Lead-free tin-spraying process capability testing and control methods for different solder mask thicknesses

Abstract

The present invention discloses a lead-free tin-spraying process capability testing method and control method for different solder mask thicknesses. The testing method comprises the following steps: printing solder mask ink on a test board formed with a circuit circle PAD; making the light-blocking PAD pattern on the solder mask exposure film correspond to the circuit circle PAD on the test board; exposing and developing to form a solder mask layer; tin-spraying treatment; determining the tin-spraying process capability for different solder mask thicknesses based on the tin-on rate of the test board with different solder mask thicknesses according to different sizes of solder mask window PADs and solder mask window cycles. The method of the present invention can determine the range of the tin-spraying process capability for different solder mask thicknesses, which is conducive to clearly understanding the process capability and status of the production line, and providing effective data support for the process capability and specification design of the PCB, thereby providing the best solution for the selection of the process, effectively avoiding the quality problem of poor tinning during the PCB tin-spraying process, making the production process run smoothly, and ensuring product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board production, and in particular to a method for testing and controlling the capability of a lead-free tin-spraying process with different solder mask thicknesses. Background Art

[0002] A printed circuit board (PCB) is a board with a pre-designed printed circuit on an insulating substrate, providing conductive patterns for connecting components. The typical PCB production process includes cutting, drilling, copper plating, full-board electroplating, dry film coating, pattern plating, etching, solder mask, lettering, surface treatment (such as tin spraying), and molding. Tin spraying, also known as hot air leveling, involves heat-curing the printed board after solder mask printing. After surface treatment, the printed board is immersed in molten solder. Hot air is then used to blow off excess solder from the printed board surface and metallized holes, resulting in a smooth, uniform, and bright solder coating (tin).

[0003] In their paper "Investigation and Improvement of Lead-Free Halogen-Free Air Soldering (HASL) Tinning Problems," Zhao Zhiping et al. point out that the main causes of tinning problems include excessively high solder copper content, incomplete hot air soldering pre-treatment, and inadequate solder mask development. In their paper "Poor Wetting in Lead-Free Halogen-Free Air Soldering (HASL)" and "Solutions," Chang Chengxiang et al. point out that the main causes of poor wetting are uneven surface finishes on PCB pads and alloying of the pads, which reduces solderability. However, neither paper found an effect of solder mask thickness on HASL process performance.

[0004] Our company's lead-free tin-spraying boards frequently experience poor tinning. On-site follow-up by the applicant revealed that the poor tinning was primarily concentrated in the solder mask openings on the large copper surfaces. Section analysis revealed that the solder mask thickness on the copper surfaces at these locations exceeded 45µm. Therefore, the analysis concluded that the poor tinning was related to the solder mask thickness. Currently, there is no clear method for defining the process capability of tin-spraying for different solder mask thicknesses. Consequently, poor tinning requires rework, which impacts production efficiency, increases production costs, and increases quality risks. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned technical deficiencies and propose a lead-free tin-spraying process capability testing method and control method for different solder mask thicknesses, so as to solve the technical problems in the prior art that there is no clear method to define the process capability of tin-spraying with different solder mask thicknesses and the quality problem of poor tinning can only be reworked.

[0006] A first aspect of the present invention provides a method for testing the capability of a tin-spraying process with different solder mask thicknesses, comprising the following steps:

[0007] Forming a circuit circle PAD on the test board;

[0008] Printing solder resist ink on a test board on which a circuit circle PAD is formed;

[0009] Attach the solder mask exposure film to the solder mask ink on the test board, and make the light-blocking PAD pattern on the solder mask exposure film correspond to the circuit circle PAD on the test board;

[0010] Expose and develop the test board with the solder mask exposure film attached to it to remove the solder mask ink at the solder mask opening to form a solder mask layer;

[0011] Performing tin spraying treatment on the surface of the test board on which the solder mask layer is formed;

[0012] The tinning rate of the test board with different solder mask thickness is determined by the tinning process capability of different solder mask thickness according to the different sizes of solder mask window PAD and solder mask window cycle.

