SMT surface mounting technology for PCBA mainboard

Abstract

The invention discloses an SMT surface mounting technology for a PCBA mainboard, and the technology comprises the following steps: S1, carrying out the pretreatment of a PCBA board, a, carrying out the laser cleaning, placing the PCBA in high-precision laser cleaning equipment, and carrying out the high-precision laser cleaning, so as to remove an oxidation layer and pollutants on the surface of a bonding pad, b, carrying out the plasma activation treatment, and carrying out the plasma activation treatment on the surface of the bonding pad; in the step a, the PCBA board subjected to laser cleaning is placed in a radio frequency plasma cleaning machine to be subjected to plasma activating treatment, and the wettability of subsequent soldering paste is enhanced. According to the SMT surface mounting process, the position deviation during mounting can be effectively reduced, the position accuracy during mounting is improved, the position deviation condition during element mounting is effectively avoided, and the surface mounting quality is improved. According to the gradient reflow soldering device, the surface mount processing quality can be greatly improved, meanwhile, the gradient reflow soldering temperature change process can be smoother and smoother, the condition of pseudo soldering or warping caused by uneven temperature curves in the reflow soldering stage is effectively avoided, and the process quality of the gradient reflow soldering process is effectively improved.

Description

Technical Field

[0001] The present invention discloses an SMT surface mounting process for a PCBA motherboard, belonging to the technical field of SMT surface mounting technology. Background Art

[0002] PCBA board is translated into printed circuit board assembly in Chinese. It is based on a PCB (printed circuit board), and through processes such as SMT (surface mount technology) and DIP (plug-in technology), electronic components (such as resistors, capacitors, inductors, chips, etc.) are installed on the PCB, and a series of processes such as soldering and testing are carried out, and finally an electronic component with a specific function is formed; The surface mounting technology of electronic circuits is called surface mounting or surface mount technology. It is a circuit assembly technology that mounts leadless or short-lead surface mount components (abbreviated as SMC / SMD, called chip components in Chinese) on the surface of a printed circuit board (Printed Circuit Board, PCB) or the surface of other substrates, and is soldered and assembled by methods such as reflow soldering or dip soldering; The SMT chip mounting technology is widely used in the manufacturing of electronic products such as mobile phones, computers, and household appliances, and is an indispensable core process in modern electronic manufacturing; The SMT chip mounting technology realizes the efficient installation of electronic components through a high-precision and automated process flow, and promotes the development of miniaturization, light weight, and high performance of electronic products; In the SMT chip mounting process of traditional PCBA boards, the mounter is affected by factors such as mechanical vibration and thermal expansion, resulting in the deviation of the component mounting position, and it is easy to have the situation of inaccurate mounting position in the chip mounting process. At the same time, in the reflow soldering stage, due to the uneven temperature curve, defects such as false soldering and warping are likely to occur. Therefore, the present invention proposes an SMT surface mounting process for a PCBA motherboard. Summary of the Invention

[0003] The purpose of the present invention is to provide an SMT surface mounting process for a PCBA motherboard to solve the above deficiencies.

[0004] An SMT surface mounting process for a PCBA motherboard, the process comprising the following steps: S1, pre-treat the PCBA board; a. Laser cleaning, place the PCBA in a high-precision laser cleaning device for high-precision laser cleaning work to remove the oxide layer and contaminants on the surface of the solder pad, so as to improve the adhesion of the subsequent solder paste processing; b. Plasma activation treatment, place the PCBA board after laser cleaning in step S1, a in a radio frequency plasma cleaning machine for plasma activation treatment to enhance the wettability of the subsequent solder paste; S2, solder paste printing; a, Stencil alignment: Use a fully automatic stencil alignment system to align the PCBA board after activation in step S1, b. The stencil is in contact with the PCBA board. b, Solder paste printing: Place the PCBA board after stencil alignment in step S2, a into a fully automatic solder paste printer for solder paste printing. S3, Component placement a, Vision alignment: Use a high frame rate 3D vision module to perform vision alignment on the PCBA board after solder paste printing in step S2, b. The high frame rate 3D vision module has a frame rate of 2000fps and a resolution of 12MP. b, Dynamic compensation placement: Use a piezoelectric ceramic micro-motion platform and a six-axis robotic arm to perform compensation placement on the PCBA board after vision alignment in step S3, a. c, Pre-inspection after placement: Place the product after placement in step S3, b onto an on-line 2D vision inspection module for pre-inspection after placement. Among them, the inspection speed of the 2D vision inspection module is 0.1s / component, and the offset tolerance is ±0.01mm. S4, Gradient reflow soldering a, Preheating stage: Use a multi-zone reflow soldering furnace to preheat the product after pre-inspection in step S3, c. b, Constant temperature stage: Use a multi-zone reflow soldering furnace to perform constant temperature treatment on the semi-finished product after preheating treatment in step S4, a. c, Reflow stage: Heat the temperature of the multi-zone reflow soldering furnace to the peak temperature. The peak temperature is 245°C, ±3°C, and the time above the liquidus line is 40 - 60 seconds. d, Cooling stage: The multi-zone reflow soldering furnace performs cooling treatment. The cooling rate is -2~-4°C / s, and the end temperature is less than or equal to 100°C. S5, Product cleaning a, Aqueous cleaning: Place the cooled product in step S4, d into a high-pressure spray cleaning machine for high-pressure spray cleaning.

