Reason for SMT placement machine throwing materials and horizontal difference in Reflow Soldering

Analysis of the main reason for SMT placement machine throwing Materials 

In the SMT production process, how to control production costs and improve production efficiency is of great concern to business owners and engineers, these problems are greatly related to the throwing rate of SMT placement machines. The following describes the throwing rate of SMT placement machines.

The so-called throwing refersDuring the production process of SMT placement machine, the device is not pasted after being sucked. Instead, the device is pushed to the bin or other places, or the above throwing action is executed without being sucked.. Material throwing results in material loss, prolonged production time, reduced production efficiency, and increased production costs. In order to optimize production efficiency and reduce costs, the high throwing rate must be solved.

 

Main Causes and Countermeasures for throwing materials:

Cause 1: nozzle problems,Suction nozzle deformation, blockage, damage, resulting in insufficient air pressure, air leakage, resulting in suction is not available, the extraction is not correct, the recognition is not passed and throwing. Countermeasure: clean and replace the suction nozzle;

Cause 2: Identify system problems,Poor vision, non-clean vision or laser lens, debris interference identification, improper selection of recognition light source, insufficient intensity and gray scale, or the identification system may be broken. Countermeasure: clean and wipe the identification system surface, keep clean and free of debris, adjust the intensity and gray level of the light source, and replace the identification system components;

Cause 3: location problems,The picking height is incorrect because it is not in the center of the picking(Generally, when the part is hit, the pressure is 05MM MPa), leading to the deviation, the picking is incorrect, there is an offset, the identification is inconsistent with the corresponding data parameters, and the identification system is discarded as invalid materials. Countermeasure: Adjust the picking position;

 

Cause 4: vacuum,Due to insufficient air pressure, the vacuum tunnel is not smooth, and some guide blocks the vacuum tunnel.Or a vacuum leak causes insufficient air pressure and the device may not be able to pick up or drop it on the way to the sticker. Countermeasure: Adjust the pressure steep slope to the required pressure value (for example, 0.5 ~~ 6Mpa-Huang Pai SMT placement machine), clean air pressure pipes, repair leaking gas paths;

Cause 5: Program problems,The component parameter settings in the edited program are incorrect., The physical size and brightness of the object are discarded because the identification fails. Countermeasure: Modify the component parameters and search for the optimal parameter settings of the component;

Cause 6: the problem of incoming materials, irregular incoming materials, non-conforming products such as pin oxidation. Countermeasure: iqc should check incoming materials and contact component suppliers;

Cause 7: The feeding device is faulty, the feeding device is deformed at the position, and the feeding device is poorly fed (the spine gear of the feeding device is damaged, the feed belt hole is not stuck on the spine gear of the feeding device, there is foreign body under the feeding device, and the spring is aging, or poor electrical), resulting in insufficient or poor retrieval of materials and throwing materials, there is damage to the feeding device. Countermeasure: Adjust the feeding device, clean the feeding platform, and replace the bad parts or feeding device. When there is a throwing phenomenon, you can first ask the on-site personnel to describe it, then, we can find out the problem based on the observation and analysis, so that we can effectively locate the problem and solve it. At the same time, we can improve the production efficiency, but it usually takes up the machine production time.

After the placement machine is mounted, the PCB Board is directly inserted into the Reflow Soldering fixed electronic components.Horizontal Temperature DifferenceThis results in uneven effect.

Due to the very small reflow soldering process window, it is very important to control the transverse temperature difference. The temperature in reflow soldering is generally affected by five factors:

　1. Hot air transmission 

Currently, mainstream lead-free reflow soldering furnaces adoptFull hot airIn the development process of reflow soldering furnace, there is also an infrared heating method, but due to the existence of Infrared HeatingDifferent color devices have different infrared reflectivity.And becauseThe shadow effect is generated when the adjacent original device is blocked.In both casesLead-free solder due to temperature difference may jump out of the Process WindowTherefore, the infrared heating technology has been gradually replaced by the Full-hot-air or infrared + hot-air compound Heating Method in the reflow soldering furnace. In Lead-free soldering, the heat transfer effect should be emphasized, especially for large-heat-capacity raw devices, if they cannot be fully heat transferred, this will cause the temperature rise to lag significantly behind the small thermal capacity device, resulting in horizontal temperature difference.

　2. Chain Speed Control 

The chain speed control will affect the horizontal temperature difference of the circuit board. In general, reducing the chain speed will give more time for devices with large thermal capacity to increase the temperature, thus reducing the horizontal temperature difference. But after all, the setting of the furnace temperature curve depends on the requirements of the solder paste, so unlimited reduction of the chain speed is unrealistic in actual production.

　　3. Control of wind speed and air volume 

If other conditions remain unchanged in the reflux furnace, the fan speed in the reflux furnace is reduced by 30%, the temperature on the PCB is reduced by about 5-10 degrees (of course, it is mainly reflected in the difference in the heat absorption capability of the PCB ). It can be seen that the importance of wind speed and air volume control on temperature control. To control the wind speed and air volume, pay attention to the following two points:

(1). the fan speed should be implementedVariable Frequency ControlTo reduce the effect of voltage fluctuation on it;

(2) tryReduce the exhaust air volume of the deviceBecause the central load of pumping and exhaust is often unstable, it is easy to affect the flow of hot air in the furnace.

　　4. Impact of reflow soldering Structure 

　　Reflow Soldering Transmission Mode: 

It is generally divided into three types,Rail, mesh, rail, and mesh, The temperature close to the rail end is generally low, so the reflux welding guide should be far away from the return air, it is not recommended to use the maximum width limit to weld the product. If the single panel is used, the mesh belt or single guide rail can easily achieve less horizontal temperature difference.

　　Reflow Soldering duct structure: 

Generally, the hot air duct is divided into single air duct and dual air duct. The structure of single air duct is relatively simple and easy to maintain. It is the mainstream method of low-end reflux welding, but it is precise and requires high hot air efficiency, generally, dual-duct reflow soldering is required. This type of reflow soldering equipment is usually used for high-end reflow soldering because of its high manufacturing cost.

　　5. device Stability 

Even if we get the most accurate temperature curve setting, we still need to ensure the stability, repeatability and consistency of the equipment to achieve it. Especially for lead-free production, if the device is slightly drifting, it is easy to jump out of the process window, resulting in cold welding or damage to the original device. Therefore, more and more manufacturers have begun to propose stability testing requirements for the equipment.