SMT equipment mainly considers its placement accuracy and placement speed when purchasing SMT equipment. In actual use, in order to effectively improve product quality, reduce production costs, and improve production efficiency, how to increase and maintain the placement rate of SMT equipment is The primary issue facing users.

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1. The meaning of placement rate

    The so-called placement rate refers to the ratio of the actual placement number of the device to the suction number within a certain period of time, that is: placement rate = ×100% suction number, where the total number of discarded parts refers to the number of suction errors, the number of recognition errors, the number of stand-alone pieces, Missing counts, etc., and recognition errors are divided into two types: device specification and size errors and poor device optical recognition. Whether it is a small machine, a medium machine, a large machine, or a medium-speed machine or a high-speed machine, the placement machine is mainly composed of a device storage and transportation device, an XY table, a placement head and a control system. The placement head is the core and key component of the placement machine. The placement head is generally divided into a fixed head and a rotating head. The fixed head is generally arranged with multiple heads, ranging from 2 to 8, which can be picked up at the same time or separately, and the rotating head It is divided into rotation in the horizontal plane and rotation in the vertical plane.

A. The device sucks up the suction nozzle to switch the height of the suction

B, θI rotation (±90’)

C. Device optical recognition

D. Device attitude detection θ2 rotation (±90’)

E. Mounting device/nozzle height switching

F, θ3 rotation (±180’-θ) nozzle origin detection defect removal

G. Nozzle conversion

H. The nozzle number detection is based on the pick-up from the placement machine 　

      The whole process of placement, from the point of view of equipment alone, with the correct setting of the nozzle pickup height and the position of the nozzle center relative to the feeder, the main factor that affects the equipment placement rate is the pickup position According to the production information of equipment statistics, its influence accounts for more than 80% of the entire influencing factors. The reasons are: on the one hand, the feeder on the device storage and transportation device, and the suction nozzle on the other. About 60% of the film of the feeder of the two are caused by the pollution of the suction nozzle.

 

2. The influence of the feeder The influence of the feeder mainly focuses on abnormal feeding.

 

   There are several driving methods for the feeder, such as motor drive, mechanical drive, and cylinder drive. Here, the mechanical drive is taken as an example to illustrate the influence of the feeder on the placement rate:

1. The driving part is worn mechanically and driven by the cam main shaft to drive the feeding mechanism to quickly tap the strike arm of the feeder, and the ratchet wheel connected to it through the connecting rod drives the component braid to advance by one pitch, and at the same time drives the plastic The take-up reel removes the plastic cap on the braid, and the suction nozzle descends to complete the pickup action. However, due to the high-speed access of the feeder to the feeder, the pawl of the feeder is severely worn after a long time of use, causing the pawl to fail to drive the plastic tape of the reel to peel off normally, making the suction nozzle unable to complete the work of picking up parts. Therefore, the feeder should be carefully checked before installing the braid. The worn-out feeder of the pawl wheel should be repaired immediately, and the one that cannot be repaired should be replaced in time.

　　

2. The structural parts of the feeder are deformed due to long-term use or improper operation by the operator, the press belt cover plate, thimble, spring and other movement mechanisms are deformed, rusted, etc., which will cause the device to attract deviation, stand up or fail to absorb the device. Therefore, it should be checked regularly and the problems should be dealt with in time to avoid a large amount of waste of components. At the same time, the common feeder should be correctly and firmly installed on the platform of the feeder, especially the equipment without feeder height detection, otherwise it may be Cause damage to the feeder or equipment.

　　

3. Poor feeder lubrication Generally, it is easy to overlook the maintenance and maintenance of the feeder, but regular cleaning, cleaning, and lubrication are essential tasks.

 

Third, the influence of the suction nozzle

 

   The suction nozzle is also another important factor that affects the placement rate. The causes are internal and external: 　

 

1. The internal reason is that the vacuum negative pressure is insufficient. The mechanical valve on the placement head is automatically switched before the suction nozzle picks up the parts, and the air blow is converted to the real suction, which generates a certain negative pressure. When the parts are sucked, the negative pressure sensor When the detection value is within a certain range, the machine is normal, otherwise the suction is bad. Generally, the negative pressure from the pick-up position to the mounting position of the suction nozzle should be at least 400mmHg or more. When mounting large components, the negative pressure should be more than 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 become black due to contamination and clogging due to the surrounding environment or the 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 half a year to ensure unobstructed air flow.

　　

2. On the one hand, the external cause is the pressure relief of the air supply circuit, such as the aging and rupture of the rubber air pipe, the aging and wear of the seal, and the wear of the suction nozzle after long-term use. On the other hand, it is due to the adhesive or the dust in the external environment, especially A large amount of waste generated by the components of the paper tape packaging after cutting causes the suction nozzle to be blocked. Therefore, because the cleanliness of the suction nozzle is checked daily, the pickup of the suction nozzle is monitored at any time, and the suction of the clogged or poor pickup The nozzle should be cleaned or replaced in time to ensure good condition. 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.

 

 

Fourth, the device inspection system is a necessary guarantee for placement accuracy and placement correctness

 

  The device detection system is divided into device optical recognition system and device attitude detection.　　