[0013] A second aspect of the present invention provides a method for controlling the capability of a lead-free tin-spraying process with different solder mask thicknesses, comprising the following steps:

[0014] Design the circuit circle PAD diameter and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film according to the theoretical thickness of the solder mask layer;

[0015] Forming circuits and circuit circle PADs on the circuit board and printing solder resist ink;

[0016] Attach the solder mask exposure film to the solder mask ink on the circuit board, and make the light-blocking PAD pattern on the solder mask exposure film correspond to the circuit circle PAD on the circuit board;

[0017] Expose and develop the circuit board with the solder resist exposure film attached to it to remove the solder resist ink at the solder resist window to form a solder resist layer;

[0018] The surface of the circuit board with the solder mask layer formed is subjected to tin spraying treatment.

[0019] The present invention tests the tin-spraying process capability of different solder mask thicknesses by fabricating solder mask window PADs of different sizes on a test board and performing solder mask window cycle tests. This can determine the range of tin-spraying process capability of different solder mask thicknesses, which is conducive to clearly understanding the process capability and status of the production line, providing effective data support for the process capability and standard design of PCBs, and thus providing the best solution for process selection, effectively avoiding quality problems such as poor tinning during the PCB tin-spraying process, ensuring smooth operation of the production process, and ensuring product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a diagram showing the tinning conditions of circular PADs with different diameters using Shuocheng (903-BGA) and Hafu (809KB) fluxes when the solder resist thickness is 25.25 μm in the test method of Example 1 of the present invention;

[0021] Figure 2 This is a diagram showing the tinning conditions of different line width cycles using Shuocheng (903-BGA) and Hafu (809KB) fluxes when the solder resist thickness is 25.25 μm in the test method of Example 1 of the present invention;

[0022] Figure 3 This is a diagram showing the tinning conditions of circular PADs with different diameters using Shuocheng (903-BGA) and Hafu (809KB) solder fluxes when the solder resist thickness is 39.32 μm in the test method of Example 1 of the present invention;

[0023] Figure 4 This is a diagram showing the tinning conditions of different line width cycles using Shuocheng (903-BGA) and Hafu (809KB) fluxes when the solder resist thickness is 39.32 μm in the test method of Example 1 of the present invention;

[0024] Figure 5 This is a diagram showing the tinning conditions of circular PADs with different diameters using Shuocheng (903-BGA) and Hafu (809KB) fluxes when the solder resist thickness is 64.12 μm in the test method of Example 1 of the present invention;

[0025] Figure 6 This is a diagram of the tinning conditions of different line width cycles using Shuocheng (903-BGA) and Hafu (809KB) fluxes when the solder resist thickness is 64.12 μm in the test method of Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] During the production process of the present invention, it was found through investigation that the locations with poor tinning are mainly concentrated in the large copper surface solder mask window locations. Solder mask windows refer to locations that are not covered by solder mask ink. Large copper surface solder mask windows include solder mask window PAD and solder mask window cycle. Circuit circle PAD refers to a circular pad made of outer layer circuit; the function of solder mask window PAD is to expose the pad and not be covered by solder mask layer; the cycle represents the production date of the circuit board, which is generally a year week (such as 2146, indicating production in the 46th week of 2021) or an anniversary (such as 4621, indicating production in the 46th week of 2021), and the solder mask window cycle is to transfer the cycle number on the solder mask exposure film to the solder mask layer through a graphic, that is, the solder mask is exposed and developed to produce the corresponding number.

[0028] Based on this, a first aspect of the present invention provides a method for testing the capability of a tin-spraying process with different solder mask thicknesses, comprising the following steps:

[0029] S101, forming a circuit circle PAD on a test board; wherein the diameter of the circuit circle PAD is 0.25-0.55 mm;

[0030] S102, printing solder resist ink on the test board with the circuit circle PAD formed thereon;

[0031] S103. Attach the solder resist exposure film to the solder resist ink of the test board, and make the light-blocking PAD pattern on the solder resist exposure film correspond to the circuit circle PAD on the test board; wherein, the solder resist exposure film is designed with a light-blocking PAD pattern with a diameter of 0.25-0.55mm and a light-blocking periodic pattern with a line width of 0.2-0.5mm, and after the pattern transfer, the light-blocking PAD pattern forms a solder resist window PAD on the solder resist layer at a position corresponding to the circuit circle PAD position, exposing the circuit circle PAD; after the pattern transfer, the light-blocking periodic pattern forms a solder resist window period on the solder resist layer at a position corresponding to the large copper surface position of the circuit layer.

