How to avoid “Suction Error” at SMT Production

At SMT production ,machine happens problem of “Suction Error” will affect the factory’s production efficiency . What we should do is to know clearly where is the problem and solve it ,or try our best to avoid the problem before it happen the Suction Error .

1. SMT machine components suction error

The process of components be removed from the packaging braid by the high-speed movement mounter head to be mounted on the PCB ,

may happen errors of fail picking or drop after pick up etc.These error can cause a large number of component waste. According to our experiences, component suction error is usually caused by the following reasons:

A.Vacuum negative pressure is insufficient:

When nozzle pick the components, will produce a certain negative pressure to make the component adsorded on suction mouth.

Normally adopts the negative pressure test method to judge if nozzle picking component is abnormal or not, when the negative pressure sensor readings within a certain range, the machine thinks it’s normal, whereas suction abnormal. When suck component, vacuum negative pressure should be above 53.33 kPa, in this way can have enough quantity of vacuum to suction component .If vacuum negative pressure is insufficient, will not be able to provide enough suction to pick the components. During using, we often need to check the vacuum negative pressure , and regular cleaning suction nozzle, at the same time also note each SMT head’s vacuum filter core’s pollution situation , its role is to filter the suction nozzle’s air, if the core’s pollution to be black need to be replaced, in order to keep the air flowing.

B.

Suction nozzle’s wear, deformation , jams, or damage would caused air pressure insufficient, lead to suction failure, so need check the wear degree of suction nozzle, the serious one need to be replaced.

C. The influence of the feeder:

Feeder feed bad (feeder gear damage);

Material tape’s hole not properly on the gear of feeder;

Feeder bottom has the eyewinker(spring wear),

Tape pressure cover , springs and other running structures have deformation, rust, etc.;

which can lead to component suction shifting, vertical slices or can’t pick.Therefore should be regularly check, found that the problem handled in time, in case a large amount of waste.

D. Suction height influence:

The ideal suction height is when suction nozzle touch the surface of component, continualy press downward 0.05mm, if the depth of the press is too big, would cause components was pressed in the material slot but can’t afford to take. If a certain component suction situation is bad, can be appropriately adjust suction height slightly upward, such as 0.05 mm.

E. Original material problem

Some manufacturers of electronic component with packaging quality problems, such as tooth hole pitch error is bigger, paper tape and plastic viscous force is too large, or the material slot size is too small and so on, are the reason cause component can’t pick up.

2. Pick&Place machine identify error to component

SMT machine vision detection system consists of two parts : Components thickness detection system and optical identification system. So, on the analysis of the identification error can see below two aspects.

A, Components thickness detection error

Detect the thickness of the component, is through the linear sensor which installed on the structure,test from the side of the device, and compared with the thickness of the component library setting value, can determine the components’s bad adsorbing state (vertical slices, side suction, oblique, leakage, etc.), when the thickness of the component library setting value and measured value is beyond the scope of allowed error, there will be a bad thickness detection, lead to component loss. Therefore is very important to correctly set the thickness of the elements in the component library , also often clean the linear sensor, in order to prevent the adhesion of the dust, debris, or oil pollution etc ..which would affect the test of component’s thickness and suction status.

B,Component visual inspection error

Optical identify system is installed in a upward CCD camera system, it does optical imaging by camera identify the component outline shape during the mounter head’s spinning, meanwhile measured and recorded the camera device center position and rotating angle , and passed to the drive control system, thus make the compensation to x, y coordinates deviation and θ Angle deviation. Its advantage lies in the accuracy and the flexibility of the device can be applied to all kinds of size and shape. It has two kinds of identify method of backlight identify way and the former light identify way. Former light identify way based on component’s lead . Recognition accuracy is not affected by the size of the suction nozzle, can clearly detect device’s electrode position, even if the device, which component lead hidden within the component out shape, like LCC, SOJ etc.. can also mount correctly . The backlight identify based on component shape , mainly used to identify the chip resistance capacity components and triode, etc..recognition accuracy will be affected by suction nozzle size.

By R.Q.S