Several approaches are practiced for depaneling printed circuit boards. They involve:
Punching/die cutting. This process requires a different die for PCB Depaneling, that is not really a practical solution for small production runs. The action could be either a shearing or crushing method, but either can leave the board edges somewhat deformed. To minimize damage care should be delivered to maintain sharp die edges.
V-scoring. Typically the panel is scored for both sides to your depth of approximately 30% from the board thickness. After assembly the boards could be manually broken from the panel. This puts bending strain on the boards that can be damaging to a number of the components, in particular those near to the board edge.
Wheel cutting/pizza cutter. A different strategy to manually breaking the web after V-scoring is to apply a “pizza cutter” to reduce the other web. This involves careful alignment involving the V-score and the cutter wheels. It also induces stresses within the board which can affect some components.
Sawing. Typically machines that are employed to saw boards from a panel use a single rotating saw blade that cuts the panel from either the top or the bottom.
Each of these methods is restricted to straight line operations, thus simply for rectangular boards, and all of them to some degree crushes or cuts the board edge. Other methods are more expansive and can include the following:
Water jet. Some say this technology can be achieved; however, the authors are finding no actual users of this. Cutting is performed having a high-speed stream of slurry, which is water with an abrasive. We expect it will need careful cleaning right after the fact to get rid of the abrasive part of the slurry.
Routing ( nibbling). More often than not boards are partially routed prior to assembly. The rest of the attaching points are drilled having a small drill size, making it simpler to break the boards out of the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant loss in panel area towards the routing space, as the kerf width normally takes approximately 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This means a significant amount of panel space will be necessary for the routed traces.
Laser routing. Laser routing provides a space advantage, since the kerf width is simply a few micrometers. For instance, the little boards in FIGURE 2 were initially presented in anticipation that this panel could be routed. In this fashion the panel yielded 124 boards. After designing the design for laser Laser Depaneling, the amount of boards per panel increased to 368. So for each and every 368 boards needed, just one panel has to be produced instead of three.
Routing may also reduce panel stiffness to the level which a pallet may be required for support through the earlier steps in the assembly process. But unlike the prior methods, routing is not restricted to cutting straight line paths only.
The majority of these methods exert some extent of mechanical stress on the board edges, which can cause delamination or cause space to produce across the glass fibers. This may lead to moisture ingress, which can reduce the long-term reliability of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the last connections in between the boards and panel must be removed. Often this really is accomplished by breaking these final bridges, causing some mechanical and bending stress on the boards. Again, such bending stress may be damaging to components placed near areas that need to be broken to be able to eliminate the board from your panel. It really is therefore imperative to take the production methods into account during board layout and for panelization so that certain parts and traces are not placed in areas considered to be susceptible to stress when depaneling.
Room is also required to permit the precision (or lack thereof) that the tool path can be placed and to look at any non-precision in the board pattern.
Laser cutting. The most recently added tool to delaminate flex and rigid boards is really a laser. Inside the SMT industry several types of lasers are employed. CO2 lasers (~10µm wavelength) can provide high power levels and cut through thick steel sheets as well as through circuit boards. Neodymium:Yag lasers and fiber lasers (~1µm wavelength) typically provide lower power levels at smaller beam sizes. Both these laser types produce infrared light and could be called “hot” lasers because they burn or melt the content being cut. (Being an aside, they are the laser types, specially the Nd:Yag lasers, typically used to produce stainless-steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are used to ablate the content. A localized short pulse of high energy enters the very best layer from the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust.
Deciding on a a 355nm laser is situated on the compromise between performance and cost. In order for ablation to occur, the laser light needs to be absorbed from the materials to get cut. Within the circuit board industry they are mainly FR-4, glass fibers and copper. When looking at the absorption rates for these materials, the shorter wavelength lasers are the most suitable ones for that ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam has a tapered shape, because it is focused from the relatively wide beam for an extremely narrow beam then continuous in a reverse taper to widen again. This small area where beam is at its most narrow is called the throat. The ideal ablation occurs when the energy density placed on the fabric is maximized, which occurs when the throat from the beam is just in the material being cut. By repeatedly exceeding the identical cutting track, thin layers from the material will likely be vboqdt until the beam has cut right through.
In thicker material it may be essential to adjust the main focus in the beam, since the ablation occurs deeper in to the kerf being cut into the material. The ablation process causes some heating from the material but could be optimized to go out of no burned or carbonized residue. Because cutting is done gradually, heating is minimized.
The earliest versions of UV laser systems had enough capacity to Motorized PCB Depaneling. Present machines acquire more power and could also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the material being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how fast the beam returns to the same location) is dependent upon the way length, beam speed and whether a pause is added between passes.
An experienced and experienced system operator will be able to pick the optimum combination of settings to make certain a clean cut without any burn marks. There is not any straightforward formula to figure out machine settings; they are affected by material type, thickness and condition. Depending on the board and its application, the operator can pick fast depaneling by permitting some discoloring or perhaps some carbonization, versus a somewhat slower but completely “clean” cut.