Analysis of SMT equipment placement rate

How to improve and maintain the placement rate of
SMT equipment is an urgent problem that managers need to solve after years of use. This article takes the rotary head placement machine as an example to elaborate on the reasons that affect the low placement rate of equipment from many aspects, and introduces in detail the inspection content of common faults of SMT equipment. Keywords: placement rate, optical recognition, posture detection, state monitoring, placement machine is to absorb the device stably, quickly, completely and correctly without causing any damage to the device and the base board, and quickly and accurately place the device in the specified position. It has been widely used in military industry, home appliances, communications, computers and other industries. When purchasing SMT equipment, the main consideration is its placement accuracy and placement speed. In actual use, in order to effectively improve product quality, reduce production costs and improve production efficiency, how to improve and maintain the placement rate of SMT equipment is the primary issue facing users.
1: The meaning of placement rate The so-called placement rate refers to the ratio of the actual number of device placements to the number of suctions within a certain period of time, that is: Placement rate = ×100% suction number The total number of discarded pieces refers to the number of suction errors, identification errors, number of stand-up pieces, number of lost pieces, etc., and the identification errors are divided into two types: device size errors and poor device optical identification. Whether the placement machine is a small machine, a medium-sized machine, or a large machine, and whether it is a medium-speed machine or a high-speed machine, they are mainly composed of device storage and transportation devices, XY workbenches, placement heads, and control systems. The placement head is the core and key component of the placement machine. The placement head is generally divided into fixed heads and rotating heads. The fixed head is generally arranged in multiple heads, ranging from 2 to 8, and can pick up parts simultaneously or individually. The rotating head is divided into rotating in the horizontal plane and rotating in the vertical plane. A: Switching the device suction nozzle height
B: θI rotation (±90')
C: Device optical recognition
D: Device posture detection θ2 rotation (±90')
E: Mounting device/nozzle height switching
F: θ3 rotation (±180'-θ) Nozzle origin detection defective product elimination
G: Nozzle conversion
H: Nozzle number detection According to the entire process of the placement machine from picking up the parts to mounting, from the perspective of equipment alone, when the nozzle picking height, the center of the nozzle at the picking position and the relative position of the feeder are correctly set, the main factor affecting the equipment placement rate is the picking position. According to the production information intelligence of the equipment statistics, its influence accounts for more than 80% of the total influencing factors. The causes are: on the one hand, the feeder on the device storage and transportation device, and on the other hand, the nozzle. Among the two, about 60% of the feeder videos and about 40% are caused by nozzle contamination.
2. The influence of the feeder The main influence of the feeder is concentrated on the abnormal feeding. There are several driving modes for feeders, such as motor drive, mechanical drive and cylinder drive. Here, we take mechanical drive as an example to explain the impact of feeders on mounting rate:
1: Wear of driving part Mechanical drive relies on cam spindle to drive the feeding mechanism, quickly knocks the striking arm of the feeder, and drives the ratchet wheel connected to it through the connecting rod to drive the component tape forward by a distance, and at the same time drives the plastic tape reel to remove the plastic tape cap on the tape, and the suction nozzle descends to complete the picking action. However, due to the high-speed access of the feeding mechanism to the feeder, after long-term use, the ratchet of the feeder is seriously worn, causing the ratchet to fail to drive the plastic tape of the tape reel to peel off normally, so that the suction nozzle cannot complete the picking work. Therefore, the feeder should be carefully checked before installing the tape, and the feeder with worn ratchet wheel should be repaired immediately, and the one that cannot be repaired should be replaced in time.
2: Deformation of the feeder structure Due to long-term use or improper operation by the operator, the pressure belt cover, ejector, spring and other moving mechanisms are deformed, rusted, etc., which leads to the device being sucked off, standing or failing to suck the device. Therefore, regular inspections should be carried out and problems should be dealt with in a timely manner to avoid a large amount of device waste. At the same time, the feeder should be correctly and firmly installed on the feeder platform when installing it, especially for equipment without feeder height detection, otherwise it may cause damage to the feeder or equipment.
