A regression orthogonal test method for adjusting temperature curve of vacuum vapor phase reflow soldering

Abstract

A regression orthogonal test method for adjusting vacuum reflow soldering temperature curve is disclosed. The method combines the advantages of orthogonal test design method and regression analysis, analyzes the factors affecting the vacuum reflow soldering temperature curve, selects appropriate test points in the test range of each factor, and quickly and accurately constructs a regression model with high precision and good fitting of the actual vacuum reflow soldering curve with fewer test times. The regression coefficients obtained are not affected by the units and values of the factors, thereby simplifying the regression calculation amount and breaking through the limitations of the original orthogonal table selection, and the method is more flexible and convenient to use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic assembly process of aerospace products, and particularly relates to a method for adjusting a temperature curve of vacuum vapor phase reflow soldering. BACKGROUND

[0002] Currently, there are three ways to realize reflow soldering. First, hot air reflow soldering, which sets temperature values of each temperature zone and track speed to realize hot air reflow soldering through track transmission of printed circuit board assembly. In this way, disturbance soldering points are easily formed in the welding process due to mechanical transmission, the closed environment is not good, the temperature compensation efficiency is low, the heat quantity of heat convection by hot air makes the temperature gradient of each temperature zone large, the temperature control precision is poor, and it is not easy to adjust the ideal temperature curve. Second, vapor phase reflow soldering, which places the printed circuit board on a bracket, controls the upward moving speed of the bracket from the bottom, and realizes reflow soldering of the solder paste coated on the solder pad of the printed board by vapor phase liquid vaporization and deposition in the heating furnace. In this way, disturbance soldering points are easily formed in the welding process due to the upward and downward movement of the bracket, compared with hot air reflow soldering, vapor phase reflow soldering is conducive to the whole printed circuit board to reach thermal equilibrium through vapor phase liquid deposition, and good wetting soldering points are formed. However, with the increase of the size, thickness and large area copper area of the printed board, in order to meet the thermal equilibrium of the smallest 0201 package to the largest thermal capacity device on the whole board and the soldering quality of lead-free CBGA and BGA, the reflow soldering needs longer time and higher soldering temperature, the formed soldering points are oxidized and the surface is not smooth, which increases the BGA soldering cavity rate and affects the soldering quality and reliability. Third, vacuum vapor phase reflow soldering, which transports the printed board to the furnace stably without moving by placing the printed board on the bracket, and realizes the vapor phase reflow soldering process of the printed circuit board assembly in the vacuum environment by setting the vacuum degree to adjust the vapor phase liquid injection quantity parameters of different temperature zones. In this way, the printed circuit board does not move in the welding process, which is conducive to the wetting and forming of the soldering points, the vacuum degree is increased, the surface tension and oxidation degree of the soldering points are effectively controlled, and the soldering quality defects such as cavity, bubble and bridging are reduced. The thermal stability of reflow soldering is better in the closed environment, and the temperature control precision is higher. However, the interaction complexity of the vacuum degree, vapor phase liquid injection quantity and temperature zone interval makes the uncertainty of the open-loop temperature curve function relationship, which greatly increases the difficulty of adjusting the temperature curve, there are many problems such as poor index, poor shape and adjustment method not mastered in frequent adjustment of the temperature curve, the process preparation time is increased, the production efficiency is low, the cost of the large consumption of vapor phase liquid is increased, the process parameters are unstable, the process process capability is low, and the needs of flexible production of multi-variety and small batch rapid switching mode are not met. Therefore, based on the third way, only the temperature curve of the Sn63Pb37 solder paste recommended by the manufacturer is suitable for hot air reflow soldering, vapor phase reflow soldering and the industry standard, and the engineering practice guidance of the vacuum vapor phase reflow soldering temperature curve process technology is not strong.

[0003] The existing reflow soldering process, such as the Chinese invention with the application publication number CN107124835B and the authorization date of August 30, 2019, discloses a reflow soldering process, which includes the following steps: printing solder paste, patching, intermediate inspection, reflow soldering, and post-furnace inspection. By reducing the pressure during reflow soldering, the formation of large bubbles that form cavities during the soldering process can be avoided, or the escape of large bubbles that cause explosive exhaust can be avoided, and many small tin beads can be brought out. By reducing the pressure in the soldering area, small bubbles during the soldering process can easily escape, and it is not easy to form large bubbles and splash tin beads. In one reflow soldering process, the time in the soldering area is specified to be 30s-90s, the temperature is greater than 150℃, the pressure reduction time is 30s-50s, and the minimum air pressure is reduced to 40mbar-2mbar. When adjusting the temperature using a vacuum vapor phase reflow soldering device according to this process parameter, first, the liquid phase time in the soldering area is 30s-90s, which belongs to the general reflow soldering liquid phase time range. Currently, BGA and CBGA are the core of key devices in product applications, and BGA solder balls generally use lead-free materials that are easy to oxidize. It is necessary to reduce the soldering cavity defects and the degree of oxidation by vacuum pumping. The lower the vacuum degree, the longer the liquid phase time in the soldering area. At the same time, the soldering temperature of lead solder paste soldering lead-free devices needs to be controlled in the range of 230℃-235℃, and the vapor liquid boiling point is 240℃. The closer the temperature is to the boiling point, the longer the temperature rising time. However, the liquid phase time in the soldering area of 30s-90s cannot meet the soldering requirements of BGA and CBGA lead-free devices for vacuum vapor phase reflow soldering; secondly, 120℃-150℃ is the reflow soldering holding area in the solder paste solvent volatilization stage. At this time, the air pressure change in the vacuum furnace causes the furnace temperature to first overshoot downward and then rise for 20s-30s. The long holding time causes the solvent in the solder paste to volatilize excessively, reducing the wettability, capillary action, and spreading ability of the molten solder during the soldering stage; finally, the minimum vacuum degree is 40mbar-2mbar, which requires multiple gradient pumping. If the vacuum is pumped too fast at one time, it will cause a sudden change in the vacuum pressure in the furnace, causing displacement, tilting, and solder bridging of components and other soldering defects due to stress changes caused by vacuum pumping. SUMMARY

[0004] The technical problem solved by the present application is to overcome the shortcomings of the prior art and provide a regression orthogonal test method for adjusting the temperature curve of vacuum vapor phase reflow soldering, which realizes the fine adjustment of the temperature curve of vacuum vapor phase reflow soldering, is particularly suitable for multi-variety and batch production, meets the needs of flexible production of printed circuit board assemblies with different product input characteristics, reduces rework, and improves the soldering quality and reliability of products.

[0005] Full play the role of vacuum degree in reflow soldering, reduce oxidation, reduce surface tension, improve the quality of soldering wet, through variance analysis fitting optimization regression equation model, more scientific and effective guidance process or engineering and technical personnel to find the objective law of the mapping of each factor level change in the device to the test result data, in the case of complex printed board and component characteristics, to achieve a fast and good method to master the adjustment of vacuum vapor phase reflow soldering temperature curve. Solve the vacuum degree when the occasion is not correct, vacuum degree is not quantized, open loop temperature system of vapor phase liquid injection temperature control precision is not high, the complexity of the interaction of each influencing factor is high, the adjustment time is long and difficult to master. Design the vacuum vapor phase reflow soldering temperature curve characteristic selection table, let the process personnel be liberated from the complex one-time adjustment of the temperature curve, according to the input characteristics of components and printed boards, quickly match the best temperature curve from the applied product types and reference pictures, thereby greatly reducing the number of process tests and production preparation time, improving process process capability, ensuring process parameter stability and product consistency, especially suitable for multi-species and batch production.

