UV Laser Processing Applications in PCB Industry

UV Laser Processing Applications in PCB Industry

Today, long-life laser sources configured in laser systems are almost maintenance-free. In the production process, the laser level is Class 1 and there is no need for additional safety protection devices. The LPKF laser system is equipped with a dust suction device that does not cause emissions of harmful substances. Coupled with its intuitive and easy-to-use software control, laser technology is replacing traditional mechanical processes, saving the cost of special tools.

CO2 laser or UV laser?

For example, a PCB CO2 laser system with a wavelength of approximately 10.6 μm can be selected when PCBs are divided or cut. Its processing costs are relatively low and the laser power provided can reach several kilowatts. However, it generates a large amount of heat during the cutting process, resulting in severe carbonization of the edges.

The UV laser wavelength is 355 nm. Laser beams of this wavelength are very easy to focus optically. UV lasers with a laser power of less than 20 watts have a spot diameter of only 20 μm after focusing – and the resulting energy density is even comparable to the sun's surface.

The advantages of UV laser processing

UV lasers are especially suitable for the cutting and marking of rigid boards, hard and soft boards, soft boards and their accessories. What are the advantages of this laser process?

In the SMT industry, board sub-boards and micro-drilling in the PCB industry, UV laser cutting systems show great technical advantages. Depending on the thickness of the board material, the laser cuts one or more times along the desired profile. The thinner the material, the faster the cutting. If the accumulated laser pulses are lower than the laser pulses required to penetrate the material, scratches will only appear on the surface of the material; therefore, two-dimensional codes or barcodes can be marked on the material for follow-up process information tracking.

The pulse energy of the UV laser is only applied to the material for microseconds. There is no obvious thermal effect at a few micrometers next to the incision, so it is not necessary to consider the damage caused by the heat generated by the element. The lines and solder joints near the edges are intact and free of burrs.

In addition, the LPKF UV laser system integrated CAM software can directly import the data derived from CAD, edit the laser cutting path, form a laser cutting profile, select a processing parameter library suitable for different materials, and can directly laser process. The laser system is suitable for both mass production and sample production.

Drilling application

The through holes in the circuit board are used to connect the front and back lines of the double-sided board, or to connect any of the layers in the multilayer board. For its conductivity, it is necessary to plate the hole walls with a metal layer after drilling. Nowadays, traditional mechanical methods have been unable to meet the requirements of smaller and smaller borehole diameters: Although the spindle speed is increased, the radial speed of precision drilling tools can be reduced because the diameter is too small, and even the required machining results cannot be achieved. In addition, tool wear that is prone to wear is also a limiting factor from an economical point of view.

For the drilling of flexible circuit boards, LPKF has developed a new type of laser drilling system. The LPKFMicroLine 5000 laser device is equipped with a 533mm x 610mm table top for automated roll-to-roll operations. When drilling, the laser can first cut out the micro hole profile from the center of the hole, which is more accurate than the ordinary method. The system can drill micro-holes with a minimum diameter of 20 μm on an organic or non-organic substrate with a high aspect ratio. Such precision is very much needed for flexible circuit boards, IC substrates, or HDI circuit boards.

Prepreg cutting

In the manufacturing process of electronic components, what conditions require cutting prepreg materials? Early in the early days, prepreg materials had been used in multilayer circuit boards. Each circuit layer in the multilayer circuit board is pressed together by the action of a prepreg; according to the circuit design, the prepreg in some areas needs to be cut in advance and then pressed.

A similar process also applies to FPC cover films. The cover film is usually made of polyimide and a glue layer with a thickness of 25 μm or 12.5 μm, and is easily deformed. A single area (such as a pad) does not need to be covered by a cover film for later assembly, connection, etc.

This thin material is very sensitive to mechanical stress - it can be easily done with non-contact laser processing. At the same time, the vacuum adsorption station can well fix its position and maintain its flatness.

Soft and hard board processing

In a hard and soft bonded board, a rigid PCB and a flexible PCB are pressed together to form a multilayer board. During the lamination process, the top of the flexible PCB is not bonded together with the rigid PCB, and the rigid cover covering the top of the flexible PCB is cut and separated by laser deep cutting to leave a flexible portion to form a soft and hard bonded board.

This depth-defining machining is also suitable for blind slot machining of surface-embedded integrated components in multilayer boards. The UV laser precisely cuts the blind slot of the target layer separated from the multilayer circuit board. In this area, the target layer does not form a connection with the material it covers.

High efficiency board for PCB and FPC

The SMT rear board is a circuit board that has been assembled with a variety of electronic components. This process is already at the end of the production chain. For the sub-boards, different technologies can be selected: For commonly used PCBs, the traditional methods of knife-cutting, punching and contour milling are preferred. For more complex electronic circuits and thin substrates, especially where mechanical stress, dust, and dimensional variations are very sensitive, UV laser cutting is more advantageous. The following three charts evaluate these three methods from different factors.