Analysis of factors affecting SMT device mount rate and common failure of SMT mounter





SMT equipment in the selection of the main consideration of its mounting accuracy and speed, in the actual use of the process, in order to effectively improve the quality of products, reduce conducive to production cost, improve production efficiency, how to improve and maintain the SMT equipment mounting rate is the primary task in front of users.


One, the meaning of mount rate

The so-called mount rate refers to the ratio of actual mount number and absorption number of devices in a certain period of time, namely: mount rate = ×100% absorption number, in which the total discard number refers to the number of suction errors, identification errors, the number of vertical pieces, lost number, etc., while the identification error is divided into two types: the size error of components and the optical recognition of devices.Placement machine no matter minicomputer, medium size machine, mainframe, also no matter medium speed machine, high speed machine, they are mainly composed of device storage device, XY table, mount head and control system.Mount head is the core and key parts of the mounter, mount head generally has fixed head and rotating head of the division, fixed general multiple arrangement, less than 2, more than 8, can be taken at the same time or alone, rotating head and divided in the horizontal plane of rotation and rotation in the vertical plane.

A. Device suction nozzle suction height switch

B, I rotation (±90 ')

C. Device optical identification

D. Device attitude detection 2 rotation (±90 ')

E. Mount device/nozzle height switch

F, 3 rotation (±180 '-

G. Suction nozzle conversion

H. The suction nozzle number shall be detected according to the patch machine

In the whole process of mounting, only from the perspective of equipment, the main factors affecting the equipment mounting rate are the position of the suction nozzle when the suction nozzle height and the position of the suction nozzle center and the relative position of the feeder are set correctly. According to the production information statistics of the equipment, the influence accounts for more than 80% of the whole influencing factors.The causes are as follows: on the one hand, it is the feeder on the device storage and transportation device; on the other hand, it is the suction nozzle. About 60% of the films of the two feeders are caused by the pollution of the suction nozzle.

The influence of the feeder the influence of the feeder is concentrated in the abnormal feeding.

The driving modes of the feeder include motor drive, mechanical drive and cylinder drive, etc. The mechanical drive is taken as an example to illustrate the influence of the feeder on the mount rate:

1. The driving part is driven mechanically by the CAM spindle to drive the feeding mechanism, which can quickly find the feeding arm. The ratchet connected with it is driven by the connecting rod to advance the component braid by a distance.However, due to high-speed access to the feeder of the feeding mechanism, after a long time of use, the ratchet of the feeder is seriously worn, resulting in the ratchet can not drive the normal strip strip strip strip stripping, so that the suction nozzle can not complete the work.Therefore, before the installation of braiding, the feeder should be carefully checked. The feeder with worn ratchet wheel should be repaired immediately, and the one that cannot be repaired should be replaced in time.

2, feeder structure deformation due to long-term use or operator improper operation, the pressure plate, thimble, springs and other sports organizations deformation, corrosion, etc., which can lead to absorb partial, set pieces, or less than components, so should be regular inspection, found that the problem handled in time, lest cause device of a large amount of waste, at the same time in the installation of feeder should be properly and securely installed in the feeding platform, especially without feeder height detection equipment, otherwise it may cause feeder or equipment damage.

3. The poor lubrication of the feeder is easy to be neglected in the maintenance and maintenance of the feeder. However, regular cleaning, cleaning and lubricating are essential.

Three, the influence of suction nozzle

Suction nozzle is also another important factor that affects the mount rate. The causes are internal and external

1, the internal reason on the one hand is the vacuum negative pressure is insufficient, before the suction nozzle to take the mechanical valve attached to the head, by blowing into true it adsorption, produce a certain amount of negative pressure, when the suction part, the negative pressure sensor detection value is within a certain range, the machine is normal, otherwise bad suction.In general, the negative pressure at the suction nozzle from the pickup position to the mount position should be at least 400mmHg. When mounting large devices, 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 state of the negative pressure detection sensor should be checked regularly.On the other hand, the filter attached to the head and the filter on the mouth become black due to the pollution and blockage of the surrounding environment or the unclean air source.Therefore, the filter should be replaced regularly. The filter on the mouth should be replaced at least once a half a month, and the filter on the head should be replaced at least once a half a year to ensure the smooth flow.

