PCBA Tech - SMT model patch placement defects and quality analysis

The key factors that affect the quality of SMT template placement: placement force, placement speed/acceleration, placement accuracy of placement machine, components, solder paste and PCB. The smaller the components, the higher the precision requirements of the patch. A small rotation error or translation error will cause the component to be biased or even completely deviate from the pad. For fine-pitch components, extremely small rotation errors may cause the components to completely deviate and cause bridging.

Common placement defects

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

1 offset

Offset phenomenon: The component deviates from the PCB pad (the horizontal deviation does not exceed 25%, and the end surface can not deviate). Causes:

(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 axis zero point of the placement machine, causing the components to be released at a slightly higher position on the PCB, causing the original to not be released. precise.

(2) Nozzle problem

The suction nozzle end is worn, clogged or stuck with foreign matter, or the suction pressure of the placement nozzle is too low. The suction pressure of the placement nozzle is too low. The rising or rotating movement of the placement nozzle is not smooth and slow, causing the blowing timing to not match the placement head down timing. Problems such as the parallelism of the worktable and the poor detection of the origin of the suction nozzle cause deviation.

(3) Procedural issues

The program parameter settings are poor, and the center data of the nozzle and the initial data settings of the camera of the optical recognition system are not accurate enough.

Ways to improve:

(1) Check whether the rails of the placement machine are deformed and whether the PCB placement is stable and correct.

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

(3) The calibration procedure makes 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 pieces

Phenomenon: The components are lost in the placement position. cause:

(1) The problem of air leakage and blockage

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

(2) Thickness setting problem

The thickness of the component or PCB is set incorrectly. If the component or PCB is thinner and the database is thicker, then when the suction nozzle is mounted, the component will be put down before it reaches the position of the PCB pad, and the PCB is moving, Due to inertia, flying parts

(3) PCB board problem

If the warpage of the PCB board exceeds the allowable error of the device. Or improper placement of support pin components, uneven placement of support pins, inconsistent heights, poor flatness of the workbench support platform, etc., make the printed board support uneven and cause flying parts.

Ways to improve:

(1) Regularly check whether the suction nozzle is clean. Intensify the monitoring of the pick-up situation of the suction nozzle, find out the damaged parts that cause the air supply problem and replace them in time to ensure a good condition. (2) Thickness setting problem

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

(3) PCB board problem

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

3 throwing

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

(1) Nozzle problem

Problems such as the deformation, blockage, and damage of the suction nozzle may cause many problems such as insufficient air pressure, air leakage, unreliable or incorrect retrieving, and failure to identify.

(2) Identify system problems

Identify the poor vision of the system. After the light source of the optical camera system is used for a period of time, the light intensity will gradually decrease, and the gray value will also be reduced. When the light source intensity and gray value do not meet the requirements, the image will not be recognized. Or there is debris at the laser head that interferes with recognition. There is also the possibility that the identification system is damaged

(3) Programming issues

Whether the edited program is consistent with the SMT component parameter settings. The reclaiming material must be in the center of the material. If the reclaiming height is incorrect, or the reclaiming deviation, the reclaiming is not correct, etc., the identification system and the corresponding data parameters will not match, which will not be recognized by the identification system and be discarded as invalid materials., Or the parameter settings of the SMT component 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 because it cannot be identified

(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. If the pawl is severely worn, the pawl will not be able to drive the plastic tape of the take-up reel to peel off normally, making the suction nozzle unable to complete the pick-up work normally. If the position of the feeder is deformed, the feeder feeds poorly (such as the feeder ratchet gear is damaged, the material belt hole is not stuck on the feeder ratchet gear, there is foreign matter under the feeder, the spring is aging, or the electrical failure), There is a foreign object