[0005] Preferably, in step S1, a, the wavelength of the high-precision laser cleaning equipment is 1064nm, the flushing mode is pulse mode, its power is 70 - 100W, the scanning speed is 200 - 400mm / s, the spot diameter is between 48 - 54μm, and the surface roughness after cleaning in step S1, a is between 0.2 - 0.5μm.

[0006] Preferably, in S1, b, the gas ratio of the radio frequency plasma cleaning machine is 80% argon and 20% oxygen. The processing time of the radio frequency plasma cleaning machine is 20 - 40s, the radio frequency power is between 2000 - 400W, and the frequency is between 12.85 - 14.12.

[0007] Preferably, in S2,a, the visual positioning accuracy of the full-automatic stencil alignment system is ±5μm, and the stencil tension is 32 - 50 N / cm².

[0008] Preferably, in step S2,b, the type of solder paste is nano-silver solder paste. The squeegee pressure of the full-automatic solder paste printer is 5 - 7 kgf, the angle is 55 - 65°, the printing speed is 40 - 60 mm / s, the de-molding speed is 0.2 - 0.5 mm / s, the printing thickness is 80 ± 4μm, the volume error is ≤5%, and the area coverage rate is ≥95%.

[0009] Preferably, in step S4,a, the temperature range of the multi-zone reflow soldering furnace rises from room temperature to 150°, the heating rate is 2 - 4 °C / s, and the time is 50 - 70 s.

[0010] Preferably, in step S4,c, nitrogen is filled for protection, where the oxygen content is ≤100 ppm and the flow rate is 15 - 25 L / min.

[0011] Preferably, in step S5,a, the cleaning solution of the high-pressure spray cleaning machine is deionized water plus surfactant. The cleaning pressure of the high-pressure spray cleaning machine is 2 - 3 bar, the cleaning temperature is 40 - 50 °C, and the cleaning time is 3 - 5 min.

[0012] Preferably, the compensation range in step S3,b is: ±0.5 mm for X / Y axes, ±2° for θ axis, the compensation frequency is ≥500 Hz, and the pick-and-place pressure is 0.5 - 2.0 N.