2, the leakage of the external reason is air circuit, such as rubber tracheal aging, rupture, seals aging, wear and suction nozzle after long time use wear, etc., on the other hand is because of the adhesive or the external environment of dust, especially paper braid packaging components after the cut off of a large number of scraps, cause the suction nozzle blocking, so for daily check the suction nozzle is clean degree, monitoring system of the suction nozzle to take at any time, to block or take negative suction nozzle should be timely clean or replace, in order to assure a good condition, at the same time when installing a suction nozzle, must ensure that the correct, firm installation, otherwise it will cause the suction nozzle or equipment damage.

Device detection system is the necessary guarantee of mounting accuracy and mounting accuracy

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

1, the optical recognition system is fixed installation of an optical imaging system, it is the rotation of the head in process, camera to identify components outline to optical imaging, at the same time relative to the camera device center position and rotating Angle measured and recorded, passed to the drive control system, thus to x, y coordinates deviation and theta Angle deviation compensation, its advantage lies in the accuracy and the flexibility of the device can be applied to all kinds of shape.It has a reflection recognition mode based on the device electrical identification, the recognition accuracy is not affected by the size of the suction nozzle, generally SOP, QFP, BGA, PLCC and other devices use reflection recognition mode.

The transmission identification method is based on the shape of the element, and the identification 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 identified in the image.After 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 higher the gray value, the clearer the digital image will be.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 as the light intensity of the light source decreases, so when the gray value is lower than a certain value, the image cannot be recognized, so it must be regularly corrected and detected re-calibration adjust the aperture focus.The gray value is 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, dust and devices on the lens, glass and reflector should be cleaned regularly to prevent dust or devices from affecting the intensity of the light source, resulting in poor identification.On the other hand, you must set up the initial data about the camera correctly.

2. The attitude detection of the whole part is to detect the suction state of the part through high-speed scanning from the transverse direction of the part through the linear sensor mounted on the frame, and accurately detect the thickness of the part. When the thickness value set in the part store and the measured value exceed the allowable error range, the thickness detection will be poor, resulting in the loss of the part.Therefore, it is very important to set up the data of the components in the part store and the reference data of the thickness detection and control sequence.At the same time, the linear sensor should be cleaned frequently to prevent the thickness of dust, debris, oil and other components adhering to it and the detection of the suction state.

Five, device braid is bad

The device mounting accuracy is the result of multiple factors acting together. In addition to the causes of the device itself, the poor device braiding also has a great impact on the device, mainly manifested in:

A. large error of perforation spacing.

B. poor device shape.

C. The braid square hole is irregular or too large, causing the device to be suspended or flipped laterally.

D. the adhesive force between the paper tape and the plastic hot-pressed tape is too strong to peel off normally, or the device is stuck to the bottom band.

E. there is oil at the bottom of the device.

Six, placement machine common failure

1. In case of failure, it is suggested to solve the problem as follows:

A. analyze in detail the working order of the equipment and the logical relationship between them.

B. Know the location, link and degree of the fault, as well as whether there is abnormal sound.

C. Understand the operation process before the failure.

D. Whether it happened in the specific attachment head and suction mouth.

E. whether it happens to a particular device.

F. Whether it happens in a specific batch.

G) whether it happened at a particular time.

2. Analysis of common faults

A. Component mount offset mainly refers to the position deviation of components in x-y after they are mounted on PCB, and the reasons are as follows:

(1) reason of PCB board a: the bending degree of PCB board is beyond the allowable range of equipment.The maximum upwarping is 1.2mm, and the maximum downwarping is 0.5mm.B: the height of the support pins is inconsistent, resulting in uneven PCB support.C: poor planeness of the support platform of the workbench d: low accuracy and poor consistency of circuit board wiring, especially large difference between batch and batch.

(2) the air pressure of the fitting suction nozzle is too low, and it should be above 400mmHG in the fitting and fitting.

(3) abnormal blowing pressure during mounting.

(4) the amount of adhesive and solder paste is abnormal or deviated.As a result, the position of the component will drift during mounting or welding, and too little will cause the component to deviate from the original position during high-speed movement of the workbench after mounting, and the coating position will be inaccurate, and the corresponding deviation will occur due to its tension.

(5) incorrect program data equipment.

(6) poor base plate positioning.

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

(8) the coupling between the power part and the transmission part of the x-y table is loose.

(9) the fitting head suction nozzle is not installed properly.

(10) the timing sequence of blowing does not match the timing sequence of drop of mounting head.

(11) the initial data Settings of the nozzle center data and the camera of the optical recognition system are not good.