[0006] The technical scheme provided by the application is as follows:

[0007] A regression orthogonal test method for adjusting a vacuum vapor phase reflow soldering temperature curve, comprising:

[0008] S1, determining the key parameters of vacuum vapor phase reflow soldering as vacuum degree, peak temperature and liquid phase time according to product input characteristics, wherein the product input characteristics include printed board characteristics and component characteristics;

[0009] S2, making a process board according to the printed board characteristics, setting process parameters according to the key parameters determined in S1, wherein the process parameters include multiple temperature segments; using the process board to perform vacuum vapor phase reflow soldering according to the process parameters and collecting temperature in real time to obtain a time-temperature waveform;

[0010] determining a pass criterion;

[0011] determining the running time and heating rate of each temperature segment according to the temperature segments and the waveform;

[0012] comparing the running time and heating rate of each temperature segment with the pass criterion, if the pass criterion is met, the temperature curve of the temperature segment does not need to be adjusted, and S6 is entered; if the pass criterion is not met, the temperature curve of the temperature segment is adjusted according to S3;

[0013] S3, for a temperature segment that does not meet the pass criterion, determining the main factors of the regression orthogonal test as vacuum degree, temperature interval and vapor phase liquid injection amount; calculating the upper level, zero level and lower level of each main factor, and calculating the corresponding code level according to the upper level, zero level and lower level of each factor;

[0014] According to the coding level, a plurality of test schemes of the regression orthogonal design are selected in a regression orthogonal test table; according to the plurality of test schemes of the regression orthogonal design, experiments are sequentially performed by using the process board to obtain test index results;

[0015] According to the test index results and the regression equation, equation coefficients are calculated and obtained, and the equation coefficients correspond to the main factors;

[0016] S4, according to the regression equation and the equation coefficients of S3, the F distribution value of each main factor is calculated, the significance test of the F distribution value is performed, and the result is that the main factor is a key factor or a non-key factor, the corresponding coefficient of the key factor is determined according to the regression equation in S3, the sign of the corresponding coefficient of the key factor is determined according to the sign of the corresponding coefficient of the key factor, and the regression equation after the arrangement is determined; according to the regression equation after the arrangement, updated process parameters are calculated and obtained; the updated process parameters include the temperature response time, the temperature interval and the vapor phase liquid injection amount;

[0017] S5, the temperature response time, the temperature interval and the vapor phase liquid injection amount obtained in S4 are compared with the qualified criterion determined in S2, if the temperature response time, the temperature interval and the vapor phase liquid injection amount do not meet the qualified criterion, S3 and S4 are repeated, and each time the iteration is performed on the four process parameters of the temperature response time, the temperature interval, the vapor phase liquid injection amount and the liquid phase time until the temperature response time, the temperature interval and the vapor phase liquid injection amount meet the qualified criterion;

[0018] S6, after each temperature segment of the temperature curve meets the qualified criterion, the process parameters finally determined are modified and saved in the vacuum vapor phase reflow soldering equipment, and the temperature curve debugging mode is exited.

[0019] Optionally, in S2, the process parameters further include the vacuum degree, the vapor phase liquid injection amount, the exhaust time and the liquid phase time;

[0020] The qualified criterion includes the temperature rise rate and the temperature rise time range.

[0021] The temperature rise rate is calculated according to the lowest temperature, the highest temperature and the running time in the temperature segment.

[0022] Optionally, the process parameters are set according to the reflow soldering key parameters determined in S1, including:

[0023] The product input characteristics include component characteristics and printed board characteristics, the component characteristics are the packaging form of the component, and the component pin soldering end and the packaging material, the specific heat capacity can be determined according to the packaging form of the component; the printed board characteristics are the printed board area, the printed board layer number, the printed board thickness and the printed board copper clad area.

[0024] According to the component characteristics and the oxidation degree of the component pin soldering end, the vacuum degree process parameter is determined;

[0025] According to the component characteristics and the percentage of lead in the solder paste, the peak temperature process parameter is determined;

[0026] According to the product input characteristics, the vacuum degree and the peak temperature, the liquid phase time process parameter is determined;

[0027] According to the reflow soldering temperature curve recommended by the solder paste manufacturer and the component manufacturer, the temperature segmentation is determined, and the temperature interval of each temperature segmentation is obtained;

[0028] According to the component characteristics and the printed board characteristics, the evacuation time of the vacuum vapor phase reflow soldering is determined, and the cooling rate process parameter is determined.

[0029] Optionally, the main factors of the regression orthogonal test are the vacuum degree, the temperature interval and the vapor phase liquid injection amount, and the method comprises the following steps:

[0030] The level of the vacuum degree is the vacuum degree range of a temperature segmentation which does not satisfy the qualified criterion;

[0031] The level of the temperature interval is the temperature interval of a temperature segmentation which does not satisfy the qualified criterion;

[0032] The level of the vapor phase liquid injection amount is the vapor phase liquid injection amount range of a temperature segmentation which does not satisfy the qualified criterion.

[0033] Optionally, the upper level of each main factor is the maximum value of the corresponding value interval, the lower level is the minimum value of the corresponding value interval, and the zero level = (the upper level + the lower level) / 2.

[0034] Optionally, in the S3, the regression equation is:

[0035] t = a ± b1V1 ± b2V2 ± b3V3 ± b 12 V1V2 ± b 13 V1V3,

[0036] Wherein, V1 is the vacuum degree; V2 is the temperature interval; V3 is the vapor phase liquid injection amount; t is the temperature rising response time;

[0037] n = m0 + m c , wherein n is the test number, m0 is the zero level test number, and m c is the test number defined by the orthogonal table;

[0038] Wherein, a is the regression equation constant, t i is the temperature rising response time of each test, and n is the test number;

[0039] Wherein, b1 is the partial regression coefficient of vacuum in the regression equation, is the vacuum of each test, m c is the test number defined by the orthogonal table;

[0040] Wherein, b2 is the partial regression coefficient of temperature interval in the regression equation, is the temperature interval of each test, m c is the test number defined by the orthogonal table;

[0041] Wherein, b3 is the partial regression coefficient of vapor phase liquid injection amount in the regression equation, is the vapor phase liquid injection amount of each test, m c is the test number defined by the orthogonal table;

[0042] Wherein, b 12 is the partial regression coefficient of the interaction between vacuum and temperature interval in the regression equation, (V1V2) i is the interaction between vacuum and temperature interval of each test, m c is the test number defined by the orthogonal table;

[0043] Wherein, b 13 is the partial regression coefficient of the interaction between vacuum and vapor phase liquid injection amount in the regression equation, (V1V3) i is the interaction between vacuum and vapor phase liquid injection amount of each test, m c is the test number defined by the orthogonal table.

[0044] Optionally, in S4, according to the regression equation and equation coefficients of S3, the F distribution value of each main factor is calculated, the significance test of the F distribution value is performed, and the result is that the main factor is a key factor or a non-key factor; according to the key factor and the regression equation in S3, the corresponding coefficient of the key factor is determined, according to the positive or negative sign of the corresponding coefficient of the key factor, the regression equation after arrangement is determined; according to the regression equation after arrangement, the temperature response time, the temperature interval and the vapor phase liquid injection amount are calculated, including:

[0045] According to the regression equation and equation coefficients of S3, the partial regression sum of squares of each main factor is calculated; the total sum of squares is calculated; the total partial regression sum of squares is calculated according to the partial regression sum of squares of each main factor; the residual sum of squares is calculated according to the total sum of squares and the total partial regression sum of squares; the degrees of freedom and the mean square value are calculated according to the partial regression sum of squares of each main factor; the F distribution value of each main factor is calculated according to the mean square value and the residual sum of squares;

[0046] Under the condition of a given significant level α, the significance test of F distribution value is performed on each main factor to determine whether the main factor is a key factor or a non-key factor;

[0047] The key factor is substituted into the regression equation in S3 to obtain a simplified regression equation; the positive or negative sign of the coefficient of the key factor in the simplified regression equation is found, and when the coefficient takes a positive sign, it indicates that the upper level of the key factor has a significant influence on the test index result; when the coefficient takes a negative sign, it indicates that the lower level of the key factor has a significant influence on the test index result;

[0048] According to the positive or negative sign of the coefficient of the key factor, the corresponding code is calculated, and the simplified regression equation is substituted back according to the corresponding code to establish a sorted regression equation;

[0049] According to the sorted regression equation, the temperature response time, temperature interval and vapor phase liquid injection amount are calculated and obtained.

