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Common placement defects and quality analysis of SMT sample patch(placement of pnp machines)
Post Date:2022-06-21 12:56:25 Visit:6

The key factors that affect the quality of the placement: placement force, speed/acceleration of placement, placement accuracy of placement machine, components, solder paste and PCB. The smaller the components, the higher the precision requirements of the patch. Small rotational or translational errors can cause components to be misplaced or even completely off the pad. For fine pitch components, very small rotational errors will likely cause the components to deviate completely and cause bridging.


 Common placement defects


SMD defects: missing components, wrong components, reversed polarity of components, not meeting the minimum electrical clearance, and misaligned components.


1 offset


Offset phenomenon: The components deviate from the pad (the lateral deviation does not exceed 25%, and the end face cannot deviate). The reasons are:


(1) Height problem


If the PCB is not properly supported in the placement machine, it will sink, so that the height of the PCB surface will be lower than the zero point of the axis of the placement machine, causing the components to be released at a slightly higher position on the PCB, resulting in insufficient release of the original. precise.


(2) Nozzle problem


The end of the nozzle is worn, blocked or stuck with foreign objects, or the suction air pressure of the placement nozzle is too low. The rising or rotating movement of the placement nozzle is not smooth and slow, resulting in a mismatch between the blowing timing and the descending timing of the placement head. Misalignment is caused by problems such as the parallelism of the table and poor detection of the origin of the nozzle.


(3) procedural problems


The program parameters are poorly set, and the center data of the nozzle and the initial data of the camera of the optical recognition system are not accurate enough.


Ways to improve:


(1) Check whether the guide rail of the placement machine is deformed, and whether the placement of the PCB is stable and correct.


(2) Regularly check and clean the suction nozzle, maintain the parts that are easy to wear, and focus on lubrication and maintenance. Debug table and nozzle origin detection.


(3) Correct the procedure to make the database parameters consistent with the identification parameters of the identification system. And timely check the placement and printing results of the placement process.


2 missing parts


Phenomenon: Components are lost at the patch position. cause:


(1) Air leakage and blockage of air source


The aging and rupture of the rubber air pipe, the aging and wear of the seals, and the wear of the suction nozzle after long-term use cause the air source circuit to release pressure. Or waste dust, etc., cause the suction nozzle to be blocked, so that the placement head cannot successfully pick up components.


(2) Thickness setting problem


The thickness of the component or PCB is incorrectly set. If the component or PCB is thinner and the database is thicker, then when the nozzle is in the patch, the component will be put down before it reaches the PCB pad position, and the PCB is moving. , due to inertial action will cause flying parts


(3) PCB board problems


For example, the warpage of the PCB board exceeds the allowable error of the equipment. Or improper placement of support pin components, uneven placement of support pins, inconsistent height, poor flatness of the workbench support platform, etc., make the printed board support uneven, and also lead to flying parts.


Ways to improve:


(1) Regularly check whether the suction nozzle is clean. Increase the monitoring of the pick-up of the nozzle, find out the damaged parts that cause the air source problem and replace them in time to ensure a good state.


(2) Thickness setting problem


Change the thickness database parameters to the appropriate settings. Replace with appropriate braid.


(3) PCB board problems


Check whether the PCB board in the previous process meets the quality requirements, and relocate the PCB and tape. Check whether the working platform meets the production requirements and make reasonable adjustments and improvements.


3 throw


Phenomenon: During the production process, after the material is sucked, it is not pasted but placed in the material box or other places. Or perform an action without expecting it. Reason:


(1) Nozzle problem


Problems such as deformation, blockage and damage of the suction nozzle may cause many problems such as insufficient air pressure, air leakage, unaffordable or incorrect material retrieval, and inability to pass through the identification.


(2) Identify system problems


Identify poor system vision. After the light source of the optical camera system is used for a period of time, the light intensity will gradually decrease, and at the same time, the gray value will also decrease. When the light source intensity and gray value do not meet the requirements, the image will not be recognized. Or there are sundries at the laser head that interfere with the identification. It is also possible to identify that the system is damaged


(3) Program setting problem


Check whether the edited program conforms to the settings of the component parameters. The reclaiming material must be at the center of the material. If the reclaiming height is incorrect, or the reclaiming offset or reclaiming is not correct, the identification system will not match the corresponding data parameters, which will cause the identification system to fail to recognize and discard it as invalid material. , or the component parameter settings in the edited program do not match the parameter settings such as the brightness or size of the incoming material, which will cause the component to be discarded without recognition.


(4) Feeder problem


Due to long-term use or improper operation of the feeder, the drive part of the feeder will be worn or structurally deformed. The pawl will continue to wear and tear. If the pawl is seriously worn, the pawl will not be able to drive the plastic tape of the reel to peel off normally, so that the suction nozzle cannot normally complete the pick-up work. If the position of the feeder is deformed, the feeder is not fed properly (such as the ratchet gear of the feeder is damaged, the tape hole is not stuck on the ratchet gear of the feeder, there is a foreign object under the feeder, the spring is aged, or the electrical is defective) , there is a foreign body under


(5) Incoming material problem


Problems such as irregularity and unqualified pins of incoming materials or components will also cause unidentified materials to be thrown.


Ways to improve:


(1) Do a good job in monitoring the pickup of the nozzle. The blocked or bad pick-up nozzle should be cleaned or replaced in time to ensure a good condition. When installing the nozzle, it must be installed correctly and firmly.


(2) Regularly clean and wipe the dust and device dirt on the lens, glass sheet and reflector of the identification system to keep it clean and free of debris and prevent the light source from being affected by dust or devices. Periodically perform calibration checks, such as re-calibration and adjustment of aperture focus. When the light intensity of the light source is too weak to identify the device, only the light source can be replaced.


(3) When installing the co-feeder, it should be installed on the platform of the feeding part correctly and firmly. Before installing the tape, carefully check whether the pawl wheel of the feeder is worn and repaired. If it cannot be repaired, it should be replaced in time. Do a good job in the daily maintenance and maintenance of the feeder, such as cleaning, cleaning, oiling and lubrication.


(4) Strict screening and testing of incoming materials to prevent the use of wrong materials.


(5) The relevant initial data of the camera must be set correctly. If there is any error, you need to modify the program and component parameters such as the reclaiming position.


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