1. The optical recognition system is an optical camera system that is fixedly installed. It recognizes the contours of the components through the camera during the rotation of the placement head to perform optical imaging. At the same time, the center position and rotation angle of the device relative to the camera are measured and recorded. Then, it is transferred to the transmission control system to compensate for the XY coordinate position deviation and the θ angle deviation. The advantage lies in the accuracy and the flexibility of being applicable to devices of various specifications and shapes. It has a reflection recognition method based on the device electrode, and the recognition accuracy is not affected by the size of the nozzle. Generally, SOP, QFP, BGA, PLCC and other devices adopt the reflection recognition method.

     The transmission recognition method is based on the shape of the component, and the recognition accuracy is affected by the size of the nozzle. When the shape of the nozzle is larger than the contour of the device, the contour of the nozzle is recognized in the image. As the light source of the optical camera system is used for a period of time, the light intensity will gradually decrease, because the light intensity is proportional to the gray value converted by the solid-state camera, the larger the gray value, the clearer the digital image. Therefore, as the light intensity of the light source decreases, the gray value also decreases, but the gray value stored in the machine will not automatically decrease with the decrease of the light intensity of the light source. When the gray value is lower than a certain value When the value is set to the value, the image cannot be recognized, so it is necessary to perform regular calibration test ①re-calibration ②adjust the focal length of the iris. The gray value will be proportional to the light intensity of the light source. When the light intensity of the light source is too weak to identify the device, the light source must be replaced. At the same time, the lens, glass sheet and dust and devices on the reflector should be cleaned regularly to prevent the dust or the device from affecting the intensity of the light source and causing poor recognition; another The relevant initial data of the camera must also be correctly set.

　　

2. The posture detection of the whole piece is through the linear sensor installed on the rack, scanning from the lateral direction of the device at high speed to detect the adsorption state of the device, and accurately detect the thickness of the device, when the thickness value set in the parts library and the actual measured value When it exceeds the allowable error range, poor thickness detection will occur, resulting in parts loss. Therefore, it is very important to correctly set the data of the devices in the parts library and the reference data of the thickness detection control order, and the thickness of the devices must be retested frequently. At the same time, the linear sensor should be cleaned frequently to prevent the detection of the thickness and adsorption state of the device such as dust, debris, and oil stains adhering to it.

 

Fifth, the device is poorly taped

 

   The accuracy of device placement is the result of multiple factors. In addition to the device's own reasons, poor device braiding also has a great impact on it, mainly in:

A. The pitch error of the perforations is relatively large.

B. The shape of the device is not good.

C. The shape of the braided square hole is irregular or too large, which causes the device to be hung up or turned over horizontally.

D. The adhesive force 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 stain on the bottom of the device.

 

Six, common faults of the placement machine

 

1. When a fault occurs, it is recommended to solve the problem according to the following ideas:

A. Detailed analysis of the working sequence of the equipment and the logical relationship between them.

B. Understand the location, link and extent of the fault, and whether there is any abnormal sound.

C. Understand the operation process before the failure occurs.

D. Whether it occurs on a specific placement head or nozzle.

E. Whether it occurs on a specific device.

F. Whether it occurs in a specific batch.

G. Does it happen at a specific moment?

 

2. Analysis of common faults

A. Component placement offset mainly refers to the position offset in X-Y after the components are mounted on the PCB. The causes are as follows:

(1) The reason for the PCB board a: The warpage of the PCB board exceeds the allowable range of the device. The maximum upturn is 1.2MM, and the maximum downturn is 0.5MM. b: The height of the support pins is inconsistent, resulting in uneven support of the printed board. c: The flatness of the workbench support platform is poor. d: The circuit board has low wiring accuracy and poor consistency, especially the large difference between batch and batch.

(2) The suction pressure of the placement nozzle is too low, and the pickup and placement should be above 400mmHG.

(3) The blowing pressure is abnormal during placement.

(4) The amount of adhesive and solder paste applied is abnormal or deviated. This leads to component placement or welding when the position drifts. Too few components cause the component to deviate from the original position when the worktable moves at high speed after placement, the coating position is inaccurate, and the corresponding deviation occurs due to its tension.

(5) The program data device is incorrect.

(6) Poor positioning of the substrate.

(7) The movement of the mounting nozzle is not smooth and slow when it rises.

(8) The coupling between the power part and the transmission part of the X-Y worktable is loose.

(9) Poor installation of the nozzle of the placement head.

(10) The blowing sequence does not match the placement head descending sequence.

(11) The initial data settings of the nozzle center data and the camera of the optical recognition system are poor.

　　

B. Device mounting angle deviation mainly refers to the angular direction rotation deviation when the device is mounted. The main reasons for it are as follows:

(1) The reason for the PCB board a: The warpage of the PCB board exceeds the allowable range of the equipment b: The height of the support pins is inconsistent, which makes the printed board support uneven. C: The flatness of the workbench support platform is poor. d: The circuit board has low wiring accuracy and poor consistency, especially the large difference between batch and batch.