[0050] Optionally, in S4, the total sum of squares is: Wherein, SS T is the total sum of squares, m c is the number of tests defined by the orthogonal table

[0051] Partial regression sum of squares:

[0052] Wherein, SS1 is the partial regression sum of squares of vacuum degree, m c is the number of tests defined by the orthogonal table, and b1 is the partial regression coefficient of vacuum degree in the regression equation;

[0053] Wherein, SS2 is the partial regression sum of squares of temperature interval, m c is the number of tests defined by the orthogonal table, and b2 is the partial regression coefficient of temperature interval in the regression equation;

[0054] Wherein, SS3 is the partial regression sum of squares of vapor phase liquid injection amount, m c is the number of tests defined by the orthogonal table, and b3 is the partial regression coefficient of vapor phase liquid injection amount in the regression equation;

[0055] Wherein, SS 12 is the partial regression sum of squares of the interaction between vacuum degree and temperature interval, m c is the number of tests defined by the orthogonal table, and b 12 is the partial regression coefficient of the interaction between vacuum degree and temperature interval in the regression equation;

[0056] Wherein, SS 13Partial regression sum of squares for interaction between vacuum and temperature interval, SS c Number of tests defined by orthogonal table, b 13 Partial regression coefficient for interaction between vacuum and temperature interval in regression equation, SS 12 Partial regression sum of squares for interaction between vacuum and temperature interval, SS

[0057] Total partial regression sum of squares:

[0058] SS R = SS1 + SS2 + SS3 + SS 12 + SS 13 , where SS R is total partial regression sum of squares, SS1 is partial regression sum of squares for vacuum, SS2 is partial regression sum of squares for temperature interval, SS3 is partial regression sum of squares for vapor injection amount, and SS 13 is partial regression sum of squares for interaction between vacuum and vapor injection amount.

[0059] Residual sum of squares:

[0060] SS e = SS T - SS R , where SS e is residual sum of squares, SS T is total sum of squares, and SS R is total partial regression sum of squares.

[0061] Degrees of freedom:

[0062] df R = ∑df 一次项 + ∑df 交互项 = m, where ∑df 一次项 is partial regression sum of squares for each factor, and ∑df 交互项 is partial regression sum of squares for interaction factors.

[0063] df e = ∑df T - df R = n - 1 - m, where df e is residual degrees of freedom, ∑df T = n - 1, and n is number of tests.

[0064] Mean square value:

[0065] where MS i is mean value for each factor or interaction factor, SS i is partial regression sum of squares for each factor and interaction factor, and df i is degrees of freedom for each factor and interaction factor.

[0066] Wherein, MS e is the mean of the residuals, SS e is the sum of squares of the partial regression of the residuals; df e is the degree of freedom of the residuals;

[0067] F distribution value:

[0068] Wherein, F i is the F distribution value, MS i is the mean of each factor or interaction factor, MS e is the mean of the residuals.

[0069] Optionally, in S4, at least one F distribution value significance test is performed on each main factor, and the judgment result of each main factor is a key factor or a non-key factor, comprising:

[0070] The F critical value at the significant level α=0.05 and α=0.01 is obtained by querying the regression orthogonal test table, and the F distribution value of the parameter is compared with the F critical value, and the judgment result of each main factor is a significant factor or a non-significant factor;

[0071] The degree of freedom of the partial regression sum of squares of the non-significant factor is incorporated into the residual sum of squares parameter, the F distribution value of each parameter is recalculated, and the F distribution significance test is performed again, and the judgment result of each significant factor is a key factor or a non-key factor.

[0072] The orthogonal regression test design method solves the problem that the traditional orthogonal test can only be limited to a certain process level, but not the optimization scheme of the process parameters in a certain process parameter range, discovers the law between the levels of the influencing factors with reasonable test design and fewer test times, establishes a mathematical model of the fitting regression equation, accurately predicts the test index result, determines the significance and change trend of the influencing factors through F distribution variance analysis, and simplifies the regression equation.

[0073] The present application solves the problems of the interaction complexity of the vacuum degree, the vapor phase liquid injection amount, the temperature interval and the exhaust time process parameters, the problem that the method of frequent adjustment of the temperature curve is not mastered and the index is not good, iteratively optimizes the process parameters to improve the temperature control precision of the vapor phase liquid injection amount, realizes the fine requirement of adjusting the vacuum vapor phase reflow soldering temperature curve, thereby greatly reducing the test times and the production preparation time, improving the process process capability, ensuring the process parameter stability and the product consistency, and being especially suitable for multi-variety and batch production, meeting the needs of flexible production of printed circuit board assemblies with different product input characteristics, and improving the welding quality and reliability of the products.

[0074] The regression orthogonal test method for adjusting a vacuum vapor phase reflow soldering temperature curve has the following beneficial effects:

[0075] (1) The regression orthogonal test method for adjusting a vacuum vapor phase reflow soldering temperature curve provided by the present application combines industry standards and temperature curve parameters recommended by mainstream solder paste manufacturers, designs a vacuum vapor phase reflow soldering temperature curve graph, defines a vacuum reflow soldering process: heating (A) → holding (B1) → overage (B2) → reflow soldering (C) → cooling (D), gives a vacuum vapor phase reflow soldering qualification criterion method and core temperature points, and through the explanation of the welding quality of each technical index parameter of the temperature curve, helps process and engineering technical personnel to understand and master, can quickly and effectively analyze welding defect problems and position accurately, meets the technical index parameters of the vacuum vapor phase reflow soldering temperature curve, and the adjustment method is good and fast.

[0076] (2) The regression orthogonal test method for adjusting a vacuum vapor phase reflow soldering temperature curve provided by the present application gives a setting method of the time and vacuum degree, and a setting method of the exhaust cooling time before the peak temperature of the reflow soldering starts to drop to the circuit board, reduces the difficulty of increasing the test times and adjusting the curve due to unsuitable process parameters, and improves the welding quality and reliability of BGA, CBGA and CCGA packaging core key devices.

[0077] (3) The regression orthogonal test method for adjusting a vacuum vapor phase reflow soldering temperature curve provided by the present application compares the test data and index requirement criteria of each temperature zone, finds the critical and out-of-tolerance data, uses the regression orthogonal test design method to establish a regression equation with good fitting goodness, finds the mapping relationship between each factor level and the index, sets the index to calculate the injection amount of the vapor phase liquid, gives the injection amount range of the vapor phase liquid in each temperature zone, improves the control precision of the vapor phase liquid, reduces waste, saves cost and environmental pollution.

[0078] (4) The regression orthogonal test method for adjusting a vacuum vapor phase reflow soldering temperature curve provided by the present application creates a characteristic selection table and a process parameter table of the vacuum vapor phase reflow soldering temperature curve, and liberates process or engineering technical personnel from the difficult and complex work of adjusting the temperature curve, on the one hand: reduces the temperature curve adjustment time, avoids continuous adjustment of the curve for more than 2 hours, inhales too much flux residue and vapor phase liquid volatile gas, and causes respiratory diseases and other HSE occupational health problems; on the other hand: reduces the process test times and production preparation time, improves the work efficiency, makes the process capacity sufficient, and ensures the quality and reliability of the product. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0080] Figure 2 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0081] Figure 3 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0082] Figure 4 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0083] Figure 5 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0084] Figure 6 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0085] Figure 7 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0086] Figure 8 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0087] Figure 9 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application;

[0088] Figure 10 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application; DETAILED DESCRIPTION

[0089] In order to make the purpose, technical scheme and advantages of the present application more clear, the following will combine the drawings to make a further detailed description of the disclosed embodiments of the present application.

[0090] Figure 1 is a schematic diagram of a vacuum vapor phase reflow soldering temperature curve of the present application, which is divided into four parts, i.e. a temperature rising zone (A), a preheating and holding zone (B1, B2), a reflow soldering zone (C) and a cooling zone (D), as shown in Table 1.