[0013] Preferably, in step S4,b, the temperature range of the multi-zone reflow soldering furnace is 150 - 200 °C, the heating rate is 0.5 - 0.8 °C / s, and the time is 80 - 110 s.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: A PCBA motherboard SMT surface mounting process of this method includes using a high-frame-rate 3D vision module to perform visual alignment work on the PCBA board after solder paste printing. The high-frame-rate 3D vision module is 2000 fps and the resolution is 12 MP. Then, a piezoelectric ceramic micro-motion platform and a six-axis robotic arm are used to perform compensation pick-and-place work on the PCBA board. By integrating the high-frame-rate 3D vision module and the piezoelectric ceramic micro-motion platform, the position of the component is detected in real time and the X / Y / θ axis deviations are compensated. In this way, the position deviation during pick-and-place can be effectively reduced, the position accuracy during chip mounting can be improved, the situation of component position offset during chip mounting can be effectively avoided, and the chip mounting processing quality can be greatly improved. At the same time, gradient reflux soldering undergoes three stages: preheating, constant temperature, reflux, and cooling. In the preheating stage, the temperature range of the multi-zone reflux soldering furnace rises from room temperature to 150°C at a heating rate of 2 - 4°C / s for 50 - 70 s. In the constant temperature stage, the temperature range of the multi-zone reflux soldering furnace is between 150 - 200°C at a heating rate of 0.5 - 0.8°C / s for 80 - 110 s. In the cooling stage, the cooling rate is -2 to -4°C / s, and the end temperature is less than or equal to 100°C. This can make the temperature change process of gradient reflux soldering smoother and more stable, effectively avoiding the situation of solder joint voids or warping caused by uneven temperature curves during the reflux soldering stage, effectively improving the process quality of the gradient reflux soldering process. At the same time, by combining nitrogen protection, the oxidation of solder joints can be effectively reduced, the processing effect of gradient reflux soldering can be improved, the soldering defect rate can be effectively reduced, and the product soldering yield can be increased. Detailed implementation manner

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] Embodiment 1: An SMT surface mounting process for a PCBA motherboard, which includes the following steps: S1, pre-treat the PCBA board; a. Laser cleaning: Place the PCBA in a high-precision laser cleaning device for high-precision laser cleaning to remove the oxide layer and contaminants on the surface of the solder pads, so as to improve the adhesion of the subsequent solder paste processing; b. Plasma activation treatment: Place the PCBA board after laser cleaning in step S1, a in a radio frequency plasma cleaning machine for plasma activation treatment to enhance the wettability of the subsequent solder paste; S2, solder paste printing; a. Stencil positioning: Use a fully automatic stencil alignment system to perform stencil positioning on the activated PCBA board in step S1, b, and the stencil is in contact with the PCBA board; b. Solder paste printing: Place the PCBA board after stencil positioning in step S2, a into a fully automatic solder paste printer for solder paste printing work; S3, component mounting; a. Visual alignment: Use a high frame rate 3D vision module to perform visual alignment on the PCBA board after solder paste printing in step S2, b. The high frame rate 3D vision module is 2000 fps and the resolution is 12 MP; b. Dynamic compensation mounting: Use a piezoelectric ceramic micro-motion platform and a six-axis robotic arm to perform compensation mounting on the PCBA board in visual alignment in step S3, a. c. Pre-inspection after mounting: Place the product after mounting in step S3, b onto an online 2D vision inspection module for pre-inspection after mounting. Among them, the inspection speed of the 2D vision inspection module is 0.1 s / component, and the offset tolerance is ±0.01 mm. S4. Gradient reflow soldering a. Preheating stage: Use a multi-zone reflow soldering furnace to preheat the product after pre-inspection in step S3, c. b. Constant temperature stage: Use a multi-zone reflow soldering furnace to perform constant temperature treatment on the semi-finished product after preheating in step S4, a. c. Reflow stage: Heat the temperature of the multi-zone reflow soldering furnace to the peak temperature. The peak temperature is 245 °C, ±3 °C, and the time above the liquidus line is 40 - 60 seconds. d. Cooling stage: The multi-zone reflow soldering furnace performs cooling treatment. The cooling rate is -2 to -4 °C / s, and the end temperature is less than or equal to 100 °C. S5. Product part cleaning a. Water-based cleaning: Place the cooled product in step S4, d into a high-pressure spray cleaning machine for high-pressure spray cleaning.

[0017] In this embodiment, in step S1, a, the wavelength of the high-precision laser cleaning equipment is 1064 nm, the flushing mode is the pulse mode, its power is 70 - 100 W, the scanning speed is 200 - 400 mm / s, the spot diameter is between 48 - 54 μm, and the surface roughness after cleaning in step S1, a is between 0.2 - 0.5 μm.

[0018] In this embodiment, in S1, b, the gas ratio of the radio frequency plasma cleaning machine is: 80% argon and 20% oxygen. The processing time of the radio frequency plasma cleaning machine is 20 - 40 s, the radio frequency power is between 2000 - 400 W, and the frequency is between 12.85 - 14.12.

[0019] In this embodiment, in S2, a, the visual positioning accuracy of the full-automatic stencil alignment system is ±5 μm, and the stencil tension is 32 - 50 N / cm².

