Several approaches are used for depaneling printed circuit boards. They consist of:
Punching/die cutting. This method needs a different die for PCB Depaneling, that is not really a practical solution for small production runs. The action can be either a shearing or crushing method, but either can leave the board edges somewhat deformed. To reduce damage care should be delivered to maintain sharp die edges.
V-scoring. Typically the panel is scored on both sides to your depth of around 30% in the board thickness. After assembly the boards may be manually broken out from the panel. This puts bending strain on the boards which can be damaging to a few of the components, especially those near the board edge.
Wheel cutting/pizza cutter. A different method to manually breaking the web after V-scoring is to use a “pizza cutter” to slice the other web. This involves careful alignment involving the V-score and also the cutter wheels. In addition, it induces stresses in the board which may affect some components.
Sawing. Typically machines that are used to saw boards from a panel make use of a single rotating saw blade that cuts the panel from either the best or even the bottom.
Each of these methods is limited to straight line operations, thus just for rectangular boards, and each of them to some degree crushes or cuts the board edge. Other methods are definitely more expansive and include the following:
Water jet. Some say this technology can be achieved; however, the authors have discovered no actual users from it. Cutting is carried out with a high-speed stream of slurry, which is water having an abrasive. We expect it will require careful cleaning after the fact to get rid of the abrasive area 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 easier to interrupt the boards 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 normally takes as much as 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. What this means is a lot of panel space will likely be needed for the routed traces.
Laser routing. Laser routing offers a space advantage, since the kerf width is only a few micrometers. As an example, the small boards in FIGURE 2 were initially presented in anticipation the panel would be routed. In this fashion the panel yielded 124 boards. After designing the layout for laser Laser PCB Depaneling, the amount of boards per panel increased to 368. So for each and every 368 boards needed, just one single panel has to be produced rather than three.
Routing could also reduce panel stiffness to the stage that the pallet is usually necessary for support through the earlier steps in the assembly process. But unlike the previous methods, routing is not restricted to cutting straight line paths only.
Most of these methods exert some extent of mechanical stress on the board edges, which can cause delamination or cause space to produce around the glass fibers. This may lead to moisture ingress, which in turn is able to reduce the long-term reliability of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the last connections involving the boards and panel have to 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 could be damaging to components placed near areas that need to be broken so that you can eliminate the board through the panel. It is therefore imperative to take the production methods into consideration during board layout and for panelization to ensure that certain parts and traces are not positioned in areas regarded as susceptible to stress when depaneling.
Room is additionally required to permit the precision (or lack thereof) in which the tool path can be put and to take into account any non-precision within the board pattern.
Laser cutting. Probably the most recently added tool to delaminate flex and rigid boards is actually a laser. Inside the SMT industry several types of lasers are being employed. CO2 lasers (~10µm wavelength) provides 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 may be called “hot” lasers since they burn or melt the content being cut. (Being an aside, they are the laser types, particularly the Nd:Yag lasers, typically utilized 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 top layer in the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust.
Deciding on a a 355nm laser is based on the compromise between performance and cost. To ensure ablation to happen, the laser light must be absorbed from the materials to become cut. Within the circuit board industry these are mainly FR-4, glass fibers and copper. When examining the absorption rates for these materials, the shorter wavelength lasers are the best ones for your ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam has a tapered shape, as it is focused coming from a relatively wide beam to an extremely narrow beam then continuous in a reverse taper to widen again. This small area where beam is at its most narrow is known as the throat. The perfect ablation happens when the energy density put on the content is maximized, which occurs when the throat from the beam is merely within the material being cut. By repeatedly groing through the identical cutting track, thin layers from the material will likely be vboqdt till the beam has cut all the way through.
In thicker material it could be necessary to adjust the main focus from the beam, because the ablation occurs deeper to the kerf being cut to the material. The ablation process causes some heating in the material but can be optimized to leave no burned or carbonized residue. Because cutting is done gradually, heating is minimized.
The earliest versions of UV laser systems had enough power to Motorized PCB Depaneling. Present machines have more power and can also be used to depanel circuit boards approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature increase in the fabric 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 path length, beam speed and whether a pause is added between passes.
An experienced and experienced system operator will be able to select the optimum combination of settings to make sure a clean cut without any burn marks. There is absolutely no straightforward formula to find out machine settings; they may be affected by material type, thickness and condition. Depending on the board and its application, the operator can select fast depaneling by permitting some discoloring or even some carbonization, versus a somewhat slower but completely “clean” cut.