[0091] Table 1: Parameter explanation of vacuum vapor phase reflow soldering zone

[0092]

[0093] A good temperature curve should have the following characteristics:

[0094] 1) The key to a good temperature curve is the BGA soldering quality.

[0095] 2) The maximum thermal capacity on the printed circuit board and the minimum capacity at the end of preheating temperature intersection point, that is, the whole board temperature reaches thermal equilibrium;

[0096] 3) The highest peak temperature on the whole board meets the heat resistance requirements of components and devices, and the lowest peak temperature meets the requirements of solder joint formation;

[0097] 4) The difference between the highest temperature and the lowest temperature on the BGA package is less than 5℃, and generally not more than 7℃

[0098] 5) The difference between the set temperature and the welding peak temperature determines the strain and welding stress of the components on the printed board, which is usually more important than the heating rate or cooling rate;

[0099] 6) The shorter the LTD, the longer the True TAL.

[0100] The longer the LTD, the more serious the BGA package temperature difference and the more serious the deformation, and the more likely to occur ball hole defect (HoP) and shrinkage fracture; The shorter the True TAL, the shorter the time of liquid coexistence of solder balls in the center and periphery, and the more likely to occur ball hole defect (HoP), therefore, the shorter the LTD, the longer the True TAL.

[0101] 7) According to the reflow soldering temperature curve and core temperature point recommended by the solder paste manufacturer and component manufacturer, combined with the actual printed circuit board and component characteristics, select the temperature section, recommend the core temperature parameter setting, such as Table 2.

[0102] According to the core temperature point, determine the temperature section, and obtain the temperature interval of each temperature section;

[0103] Table 2 Core temperature parameters

[0104]

[0105]

[0106] The starting temperature is the ambient temperature (23±5)℃, and the end of heating is the peak temperature of 230℃. The peak temperature of lead-free BGA is 235℃, and the actual core temperature point is set to 230℃. The temperature is cooled from 230℃ to 235℃ by vacuumizing in the last temperature section.

[0107] Figure 2 A kind of vacuum vapor phase reflow soldering temperature curve in vacuum interface schematic diagram;It is divided into 3 stages of vacuum, ① pre-vacuum (Pre Vac), ② process vacuum (vacuum in each temperature process), ③ final vacuum (Final Vac) (vacuum after the last vapor phase liquid injection soldering is completed);

[0108] ① Pre Vac, the whole process of printed circuit board from entering the furnace to the furnace is applied vacuum, vacuum degree does not affect the temperature curve singularity of the intermediate process (heating, holding, reflow soldering);

[0109] ② Vacuum in each temperature zone, selectively applied vacuum in each temperature zone, increase the temperature gradient to change the temperature curvature, especially in the eutectic point near the temperature in the unstable process, if the vacuum degree is not suitable, it will affect the soldering quality;

[0110] ③ Final Vac, using the principle of boiling point reduction of vapor phase liquid during vacuum extraction to produce temperature overshoot to meet the peak temperature requirement, such as: lead-free BGA requires peak temperature 235℃, by setting the core temperature of the last segment to 230℃, increasing the final Vac vacuum degree, the temperature can rise from 230℃ to 235℃ ~ 238℃.

[0111] Vacuum degree will accelerate the reflow soldering temperature curvature change, lower vacuum degree will increase the liquid phase time, making the solder flux in the solder paste inactivated too much, the solder joint is not smooth, wrinkled and other appearance defects. Too fast vacuum extraction speed and too large valve opening will cause the surface mounted components to displace under the action of external force, and the solder paste will splash out to form tin beads and other defects. The recommended parameters are as follows:

[0112] 1) Vacuum degree gradient setting

[0113] When the vacuum degree is less than 200mbar, at least 3 segment gradient vacuum extraction;

[0114] When the vacuum degree is 200mbar ~ 500mbar, at least 2 segment gradient vacuum extraction;

[0115] When the vacuum degree is 500mbar or more, at least 1 segment gradient vacuum extraction.

[0116] 2) Vacuum degree holding time: 15s ~ 25s;

[0117] 3) Valve opening proportion: 20% ~ 50%.

[0118] Figure 3 Pre Vac is the vacuum extraction process in the vacuum vapor phase reflow soldering temperature curve, the vacuum extraction time is controlled in 15s ~ 25s, with the lower vacuum degree, the longer holding time, the more obvious the change trend of the soldering temperature downward and then upward;

[0119] Figure 4is a schematic diagram of the temperature curve adjustment curve of vacuum vapor phase reflow soldering. The injection of the overall vapor phase liquid in the control of several temperature zones is controlled while the injection amount of the last temperature zone is also controlled. The test data analysis shows that the last stage is not the more injection amount, the higher temperature and the faster temperature rise. This is because the cold vapor phase liquid injection into the cavity needs a certain transition time to stabilize the vapor phase temperature in the cavity. The length of the time is related to the amount of injected vapor phase liquid, the system parameter of the equipment, and the vapor phase liquid temperature state equation. This transition time prolongs the liquid phase time. When the gas pressure is saturated and stable, the increase of the excess vapor phase liquid makes the temperature rise change slowly, and at the same time, the liquid phase time is further prolonged. The long liquid phase time leads to the formation of a thick IMC layer in the solder joint, which reduces the strength of the solder joint against mechanical stress and easily causes brittle fracture. Therefore, the most effective method is to vacuum, and to compensate the peak temperature value by using the vacuum temperature shock characteristics;

[0120] Figure 5 is a schematic diagram of vacuum vapor phase reflow soldering with two-stage cooling. The cooling 1 stage is from the peak temperature to 5-10℃ higher than the eutectic temperature of the solder paste. The cooling 2 stage is from the printed board assembly to the temperature dropping to 75℃. This stage is cooled by the external fan.

[0121] Figure 6 is a schematic diagram of the air cooling parameter setting of vacuum vapor phase reflow soldering. The Double-Stage time in the cold machine parameter is the waiting time of the carrier from the furnace to the waiting area under the fan. It is generally set to 25s±5s. When the printed board reaches the set parameter, the fan starts to work according to the set parameter, and stops working when the set parameter value is reached. The transmission table moves out of the working area, the printed circuit board is taken out, and the whole reflow soldering process is completed. The fan is set to 150s-180s for air cooling, and the temperature is generally reduced by 25-35℃.

[0122] Figure 7 is a schematic diagram of the exhaust parameter setting of vacuum vapor phase reflow soldering.

[0123] Combined with the characteristics of actual printed board and components, the temperature range of the exhaust parameter is set from the peak temperature to 5-10℃ higher than the eutectic temperature of the solder paste. The exhaust is generally set in the last stage. The exhaust in the middle stage will affect the temperature curve shape and prolong the temperature rise time of the later stage. When the cooling speed of the first stage of exhaust (stage 1) exceeds 15s, the temperature will drop by 10℃, and BGA solder joint shrinkage fracture is prone to occur. When the cooling speed of the second stage of exhaust (stage 2) is slow, it can be combined with the first stage to control the cooling speed at (0.5-3)℃ / s. The temperature is reduced to 5-10℃ higher than the eutectic temperature point when the furnace door is opened, which reduces the disturbance of the solder joint formation and the displacement of components during the carrier transmission process when the furnace door is opened.

[0124] Figure 8 is a vacuum vapor phase reflow soldering temperature curve parameter debugging mode schematic diagram, the device enters the test mode (test), the vapor phase liquid injection amount (injection1) ml of each temperature section is set, the mode (Modus) is adjusted to the temperature mode (tempture), the core temperature point is set according to table 2, and the running time h of each temperature zone is recorded during the debugging process or obtained from the derived temperature acquisition data. After the debugging is completed, the mode is switched from the temperature (tempture) to the holding time (holding), the running time t is recorded into the holding time (holding) to save the debugging program, and thus the temperature curve adjustment is completed;

[0125] Figure 9 is a vapor phase liquid and temperature zone parameter setting schematic diagram of vacuum vapor phase reflow soldering, the temperature curve is called after debugging, the program is run once before formal soldering, after confirming that the device parameters are normally operated, the normal printed board circuit board reflow soldering production is started.

