A number of approaches are applied for depaneling printed circuit boards. They consist of:
Punching/die cutting. This method requires a different die for PCB Depaneling, which is not a practical solution for small production runs. The action may be either a shearing or crushing method, but either can leave the board edges somewhat deformed. To lower damage care should be come to maintain sharp die edges.
V-scoring. Usually the panel is scored for both sides to a depth of around 30% in the board thickness. After assembly the boards can be manually broken out of the panel. This puts bending strain on the boards that may be damaging to some of the components, especially those near the board edge.
Wheel cutting/pizza cutter. A different strategy to manually breaking the web after V-scoring is by using a “pizza cutter” to reduce the rest of the web. This involves careful alignment between the V-score and also the cutter wheels. It also induces stresses inside the board which may affect some components.
Sawing. Typically machines that are used to saw boards away from a panel make use of a single rotating saw blade that cuts the panel from either the very best or even the bottom.
Each of these methods has limitations to straight line operations, thus only for rectangular boards, and each one to some degree crushes or cuts the board edge. Other methods tend to be more expansive and include the subsequent:
Water jet. Some say this technology can be carried out; however, the authors are finding no actual users of this. Cutting is conducted using a high-speed stream of slurry, that is water having an abrasive. We expect it should take careful cleaning after the fact to eliminate the abrasive portion of the slurry.
Routing ( nibbling). More often than not boards are partially routed prior to assembly. The remaining attaching points are drilled having a small drill size, making it simpler to break the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage could be a significant loss in panel area to the routing space, as the kerf width often takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. What this means is a lot of panel space is going to be necessary for the routed traces.
Laser routing. Laser routing provides a space advantage, since the kerf width is just a few micrometers. As an example, the little boards in FIGURE 2 were initially organized in anticipation that this panel would be routed. In this fashion the panel yielded 124 boards. After designing the layout for laser Laser PCB Cutting Machine, the number of boards per panel increased to 368. So for each and every 368 boards needed, only one panel needs to be produced instead of three.
Routing can also reduce panel stiffness to the level which a pallet may be required for support through the earlier steps within the assembly process. But unlike the prior methods, routing will not be confined to cutting straight line paths only.
The majority of these methods exert some degree of mechanical stress on the board edges, which can lead to delamination or cause space to develop across the glass fibers. This may lead to moisture ingress, which in turn can reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the final connections in between the boards and panel must be removed. Often this can be accomplished by breaking these final bridges, causing some mechanical and bending stress on the boards. Again, such bending stress can be damaging to components placed near areas that ought to be broken in order to eliminate the board from the panel. It is actually therefore imperative to take the production methods into account during board layout and for panelization in order that certain parts and traces are not placed in areas considered to be subjected to stress when depaneling.
Room can also be needed to permit the precision (or lack thereof) in which the tool path may be placed and to take into consideration any non-precision in the board pattern.
Laser cutting. Probably the most recently added tool to delaminate flex and rigid boards is a laser. In the SMT industry several types of lasers are now being employed. CO2 lasers (~10µm wavelength) provides very 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. These two laser types produce infrared light and can be called “hot” lasers since they burn or melt the fabric being cut. (As being an aside, these are the laser types, particularly the Nd:Yag lasers, typically employed to produce stainless 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.
The choice of a 355nm laser is based on the compromise between performance and cost. To ensure that ablation to happen, the laser light has to be absorbed from the materials to be cut. In the circuit board industry they are mainly FR-4, glass fibers and copper. When examining the absorption rates for such materials, the shorter wavelength lasers are the best ones for that ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, since it is focused from the relatively wide beam to an extremely narrow beam then continuous in a reverse taper to widen again. This small area where the beam are at its most narrow is known as the throat. The optimal ablation occurs when the energy density placed on the content is maximized, which takes place when the throat from the beam is merely inside the material being cut. By repeatedly going over the identical cutting track, thin layers of the material will be vboqdt up until the beam has cut right through.
In thicker material it might be necessary to adjust the main objective from the beam, because the ablation occurs deeper into the kerf being cut into the material. The ablation process causes some heating of the material but can be optimized to go out of no burned or carbonized residue. Because cutting is carried out gradually, heating is minimized.
The earliest versions of UV laser systems had enough capacity to Pneumatic PCB Depaneling. Present machines acquire more power and may also be used to depanel circuit boards approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature increase in the material being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns for 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 mixture of settings to ensure a clean cut free from burn marks. There is absolutely no straightforward formula to find out machine settings; they are influenced by material type, thickness and condition. Depending on the board and its application, the operator can choose fast depaneling by permitting some discoloring or even some carbonization, versus a somewhat slower but completely “clean” cut.