[0032] S104, exposing and developing the test board with the solder resist exposure film attached thereto to remove the solder resist ink at the solder resist openings to form a solder resist layer;

[0033] S105, performing tin spraying treatment on the surface of the test board on which the solder mask layer is formed;

[0034] S106. Determine the tinning process capability of different solder mask layer thicknesses based on the tinning rates of test boards with different solder mask layer thicknesses according to different sizes of solder mask window PADs and solder mask window cycles.

[0035] In step S101 of the present invention, forming a circuit circle PAD on the test board includes:

[0036] S1011. Apply film to a test board. GW4011 board is selected as the test board. The test board has been drilled, copper plated, and fully electroplated.

[0037] S1012. Performing alignment exposure using a circuit film; wherein the circuit film is designed with a circuit circle PAD pattern having a diameter of 0.25-0.55 mm. Furthermore, a circuit film may be designed with only one size of circuit circle PAD pattern to form a circuit circle PAD of only one size on a test board, or may be designed with multiple sizes of circuit circle PAD patterns to form circuit circle PADs of multiple sizes on a test board, which is not limited in the present invention.

[0038] S1013, development;

[0039] S1014, etching;

[0040] S1015, film removal.

[0041] In step S102 of the present invention, the thickness of the solder resist ink is 25-65 μm. In some specific embodiments of the present invention, the solder resist ink is printed by at least one of 39T white screen printing and air pressure spraying.

[0042] In step S105 of the present invention, performing tin spraying on the surface of the test board on which the solder mask layer is formed includes:

[0043] S1051, pre-treating the surface of the test board on which the solder mask layer is formed;

[0044] S1052. Apply flux to the pre-treated surface of the test board; wherein the flux can be at least one of Shuocheng SCC-903-BGA, Jutai 909A-183, Jutai 909A-197, Jutai 909A-187, and Hafu 809KB;

[0045] S1053. Perform lead-free tin spraying on the flux-coated test board. The lead-free tin spraying parameters are as follows: tin bath temperature 260-280°C, stirring tank temperature 255-275°C, over-temperature protection temperature 260-280°C, tinning time 2-8 seconds, front and rear air knife temperature 355-385°C, front and rear air knife pressure 1.5-5.5 kg / cm 2 , the distance between the front and rear air knives is 12-30mm, the front air knife is 3-15mm higher than the rear air knife, the front and rear air knife angles are 3º-5º, the rear air knife angle is 5º-7º, the air knife mouth distance is 0.25-0.3mm, the blowing time is 1-3 seconds, the air pressure of the gas tank is 6-8kg, the distance from the hanging hole to the edge of the board is 3-14mm, the copper content of the tin bath is ≤1.0%, the lead content of the tin bath is ≤500PPM, and the nickel content of the tin bath is 300-600PPM;

[0046] S1054. Post-process the test board treated with lead-free tin spraying.

[0047] Among them, the above-mentioned pre-treatment (including board insertion, micro-etching, water washing, air drying, and preheating) and post-treatment (including water washing and air drying) are all existing technologies and will not be described in detail here.

[0048] In step S106 of the present invention, determining the tinning process capability of different solder mask thicknesses based on the tinning rates of different solder mask window PAD sizes and solder mask window cycles on test boards with different solder mask thicknesses includes:

[0049] S1061. Calculate the tinning pass rate of different sizes of solder mask window PADs and solder mask window cycles on a test board with a specific solder mask thickness;

[0050] S1062. Determine the minimum size with a 100% tin pass rate on a test board of a specific solder mask thickness as the minimum 100% tin pass size of the specific solder mask thickness.