[0126] The present application provides a kind of adjustment vacuum vapor phase reflow soldering temperature curve regression orthogonal test method, as shown in Figure 10 , comprising the following steps:

[0127] Step one, according to the characteristics of printed board and components as input characteristics, determine the vacuum degree, peak temperature, liquid phase time 3 key parameter range;

[0128] In this step, the process parameters of the three key parameters of reflow soldering are determined, including:

[0129] The vacuum degree process parameter is the level of vacuum degree, which is 1 mbar-999 mbar. When the component manufacturer requires not to be suitable for soldering in a vacuum environment, the vacuum degree is set to 999 mbar. When soldering surface-mounted resistors and capacitors, the vacuum degree control range is 700 mbar-999 mbar. When soldering surface-mounted resistors and capacitors, including QFP, SOP, QFN, LCCC, LGA packaged devices, the vacuum degree control range is 500 mbar-999 mbar. When soldering BGA, CBGA, CCGA packaged devices, the vacuum degree control range is 100 mbar-500 mbar. When there is a special use occasion, the vacuum degree is less than 100 mbar.

[0130] The peak temperature process parameter is the peak temperature range of general components, which is 215℃-225℃. When the pins, soldering ends and solder balls of components are lead-free materials (such as BGA lead-free solder balls), the packaging temperature range is 230℃-235℃. When there is a special use environment or requirement, execute according to the requirements of component manufacturers or technical documents.

[0131] The liquid phase time process parameter is 60s-120s, and the liquid phase time is 60s-90s in the temperature change period of 183℃-peak temperature-183℃ for the lead solder paste, and the liquid phase time is 90s-120s in the temperature change period of 217℃-peak temperature-217℃ for the lead-free solder paste.

[0132] In this step, according to the product input characteristics: component characteristics are that the component surface is lead-free BGA, and the soldering surface is mainly composed of surface-mounted resistors, capacitors, QFP, SOP, QFN and SMD packaging devices; and the printed board characteristics are that the printed board layer number is 10 layers, the printed board area is 160cm 2 , the printed board thickness is 2.5mm, and the copper area of the printed board accounts for 80% of the whole board area;

[0133] According to the product input characteristics, the process parameters of the three key parameters are determined as follows: the vacuum degree range is 100mbar-500mbar, the peak temperature range is 230℃-235℃, and the liquid phase time range is 90s-120s;

[0134] In step two, a process board is made according to the printed board characteristics, and the vacuum degree, temperature segmentation, temperature interval, vapor phase liquid injection amount and exhaust time are set to obtain the determined process parameters; and the test data of temperature collection is recorded in the debugging mode.

[0135] In this step, the process parameters are set according to the reflow soldering key parameters determined in S1, including:

[0136] The temperature segmentation process parameter is 1-6 segments, when the soldering surface-mounted resistors, capacitors, QFP, SOP packaging devices, the printed board thickness is not more than 2mm, the printed board layer number is not more than 4 layers, the printed board area is not more than 150cm 2 , and the copper area accounts for not more than 40% of the printed board area, 3-segment temperature curve is selected; when the soldering contains BGA, CBGA, CCGA, QFP, SOP, QFN, LCCC, LGA, SMD packaging devices and metal shell large heat capacity devices, the printed board thickness is not more than 3mm, the printed board layer number is 6-12 layers, and the printed board area is in the range of 150cm 2 -900cm 2 , the copper area accounts for the range of 40%-80% of the printed board area, 4-5 segments are selected; when the soldering contains BGA, CBGA, CCGA, LCCC packaging and metal shell large heat capacity devices, the printed board thickness is greater than 3mm, the printed board layer number is greater than 12 layers, and the printed board area is greater than 900cm 2 , the copper area accounts for more than 80% of the printed board area, 6 segments are selected;

[0137] Temperature interval process parameters are according to the reflow soldering temperature curve recommended by the solder paste manufacturer and component manufacturer, determine the temperature segmentation, obtain the temperature interval of each temperature segmentation, as follows:

[0138] Temperature segmentation 1: 25℃-100℃, or 25℃-120℃;

[0139] Temperature segmentation 2: 100℃-150℃, or 120℃-160℃;

[0140] Temperature segmentation 3: 150℃-180℃, or 160℃-180℃;

[0141] Temperature segmentation 4: 180℃-215℃, or 180℃-220℃;

[0142] Temperature segmentation 5: 215℃-225℃, or 220℃-230℃;

[0143] Temperature segmentation 6: 225℃-230℃, or 230℃-235℃;

[0144] Vapor phase liquid injection process parameters are in the range of 0ml-1000ml for each temperature interval, and the vapor phase liquid injection amount is determined according to the temperature segmentation; when the temperature segmentation is 1-3, the temperature is set below 180℃, and the vapor phase liquid injection amount of each segment is controlled in the range of 200ml-500ml; when the temperature segmentation is 4, the temperature setting range is 180℃-215℃ or 180℃-220℃, and the vapor phase liquid injection amount of each segment is controlled in the range of 500ml-900ml; when the temperature segmentation is 5-6, the temperature setting range is 215℃-235℃ or 220℃-235℃, and the vapor phase liquid injection amount of each segment is controlled in the range of 400ml-800ml; the total of the vapor phase liquid injection amount of 1-6 segments is controlled in the range of 1500ml-2500ml;

[0145] The exhaust time process parameter is in the range of 30s-120s, and the exhaust time is set according to different materials and components to control the cooling rate, plastic package: <=2℃ / s; ceramic: (2-4)℃ / s; mixed: (2-2.4)℃ / s; the exhaust time is divided into two stages, stage 1 frequency is 50Hz, time control in 5s-30s; stage 2 frequency is 60Hz, time control in 30s-90s;

[0146] The determination steps of the process parameters are:

[0147] Determine the vacuum degree, according to S1 in the range of 100mbar-500mbar, use 40 times magnifying lens to check whether there is oxidation on the surface of lead-free BGA soldering ball, select higher vacuum degree, determine the vacuum degree parameter as 200mbar, adopt 3-stage gradient vacuum pumping;

[0148] Determine the temperature section, select 4 or 5 sections, considering the copper area of 80%, determine the temperature section as 5;

[0149] Determine the temperature section, the vapor phase liquid injection amount of each of the first 3 sections is controlled in the range of 200ml-500ml, considering the copper area of 80%, the solder paste temperature reaches close to the eutectic point 183℃, the maximum and minimum heat capacity components on the whole board reach thermal equilibrium, a lower vapor phase liquid injection amount is set for the temperature section of 160℃-180℃ to reduce the heating rate, the vapor phase liquid injection amount of 160℃-180℃ is determined as 220ml; considering that the peak temperature of the lead-free BGA reaches 235℃ and the liquid phase time is controlled within 120s, the vapor phase liquid injection amount of the 4th temperature section in the range of 180℃-220℃ is increased to control the heating rate of 1.5℃ / s±0.1℃ / s, the vapor phase liquid injection amount control range is set as 700ml±100ml according to engineering experience, the vapor phase liquid injection amount of the 5th temperature section in the range of 220℃-230℃ is relatively reduced, the vacuum degree temperature shock physical process is used to reach the required peak temperature of 235℃, and the vapor phase liquid injection amount control range is set as 450ml±100ml according to engineering experience;

[0150] The exhaust time, the lead-free BGA body is a ceramic material, the cooling rate is controlled in the range of 2℃ / s-4℃ / s, according to engineering experience, the 1st stage is set as 50Hz, the exhaust time is in the range of 5s-30s, the exhaust time is determined as 5s, the 2nd stage is set as 60Hz, and the exhaust time is in the range of 30s-90s, the exhaust time is determined as 60s;

[0151] Specifically, in this step, first, points are taken on the process board (principle: minimum, large heat capacity, BGA center, corner), and the thermocouple is welded on the points with high-temperature solder (melting point above 260℃); second, the process parameters are determined and recorded in the equipment, the program is run empty first to preheat, and finally, the process board is placed in the equipment, the thermocouple device on the process board is inserted into the equipment sensor interface, and the correspondence between each sensor number and the temperature collection point on the process board is recorded; the temperature curve debugging mode of the equipment is entered and the real-time sampling waveform diagram is opened, and the vacuum vapor phase reflow soldering is carried out according to the determined process parameters.

