liquids, they can be better and more evenly filled into the chamber;

[0082] Specifically, in step S5, when nitrogen (N2) is charged, the charging rate is 40-60 SL / min. The charging rates of formic acid (HCOOH) charged in step S4 and nitrogen (N2) charged in step S5 are strictly controlled at 40-60 SL / min, and the charging time is strictly controlled at 1-3 min to avoid excessively high or low concentrations of formic acid or nitrogen (N2) in the chamber, which may lead to the formation of voids or failure to protect the device.

[0083] (2) Device welding stage: including steps S7-S14.

[0084] S7, slowly evacuate the chamber until the pressure is between 4-3 mbar again, and maintain the temperature of the DBC ceramic substrate at 175-185°C;

[0085] S8, charging formic acid (HCOOH) until the pressure inside the chamber reaches 520.0-490.0 mbar or after charging formic acid for 2-5 minutes, stop charging formic acid;

[0086] S9, fill nitrogen (N2) until the pressure in the chamber reaches 950.0-900.0 mbar, and stop filling; after the substrate temperature rises to 195-210°C, keep the DBC ceramic substrate at this temperature for 0.5-2 minutes, and then enter the high-temperature soldering process.

[0087] Furthermore, the high temperature solder welding process includes steps S10-S14, specifically:

[0088] S10, continue to heat up until the temperature of the DBC ceramic substrate reaches 255-260.0°C, and then slowly start to evacuate. In this embodiment, the evacuation rate is preferably 5-15L / S;

[0089] Keep the DBC ceramic substrate at 255-260°C for 0.5-2 minutes; then continue to heat it up to 275-280°C. Furthermore, in order to further improve production efficiency, the time taken to heat from 255-260.0°C to 275-280°C is preferably controlled within 2-4 minutes;

[0090] S11, continue to evacuate until the chamber pressure is less than 8.5-6mbar, and wait for the temperature of the DBC ceramic substrate to reach 320-328°C;

[0091] S12. When the temperature of the DBC ceramic substrate reaches 320-328°C, quickly evacuate the chamber to keep the pressure inside the chamber below 3.5mbar, and wait until the substrate temperature rises to 330.0°C; to ensure the safety and efficiency of the process, the rapid vacuuming rate is 15-22L / S.

[0092] S13, when the temperature of the DBC ceramic substrate rises to 330.0°C, start filling with nitrogen until the pressure in the vacuum welding chamber reaches 950.0-900.0 mbar, and maintain at 330°C for 0.5-2 minutes;

[0093] S14, when the pressure in the vacuum chamber reaches 950.0-900.0 mbar, it enters the cooling stage.

[0094] Specifically, in the step S8, the filling rate of formic acid (HCOOH) is 40-60SL / min, and it is carried by nitrogen; in the step S9, the filling rate of nitrogen (N2) is 40-60SL / min; in the step S13, the filling rate of nitrogen is 60-90SL / min.

[0095] (3) Cooling stage: including steps S15-S18.

[0096] S15. Cooling is performed using cooling circulating water. When the temperature of the DBC ceramic substrate drops to 240-225°C, the cooling water is turned off to keep the temperature of the DBC ceramic substrate at about 240-225°C for 1-4 minutes, thereby controlling the cooling rate, preventing the semi-finished product after welding from dropping from high temperature too quickly, and reducing the tension in the DBC ceramic substrate during the cooling process.

[0097] S16, turn on the cooling water again until the temperature of the DBC ceramic substrate drops to 185-175°C, turn off the cooling water again, keep the temperature of the DBC ceramic substrate at 185-175°C for 1-2 minutes, and then turn on the cooling water to continue cooling;

[0098] S17, when the temperature of the DBC ceramic substrate drops to 125-120°C, the equipment starts to cool down naturally;

[0099] S18. After waiting for the temperature of the DBC ceramic substrate to reach 35-25°C, open the equipment chamber door, take out the welded product, and complete the welding process of the DPIM power chip.