[0051] A second aspect of the present invention provides a method for controlling the capability of a lead-free tin-spraying process with different solder mask thicknesses, comprising the following steps:

[0052] S201, designing the circuit circle PAD diameter and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film according to the theoretical thickness of the solder mask layer;

[0053] S202, forming circuits and circuit circle PADs on the circuit board and printing solder resist ink;

[0054] S203, attaching a solder resist exposure film to the solder resist ink of the circuit board, and making the light-blocking PAD pattern on the solder resist exposure film correspond to the circuit circle PAD on the circuit board;

[0055] S204, exposing and developing the circuit board with the solder resist exposure film attached thereto to remove the solder resist ink at the solder resist openings to form a solder resist layer;

[0056] S205, performing tin spraying treatment on the surface of the circuit board where the solder resist layer is formed.

[0057] In step S201 of the present invention, the circuit circle PAD diameter and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film are designed according to the theoretical thickness of the solder mask layer, including:

[0058] According to the tin-spraying process capability testing method for different solder mask thicknesses provided by the first aspect of the present invention, the minimum 100% qualified dimension for the theoretical thickness of the solder mask is determined, and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film are designed to be ≥ the minimum 100% qualified dimension for tinning, and the line circle PAD diameter is ≥ the light-blocking PAD pattern diameter on the solder mask exposure film. In actual production, the theoretical thickness of the solder mask is generally determined based on the design data provided by the customer.

[0059] In some specific embodiments of the present invention, the circuit circle PAD diameter and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film are designed according to the theoretical thickness of the solder mask layer:

[0060] According to the tin-spraying process capability test method for different solder mask thicknesses provided by the first aspect of the present invention, the theoretical thickness of the solder mask is determined to be 25-26 μm, the minimum 100% qualified tinning diameter of the solder mask window PAD is 0.4 mm, the minimum 100% qualified tinning line width of the large copper surface solder mask window cycle is 0.2 mm, the designed circuit circle PAD diameter is ≥ the light-blocking PAD pattern diameter on the solder mask exposure film is ≥ 0.4 mm, and the light-blocking period pattern line width on the solder mask exposure film is ≥ 0.2 mm;

[0061] According to the tin-spraying process capability test method for different solder mask thicknesses provided by the first aspect of the present invention, the theoretical thickness of the solder mask is determined to be 39-40 μm, the minimum 100% qualified tinning diameter of the solder mask window PAD is 0.55 mm, the minimum 100% qualified tinning line width of the large copper surface solder mask window cycle is 0.3 mm, the designed circuit circle PAD diameter is ≥ the light-blocking PAD pattern diameter on the solder mask exposure film is ≥ 0.55 mm, and the line width of the light-blocking period pattern on the solder mask exposure film is ≥ 0.3 mm;

[0062] According to the tin spraying process capability test method for different solder mask thicknesses provided by the first aspect of the present invention, the theoretical thickness of the solder mask layer is determined to be 64~65um, the minimum 100% qualified tinning diameter of the solder mask window PAD is 0.60mm, and the minimum 100% qualified tinning line width of the large copper surface solder mask window cycle is 0.35mm. The designed circuit circle PAD diameter is ≥ the light-blocking PAD graphic diameter on the solder mask exposure film is ≥0.60mm, and the light-blocking period graphic line width on the solder mask exposure film is ≥0.35mm.

[0063] In the present invention, the above steps S202, S203, S204 and S205 are prior art and will not be described in detail here.

[0064] Example 1

[0065] This embodiment provides a method for testing the capability of a tin-spraying process with different solder mask thicknesses, comprising the following steps:

[0066] (1) A film is applied to a test board (Chao Sheng GW4011 board) that has been drilled, copper plated, and fully electroplated. A circuit film with circuit circle PAD patterns of different diameters is then used for alignment exposure. After development, etching, and film stripping, a circuit circle PAD is formed on the test board. The diameters of the circuit circle PAD patterns are 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, and 0.55 mm, respectively.

