A welding method and apparatus for a vacuum welding furnace

Abstract

This invention relates to the field of chip packaging technology, and provides a welding method and apparatus for a vacuum welding furnace, comprising: evacuating the vacuum welding furnace to reduce the pressure of the vacuum welding furnace to a slight negative pressure; setting a first heating power P₁, heating the furnace to a first preheating temperature T1 using the first heating power P₁, and setting a preheating holding time; determining a heating rate according to a heating rate formula, heating the furnace to a second preheating temperature T2 using a second heating power P2 and the heating rate, and heating the furnace to a third preheating temperature T3 using a third heating power P3 and the heating rate; heating the furnace to a peak temperature using a fourth heating power P4, and simultaneously purging nitrogen to a set positive pressure P. 正压 The full-melt holding time is determined according to the full-melt holding formula; heating is performed with the fifth heating power P5; a rapid vacuum is then applied, and the defoaming holding time is determined according to the defoaming time formula; defoaming holding is then performed; the vacuum welding furnace then performs the cooling step. No bubbles are generated inside the solder, resulting in high welding quality.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a welding method and apparatus for a vacuum welding furnace. Background Technology

[0002] Existing vacuum welding equipment is a specialized device for welding workpieces. Its main structure includes a controller, a sealable cavity, a vacuum pump, a heating device, a heating plate, and a cooling device. The heating plate is located within the sealable cavity and is used to place the workpiece. The heating and cooling devices are located below the heating plate and are connected to the controller, which regulates the heating and cooling of the heating plate. The vacuum pump is located outside the sealable cavity and performs vacuuming to ensure the welding process is conducted in an oxygen-free environment, thus ensuring welding quality, reducing internal voids, and improving the reliability of the weldment.

[0003] Existing solders are prone to internal air bubbles, resulting in low solder quality. Summary of the Invention

[0004] This invention provides a welding method for a vacuum welding furnace, which solves the problem of low welding quality caused by the easy formation of internal bubbles in the solder in the prior art.

[0005] A welding method in a vacuum welding furnace, comprising:

[0006] The vacuum welding furnace is evacuated to reduce the pressure to a slight negative pressure.

[0007] The first heating power P1 is set according to the power calculation formula. The temperature is raised to the first preheating temperature T1 according to the solder type using the first heating power P1. The preheating and holding time is set according to the solder thickness.

[0008] The heating rate is determined according to the heating rate formula. The second heating power P2 and the heating rate are used to heat the temperature to the second preheating temperature T2. The third heating power P3 and the heating rate are used to heat the temperature to the third preheating temperature T3.

[0009] The fourth heating power P4 is raised to the peak temperature, and nitrogen is simultaneously charged to the set positive pressure P according to the full melting positive pressure formula. 正压 The full fusion insulation time is determined according to the full fusion insulation formula;

[0010] The fifth heating power P5 is obtained according to the degassing formula, and a vacuum is quickly drawn. The degassing and heat preservation time is obtained according to the degassing time formula. Degassing and heat preservation are carried out according to the degassing and heat preservation time.

[0011] The vacuum welding furnace performs a cooling step.

[0012] According to the welding method of the vacuum welding furnace of the present invention, the first preheating temperature T1 = T 熔点 -Δt,T 熔点 Solder melting point temperature; Δt = 50-80℃.

[0013] According to the welding method of the vacuum welding furnace of the present invention, the power calculation formula is as follows:

[0014] First heating power P1 = (C w ·m w + C f ·m f + C s ·m s )·V1 / η

[0015] C w Specific heat capacity of the workpiece; m w : Workpiece mass; η: Thermal efficiency; C s Specific heat capacity of solder; m s Solder quality; C s Specific heat capacity of vacuum welding furnace; m f Effective quality of vacuum welding furnace.

[0016] According to the welding method of the vacuum welding furnace of the present invention, the second heating power P2 is 1.18-1.2 times the first heating power P1; the third heating power P3 is 1.08-1.1 times the second heating power P2.