[0100] It should be noted that during the welding process, the reaction equation for formic acid to reduce the oxide film is as follows:

[0101] MO+HCOOH=M+H2O+CO2;

[0102] Wherein, M represents a metal that can be reduced by formic acid, such as metal Sn, Cu, Ni, Ag, Pb, etc.

[0103] Specifically, the DBC ceramic substrate in steps S1-S18 is a direct bonded copper ceramic substrate (DBC). In addition, the DBC ceramic substrate can also be replaced by other types of ceramic substrates with electrical transmission and insulation heat dissipation, such as thin film ceramic substrate (TFC), thick film printed ceramic substrate (TPC), active metal brazing ceramic substrate (AMB), direct electroplated copper ceramic substrate (DPC) and laser activated metal ceramic substrate (LAM). The substrate of the power module described in the present invention is preferably a DBC direct bonded copper ceramic substrate with low cost, good performance and simple manufacturing process.

[0104] Example 2

[0105] This embodiment is basically the same as Embodiment 1, except that this embodiment uses low-temperature solder to further solve the DBC cracking problem during the welding process of the DPIM module.

[0106] Specifically, the low temperature solder is Sn90Sb10, that is, a low temperature solder containing 90% tin and 10% antimony. The low temperature solder Sn90Sb10 used in this embodiment can avoid the technical problem that the original undoped zirconium DBC ceramic substrate is prone to cracking during the welding process.

[0107] Furthermore, the low-temperature solder used in this embodiment can significantly reduce the technical problem of cracking of DBC ceramic substrates. In actual production activities, the cracking rate of the DPIM module ceramic substrates produced by the solder used in this embodiment is reduced to less than 1%, and the overall qualified rate is more than 95%. The traditional process uses PbSn5Ag2.5 solder (i.e., contains 92.5% lead, 5% tin, and 2.5% silver). After vacuum welding, at least 46% of the DBC ceramic substrates have obvious cracks and 5% have inconspicuous dark cracks. The difference between the two effects is obvious, and the DBC cracking problem in the welding process is completely solved.

[0108] It should be noted that the high temperature soldering process (steps S10-S14) in Example 1 is replaced by the low temperature soldering process (steps S10'-S14') in this embodiment. At the same time, the process temperature curve is also improved accordingly, such as Fig.11 and Fig.12 As shown. Fig.12 Taking the process temperature curve as an example, the low temperature solder welding process includes the following processes:

[0109] S10′, continue to heat up, wait for the temperature of the DBC ceramic substrate to reach 245-260.0°C, start to slowly evacuate, and keep it at 245-260°C for 0.5-2 minutes;

[0110] S11′, continue to evacuate the chamber and make the chamber pressure less than 8.5-6 mbar, and wait for the temperature of the ceramic substrate to reach 265-270°C;

[0111] S12′, when the temperature of the ceramic substrate reaches 265-270°C, quickly evacuate the chamber to keep the pressure inside the chamber below 3.5 mbar, and wait until the temperature of the ceramic substrate rises to 275.0°C;

[0112] S13′, when the temperature of the ceramic substrate rises to 275.0°C, nitrogen is filled in at a rate of 60-90 SL / min, and after the pressure in the chamber reaches 950.0-900.0 mbar, it is maintained at 275°C for 0.5-2 minutes;

[0113] S14′, when the pressure in the chamber reaches 950.0-900.0 mbar, it enters the cooling stage.

[0114] It should be noted that: when the DPIM product is used in a low-temperature welding environment (the low-temperature welding environment refers to the welding temperature between 180°C and 240°C when the DPIM product is welded on a PCB board), when preparing the DPIM product, the low-temperature solder Sn90Sb10 and welding process in Example 2 are used to weld its power chip to the DBC substrate.