[0067] (2) Printing solder resist ink on the test board with the circuit circle PAD; wherein the thickness of the solder resist ink is 25.25μm, 39.32μm, and 64.12μm respectively;

[0068] (3) Attach the solder mask exposure film to the solder mask ink of the test board, and make the light-blocking PAD pattern on the solder mask exposure film correspond to the circuit circle PAD on the test board in the same size; wherein, the diameters of the light-blocking PAD pattern on the solder mask exposure film are 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, and 0.55mm respectively, and the line widths of the light-blocking periodic pattern are 0.2mm, 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.45mm, and 0.5mm respectively;

[0069] (4) Expose and develop the circuit board with the solder mask exposure film attached to remove the solder mask ink at the solder mask opening to form a solder mask layer;

[0070] (5) The surface of the test board with solder mask layer is subjected to pre-treatment, flux coating, lead-free tin spraying treatment and post-treatment in sequence; among them, the tin bath temperature is 270℃, the stirring tank temperature is 265℃, the over-temperature protection temperature is 270℃, the tin immersion time is 5 seconds, the front and rear air knife temperature is 370℃, and the front and rear air knife pressure is 3.5kg / cm 2 , the distance between the front and rear air knives is 20mm, the front air knife is 10mm higher than the rear air knife, the front and rear air knife angles are 4º, the rear air knife angle is 6º, the air knife mouth distance is 0.25mm, the blowing time is 2 seconds, the air pressure of the gas tank is 7kg, the distance from the hanging hole to the edge of the board is 10mm, the copper content of the tin bath is ≤1.0%, the lead content of the tin bath is ≤500PPM, and the nickel content of the tin bath is 450PPM.

[0071] (6) The tinning rate of the test board with different solder mask thickness is determined based on the tinning rate of the test board with different solder mask thickness according to the different sizes of solder mask window PAD and solder mask window cycle. The results are shown in Table 1.

[0072]

[0073] 1. "Screen" in Table 1 indicates the screen printing method is 39T white screen printing; 2. "Air" in Table 1 indicates the screen printing method is air pressure spraying; 3. "Air + Screen" in Table 1 indicates the screen printing method is air pressure spraying + 39T white screen printing; 4. "SC" in Table 1 indicates the use of Shuocheng SCC-903-BGA flux; 5. "HF" in Table 1 indicates the use of Hafu 809KB flux.

[0074] The above tests show that:

[0075] (1) The tinning ability of lead-free tin spraying is different for different solder mask thicknesses. The thicker the solder mask thickness, the worse the tinning ability.

[0076] (2) Using 39T white screen printing (ink thickness of about 25um), the solder mask window circle PAD diameter ≥ 0.4mm tinning is 100% qualified, and the large copper surface solder mask window cycle line width ≥ 0.2mm tinning is 100% qualified; using air pressure spraying (ink thickness of about 40um), the solder mask window circle PAD diameter ≥ 0.55mm tinning is 100% qualified, and the large copper surface solder mask window cycle line width ≥ 0.3mm tinning is 100% qualified; using air pressure spraying + 39T white screen printing (ink thickness of about 65um), the solder mask window circle PAD diameter is 0.55mm and there is still about 3% poor tinning, and the large copper surface solder mask window cycle line width ≥ 0.35mm tinning is 100% qualified.

[0077] This embodiment also provides a method for controlling the capability of a lead-free tin-spraying process with different solder mask thicknesses, comprising the following steps:

[0078] (1) According to the above-mentioned tin spraying process capability test method for different solder mask layer thicknesses, the minimum tinning 100% qualified size of the theoretical thickness of the solder mask ink layer is determined, and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film are designed to be ≥ the minimum tinning 100% qualified size, and the line circle PAD diameter = the light-blocking PAD pattern diameter on the solder mask exposure film;

[0079] (2) Forming circuits and circuit circle PADs on the circuit board and printing solder mask ink;

[0080] (3) Attach the solder mask exposure film to the solder mask ink on the circuit board, and make the light-blocking PAD pattern on the solder mask exposure film correspond to the circuit circle PAD on the circuit board;

[0081] (4) Expose and develop the circuit board with the solder mask exposure film attached to remove the solder mask ink at the solder mask opening to form a solder mask layer;

[0082] (5) The surface of the circuit board with the solder mask layer is subjected to tin spraying treatment.