[0017] According to the welding method of the vacuum welding furnace of the present invention, the fourth heating power P4 = K × P3; K: solder correction coefficient.

[0018] According to the welding method of the vacuum welding furnace of the present invention, the defoaming formula is as follows:

[0019] P5 = P4 × (P 正压 / P 真空 ) 0.3 ;

[0020] P 真空 Vacuum stage pressure, P 正压： Positive pressure.

[0021] According to the welding method of the vacuum welding furnace of the present invention, the full-melting positive pressure formula is as follows:

[0022] P 正压 = 0.1 + 2×δ; δ: solder thickness value.

[0023] According to the welding method of the vacuum welding furnace of the present invention, the heating rate formula is:

[0024] V = 3.0 - 5 × δ; δ: solder thickness value.

[0025] According to the welding method of the vacuum welding furnace of the present invention, the cooling step of the vacuum welding furnace specifically includes:

[0026] The fifth heating power P5 is reduced to the sixth heating power P6, and the temperature is cooled to T. 熔点 -10℃;

[0027] The sixth heating power P6 is reduced to the seventh heating power P7, and the temperature is cooled to 145-155℃;

[0028] The seventh heating power P7 is reduced to the eighth heating power P8, and the temperature is cooled to 75-85℃;

[0029] Gradually backfill with nitrogen until the temperature and pressure are normal, then remove the workpiece.

[0030] A welding apparatus for a vacuum welding furnace, comprising:

[0031] The micro-negative pressure module is used to evacuate the vacuum welding furnace and reduce the pressure of the vacuum welding furnace to a micro-negative pressure.

[0032] The first preheating module is used to set the first heating power P1 according to the power calculation formula, heat the solder to the first preheating temperature T1 according to the solder type using the first heating power P1, and set the preheating and holding time according to the solder thickness.

[0033] The second and third preheating modules are used to determine the heating rate according to the heating rate formula. The second heating power P2 and the heating rate heat up to the second preheating temperature T2, and the third heating power P3 and the heating rate heat up to the third preheating temperature T3.

[0034] The full-fusion module is used to raise the temperature of the fourth heating power P4 to the peak temperature, and simultaneously purge nitrogen to the set positive pressure P according to the full-fusion positive pressure formula. 正压 The full fusion insulation time is determined according to the full fusion insulation formula;

[0035] The degassing module is used to obtain the fifth heating power P5 according to the degassing formula, quickly evacuate the vacuum, obtain the degassing and heat preservation time according to the degassing time formula, and degas and maintain heat according to the degassing and heat preservation time.

[0036] Cooling module, used in vacuum welding furnaces to perform cooling steps.

[0037] The present invention has the following advantages:

[0038] 1. Reduce the risk of bubble formation from the source and avoid initial defects such as solder boiling and volatile residue caused by improper preheating. Adjust preheating parameters to prevent premature melting of low-temperature solder and volatile residue inside thick solder; incorporate solder specific heat capacity into electrical energy calculation to improve power accuracy and preheating uniformity.

[0039] 2. Power increase is ≤20% to prevent sudden power changes from causing solder to "flash melt" (the surface melts first, but the inside is not heated).

[0040] 3. Positive pressure is linearly positively correlated with weld thickness. Thicker solder has more difficulty for air bubbles to escape, requiring higher pressure to compress the air bubble volume and reduce air bubble stability.

[0041] 4. By "rapidly creating a pressure difference through vacuuming and maintaining the minimum melting power", the bubbles in the molten solder can be completely released. The pressure difference is used to break the bubbles, prevent the solder from solidifying and hindering the degassing, and ensure that the void ratio is reduced to the target value. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A schematic diagram of the welding process in a vacuum welding furnace;

[0044] Figure 2 A schematic diagram of the cooling process for a vacuum welding furnace;

[0045] Figure 3 This is a schematic diagram of the welding device structure of a vacuum welding furnace. Detailed Implementation

[0046] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0047] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the structure or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0048] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0049] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or at least one embodiment or example. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0051] The following is combined with Figure 1-2 An embodiment of the present invention describes a welding method in a vacuum welding furnace, comprising:

[0052] S101. Evacuate the vacuum welding furnace to reduce the pressure to a slight negative pressure.