[0115] The melting point of the low-temperature solder Sn90Sb10 is 240°C. When the welding temperature when the DPIM product is welded on the PCB board is higher than the melting point of the low-temperature solder Sn90Sb10, the low-temperature solder melts and the DPIM product may be scrapped (the power chip may be separated from the DBC substrate due to the melting of the low-temperature solder). Therefore, for DPIM products that need to be used in a high-temperature welding environment (the high-temperature welding environment means that the welding temperature when the DPIM product is welded on the PCB board exceeds 240°C), when preparing such DPIM products, the high-temperature solder PbSn5Ag2.5 (melting point 287°C) and welding process in Example 1 are used to weld its power chip to the DBC substrate.

[0116] Furthermore, the low-temperature solder of this embodiment can be used for low-temperature welding so that the obtained DPIM module product can fully meet the environmental protection requirements of ROHS and REACH standards.

[0117] It should also be noted that for all slow vacuum pumping appearing in this application, the pumping rate is 5-15L / s; for all fast vacuum pumping appearing in this application, the pumping rate is 15-22L / s, so as to ensure the uniformity of gas filling or exhaust, ensure that the chamber is completely in a vacuum or corresponding state, improve the product welding qualification rate and reduce costs.

[0118] The above description is only a specific implementation mode of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. All technical solutions that fall within the scope defined by the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A welding process for a DPIM power module, characterized in that: include: Electrode bonding process and power chip welding process; The electrode bonding process includes: bonding the bottom pin of the frame electrode to the ceramic substrate, and cutting off the transverse connecting ribs of the frame electrode after bonding; The power chip welding process comprises: welding the power chip to the ceramic substrate with bonding electrodes by using a multi-stage temperature control process.

2. The welding process of the DPIM power module according to claim 1, characterized in that: The multi-stage temperature control process includes: a product preheating stage, a device welding stage and a cooling stage.

3. The welding process of the DPIM power module according to claim 2, characterized in that: The product preheating stage includes: S1. Place or transfer the product to be welded into the vacuum chamber and slowly evacuate the chamber; S2. When the pressure in the chamber is between 4-3 mbar, nitrogen (N2) is filled into the vacuum chamber at a rate of 40-60 SL / min. When the pressure in the chamber reaches 950.0-900.0 mbar, the filling is stopped and heating is started. S3, after the temperature rises, 3 The chamber is vacuumed again at a rate of / min, so that the pressure in the chamber is between 4-3mbar again; when the temperature of the ceramic substrate reaches 75-100℃, the next step is carried out and the temperature is continued to rise; S4, charging formic acid (HCOOH), when the pressure in the chamber reaches 610.0-580.0 mbar, stop charging formic acid, and control the charging time to be 1-3 minutes; at this time, wait for the temperature of the ceramic substrate to rise to 145-155°C, and then proceed to the next process; S5, filling with nitrogen (N2) for 1-3 minutes, and stopping the filling after the pressure in the chamber reaches 950.0-900.0 mbar; S6. After the temperature of the ceramic substrate reaches 175-185°C, the device welding stage begins.

4. The welding process of the DPIM power module according to claim 3, characterized in that: In the step S4, when formic acid (HCOOH) is charged, the charging rate is 40-60SL / min, and it is carried by nitrogen; in the step S5, when nitrogen (N2) is charged, the charging rate is 40-60SL / min.

5. The welding process of the DPIM power module according to claim 2, characterized in that: The device welding stage includes: S7, slowly evacuate the chamber until the pressure in the chamber is between 4-3 mbar again, and keep the temperature of the ceramic substrate at 175-185°C; S8, charging formic acid (HCOOH) for 2-5 minutes or stopping charging formic acid after the pressure inside the chamber reaches 520.0-490.0 mbar; wherein, the charging rate when charging formic acid (HCOOH) is 40-60 SL / min, and the formic acid is carried by nitrogen. S9. Fill with nitrogen (N2) at a rate of 40-60SL / min. When the pressure in the chamber reaches 950.0-900.0mbar, stop filling. When the temperature of the ceramic substrate rises to 195-210°C, keep it at this temperature for 0.5-2 minutes, and then perform a low-temperature solder welding process or a high-temperature solder welding process, wherein the composition of the low-temperature solder is a tin-antimony alloy solder Sn90Sb10 containing 90% tin and 10% antimony, and the composition of the high-temperature solder is an alloy solder PbSn5Ag2.5 containing 92.5% lead, 5% tin and 2.5% silver.