[0083] The results show that the solder resist ink is printed using 39T white screen printing, with a thickness of 25.31um. The diameter of the light-blocking PAD pattern on the solder resist exposure film is designed to be 0.4mm, the line width of the light-blocking periodic pattern is 0.2mm, and the diameter of the circuit circle PAD is 0.4mm. The tinning is 100% qualified.

[0084] The solder mask ink is printed by air pressure spraying, with a thickness of 39.46um. The diameter of the light-blocking PAD pattern on the solder mask exposure film is designed to be 0.55mm, the line width of the light-blocking periodic pattern is 0.3mm, and the diameter of the circuit circle PAD is 0.55mm. The tinning is 100% qualified.

[0085] The printing method of solder mask ink is 39T white screen printing + air pressure spraying, the thickness of solder mask ink is 64.22um, the diameter of the light-blocking PAD pattern on the solder mask exposure film is designed to be 0.60mm, the line width of the light-blocking periodic pattern is 0.35mm, the diameter of the circuit circle PAD is 0.60mm, and the tinning is 100% qualified.

[0086] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for testing the capability of a tin-spraying process with different solder mask thicknesses, characterized in that: The following steps are involved: Forming circuit circle PAD on the test board, including: laminating film on the test board, using circuit film for alignment exposure, developing, etching, and film stripping; Printing solder resist ink on the test board on which the circuit circle PAD is formed; A solder mask exposure film is attached to the solder mask ink of the test board, and the light-blocking PAD pattern on the solder mask exposure film is made to correspond to the circuit circle PAD on the test board; after pattern transfer of the light-blocking PAD pattern, a solder mask window PAD is formed on the solder mask layer at a position corresponding to the circuit circle PAD, so that the circuit circle PAD is exposed; Expose and develop the test board with the solder resist exposure film attached to it to remove the solder resist ink at the solder resist window to form a solder resist layer; Performing tin spraying treatment on the surface of the test board where the solder resist layer is formed; Determine the tinning process capability of different solder mask thicknesses based on the tinning rates of different sizes of solder mask window PADs and solder mask window cycles on test boards with different solder mask thicknesses; including: calculating the tinning pass rates of different sizes of solder mask window PADs and solder mask window cycles on test boards with a certain solder mask thickness, and determining the minimum size with a 100% tinning pass rate on a test board with a certain solder mask thickness as the minimum 100% tinning pass size for the specific solder mask thickness.

2. The method for testing the tin-spraying process capability of different solder mask thicknesses according to claim 1, characterized in that: The diameter of the circuit circle PAD is 0.25-0.55mm; the solder resist exposure film is designed with a light-blocking PAD pattern with a diameter of 0.25-0.55mm and a light-blocking periodic pattern with a line width of 0.2-0.5mm; after the light-blocking periodic pattern is transferred, a solder resist window period is formed on the solder resist layer at a position corresponding to the large copper surface of the circuit layer.

3. The method for testing the tin-spraying process capability of different solder mask thicknesses according to claim 1, wherein: The thickness of the solder resist ink is 25-65 μm.

4. The method for testing the tin-spraying process capability of different solder mask thicknesses according to claim 1, wherein: The tin spraying treatment on the surface of the test board formed with the solder resist layer comprises: Pre-treating the surface of the test board on which the solder mask layer is formed; Apply flux to the surface of the pre-treated test board; Conduct lead-free tin spraying treatment on the test board coated with flux; Post-processing of the test board treated with lead-free tin spraying.

5. The method for testing the tin-spraying process capability of different solder mask thicknesses according to claim 1, wherein: Lead-free tin spraying parameters are: tin bath temperature 260-280℃, stirring tank temperature 255-275℃, over-temperature protection temperature 260-280℃, tin immersion time 2-8 seconds, front and rear air knife temperature 355-385℃, front and rear air knife pressure 1.5-5.5kg / cm 2 , the distance between the front and rear air knives is 12-30mm, the front air knife is 3-15mm higher than the rear air knife, the front and rear air knife angles are 3º-5º, the rear air knife angle is 5º-7º, the air knife mouth spacing is 0.25-0.3mm, the blowing time is 1-3 seconds, the air pressure of the gas tank is 6-8kg, the distance from the hanging hole to the edge of the board is 3-14mm, the copper content of the tin bath is ≤1.0%, the lead content of the tin bath is ≤500PPM, and the nickel content of the tin bath is 300-600PPM.

