Many techniques are applied for depaneling printed circuit boards. They consist of:
Punching/die cutting. This technique 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 reduce damage care should be taken to maintain sharp die edges.
V-scoring. Typically the panel is scored on both sides to a depth of approximately 30% in the board thickness. After assembly the boards may be manually broken out from the panel. This puts bending strain on the boards that can be damaging to a few of the components, particularly those close to the board edge.
Wheel cutting/pizza cutter. A different method to manually breaking the internet after V-scoring is by using a “pizza cutter” to reduce the other web. This calls for careful alignment involving the V-score as well as the cutter wheels. It also induces stresses within the board which can affect some components.
Sawing. Typically machines that are used to saw boards from a panel use a single rotating saw blade that cuts the panel from either the very best or even the bottom.
All these methods has limitations to straight line operations, thus simply for rectangular boards, and each one to some degree crushes and cuts the board edge. Other methods are more expansive and may include these:
Water jet. Some say this technology can be done; however, the authors are finding no actual users of it. Cutting is conducted with a high-speed stream of slurry, that is water with the abrasive. We expect it will need careful cleaning after the fact to get rid of the abrasive part of the slurry.
Routing ( nibbling). Usually boards are partially routed just before assembly. The remaining attaching points are drilled using a small drill size, making it easier to break the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant loss of panel area to the routing space, because the kerf width often takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This means a lot of panel space is going to be needed for the routed traces.
Laser routing. Laser routing supplies a space advantage, as the kerf width is simply a few micrometers. For example, the small boards in FIGURE 2 were initially presented in anticipation that this panel will be routed. In this way the panel yielded 124 boards. After designing the design for laser Laser Depaneling, the quantity of boards per panel increased to 368. So for each 368 boards needed, just one panel needs to be produced rather than three.
Routing may also reduce panel stiffness to the level which a pallet is usually necessary for support throughout the earlier steps inside the assembly process. But unlike the earlier methods, routing will not be limited to cutting straight line paths only.
Many of these methods exert some degree of mechanical stress on the board edges, which can lead to delamination or cause space to produce around the glass fibers. This might lead to moisture ingress, which often can reduce the long term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the final connections between the boards and panel need to 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 ought to be broken to be able to remove the board from the panel. It is actually therefore imperative to accept production methods into consideration during board layout and for panelization to ensure that certain parts and traces usually are not positioned in areas known to be subject 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 look at any non-precision within the board pattern.
Laser cutting. The most recently added tool to delaminate flex and rigid boards is really a laser. Within the SMT industry several types of lasers are now being employed. CO2 lasers (~10µm wavelength) can provide 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 could be called “hot” lasers as they burn or melt the fabric being cut. (As an aside, these are the basic laser types, specially the Nd:Yag lasers, typically utilized to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are used to ablate the fabric. 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 option of a 355nm laser is situated on the compromise between performance and expense. To ensure ablation to occur, the laser light needs to be absorbed through the materials to be cut. Inside the circuit board industry these are mainly FR-4, glass fibers and copper. When examining the absorption rates for such 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 features a tapered shape, because it is focused coming from a relatively wide beam with an extremely narrow beam then continuous in a reverse taper to widen again. This small area where beam reaches its most narrow is referred to as the throat. The optimal ablation occurs when the energy density placed on the fabric is maximized, which occurs when the throat in the beam is just within the material being cut. By repeatedly groing through exactly the same cutting track, thin layers from the material will be vboqdt up until the beam has cut right through.
In thicker material it could be essential to adjust the main focus in the beam, because the ablation occurs deeper into the kerf being cut into the material. The ablation process causes some heating from 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 Motorized PCB Depaneling. Present machines get more power and may also be used to depanel circuit boards approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature surge in the fabric being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how rapidly the beam returns for the same location) is determined by the road length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator can choose the optimum blend of settings to ensure a clean cut free of burn marks. There is 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 choose fast depaneling by permitting some discoloring or even some carbonization, versus a somewhat slower but completely “clean” cut.