[0020] In this embodiment, in step S2, b, the type of solder paste is nano-silver solder paste. The squeegee pressure of the full-automatic solder paste printer is 5 - 7 kgf, the angle is 55 - 65°, the printing speed is 40 - 60 mm / s, the demolding speed is 0.2 - 0.5 mm / s, the printing thickness is 80 ± 4 μm, the volume error is ≤5%, and the area coverage rate is ≥95%.

[0021] In this embodiment, in step S4, a, the temperature range of the multi-zone reflow soldering furnace is increased from room temperature to 150°, the heating rate is 2-4 °C / s, and the time is 50-70 s.

[0022] In this embodiment, in step S4, c, nitrogen is filled for protection, wherein the oxygen content ≤ 100 ppm and the flow rate is 15-25 L / min.

[0023] In this embodiment, in step S5, a, the cleaning solution of the high-pressure spray cleaning machine is deionized water plus surfactant. The cleaning pressure of the high-pressure spray cleaning machine is 2-3 bar, the cleaning temperature is 40-50 °C, and the cleaning time is 3-5 min.

[0024] In this embodiment, the compensation range in step S3, b: X / Y axis ±0.5 mm, θ axis ±2°, compensation frequency: ≥500 Hz, placement pressure: 0.5-2.0 N.

[0025] In this embodiment, in step S4, b, the temperature range of the multi-zone reflow soldering furnace is 150-200 °C, the heating rate is 0.5-0.8 °C / s, and the time is 80-110 s.

[0026] An SMT surface mounting process for a PCBA motherboard of this method, which includes using a high-frame-rate 3D vision module to perform visual alignment on the PCBA board after solder paste printing. The high-frame-rate 3D vision module is 2000 fps and the resolution is 12 MP. Then, a piezoelectric ceramic micro-motion platform and a six-axis robotic arm are used to perform compensation placement on the PCBA board. By integrating the high-frame-rate 3D vision module and the piezoelectric ceramic micro-motion platform, the component position is detected in real time and the X / Y / θ axis deviation is compensated. In this way, the position deviation during placement can be effectively reduced, the position accuracy during chip placement can be improved, and the situation of component position deviation during chip placement can be effectively avoided, which can greatly improve the chip placement processing quality; At the same time, gradient reflow soldering passes through three stages: preheating, constant temperature, reflow, and cooling. In the preheating stage, the temperature range of the multi-zone reflow soldering furnace is increased from room temperature to 150°, the heating rate is 2-4 °C / s, and the time is 50-70 s. In the constant temperature stage, the temperature range of the multi-zone reflow soldering furnace is 150-200 °C, the heating rate is 0.5-0.8 °C / s, and the time is 80-110 s. In the cooling stage, the cooling rate is -2~-4 °C / s, and the end temperature is less than or equal to 100 °C. In this way, the temperature change process of gradient reflow soldering can be made smoother and more even, effectively avoiding the situation of false soldering or warping caused by uneven temperature curves during the reflow soldering stage, effectively improving the process quality of the gradient reflow soldering process. At the same time, by combining nitrogen for protection, the oxidation of solder joints can be effectively reduced, the processing effect of gradient reflow soldering can be improved, the soldering defect rate can be effectively reduced, and the soldering yield of products can be improved.