[0053] The optimal negative pressure is 80-100 kPa;

[0054] S102. Set the first heating power P1 according to the power calculation formula, and heat up to the first preheating temperature T1 according to the solder type using the first heating power P1. Set the preheating and holding time according to the solder thickness. The holding time is 28-32s for solder thickness less than 0.15mm and 38-42s for solder thickness greater than 0.15mm.

[0055] S103. Determine the heating rate according to the heating rate formula. The second heating power P2 and the heating rate are used to heat the temperature to the second preheating temperature T2. The third heating power P3 and the heating rate are used to heat the temperature to the third preheating temperature T3.

[0056] S104, the fourth heating power P4, heats up to the peak temperature, and simultaneously, nitrogen is charged to the set positive pressure P according to the full melt positive pressure formula. 正压 The full fusion insulation time is determined according to the full fusion insulation formula;

[0057] S105. According to the bubble removal formula, the fifth heating power P5 is obtained for heating, rapid vacuuming is performed, and the bubble removal and heat preservation time is obtained according to the bubble removal time formula. Bubble removal and heat preservation are performed according to the bubble removal and heat preservation time.

[0058] Formula for foam removal time:

[0059] t 排泡 = 15 + 50×δ; δ: solder thickness. The basic debubbling time is 15s (to allow bubbles to escape from thin solder). For every 0.1mm increase in thickness of the solder, the debubbling time is extended by 5s.

[0060] By "rapidly creating a pressure difference through vacuuming and maintaining the lowest possible molten power," bubbles in the molten solder are completely expelled. The pressure difference breaks up the bubbles, preventing solder solidification from hindering bubble removal and ensuring the void ratio is reduced to the target value. Increasing the power ensures the solder remains in a molten state (temperature maintained at T). 熔点 (above +5℃) to provide a flow channel for bubble escape.

[0061] S106. The vacuum welding furnace performs a cooling step.

[0062] In some embodiments, the first preheating temperature T1 = T 熔点 -Δt,T 熔点 Solder melting point temperature; Δt = 50-80℃.

[0063] In some embodiments, the power calculation formula is as follows:

[0064] First heating power P1 = (C w ·m w + C f ·m f + C s ·m s )·V1 / η

[0065] C w Specific heat capacity of the workpiece; m w : Workpiece mass; η: Thermal efficiency; C s Specific heat capacity of solder; m s Solder quality; C s Specific heat capacity of vacuum welding furnace; m f Effective mass of the vacuum welding furnace. m s Solder quality = Welding area × Welding thickness × Solder density (Sn-based solder ≈ 7300, Au-Sn ≈ 14500); m f Effective mass of a vacuum welding furnace: The total mass of furnace components involved in heat exchange (including heating elements, furnace liner, insulation layer, etc.). η = Thermal efficiency 0.7-0.85. Reduce the risk of bubble formation from the source, avoiding initial defects such as solder boiling and volatile residues caused by improper preheating. Targeted adjustment of preheating parameters prevents premature melting of low-temperature solder and volatile residues inside thick solder.

[0066] The specific heat capacity of the solder is incorporated into the electrical energy calculation, which improves the accuracy of power output and enhances the uniformity of preheating.

[0067] In some embodiments, the second heating power P2 is 1.18-1.2 times the first heating power P1; the third heating power P3 is 1.08-1.1 times the second heating power P2. T2=T 熔点 -10℃, T 3= T 熔点 +5℃. Power increases are all ≤20% to prevent sudden power surges that could cause solder "flash melting" (the surface melts before the interior heats up), leading to bubble formation. Power is increased in two stages to ensure the heating rate meets the standard.