3: Poor lubrication of the feeder Generally, the maintenance and care of the feeder are easily overlooked, but regular cleaning, washing, and lubrication are essential work.
3. The influence of the nozzle The nozzle is also another important factor affecting the placement rate. The causes are internal and external.
1: The internal reason is that the vacuum negative pressure is insufficient. Before the nozzle takes the part, the mechanical valve on the placement head is automatically converted, and the air blowing is converted to true adsorption, which generates a certain negative pressure. After the part is sucked, when the negative pressure sensor detection value is within a certain range, the machine is normal, otherwise the adsorption is poor. Generally, the negative pressure from the pickup position to the placement position should be at least 400mmHg. When placing large components, the negative pressure should be above 70mmHg. Therefore, the filter in the vacuum pump should be cleaned regularly to ensure sufficient negative pressure. At the same time, the working status of the negative pressure detection sensor should be checked regularly. On the other hand, the filter on the placement head and the filter on the suction nozzle are blackened due to contamination and blockage caused by the surrounding environment or impure air source. Therefore, the filter should be replaced regularly. Generally, the filter on the suction nozzle should be replaced at least once every half a month, and the filter on the placement head should be replaced at least once every six months to ensure smooth airflow.
2: External reasons On the one hand, the air source circuit is depressurized, such as aging and rupture of rubber air pipes, aging and wear of seals, and wear of nozzles after long-term use. On the other hand, it is caused by dust in adhesives or the external environment, especially the large amount of waste generated after the components packaged by paper tapes are cut off, which causes the nozzle to be blocked. Therefore, the cleanliness of the nozzle should be checked daily, and the nozzle's pickup should be monitored at any time. The nozzle that is blocked or poorly picked up should be cleaned or replaced in time to ensure a good state. At the same time, when installing the nozzle, it must be installed correctly and firmly, otherwise it will cause damage to the nozzle or equipment.
Four: Component detection system The component detection system is a necessary guarantee for mounting accuracy and mounting correctness. It is divided into component optical recognition system and component posture detection. 1: The optical recognition system is a fixedly installed optical camera system. It uses the camera to identify the outline of the components during the rotation of the placement head to form an optical image. At the same time, the center position and rotation angle of the device relative to the camera are measured and recorded, and transmitted to the transmission control system to compensate for the XY coordinate position deviation and theta angle deviation. Its advantages lie in its accuracy and flexibility in being applicable to devices of various specifications and shapes. It has a reflection recognition method that uses the device electrode as the recognition basis, and the recognition accuracy is not affected by the size of the nozzle. Generally, SOP, QFP, BGA, PLCC and other devices use a reflection recognition method. The transmission recognition method uses the component shape as the recognition basis, and the recognition accuracy is affected by the size of the nozzle. When the nozzle shape is larger than the device outline, there is a nozzle outline in the recognition image. After the light source of the optical camera system has been used for a period of time, the light intensity will gradually decrease. Because the light intensity is proportional to the grayscale value converted by the solid-state camera, the larger the grayscale value, the clearer the digital image. Therefore, as the light intensity of the light source decreases, the grayscale value also decreases, but the grayscale value stored in the machine will not automatically decrease as the light intensity of the light source decreases. When the grayscale value is lower than a certain value, the image cannot be recognized. Therefore, regular calibration and detection must be performed ① Recalibration ② Adjust the aperture focal length. The grayscale value will be proportional to the light intensity of the light source. When the light intensity of the light source is so weak that the device cannot be recognized, the light source must be replaced. At the same time, the dust and devices on the lens, glass sheet and reflector should be cleaned regularly to prevent dust or devices from affecting the light intensity, resulting in poor recognition. On the other hand, the relevant initial data of the camera must be set correctly.
2: The whole-piece posture detection is to scan the device at high speed from the horizontal direction of the device through the linear sensor installed on the rack to detect the device's adsorption state and accurately detect the thickness of the device. When the thickness value set in the component library and the actual measured value exceed the allowable error range, poor thickness detection will occur, resulting in component loss. Therefore, it is crucial to correctly set the data of the device in the component library and the benchmark data of the thickness detection control sequence, and the thickness of the device must be re-tested frequently. At the same time, the linear sensor should be cleaned frequently to prevent dust, debris, oil stains, etc. from adhering to it and to detect the thickness and adsorption state of the device.