B. Device mount Angle deviation mainly refers to the Angle direction rotation deviation during device mount, which is mainly caused by the following aspects:

(1) cause of PCB board: a: the bending degree of PCB board is beyond the allowable range of equipment; b: the height of support pins is not consistent, which makes the PCB board support uneven.C: poor planeness of the support platform of the workbench.D: the wiring accuracy of the circuit board is low and the consistency is poor, especially the big difference between batch and batch.

(3) abnormal blowing pressure during mounting.

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

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

(7) the upward or rotational movement of the mount suction nozzle is not smooth and relatively slow.

(8) the parallelism between the suction nozzle unit and the x-y table is not good or the origin of the suction nozzle is not detected well.

(9) improper installation of optical camera with moving or data equipment.

C. Component loss: mainly refers to the loss of components between the position of the suction piece and the position of the patch.

The main reasons are as follows:

(1) program data device error

(2) the pressure is too low when the suction nozzle is attached.Remove and mount above 400MMHG.

(3) the timing sequence of blowing does not match the timing sequence of fitting should fall

(4) the attitude sensor is not good and the reference device is wrong.

(5) cleaning and maintenance of reflector and optical recognition camera.

D. abnormal pickup:

(1) the braiding 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 hot-pressed plastic strip is not peeled off and the hot-pressed plastic strip is not normally pulled up.

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

(5) wrong mount speed selection of mount head.

(6) the feeder is not firmly installed, the thimble movement of the feeder is not smooth, the quick opening and closing device and the pressure belt is not good.

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

(8) the braiding shall not be discontinuous with the normal rotation of the gear or the operation of the feeder.

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

(10) the central axis of the suction nozzle at the pickup position does not coincide with the lead of the central axis of the feeder, and there is deviation.

(11) the falling time of the suction nozzle is out of sync with the time of the suction film.

(12) there is vibration in the feeding department

(13) element thickness data device is not correct.

(14) the initial value of the absorber height is wrong.

E, the randomness of the patch is mainly refers to the suction nozzle in the low point of the patch position is not attached to the leakage paste.

(1) the warpage of PCB exceeds the allowable range of the equipment, with the maximum warpage of upwarping being 1.2mm and the maximum bending of downwarping being 0.4mm.

(2) the height of the support pin is inconsistent or the planeness of the support platform of the workbench is poor.

(3) the suction nozzle is stuck with alternating fluid or the suction nozzle is seriously magnetized.

(4) the vertical motion system of L suction nozzle runs slowly.

(5) the timing sequence of blowing does not match the timing sequence of drop of mounting head.

(6) insufficient amount of glue on the printed board, leakage point or machine pin is too long.

(7) the suction nozzle mounting height equipment is poor.

(8) poor switching of solenoid valve, too little blowing pressure.

(9) when NG occurs in a suction nozzle, the action of device STOPPER is not smooth and cannot be reset in time.

F, the bad attitude of the piece: mainly pointing out the situation of instant piece, oblique piece.

(1) poor vacuum suction air pressure regulation.

(2) the suction nozzle vertical motion system runs slowly.

(3) the falling time of the suction nozzle is out of sync with the time of the suction film.

(4) the initial value of the height of the absorber or the thickness of the element is set incorrectly, and the distance between the suction nozzle and the platform of the feeding part is not correct at the low point.

(5) the packing specification of the brapping is poor, and the components shake in the mounting belt.

(6) poor movement of the material supplier's thimble, fast load closure device and bad pressure belt.

(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.

7. Unscientific management methods

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

A. Establish regular staff training system to improve staff quality.People are the soul of an enterprise and the root of its entrepreneurship and development.Therefore, we must pay attention to the training of staff skills and ideas, should be able to skillfully and correctly operate the equipment, the correct installation, use the feeder, regular maintenance, maintenance equipment, in order to effectively ensure product quality, reduce material consumption, 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 failure surface, and pursue maximum utilization efficiency of equipment.

C. Improve equipment maintenance files.

Maintenance record.Record failure phenomena, analysis process, treatment, replacement of spare parts, etc.

(2) maintenance spare parts replacement record.Analyze the cause of spare parts replacement, spare parts replacement cycle, reduce spare parts backlog funds, reduce production costs.

D. Improve equipment operation files.

Equipment running state timely login table.

(2) equipment operation status list.

Running state monitoring diagram.

(4) maintenance workers on duty equipment running status monitoring chart.

(5) list of monthly operation of equipment.

6. Equipment monthly operating status summary table.


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