[0152] The heating response time t of each temperature section is recorded, and the temperature section, the heating response time t, the liquid phase time and the peak temperature process parameters are recorded and calculated according to the temperature curve waveform diagram. The actual vacuum vapor phase reflow soldering temperature curve process record of the lead-free BGA is shown in Table 3.

[0153] Specifically, it comprises:

[0154] According to the key parameters in aerospace industry standard QJ3173 "Technical requirements for reflow soldering of aerospace electronic and electrical products" and S1, the qualified criterion is determined. The qualified criterion includes the temperature rising rate and the temperature rising time range, which is obtained according to the standard.

[0155] According to the temperature segmentation and the waveform diagram, the temperature rising response time t of each temperature interval is determined.

[0156] According to the lowest temperature, the highest temperature and the temperature rising response time t in the temperature segmentation, the temperature rising rate is calculated.

[0157] The temperature rising response time t and the temperature rising rate are compared with the qualified criterion. If the qualified criterion is met, it indicates that the temperature curve of the temperature segmentation does not need to be adjusted to enter the fifth step. If the qualified criterion is not met, the temperature curve of the corresponding temperature segmentation needs to be adjusted according to step three. That is, the temperature curve of each temperature segmentation that does not meet the qualified criterion is adjusted according to step three.

[0158] Table 3 Orthogonal test 5-segment temperature curve record table

[0159]

[0160] Step three, according to the regression orthogonal test table (the regression orthogonal test table is derived from "Test design and data processing (second edition)"), a regression equation is established to determine the influence degree of each factor. If the test data is qualified, enter step five.

[0161] In this step, the fifth temperature zone 220℃-230℃, the temperature rising response time t is 16s, 0.33℃ / s, which is judged as not meeting the standard range (8s-10s, 0.50℃ / s-0.625℃ / s). The regression orthogonal test is performed on the fifth temperature zone to determine the functional relationship between the temperature rising response time t and the three main factors of vacuum degree, temperature interval and vapor phase liquid injection amount.

[0162] Specifically, the regression orthogonal test includes:

[0163] (1) Factor level coding is performed

[0164] According to the process experience, the three main factors are determined as vacuum degree, temperature interval and vapor phase liquid injection amount. The level of the temperature interval is the temperature interval of the fifth temperature zone, which is 225℃-230℃. The level of the vacuum degree is 200mbar-400mbar. The level of the vapor phase liquid injection amount is 350ml-550ml.

[0165] The upper level, zero level and lower level of the three main factors are calculated respectively. According to the upper level, zero level and lower level of each factor, the corresponding factor level coding is calculated.

[0166] The levels of each factor are: vacuum degree x1=200mbar-400mbar, temperature interval x2=225℃-230℃, vapor phase liquid injection amount x3=350ml-550ml.

[0167] wherein x j1 is the lower level of factor x j , x j2 is the upper level of factor x j , and x j0 is the zero level of factor x j ;

[0168] wherein△j is the variation interval of factor x j ;

[0169] Taking the vacuum degree as an example, the upper level x12=400mbar and the lower level x11=200mbar are determined, and the zero level x10 is calculated as follows:

[0170] The encoding of the factor level is: linear transformation of the factor level, i.e.: wherein V j is the encoding of factor X j , also called the standard variable, X j is the natural variable of the factor, x j0 is the zero level of factor x j , and△j is the variation interval of factor x j ;

[0171] In this example, the encoding of x j2 , x j0 , and x j1 is V j2 =1, V j0 =0, and V j1 =-1, respectively, and the calculation method is as follows:

[0172] The upper level encoding is calculated as follows:

[0173] The zero level encoding is calculated as follows:

[0174] The lower level encoding is calculated as follows:

[0175] △1=x12-x10=400-300=100mbar, or△1=x10-x11=300-200=100mbar

[0176] Encode the levels of other factors, and the encoding results are shown in Table 4.

[0177] Table 4 Encoding table of factor levels

[0178]

[0179] (2) Orthogonal table selection and determination of test scheme

[0180] According to the factor level coding table, considering the interaction between factors, the orthogonal table is determined as 5 factors and 2 levels, and the orthogonal table L8(2 7 is selected from the regression orthogonal test table according to the coding obtained in the previous step. After coding conversion, Table 5 is obtained. No zero level test is performed, and the total number of tests n = m0+m c = 0 + 8 = 8. Among them, m0 is the number of zero level (0) tests, and m c is the number of tests specified by the orthogonal table.

[0181] Table 5 Regression orthogonal design test scheme and test results

[0182]

[0183]

[0184] According to the regression orthogonal design test scheme in Table 5 (including the specification variables of factor levels and the input parameters of the vacuum reflow soldering furnace), 8 experiments are performed in turn using process boards, and the test index results are obtained;

[0185] According to the test index results (temperature rise response time and peak temperature), according to the regression equation, the equation coefficients are calculated and obtained, and the intermediate process result values related to the calculation are listed, as shown in Table 6.

[0186] Table 6 Regression orthogonal design calculation table

[0187]

[0188] The regression equation is derived from the book "Test Design and Data Processing (Second Edition)". According to the regression equation:

[0189] t = a ± b1V1 ± b2V2 ± b3V3 ± b 12 V1V2 ± b 13 V1V3, the equation coefficients are calculated as follows:

[0190]

[0191] Among them,

[0192] The regression equation is obtained as:

[0193] t = 12.125 + 0.125V1 + 0.875V2 - 2.875V3 + 0.375V1V2 - 0.375V1V3

[0194] According to the absolute value of the partial regression coefficient in the regression equation, the primary and secondary order of each factor and interaction can be obtained: V3>V2>V1V2=V1V3>V1, and the priority order of the main factors affecting the temperature rising time t is the vapor phase liquid injection amount, the temperature interval, and the vacuum degree.

[0195] Step four, through the analysis of variance table (Table 7), the regression equation is obtained, the temperature rising response time t and the temperature interval are calculated to obtain the vapor phase liquid injection amount, the process parameters of the equipment are modified, the process board is used to re-perform the vacuum vapor phase reflow soldering, and the test index results (temperature rising response time and peak temperature) and the liquid phase time are recorded for interpretation, if unqualified, repeat step four, if qualified, enter step five;

[0196] In this step, the regression equation is analyzed by variance, as follows:

[0197] Total sum of squares:

[0198] Partial regression sum of squares:

[0199]

[0200] Total partial regression sum of squares:

[0201] SS R =SS1+SS2+SS3+SS 12 +SS 13 =0.125+6.125+66.125+1.125+1.125=74.625Residual sum of squares: SS e =SS T -SS R =74.875-74.625=0.25

[0202] According to the above parameters including total sum of squares, partial regression sum of squares, total partial regression sum of squares, partial regression sum of squares, residual sum of squares, degrees of freedom, mean square value and F distribution value, the calculation results of the first variance analysis table are obtained, as shown in Table 7.

[0203] Table 7 First variance analysis table

[0204]

[0205] Significance test of F distribution value:

[0206] The regression orthogonal test table (the regression orthogonal test table is derived from the book "Experimental Design and Data Processing (Second Edition)") is consulted, the F critical value when the significant level a=0.05 and a=0.01 is obtained, the F distribution value of the parameter is compared with the F critical value of the table, and the significance test judgment standard is as follows:

[0207] When F distribution value <= F critical value, it means that the factor has no significant effect on the test index result;

[0208] When F distribution value > F critical value, it means that the factor has significant effect on the test index result;

[0209] When F distribution value >> F critical value, it means that the factor has very significant effect on the test index result;

[0210] Finally, the judgment result of each main factor is significant factor or insignificant factor;

[0211] When the significance level α = 0.01 or 0.05 is given, the F distribution value of the parameters V1, V2, V3, V1V2, V1V3 is judged for significance test;

[0212] The critical value is obtained by looking up the F distribution table, and the difference between F value and critical value is compared. The greater the difference, the more significant the effect of the factor or interaction on the test result is;

[0213] In this example, F 0.05 (1,2) = 18.51, F 0.01 (1,2) = 98.49, F 0.05 (5,2) = 19.30, F 0.01 (5,2) = 99.30;

[0214] When the significance level α = 0.05, the factor V2 (temperature interval) and V3 (vapor phase liquid injection amount) have significant effect on the test index result (temperature response time t), and other factors are not significant. The partial regression sum of squares and degrees of freedom of V1, V1V2, V1V3 in the parameters are incorporated into the residual SS e , and the second variance analysis is carried out, as shown in Table 8.