(2) The suction pressure of the placement nozzle is too low, and the pickup and placement should be above 400mmHG.

(3) The blowing air pressure is abnormal during placement.

(4) The amount of adhesive and solder paste applied is abnormal or deviated.

(5) The program data device is incorrect.

(6) The end of the suction nozzle is worn, blocked or stuck with foreign matter.

(7) The uptake or rotation of the mounting nozzle is not smooth and slow.

(8) The parallelism between the nozzle unit and the X-Y table is poor or the nozzle origin detection is poor.

(9) Improper installation of optical cameras or improper data equipment.

(10) The blowing sequence does not match the placement head descending sequence.

　　

C. Loss of components: mainly refers to the loss of components between the suction position and the placement position.

The main reasons for this are as follows:

(1) Program data device error

(2) The pressure of the mounting nozzle is too low. It should be more than 400MMHG during removal and placement.

(3) The blowing sequence does not match the placement sequence

(4) The posture detection sensor is bad, and the reference equipment is wrong.

(5) Cleaning and maintenance of reflectors and optical recognition cameras.

　　

D. The pickup is abnormal:

(1) The tape specification does not match the feeder specification.

(2) The vacuum pump is not working or the suction pressure of the suction nozzle is too low or too low.

(3) The plastic hot pressing tape braided at the pickup position is not peeled off, and the plastic hot pressing tape is not pulled up normally.

(4) The vertical movement system of the suction nozzle is slow.

(5) The placement speed of the placement head is selected incorrectly.

(6) The feeder is not firmly installed, the feeder thimble does not move smoothly, the quick switch and the press belt are not good.

(7) The paper cutter cannot cut the braid normally.

(8) The braid cannot follow the normal rotation of the gear or the feeder is not running continuously.

(9) The suction nozzle is not at the low point at the suction position, the lowering height is not in place or there is no movement.

(10) In the pickup position, the center axis of the suction nozzle does not coincide with the center axis of the feeder, and there is a deviation.

(11) The falling time of the suction nozzle is not synchronized with the suction time.

(12) Vibration in the feeding part

(13) The component thickness data device is incorrect.

(14) The initial value of the suction piece height is wrong.

　　

E. Random non-attachment mainly refers to the fact that the suction nozzle is not attached at the low point of the patch position and there is a missed attachment.

The main reasons for this are as follows:

(1) The warpage of the PCB board exceeds the allowable range of the equipment, the maximum warpage is 1.2mm, and the maximum warpage is 0.4mm.

(2) The height of the support pins is inconsistent or the flatness of the support platform of the worktable is poor.

(3) There is liquid on the suction nozzle or the suction nozzle is severely magnetized.

(4) The vertical movement system of the L nozzle runs slowly.

(5) The blowing sequence does not match the placement head descending sequence.

(6) The amount of glue on the printed board is insufficient, missing points, or the machine pins are too long.

(7) The nozzle mounting height equipment is defective.

(8) The solenoid valve is poorly switched and the blowing pressure is too small.

(9) When a nozzle appeared NG, the device placement STOPPER cylinder did not move smoothly and was not reset in time.

　　

F. Poor posture for picking up: Mainly refers to the presence of standing or oblique films.

The main reasons for this are as follows:

(1) Poor adjustment of vacuum suction pressure.

(2) The vertical movement system of the suction nozzle runs slowly.

(3) The falling time of the suction nozzle is not synchronized with the suction time.

(4) The initial value of the height of the suction piece or the thickness of the component is set incorrectly, and the distance between the suction nozzle and the feeder platform when the suction nozzle is at a low point is incorrect.

(5) The packaging specifications of the braid are not good, and the components are shaking in the installation belt.

(6) The feeder thimble does not move smoothly, the fast closing device and the press belt are not good.

(7) The center axis of the feeder does not coincide with the vertical center axis of the suction nozzle, and the deviation is too large.

 

Seven, management methods are not scientific

 

   Basic management how to make good use of high-performance equipment to create maximum profits is the goal pursued by the enterprise. How to achieve the goal depends mainly on scientific management methods: 　

A. Establish a regular employee training system to improve the quality of employees. People are the soul of an enterprise and the foundation of enterprise entrepreneurship and development. Therefore, we must pay attention to the skill training and ideological training of the staff team. They should be able to operate the equipment proficiently and correctly, install and use the feeder correctly, and maintain and maintain the equipment regularly 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, thereby reducing equipment downtime due to temporary failures, and pursuing maximum equipment utilization efficiency.

　　

C. Complete equipment maintenance files. ① Maintenance records. Record the phenomenon of the failure, the analysis process, the processing situation, the replacement of spare parts, etc. ② Maintain spare parts replacement records. Analyze the reasons for the replacement of spare parts, the replacement cycle of spare parts, reduce the backlog of spare parts, and reduce production costs.

　　

D. Complete equipment operation files. ①The operation status of the equipment is logged in the table in time. ② List of equipment operating status. ③Operating status monitoring diagram. ④The monitoring diagram of the operation status of the equipment on duty by the maintenance worker. ⑤ Monthly equipment shipment