PCBA Tech - Factors affecting the placement rate of SMT equipment

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

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-ups, 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 two to eight, 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 for this are: on the one hand, the feeder on the device storage and transportation device, on the other hand, the suction nozzle, about 60% of the film of the feeder of the two, and about 40% 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 modes of 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 smt 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, which can be caused by internal reasons as well as external reasons.

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 nozzle should be replaced at least once every half a month, and the filter on the smt head should be replaced at least once every half a year to ensure unobstructed airflow.