UV laser processing applications in the PCB industry

- Dec 16, 2019-

UV laser processing applications in the PCB industry

Summary of content: For laser cutting or drilling in the circuit board industry, only a few watts or more than 10 watts of UV laser is required, and no kW-level laser power is required. The use of circuit boards is becoming increasingly important. Due to the flexible processing method, high-precision processing effect and flexible and controllable processing process, the UV laser processing system has become the first choice for laser drilling and cutting of flexible circuit boards and thin PCBs.

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Figure 1: Comparison of cutting grooves for CO2 laser (left) and UV laser (right). UV laser produces less thermal effect, and its cutting edges are clean and neat.

Now, the long-life laser source configured by the laser system is basically close to maintenance-free. In the production process, the laser level is level 1 and no other protection devices are required for safety. The LPKF laser system is equipped with a vacuum cleaner, which does not cause the emission 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, when PCB layout or cutting, you can choose a CO2 laser system with a wavelength of about 10.6 μm. Its processing cost is relatively low, and the laser power provided can reach several kilowatts. However, it generates a lot of thermal energy during the cutting process, which causes severe carbonization of the edges.

The holmium UV laser has a wavelength of 355 nm. Laser beams of this wavelength are easily optically focused. Focusing UV lasers with less than 20 watts of laser power has a spot diameter of only 20 μm and it produces energy density that is comparable to the surface of the sun.

The advantages of UV laser processing

Holmium UV laser is particularly suitable for cutting and marking of rigid boards, flexible and rigid boards, flexible boards and their accessories. So what are the advantages of this laser process?

In the field of circuit board sub-boards in the SMT industry and micro-drilling in the PCB industry, UV laser cutting systems have shown great technical advantages. Depending on the thickness of the circuit board material, the laser cuts one or more times along the required contour. The thinner the material, the faster the cutting speed. If the accumulated laser pulse is lower than the laser pulse required to penetrate the material, only scratches will appear on the surface of the material; therefore, a two-dimensional code or barcode can be marked on the material for information tracking in subsequent processes.

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Figure 2: Multiple components on one substrate, even if they are close to the circuit, they can be safely separated.

The pulse energy of the holmium UV laser only acts on the material for microseconds. There is no obvious thermal effect at the few micrometers next to the incision, so there is no need to consider the damage caused by the heat it generates. Routes and solder joints near the edges are intact and burr-free.

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

Drilling applications

 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 of the multilayer board. In order to conduct electricity, the wall of the hole needs to be plated with a metal layer after drilling. Today, traditional mechanical methods can no longer meet the requirements of smaller and smaller drilling diameters: Although the spindle speed is increased, the radial speed of precision drilling tools will be reduced because the diameter is too small, and even the required machining results cannot be achieved. In addition, from an economic perspective, consumable tool consumables are also a limiting factor.

For 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 610 mm work surface for automatic roll-to-roll operations. When drilling, the laser can first cut out the microhole contour from the center of the hole, which is more accurate than ordinary methods. The system can drill micro-holes with a minimum diameter of 20 μm in organic or non-organic substrates with a high aspect ratio. Flexible circuit boards, IC substrates, or HDI circuit boards all require such accuracy.

Pre-Cut Cutting

 Which circumstances require cutting the prepreg material during the manufacturing of electronic components? Early on, prepreg materials have been used in multilayer circuit boards. The various circuit layers in the multilayer circuit board are pressed together by the action of the prepreg; according to the circuit design, the prepreg in some areas needs to be cut open in advance and then pressed.

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          Figure 3: The laser process can be used to form precise contours on sensitive overlays.

    A similar process is also applicable to FPC cover film. The cover film is usually made of polyimide and an adhesive layer having 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 and other work.

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

Processing of soft and hard board

In a rigid-flex board, a rigid PCB and a flexible PCB are pressed together to form a multilayer board. During the pressing process, the flexible PCB is not pressure-bonded with the rigid PCB, and the rigid cover covering the flexible PCB is cut and separated by laser depth-cutting, leaving the flexible part to form a rigid-soft board.

This kind of fixed depth processing is also suitable for blind slot processing of embedded components in the surface of multilayer boards. The UV laser will accurately cut the blind groove of the target layer separated from the multilayer circuit board. In this area, the target layer cannot form a connection with the material covered by it.

Efficient PCB and FPC board

SMT sub-board after cutting a variety of electronic components has been assembled circuit board, this process is already at the end of the production chain. For the sub-board, different technologies can be selected: For the commonly used PCB, priority is given to the use of traditional cutting, stamping and contour milling processes. For more complicated electronic circuits and thin substrates, especially those that are very sensitive to mechanical stress, dust and dimensional deviation, it is more advantageous to use UV laser to cut the sub-board. The three charts below evaluate these three methods from different factors.

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    Figure 4: Comparison of splitting methods: Other methods cannot achieve the splitting quality of UV lasers.

For complete contour cutting, the German LPKF company will recommend that the thickness of the cutting material not exceed 1.6mm according to the different laser sources used. For some thicker materials and expensive assembly components, safety and quality aspects are given priority, followed by cutting time.

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Figure 5: In Tab-Cut, the laser cuts the breakpoint board.

Cutting the breakpoint board, the laser system will cut the connection point through a previously described process. This cutting process can be performed close to the edge components, and it is also very economical for thicker circuit boards.

Other application areas

Since the UV laser has a short wavelength, it can be applied to most materials processing. It can be used, for example, in the electronics industry:

Processing TCO / ITO glass without damage to the substrate

Drilling in flexible or thin materials

Opening window with solder mask or cover film

Rigid / flexible / flexible circuit board

Slotted

Rework of assembled or unassembled circuit boards

Cutting Sintered Ceramics

Precision cutting LTCC

 

Not only limited to the processing of circuit boards, the UV laser system can also complete the cutting, direct writing and drilling of LTCC components in one processing operation.


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