5. Poor device taping The accuracy of device placement is the result of multiple factors. In addition to the reasons of the equipment itself, poor device taping also has a great impact on it, mainly manifested in: A: The error of the tooth hole spacing is large. B: The shape of the device is poor. C: The square hole of the taping is irregular or too large, which causes the device to be hung or flipped horizontally. D: The adhesion between the paper tape and the plastic hot pressing tape is too large and cannot be peeled off normally, or the device is stuck on the bottom tape. E: There is oil on the bottom of the device.
6: Basic management How to make good use of equipment with excellent performance to create maximum profit is the goal pursued by the enterprise. How to achieve the goal mainly depends on scientific management methods:
A: Establish a regular employee training system to improve the quality of employees. People are the soul of the enterprise and the foundation of the enterprise's entrepreneurship and development. Therefore, it is necessary to pay attention to the skills training and ideological training of the staff team. They should be able to operate the equipment skillfully and correctly, install and use the feeder correctly, and regularly maintain and maintain the equipment to effectively ensure product quality, reduce material consumption, and improve production efficiency.
B: Establish a regular equipment maintenance plan. Promote TPM management, implement preventive performance maintenance and overhaul, so as to reduce the downtime of equipment due to temporary faults and pursue the maximum equipment utilization efficiency.
C: Improve equipment maintenance files. ①: Maintenance records. Record the phenomenon of failure, analysis process, handling situation, spare parts replacement, etc. ②: Maintenance spare parts replacement records. Analyze the reasons for spare parts replacement, spare parts replacement cycle, reduce spare parts backlog funds, and reduce production costs.
D: Improve equipment operation files. ①: Timely log table of equipment operation status. ②: Equipment operation status list. ③: Operation status monitoring chart. ④: Maintenance worker on duty equipment operation status monitoring chart. ⑤: Equipment monthly operation status list. ⑥: Equipment monthly operation status summary table.
VII: Common faults of placement machines
1: When a fault occurs, it is recommended to solve the problem according to the following ideas:
A: Analyze the working sequence of the equipment and the logical relationship between them in detail.
B: Understand the location, link and degree of the fault, and whether there is any abnormal sound.
C: Understand the operation process before the fault occurs.
D: Whether it occurs on a specific placement head or nozzle.
E: Whether it occurs on a specific device.
F: Does it happen in a specific batch?
G: Does it happen at a specific time?
2: Analysis of common faults.
A: Component placement offset mainly refers to the position offset in XY after the components are placed on the PCB. The reasons for this are as follows:
(1): PCB board reason a: The curvature of the PCB board exceeds the allowable range of the equipment. The maximum upward curvature is 1.2MM, and the maximum downward curvature is 0.5MM. b: The support pin height is inconsistent, resulting in uneven support of the printed circuit board. c: The flatness of the workbench support platform is poor d: The wiring accuracy of the circuit board is low and the consistency is poor, especially the difference between batches is large.
(2): The suction air pressure of the placement nozzle is too low, and it should be above 400mmHG when picking up and placing.
(3): The blowing pressure during placement is abnormal.
(4): The amount of adhesive or solder paste applied is abnormal or deviated. It causes the position of the component to drift during placement or welding. Too little causes the component to deviate from its original position when the workbench moves at high speed after placement. The coating position is inaccurate, and the corresponding offset occurs due to its tension.
(5): The program data equipment is incorrect.
(6): The substrate positioning is poor.
(7): The movement of the placement nozzle is not smooth when it rises, and it is relatively slow.
(8): The coupling between the power part and the transmission part of the XY worktable is loose.
(9): The placement head nozzle is installed improperly.
(10): The blowing timing does not match the placement head descending timing.
(11): The initial data setting of the nozzle center data and the camera of the optical recognition system is poor.
