How to solve the problem of burning the substrate when laser welding PCB?

in Laser Welding FAQs, , , ,

With the development and advancement of electronics, new requirements for PCB substrate materials have been put forward, thus driving the continuous development of copper-clad laminate standards. In a complete circuit board manufacturing process, welding is an essential process.

Generally speaking, the substrate is the copper-clad board. It is used as the base material for manufacturing PCB because it has three major functions: conductivity, insulation and support.

In the welding of the substrate, laser welding is currently the most mature technology used, but it is difficult for the most mature technology to guarantee a 100% welding yield. It is important to understand that laser welding is a highly efficient and precise welding method that uses a high energy density laser beam as the heat source. In hundreds of batch welding, there is always the problem of laser burning of the substrate.

How can we avoid this problem of burning the substrate when laser welding PCB?


High-energy localized rapid heating leads to thermal expansion and deformation of the solder joint copper foil, and the solder joint copper foil is separated from the substrate.


In the first stage, the solder joint is continuously and steadily heated from low temperature to high temperature. For example, the solder joint welding process requires a temperature of 350°C, then we can set the temperature from 280°C to 350°C for 0.3S, which can generally solve this problem.


The controller of the laser welding machine adopts the power mode, but there is no professional laser engineer to adjust it.


Power mode is the continuous output of energy to the welded joint according to the set output power, independent of the actual welding temperature. Power mode is suitable for welded joints that dissipate heat quickly. Currently, laser welding is controlled by closed-loop, and temperature mode is generally used for non-specialized welded joints.


In temperature mode, the temperature overload of the laser welding machine exceeds the set welding temperature.

As we all know, current laser welding machines use a closed-loop control system. After setting the temperature, the controller automatically calculates the required output power. The power is calculated by collecting the real-time temperature, and temperature collection is the most important part of the closed-loop control of the laser welding machine. The temperature overload is due to the lack of timely temperature feedback, which causes the controller to keep increasing the output energy in order to get the feedback temperature.

Solution 1:

Use an on-line infrared thermometer. This system is integrated in the semiconductor laser, suitable for online measurement of the temperature of the laser processing point, and through the serial port connected to other lasers can continuously output the corresponding signal as other systems. It also can externally control the system through the IO signal to execute the command work, and output IO signal after the command is executed.

Temperature measurement range: 100-400℃, response speed 40us, with thermometer and controller, and laser closed-loop control, support software trigger and external trigger.

Solution 2:

Add power limit in temperature mode. If the temperature overload in temperature mode is caused by untimely feedback, we can observe the output power of the overload place according to the temperature curve of the temperature-controlled laser welding machine to limit the power, which can also be a good solution to the overload problem.

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