A lot of methods are used for depaneling printed circuit boards. They include:
Punching/die cutting. This technique needs a different die for PCB Depaneling, that is not just 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 minimize damage care must be come to maintain sharp die edges.
V-scoring. Often the panel is scored on both sides to your depth of around 30% of the board thickness. After assembly the boards may be manually broken out of the panel. This puts bending strain on the boards that can be damaging to a few of the components, particularly those near to the board edge.
Wheel cutting/pizza cutter. A different method to manually breaking the web after V-scoring is by using a “pizza cutter” to cut the rest of the web. This requires careful alignment involving the V-score and the cutter wheels. It also induces stresses in the board which might affect some components.
Sawing. Typically machines that are used to saw boards away from a panel use a single rotating saw blade that cuts the panel from either the best or even the bottom.
Each one of these methods has limitations to straight line operations, thus only for rectangular boards, and each of them to some degree crushes and cuts the board edge. Other methods are definitely more expansive and include these:
Water jet. Some say this technology can be done; however, the authors have discovered no actual users of it. Cutting is carried out using a high-speed stream of slurry, which can be water with the abrasive. We expect it should take careful cleaning after the fact to remove the abrasive part of the slurry.
Routing ( nibbling). More often than not boards are partially routed just before assembly. The other attaching points are drilled using 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 can be quite a significant loss in panel area for the routing space, because the kerf width often takes as much as 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. What this means is a significant amount of panel space will likely be required for the routed traces.
Laser routing. Laser routing provides a space advantage, since the kerf width is simply a few micrometers. For instance, the small boards in FIGURE 2 were initially laid out in anticipation that this panel would be routed. In this fashion the panel yielded 124 boards. After designing the design for laser Laser Depaneling, the quantity of boards per panel increased to 368. So for every 368 boards needed, just one single panel needs to be produced as opposed to three.
Routing could also reduce panel stiffness to the point that the pallet is usually necessary for support throughout the earlier steps in the assembly process. But unlike the prior methods, routing is not really confined 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 develop across the glass fibers. This can lead to moisture ingress, which is effective in reducing the long-term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the final connections involving the boards and panel must be removed. Often this is accomplished by breaking these final bridges, causing some mechanical and bending stress on the boards. Again, such bending stress could be damaging to components placed near areas that need to be broken to be able to remove the board from the panel. It is actually therefore imperative to accept the production methods under consideration during board layout and then for panelization so that certain parts and traces usually are not put into areas considered to be subjected to stress when depaneling.
Room is also needed to permit the precision (or lack thereof) in which the tool path can be placed and to take into account any non-precision in the board pattern.
Laser cutting. Probably the most recently added tool to delaminate flex and rigid boards is really a laser. Within the SMT industry several kinds of lasers are now being employed. CO2 lasers (~10µm wavelength) can provide high power levels and cut through thick steel sheets and also 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 content being cut. (As an aside, these 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 contrary, are employed to ablate the material. A localized short pulse of high energy enters the best layer of the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust.
The option of a 355nm laser relies on the compromise between performance and cost. To ensure ablation to take place, the laser light has to be absorbed through 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 these particular materials, the shorter wavelength lasers are the most appropriate ones for the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam includes a tapered shape, as it is focused from the relatively wide beam with an extremely narrow beam and then continuous in a reverse taper to widen again. This small area where the beam are at its most narrow is called the throat. The perfect ablation takes place when the energy density applied to the content is maximized, which occurs when the throat of the beam is merely in the material being cut. By repeatedly groing through exactly the same cutting track, thin layers from the material is going to be vboqdt until the beam has cut all the way through.
In thicker material it could be necessary to adjust the main focus in the beam, because the ablation occurs deeper into the kerf being cut in to the material. The ablation process causes some heating in 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 capability to Pneumatic PCB Depaneling. Present machines get more power and could also be used to depanel circuit boards approximately 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 quickly the beam returns towards the same location) is determined by the way length, beam speed and whether a pause is added between passes.
An educated and experienced system operator will be able to pick the optimum blend of settings to make sure a clean cut free of burn marks. There is no straightforward formula to determine machine settings; they may be affected by material type, thickness and condition. Depending on the board as well as its application, the operator can pick fast depaneling by permitting some discoloring or even some carbonization, versus a somewhat slower but completely “clean” cut.