B: The device placement angle deviation mainly refers to the angular rotation deviation when the device is placed. The main reasons for its occurrence are as follows: (1): PCB board reasons
a: The warpage of the PCB board exceeds the allowable range of the equipment
b: The height of the support pins is inconsistent, making the printed circuit board support uneven.
C: The flatness of the workbench support platform is poor.
d: The wiring accuracy of the circuit board is low and the consistency is poor, especially the difference between batches is large.
(2): The suction pressure of the placement nozzle is too low. It should be above 400mmHG when picking up and placing.
(3): The blowing pressure is abnormal during placement.
(4): The amount of adhesive or solder paste applied is abnormal or deviated.
(5): The program data equipment is incorrect.
(6): The end of the nozzle is worn, blocked or stuck with foreign matter.
(7): The rising or rotating movement of the mounting nozzle is not smooth and is relatively slow.
(8): The parallelism between the nozzle unit and the XY worktable is poor or the nozzle origin detection is poor.
(9): The optical camera is installed with improper vibration or data equipment.
(10): The blowing timing does not match the placement head descending timing.
C: Component loss: It mainly refers to the loss of components between the suction position and the placement position. The main reasons for its occurrence are as follows:
(1): Program data equipment error
(2): The suction air pressure of the mounting nozzle is too low. It should be above 400MMHG during removal and placement.
(3): The blowing timing does not match the placement descending timing
(4): The posture detection sensor is poor and the reference equipment is wrong.
(5): Cleaning and maintenance of the reflector and optical recognition camera.
D: Abnormal pick-up:
(1): The tape specifications do not match the feeder specifications.
(2): The vacuum pump does not work or the suction pressure of the nozzle is too low.
(3): The plastic heat-pressing tape of the tape is not peeled off at the pick-up position, and the plastic heat-pressing tape is not pulled up normally.
(4): The vertical movement system of the nozzle is slow.
(5): The placement speed of the placement head is wrong.
(6): The feeder is not installed firmly, the feeder ejector pin does not move smoothly, the quick opener and closeer and the tape pressing are defective.
(7): The paper cutter cannot cut the tape normally.
(8): The tape cannot rotate normally with the gear or the feeder runs discontinuously.
(9): The nozzle is not at the low point at the pick-up position, the descending height is not in place or there is no movement. (10): The
center axis of the nozzle does not coincide with the center axis lead of the feeder at the pick-up position, and there is a deviation.
(11): The nozzle descent time is not synchronized with the pick-up time.
(12): There is vibration in the feeder part (13): The component thickness data device is incorrect.
(14): The initial value of the suction height is incorrect.
E: Random non-patch mainly refers to the nozzle not being able to mount the patch at the low point of the patch position. The main reasons for this are as follows:
(1): The warpage of the PCB board exceeds the allowable range of the equipment, with a maximum upward warpage of 1.2MM and a maximum downward warp of 0.4MM.
(2): The support pin height is inconsistent or the flatness of the workbench support platform is poor.
(3): The nozzle is sticky with liquid or the nozzle is severely magnetized.
(4): The vertical motion system of the L nozzle is slow.
(5): The blowing sequence does not match the timing of the placement head descent.
(6): The amount of glue on the printed circuit board is insufficient, there are leaks, or the machine plug-in pins are too long.
(7): The nozzle placement height equipment is faulty.
(8): The solenoid valve switches poorly and the blowing pressure is too low.
(9): When a nozzle fails to function properly, the component placement STOPPER cylinder does not move smoothly and is not reset in time.
F: Poor component pickup posture: mainly refers to the appearance of vertical pieces, inclined pieces, etc. The main reasons for this are as follows:
(1): Poor vacuum suction pressure regulation.
(2): The vertical motion system of the nozzle is slow.
(3): The nozzle descent time is not synchronized with the suction time.
(4): The initial value of the suction height or component thickness is set incorrectly, and the distance between the nozzle and the feed platform is incorrect when the nozzle is at the low point.
(5): The tape packaging specifications are poor, and the components shake in the mounting tape.
(6): The ejector pin of the feeder does not move smoothly, and the quick closer and the pressure belt are defective.
(7): The center axis of the feeder does not coincide with the vertical center axis of the nozzle, and the offset is too large.