A lot of approaches are used for depaneling printed circuit boards. They consist of:
Punching/die cutting. This method demands 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 minimize damage care has to be delivered to maintain sharp die edges.
V-scoring. Usually the panel is scored on both sides to a 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 that may be damaging to a few of the components, especially those near to the board edge.
Wheel cutting/pizza cutter. Another strategy to manually breaking the web after V-scoring is to use a “pizza cutter” to cut the other web. This involves careful alignment between the V-score and also the cutter wheels. It also induces stresses inside the board which might affect some components.
Sawing. Typically machines that are utilized to saw boards away from a panel use a single rotating saw blade that cuts the panel from either the best or perhaps the bottom.
Each of these methods has limitations to straight line operations, thus simply for rectangular boards, and all of them to a few degree crushes and/or cuts the board edge. Other methods tend to be more expansive and may include the subsequent:
Water jet. Some say this technology can be done; however, the authors have discovered no actual users from it. Cutting is carried out with a high-speed stream of slurry, which is water with an abrasive. We expect it will require careful cleaning following the fact to get rid of the abrasive portion of the slurry.
Routing ( nibbling). Most of the time boards are partially routed just before assembly. The other attaching points are drilled with a small drill size, making it simpler to get rid of the boards from 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 up to 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 needed for the routed traces.
Laser routing. Laser routing supplies a space advantage, since the kerf width is only a few micrometers. As an example, the small boards in FIGURE 2 were initially organized in anticipation that the panel will be routed. In this fashion the panel yielded 124 boards. After designing the design for laser Laser PCB Depaneling, the amount of boards per panel increased to 368. So for each 368 boards needed, only one panel needs to be produced instead of three.
Routing could also reduce panel stiffness to the level which a pallet may be needed for support during the earlier steps within the assembly process. But unlike the earlier 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 cause delamination or cause space to develop around the glass fibers. This might lead to moisture ingress, which in turn can reduce the long term reliability of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the ultimate connections between 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 ought to be broken in order to remove the board from the panel. It is actually therefore imperative to accept production methods under consideration during board layout and for panelization to ensure that certain parts and traces usually are not put into areas regarded as subject to stress when depaneling.
Room is additionally needed to permit the precision (or lack thereof) with which the tool path may be placed and to take into consideration any non-precision in 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 being employed. CO2 lasers (~10µm wavelength) provides very 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 may be called “hot” lasers since they burn or melt the fabric 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 other hand, are utilized to ablate the content. A localized short pulse of high energy enters the very best layer in 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 expense. To ensure ablation to take place, the laser light must be absorbed through the materials to become cut. Inside the circuit board industry these are generally mainly FR-4, glass fibers and copper. When thinking about the absorption rates for these 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 has a tapered shape, because it is focused from a relatively wide beam with 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 takes place when the energy density put on the material is maximized, which happens when the throat of the beam is merely inside the material being cut. By repeatedly exceeding 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 might be essential to adjust the main objective from the beam, because the ablation occurs deeper in to the kerf being cut to the material. The ablation process causes some heating in the material but may be optimized to depart no burned or carbonized residue. Because cutting is done gradually, heating is minimized.
The earliest versions of UV laser systems had enough power to Manual PCB Depaneling. Present machines get more power and can also be used to depanel circuit boards up to 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 rapidly the beam returns to 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 choose the optimum combination of settings to ensure a clean cut free from burn marks. There is absolutely no straightforward formula to figure out machine settings; they may be relying on material type, thickness and condition. Depending on the board along with its application, the operator can choose fast depaneling by permitting some discoloring as well as some carbonization, versus a somewhat slower but completely “clean” cut.