[0068] In some embodiments, the fourth heating power P4 = K × P3; K: solder correction factor (lead-free 1.05, low temperature 1.03, eutectic 1.10). In traditional fixed power processes, low temperature solders are prone to Bi segregation (shear strength decreases by 30%) due to excessive power, while eutectic solders are prone to insufficient melting (void rate ≥5%) due to insufficient power. By adjusting the K value, both reliability and low void rate are considered.

[0069] The solder transitions from "semi-melted" to "fully melted and wetted" by using the fourth heating power P4, which is a constant peak power and gradient pressure. The solder is fully melted, the bubbles are compressed and contracted, and a uniform solder layer is formed.

[0070] In some embodiments, the defoaming formula is:

[0071] P5 = P4 × (P 正压 / P 真空 ) 0.3 ;

[0072] P 真空 Vacuum stage pressure, P 正压： Positive pressure. Compensates for heat loss in a vacuum environment and maintains the solder in a molten state.

[0073] In some embodiments, the full-fusion positive pressure formula is:

[0074] P 正压 = 0.1 + 2×δ; δ: solder thickness. Positive pressure is linearly positively correlated with solder thickness. Thicker solder has more difficulty for air bubbles to escape, requiring higher pressure to compress the bubble volume and reduce bubble stability.

[0075] For example: δ=0.1mm: P 正压 =0.1 + 2 × 0.1 = 0.3 MPa;

[0076] δ=0.2mm: P 正压 =0.1+2×0.2=0.5MPa.

[0077] In some embodiments, the full-melting insulation formula is:

[0078] t 保温 = 30 + 100×δ; δ: solder thickness. The basic holding time is 30s (to ensure the melting of thin solder). For every 0.1mm increase in thickness of the solder, the holding time is extended by 10s to ensure sufficient heat transfer inside the solder and avoid "external melting and internal solidification".

[0079] For example: δ=0.1mm: t 保温 =30+100×0.1=40s.

[0080] For every 0.1mm increase in thickness of the solder, the holding time is extended by 10 seconds to ensure sufficient heat transfer within the solder, avoid "external melting and internal solidification," and effectively compress air bubbles inside the thick solder.

[0081] In some embodiments, the heating rate formula is:

[0082] V = 3.0 - 5 × δ; δ: solder thickness. The heating rate calculated by the heating rate formula reduces the internal and surface temperature difference.

[0083] For example: δ=0.1mm: V=3-5×0.1=2.5℃ / s;

[0084] δ=0.2mm: V=3-5×0.2=2℃ / s

[0085] In some embodiments, the cooling step performed in the vacuum welding furnace specifically involves:

[0086] S201, the fifth heating power P5 is reduced to the sixth heating power P6, and cooling is achieved at T. 熔点 -10℃; Significantly reduce power (30% reduction), quickly exit the melting zone; P6=0.7×P5;

[0087] S202, the sixth heating power P6 is reduced to the seventh heating power P7, and the temperature is cooled to 145-155℃; P7 = 0.5 × P6. Moderate power reduction (50% reduction) is used to control mid-solidation stress.

[0088] S203, the seventh heating power P7 is reduced to the eighth heating power P8, and the temperature is cooled to 75-85℃; P8 = 0.3 × P7; the temperature is slowly reduced to a safe temperature.

[0089] S204. Gradually backfill with nitrogen until the temperature and pressure are normal, then remove the workpiece.

[0090] By using a "three-stage power reduction and solder thickness-adapted cooling rate", a smooth transition from "complete melting" to "solid solidification" of the solder is achieved. The aim is to control the solidification rate, reduce thermal stress, avoid void expansion and solder joint defects, and ultimately ensure the mechanical properties and reliability of the solder joint.

[0091] like Figure 3 As shown, a welding apparatus for a vacuum welding furnace includes:

[0092] The micro-negative pressure module 301 is used to evacuate the vacuum welding furnace and reduce the pressure of the vacuum welding furnace to a micro-negative pressure.

[0093] The first preheating module 302 is used to set the first heating power P1 according to the power calculation formula, heat up to the first preheating temperature T1 according to the solder type using the first heating power P1, and set the preheating and heat preservation time according to the solder thickness.