[0027] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An SMT surface mounting process for a PCBA main board, characterized in that: The process includes the following steps: S1. Pre-treat the PCBA board; a. Laser cleaning: Place the PCBA in a high-precision laser cleaning device for high-precision laser cleaning to remove the oxide layer and contaminants on the pad surface, so as to improve the adhesion of subsequent solder paste processing; b. Plasma activation treatment: Place the PCBA board after laser cleaning in step S1, a in a radio frequency plasma cleaning machine for plasma activation treatment to enhance the wettability of the subsequent solder paste; S2. Solder paste printing; a. Stencil positioning: Use a fully automatic stencil alignment system to position the stencil on the activated PCBA board in step S1, b, and the stencil contacts the PCBA board; b. Solder paste printing: Place the PCBA board after stencil positioning in step S2, a into a fully automatic solder paste printer for solder paste printing; S3. Component mounting; a. Visual alignment: Use a high-frame-rate 3D vision module to perform visual alignment on the PCBA board after solder paste printing in step S2, b. The high-frame-rate 3D vision module has a frame rate of 2000fps and a resolution of 12MP; b. Dynamic compensation mounting: Use a piezoelectric ceramic micro-motion platform and a six-axis robotic arm to perform compensation mounting on the PCBA board after visual alignment in step S3, a; c. Pre-inspection after mounting: Place the product after mounting in step S3, b into an online 2D vision inspection module for pre-inspection after mounting. Among them, the inspection speed of the 2D vision inspection module is 0.1s / component, and the offset tolerance is ±0.01mm; S4. Gradient reflow soldering; a. Preheating stage: Preheat the product after pre-inspection in step S3, c through a multi-zone reflow soldering furnace; b. Constant temperature stage: Perform constant temperature treatment on the semi-finished product after preheating treatment in step S4, a through a multi-zone reflow soldering furnace; c. Reflow stage: Heat the temperature of the multi-zone reflow soldering furnace to the peak temperature. The peak temperature is 245°C, ±3°C, and the time above the liquidus line is 40 - 60 seconds; d. Cooling stage: The multi-zone reflow soldering furnace performs cooling treatment, and the cooling rate is -2~-4°C / s, and the end temperature is less than or equal to 100°C; S5. Product cleaning; a. Aqueous cleaning: Place the cooled product in step S4, d in a high-pressure spray cleaning machine for high-pressure spray cleaning.

2. The SMT surface mounting process for a PCBA motherboard according to claim 1, characterized in that: In step S1, a, the wavelength of the high-precision laser cleaning device is 1064nm, the flushing mode is pulse mode, its power is 70 - 100W, the scanning speed is 200 - 400mm / s, the spot diameter is between 48 - 54μm, and the surface roughness after cleaning in step S1, a is between 0.2 - 0.5μm.

3. The SMT surface mounting process for a PCBA main board according to claim 1, wherein: In S1, b, the gas ratio of the radio frequency plasma cleaning machine is: 80% argon and 20% oxygen. The processing time of the radio frequency plasma cleaning machine is 20 - 40s, the radio frequency power is between 2000 - 400W, and the frequency is between 12.85 - 14.

12.

4. A SMT surface mounting process for a PCBA main board according to claim 3, wherein: In S2, a, the visual positioning accuracy of the fully automatic stencil alignment system is ±5μm, and the stencil tension is 32 - 50N / cm².

5. A SMT surface mounting process for a PCBA motherboard according to claim 1, characterized in that: In step S2, b, the type of solder paste is nano-silver solder paste. The squeegee pressure of the fully automatic solder paste printer is 5 - 7 kgf, the angle is 55 - 65°, the printing speed is 40 - 60 mm / s, the demolding speed is 0.2 - 0.5 mm / s, the printing thickness is 80 ± 4 μm, the volume error is ≤ 5%, and the area coverage rate is ≥ 95%.

6. A SMT surface mounting process for a PCBA main board according to claim 1, characterized in that: In step S4, a, the temperature range of the multi-zone reflow soldering furnace is heated from room temperature to 150 °C, the heating rate is 2 - 4 °C / s, and the time is 50 - 70 s.

7. The SMT surface mounting process for a PCBA main board according to claim 1, wherein: In step S4, c, nitrogen is filled for protection, where the oxygen content is ≤ 100 ppm and the flow rate is 15 - 25 L / min.

8. A SMT surface mounting process for a PCBA main board according to claim 1, characterized in that: In step S5, a, the cleaning solution of the high-pressure spray cleaning machine is deionized water plus surfactant. The cleaning pressure of the high-pressure spray cleaning machine is 2 - 3 bar, the cleaning temperature is 40 - 50 °C, and the cleaning time is 3 - 5 min.

9. The SMT surface mounting process for a PCBA main board according to claim 1, characterized in that: The compensation range in step S3, b: ± 0.5 mm for X / Y axis, ± 2° for θ axis, the compensation frequency: ≥ 500 Hz, and the pick-and-place pressure: 0.5 - 2.0 N.

10. A SMT surface mounting process for a PCBA motherboard according to claim 1, characterized in that: In step S4, b, the temperature range of the multi-zone reflow soldering furnace is 150 - 200 °C, the heating rate is 0.5 - 0.8 °C / s, and the time is 80 - 110 s.