6. A method for controlling the capability of lead-free tin-spraying processes with different solder mask thicknesses, characterized in that: The following steps are involved: Design the circuit circle PAD diameter and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film according to the theoretical thickness of the solder mask layer; Forming circuits and circuit circle PADs on the circuit board and printing solder resist ink; Attach the solder mask exposure film to the solder mask ink on the circuit board, and make the light-blocking PAD pattern on the solder mask exposure film correspond to the circuit circle PAD on the circuit board; Expose and develop the circuit board with the solder resist exposure film attached to it to remove the solder resist ink at the solder resist window to form a solder resist layer; Performing tin spraying treatment on the surface of the circuit board where the solder mask layer is formed; According to the theoretical thickness of the solder mask layer, the circuit circle PAD diameter and the light-blocking PAD pattern diameter and light-blocking periodic pattern line width on the solder mask exposure film are designed. According to the tin spraying process capability testing method for different solder mask thicknesses according to any one of claims 1 to 5, the minimum 100% qualified size of tinning of the theoretical thickness of the solder mask layer is determined, and the light-blocking PAD graphic diameter and the light-blocking periodic graphic line width on the solder mask exposure film are designed to be ≥ the minimum 100% qualified size of tinning, and the line circle PAD diameter is ≥ the light-blocking PAD graphic diameter on the solder mask exposure film.

7. The method for controlling lead-free tin-spraying process capability with different solder mask thicknesses according to claim 6, wherein: According to the theoretical thickness of the solder mask layer, the diameter of the circuit circle PAD and the diameter of the light-blocking PAD pattern on the solder mask exposure film and the line width of the light-blocking periodic pattern are designed as follows: According to the tin spraying process capability test method for different solder mask thicknesses, the theoretical thickness of the solder mask is determined to be 25~26um, the minimum 100% qualified diameter of the solder mask window PAD is 0.4mm, and the minimum 100% qualified line width of the large copper surface solder mask window cycle is 0.2mm. The designed circuit circle PAD diameter is ≥ the light-blocking PAD graphic diameter on the solder mask exposure film ≥0.4mm, and the light-blocking period graphic line width on the solder mask exposure film is ≥0.2mm.

8. The method for controlling lead-free tin-spraying process capability with different solder mask thicknesses according to claim 6, wherein: According to the theoretical thickness of the solder mask layer, the diameter of the circuit circle PAD and the diameter of the light-blocking PAD pattern on the solder mask exposure film and the line width of the light-blocking periodic pattern are designed as follows: According to the tin spraying process capability test method for different solder mask thicknesses, the theoretical thickness of the solder mask layer is determined to be 39~40um, the minimum 100% qualified diameter of the solder mask window PAD is 0.55mm, and the minimum 100% qualified line width of the large copper surface solder mask window cycle is 0.3mm. The designed circuit circle PAD diameter is ≥ the light-blocking PAD graphic diameter on the solder mask exposure film is ≥0.55mm, and the light-blocking period graphic line width on the solder mask exposure film is ≥0.3mm.

9. The method for controlling lead-free tin-spraying process capability with different solder mask thicknesses according to claim 6, wherein: According to the theoretical thickness of the solder mask layer, the diameter of the circuit circle PAD and the diameter of the light-blocking PAD pattern on the solder mask exposure film and the line width of the light-blocking periodic pattern are designed as follows: According to the tin spraying process capability test method for different solder mask thicknesses, the theoretical thickness of the solder mask layer is determined to be 64~65um, the minimum 100% qualified diameter of the solder mask window PAD is 0.60mm, and the minimum 100% qualified line width of the large copper surface solder mask window cycle is 0.35mm. The designed circuit circle PAD diameter is ≥ the light-blocking PAD graphic diameter on the solder mask exposure film is ≥0.60mm, and the light-blocking period graphic line width on the solder mask exposure film is ≥0.35mm.

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