[0094] The second and third preheating modules 303 are used to determine the heating rate according to the heating rate formula, the second heating power P2 and the heating rate to heat to the second preheating temperature T2, and the third heating power P3 and the heating rate to heat to the third preheating temperature T3.

[0095] The full-fusion module 304 is used to raise the temperature of the fourth heating power P4 to the peak temperature, and simultaneously purge nitrogen to the set positive pressure P according to the full-fusion positive pressure formula. 正压 The full fusion insulation time is determined according to the full fusion insulation formula;

[0096] The degassing module 305 is used to obtain the fifth heating power P5 according to the degassing formula, quickly evacuate the vacuum and obtain the degassing and heat preservation time according to the degassing time formula, and degas and maintain heat according to the degassing and heat preservation time.

[0097] Cooling module 306 is used in the vacuum welding furnace to perform the cooling step.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welding method in a vacuum welding furnace, characterized in that, include: The vacuum welding furnace is evacuated to reduce the pressure to a slight negative pressure of 80-100 kPa. The first heating power P1 is set according to the power calculation formula. The temperature is raised to the first preheating temperature T1 according to the solder type using the first heating power P1. The preheating and holding time is set according to the solder thickness. The power calculation formula is as follows: First heating power P1 = (C w ·m w + C f ·m f + C s ·m s )·V1 / η C w Specific heat capacity of the workpiece; m w : Workpiece quality; η: Thermal efficiency; C s Specific heat capacity of solder; m s Solder quality; C s Specific heat capacity of vacuum welding furnace; m f Effective quality of vacuum welding furnace; The heating rate is determined according to the heating rate formula. The second heating power P2 and the heating rate raise the temperature to the second preheating temperature T2, and the third heating power P3 and the heating rate raise the temperature to the third preheating temperature T3. The second heating power P2 is 1.18-1.2 times the first heating power P1; the third heating power P3 is 1.08-1.1 times the second heating power P2. The heating rate formula is as follows: V = 3.0 - 5 × δ; δ: solder thickness in mm; The fourth heating power P4 is raised to the peak temperature, and nitrogen is simultaneously charged to the set positive pressure P according to the full melting positive pressure formula. 正压 The full fusion insulation time is determined according to the full fusion insulation formula; The full-fusion positive pressure formula: P 正压 = 0.1 + 2×δ; δ: solder thickness in mm; The full-melt insulation formula: t 保温 = 30 + 100×δ; δ: solder thickness in mm; The fifth heating power P5 is obtained according to the degassing formula. A rapid vacuum is then created, and the degassing and heat preservation time is obtained according to the degassing time formula. Degassing and heat preservation are then performed based on the degassing and heat preservation time. The degassing formula is as follows: P5= P4 × (P 正压 / P 真空 ) 0.3 ; P 真空 Vacuum stage pressure, in MPa; P 正压： Positive pressure, expressed in MPa; The formula for foam removal time is as follows: t 排泡 = 15 + 50×δ; δ: Solder thickness value, in mm; The vacuum welding furnace performs a cooling step.

2. The welding method in the vacuum welding furnace according to claim 1, characterized in that, The first preheating temperature T1=T 熔点 -Δt,T 熔点 Solder melting point temperature; Δt = 50-80℃.

3. The welding method in the vacuum welding furnace according to claim 1, characterized in that, The fourth heating power P4 = K × P3; K: solder correction coefficient.

4. The welding method in the vacuum welding furnace according to claim 1, characterized in that, The cooling step performed in the vacuum welding furnace is specifically as follows: The fifth heating power P5 is reduced to the sixth heating power P6, and the temperature is cooled to T. 熔点 -10℃; The sixth heating power P6 is reduced to the seventh heating power P7, and the temperature is cooled to 145-155℃; The seventh heating power P7 is reduced to the eighth heating power P8, and the temperature is cooled to 75-85℃; Gradually backfill with nitrogen until the temperature and pressure are normal, then remove the workpiece.

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