6. The welding process of the DPIM power module according to claim 5, characterized in that: The high temperature solder welding process comprises: S10, continue to heat up, wait for the temperature of the ceramic substrate to reach 255-260.0℃, start to slowly evacuate, and keep it at 255-260℃ for 0.5-2 minutes; then heat up to 275-280℃, and the time from 255-260.0℃ to 275-280℃ is controlled within 2-4min; S11, continue to evacuate the chamber and make the chamber pressure less than 8.5-6mbar, and wait for the temperature of the ceramic substrate to reach 320-328℃; S12, when the temperature of the ceramic substrate reaches 320-328°C, quickly evacuate the chamber to keep the pressure inside the chamber below 3.5 mbar, and wait until the temperature of the ceramic substrate rises to 330.0°C; S13, when the temperature of the ceramic substrate rises to 330.0°C, nitrogen is started to be filled in at a rate of 60-90SL / min. After the pressure in the chamber reaches 950.0-900.0mbar, it is maintained at 330°C for 0.5-2 minutes; S14, when the pressure in the chamber reaches 950.0-900.0 mbar, it enters the cooling stage.

7. The welding process of the DPIM power module according to claim 5, characterized in that: The low temperature solder welding process comprises: S10 ′ , Continue to heat up, wait for the temperature of the ceramic substrate to reach 245-260.0℃, then start to slowly evacuate, and keep it at 245-260℃ for 0.5-2 minutes; S11 ′ , continue to evacuate the chamber and make the chamber pressure less than 8.5-6mbar, and wait for the temperature of the ceramic substrate to reach 265-270℃; S12 ′ 1. When the temperature of the ceramic substrate reaches 265-270℃, quickly evacuate the chamber to keep the pressure inside the chamber below 3.5mbar, and wait until the temperature of the ceramic substrate rises to 275.0℃; S13 ′ 1. When the temperature of the ceramic substrate rises to 275.0°C, nitrogen is filled in at a rate of 60-90 SL / min. After the pressure in the chamber reaches 950.0-900.0 mbar, it is maintained at 275°C for 0.5-2 minutes. S14 ′ , When the pressure in the chamber reaches 950.0-900.0mbar, it enters the cooling stage.

8. The welding process of the DPIM power module according to claim 2, characterized in that: The cooling stage includes: S15, cooling with cooling circulating water, when the temperature of the ceramic substrate drops to 240-225°C, turn off the cooling water, keep the temperature of the ceramic substrate at about 240-225°C for 1-4 minutes, and then turn on the cooling water again to continue cooling; S16. When the temperature of the ceramic substrate drops to 185-175°C, the cooling water is turned off again, and the temperature of the ceramic substrate is kept at 185-175°C for 1-2 minutes, and then the cooling water is turned on to continue cooling; S17, when the temperature of the ceramic substrate drops to 125-120°C, the equipment starts to cool down naturally; S18, after waiting for the temperature of the ceramic substrate to reach 35-25°C, open the equipment chamber door, take out the welded product, and end.

9. The welding process of the DPIM power module according to any one of claims 1 to 8, characterized in that: The ceramic substrate is a DBC ceramic substrate, and metal zirconium is doped in the DBC ceramic substrate with a doping concentration of 2%-8%.

10. The welding process of the DPIM power module according to any one of claims 1 to 8, characterized in that: The power chip includes an IGBT and an FRD chip, or the power chip includes at least one of a SiC, a GaN, and a MOSFET power chip.

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