[0215] Table 8 Second variance analysis table

[0216]

[0217] Looking up the F distribution table, F 0.05 (1,5) = 6.61, F 0.01 (1,5) = 16.26;

[0218] When the significance level α = 0.01 or α = 0.05, the factor V1 (vacuum degree) has no significant effect on the test index result (temperature response time t) of lead-free BGA welding in the vacuum degree range of 200-400 mbar;

[0219] When the significance level α = 0.05, the factor V2 (temperature interval) has significant effect;

[0220] When the significant level a = 0.01, the factor V3 (vapor phase liquid injection amount) has a very significant influence on the test index result (heating response time t) ;

[0221] The original regression equation is simplified, and the coding formula is obtained:

[0222] The factor V2 coefficient takes the upper level, Wherein, X2 factor is temperature interval;

[0223] The factor V3 coefficient takes the lower level, Wherein, X3 factor is vapor phase liquid injection amount;

[0224] The simplified regression equation is:

[0225]

[0226] The regression equation after arrangement is: t = -54.5625 + 0.35V2-0.02875V3

[0227] According to the range of technical index (heating response time t) in the qualified criterion, which is 8s-10s, when X2 (temperature interval) is 225℃, 227.5℃, 230℃ respectively, according to the regression equation after arrangement, the vapor phase liquid injection amount X3 is calculated and obtained, as shown in Table 9.

[0228] Table 9: Reverse calculation of vapor phase liquid injection amount

[0229]

[0230]

[0231] According to Table 9, under the condition of meeting the technical index (heating response time t) control in 8s-10s, the regression equation after arrangement is calculated, so that the vapor phase liquid injection amount is accurate to within 10ml from 450ml±100ml, the control precision of vapor phase liquid injection amount is improved from 22.2% to 2.2%, effectively reducing the waste of vapor phase liquid injection amount, and improving the temperature control precision and accuracy of the vacuum vapor phase reflow soldering adjustment method.

[0232] Step five, after the temperature curve technical index qualified criterion, exit the temperature curve debugging mode;

[0233] In this step, the 5th paragraph determines the optimized process parameters as peak temperature setting 227.5℃, actual equipment parameter setting 228℃, vapor phase liquid injection amount 559ml, and vacuum degree 400mbar, which are modified and saved in the vacuum vapor phase reflow soldering equipment.

[0234] The vacuum vapor phase reflow soldering is re-performed by using the process board, the process parameters are obtained according to the sampling data of the time-temperature waveform diagram, the peak temperature is 235.7℃ (criterion: 235℃±1℃), the liquid phase time is 102s (criterion: 90s-120s), the temperature rising response time is 8s (criterion: 8s-10s), and it is confirmed that the technical index requirements meet the qualified criterion requirements;

[0235] According to the product input characteristics, the key parameters of the temperature curve are determined, a vacuum vapor phase reflow soldering temperature curve characteristic selection table is designed, and the temperature curve is numbered, as shown in Table 10.

[0236] The key parameters of the vacuum vapor phase reflow soldering in the S1 step are determined as the vacuum degree, the peak temperature, the liquid phase time, and a vacuum vapor phase reflow soldering temperature curve process parameter table is designed, as shown in Table 11.

[0237] Combined with different product input characteristics, the iteration tables 10 and 11 are accumulated;

[0238] The process personnel are liberated from the difficult and complex one-time adjustment of the temperature curve, through the product input characteristics in Table 10 and the applied product model and picture information, the process personnel can more quickly select the most matched vacuum vapor phase reflow soldering temperature curve, so as to greatly reduce the test times and production preparation time, improve the process process capability, ensure the process parameter stability and product consistency, and the stable process process capability is particularly suitable for multi-variety and batch production, meets the needs of flexible production of printed circuit board assemblies with different product input characteristics, reduces the rework, and improves the welding quality and reliability of the product.

[0239] Table 10 Vacuum vapor phase reflow soldering temperature curve characteristic selection table

[0240]

[0241] Table 11 Vacuum vapor phase reflow soldering temperature curve process parameter table

[0242] Number: TC1

[0243]

[0244]

[0245] The above detailed description has shown, by way of illustration, the application as applied to particular embodiments and illustrative examples, but this description is not intended to limit the application to the embodiments or examples described. Those skilled in the art will be able to devise many alternative arrangements, which fall within the scope of the application, without departing from the spirit of the application. Any equivalent structure or equivalent processes that directly or indirectly incorporate the content of the specification and drawings of the application are also included in the scope of patent protection of the application. The scope of protection of the application is defined by the appended claims.

[0246] The contents not described in detail in the specification of the application are known to those skilled in the art.

Claims

1. A regression orthogonal test method for adjusting a temperature profile of vacuum reflow soldering, characterized by, The method comprises the following steps: S1, determining vacuum reflow soldering key parameters, including vacuum degree, peak temperature and liquid phase time, according to product input characteristics, the product input characteristics including printed board characteristics and component characteristics; S2, manufacturing a process board according to the printed board characteristics, and setting process parameters according to the key parameters determined in S1, the process parameters including multiple temperature segments; Using the process board to perform vacuum reflow soldering according to the process parameters and collecting temperature in real time to obtain a time-temperature waveform; Determining a qualified criterion; comparing the waveform corresponding to the temperature segment with the qualified criterion, if the qualified criterion is met, the temperature curve of the temperature segment does not need to be adjusted, and S6 is entered; if the qualified criterion is not met, the temperature curve of the temperature segment is adjusted according to S3; S3, for the temperature segment that does not meet the qualified criterion, determining main factors of a regression orthogonal test as vacuum degree, temperature interval and vapor phase liquid injection amount; calculating coding levels for the main factors; According to the coding levels, selecting multiple test schemes of the regression orthogonal design in a regression orthogonal test table; according to the multiple test schemes of the regression orthogonal design, sequentially performing experiments by using the process board to obtain test index results; According to the test index results and a regression equation, calculating to obtain equation coefficients corresponding to the main factors; S4, calculating F distribution values of each main factor according to the regression equation and the equation coefficients in S3, performing significance test according to the F distribution values to determine whether the main factors are key factors or non-key factors; determining key factor corresponding coefficients according to the key factors and the regression equation in S3; According to the positive and negative signs of the key factor corresponding coefficients, determining a sorted regression equation; calculating to obtain updated process parameters according to the sorted regression equation; S5, comparing the updated process parameters obtained in S4 with the qualified criterion determined in S2, if the updated process parameters do not meet the qualified criterion, repeating S3 and S4, and each time, iteratively performing experiments on four process parameters, including temperature rise response time, temperature interval, vapor phase liquid injection amount and liquid phase time, until the updated process parameters meet the qualified criterion; S6, after each temperature segment of the temperature curve meets the qualified criterion, taking the finally determined process parameters as the parameters of the vacuum reflow soldering.

2. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 1, wherein: In S2, the process parameters further include vacuum degree, vapor phase liquid injection amount, exhaust time and liquid phase time; The qualified criterion includes temperature rise rate and temperature rise time range; The temperature rise rate is calculated according to the minimum temperature, maximum temperature and running time in the temperature segment.

3. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 1, wherein: Setting process parameters according to the reflow soldering key parameters determined in S1, including: The product input characteristics include component characteristics and printed board characteristics, the component characteristics are packaging forms of components, and the packaging forms of the components can be used to determine component pin soldering ends and packaging materials, specific heat capacity; the printed board characteristics are printed board area, printed board layer number, printed board thickness and printed board copper clad area; Determining vacuum degree process parameters according to the oxidation degree of the component characteristics and the component pin soldering ends; Determining peak temperature process parameters according to the component characteristics and the percentage of lead in solder paste; Determining liquid phase time process parameters according to the product input characteristics, vacuum degree and peak temperature; According to the reflow soldering temperature curve recommended by the solder paste manufacturer and the component manufacturer, the temperature segments are determined, and the temperature interval of each temperature segment is obtained; According to the component characteristics and the printed board characteristics, the vacuum vapor phase reflow soldering exhaust time is determined, and the cooling rate process parameters are determined.

4. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 1, wherein: The main factors of the regression orthogonal test are vacuum degree, temperature interval and vapor phase liquid injection amount, and the regression orthogonal test comprises: The level of vacuum degree is the vacuum degree range of a temperature segment that does not meet the qualified criterion; The level of temperature interval is the temperature interval of a temperature segment that does not meet the qualified criterion; The level of vapor phase liquid injection amount is the vapor phase liquid injection amount range of a temperature segment that does not meet the qualified criterion.

5. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 4, wherein: The upper level of each main factor is the maximum value of the corresponding value interval, the lower level is the minimum value of the corresponding value interval, and the zero level=(upper level+lower level) / 2.

6. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 1, wherein, In the S3, the regression equation is: t = a ± b1V1± b2V2± b3V3± b 12 V1V2± b 13 V1V3, Wherein, V1 is the vacuum degree; V2 is the temperature interval; V3 is the vapor phase liquid injection amount; t is the temperature rising response time; n = m0+ m c where m0is the number of zero-level trials, m c is the number of trials specified by the orthogonal table; wherein a is a regression equation constant, t i is the temperature rise response time for each test, n is the number of tests; wherein b1 is the partial regression coefficient of the vacuum degree in the regression equation, is the vacuum degree of each test, m c is the number of tests specified by the orthogonal table; where b2 is the partial regression coefficient of the temperature interval in the regression equation, is the temperature interval for each test, and m c is the number of tests specified by the orthogonal table; wherein b3 is the partial regression coefficient of the vapor phase liquid injection amount in the regression equation, is the vapor phase liquid injection amount for each test, m c is the number of tests specified by the orthogonal table; wherein b 12 is the partial regression coefficient of the interaction of the vacuum degree and the temperature interval in the regression equation, (V1V2) i is the interaction of the vacuum degree and the temperature interval of each test, m c is the number of tests defined by the orthogonal table; where b 13 is the partial regression coefficient of the interaction of vacuum and the amount of injected liquid in the regression equation, (V1V3) i is the interaction of vacuum and the amount of injected liquid for each test, m c is the number of tests defined by the orthogonal table.

7. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 1, wherein: In the S4, according to the regression equation and equation coefficient of S3, the F distribution value of each main factor is calculated, the significance test of F distribution value is carried out, the judgment result is that the main factor is a key factor or a non-key factor, the corresponding coefficient of the key factor is determined according to the key factor and the regression equation in S3, and the regression equation after arrangement is determined according to the positive and negative signs of the corresponding coefficient of the key factor; According to the regression equation after arrangement, the temperature rising response time, temperature interval and vapor phase liquid injection amount are obtained, comprising: According to the regression equation and equation coefficient of S3, the partial regression sum of squares of each main factor is calculated, the total sum of squares is calculated, the total partial regression sum of squares is obtained according to the partial regression sum of squares of each main factor, the residual sum of squares is obtained according to the total sum of squares and the total partial regression sum of squares, the degrees of freedom and the mean square value are obtained according to the partial regression sum of squares of each main factor, and the F distribution value of each main factor is obtained according to the mean square value and the residual sum of squares; Under the condition of a given significant level α, the significance test of F distribution value is carried out on each main factor, and the judgment result is that the main factor is a key factor or a non-key factor; The key factor is substituted into the regression equation in S3 to obtain the regression equation after simplification, the positive and negative signs of the corresponding coefficient of the key factor in the regression equation after simplification are found, the coefficient takes a positive sign, which indicates that the influence of the key factor taking the upper level on the test index result is significant, and the coefficient takes a negative sign, which indicates that the influence of the key factor taking the lower level on the test index result is significant; According to the positive and negative signs of the corresponding coefficient of the key factor, the corresponding code is calculated, the regression equation after simplification is substituted according to the corresponding code, and the regression equation after arrangement is established; According to the regression equation after arrangement, the temperature rising response time, temperature interval and vapor phase liquid injection amount are obtained.

8. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 7, wherein: In the S4, Total sum of squares: where SS T is the total sum of squares, m c is the number of trials as defined by the orthogonal table; Partial regression sum of squares: wherein SS1 is the partial regression sum of squares of the vacuum degree, m c is the number of tests defined by the orthogonal table, and b1 is the partial regression coefficient of the vacuum degree in the regression equation. wherein SS2 is the partial regression sum of squares for temperature interval, m c is the number of experiments defined by the orthogonal table, and b2 is the partial regression coefficient of temperature interval in the regression equation. wherein SS3 is the partial regression sum of squares of the vapor phase liquid injection amount, m c is the number of experiments defined by the orthogonal table, and b3 is the partial regression coefficient of the vapor phase liquid injection amount in the regression equation; wherein SS 12 is the partial regression sum of vacuum degree and temperature interval interaction, m c is the number of tests defined by the orthogonal table, b 12 is the partial regression coefficient of vacuum degree and temperature interval interaction in the regression equation; wherein SS 13 is the partial regression sum of squares of the interaction of vacuum degree and vapor phase liquid injection amount, m c is the number of tests defined by the orthogonal table, b 13 is the partial regression coefficient of the interaction of vacuum degree and vapor phase liquid injection amount in the regression equation, SS 12 is the partial regression sum of squares of the interaction of vacuum degree and temperature interval, Total partial regression sum of squares: SS R = SS1 + SS2 + SS3 + SS 12 + SS 13 where SS R is the total partial regression sum of squares, SS1 is the partial regression sum of squares for vacuum level, SS2 is the partial regression sum of squares for temperature interval, SS3 is the partial regression sum of squares for vapor-liquid injection amount, and SS 13 is the partial regression sum of squares for the interaction between vacuum level and vapor-liquid injection amount. Residual sum of squares: SS e = SS T - SS R , where SS e is the residual sum of squares, SS T is the total sum of squares, and SS R is the total partial regression sum of squares; Degrees of freedom: df R =∑df 一次项 +∑df 交互项 = m, where ∑df 一次项 is the partial regression sum of squares for each factor, ∑df 交互项 is the partial regression sum of squares for the interaction factor; df e =∑df T -df R = n-1-m, wherein df e is the residual degree of freedom, ∑df T = n-1, n is the number of trials; Mean square value: where MS i is the mean of each factor or interaction, SS i is the partial regression sum of squares of each factor and interaction, df i is the degrees of freedom of each factor and interaction; where MS e is the mean of the residuals, SS e is the sum of squares of the residuals; df e is the degrees of freedom of the residuals; F distribution value: where F i is the F distribution value, MS i is the mean of each factor or interaction, MS e is the mean of the residuals.

9. The regression orthogonal test method for adjusting a temperature profile of a vacuum reflow soldering according to claim 7, wherein: In the S4, the significance test of F distribution value is carried out on each main factor at least once, and the judgment result of each main factor is that the main factor is a key factor or a non-key factor, comprising: Query the regression orthogonal test table, get the significant level α = 0.05 and α = 0.01 F critical value, the F distribution value of the parameters and F critical value are compared, and the judgment result of each main factor is obtained as significant factor or insignificant factor; The partial regression sum of squares degree of freedom of insignificant factor is incorporated into the residual sum of squares parameter, the F distribution value of each parameter is recalculated, and the F distribution significance test is performed again, and the judgment result of each significant factor is obtained as key factor or non-key factor.

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