Several techniques are applied for depaneling printed circuit boards. They consist of:
Punching/die cutting. This process requires a different die for PCB Depaneling, which can be not just a practical solution for small production runs. The action could be either a shearing or crushing method, but either can leave the board edges somewhat deformed. To lower damage care must be come to maintain sharp die edges.
V-scoring. Usually the panel is scored on both sides to a depth of approximately 30% from the board thickness. After assembly the boards could be manually broken out from the panel. This puts bending strain on the boards which can be damaging to a few of the components, in particular those close to the board edge.
Wheel cutting/pizza cutter. An alternate strategy to manually breaking the net after V-scoring is to use a “pizza cutter” to reduce the remaining web. This requires careful alignment involving the V-score and the cutter wheels. Additionally, it induces stresses in the board which can affect some components.
Sawing. Typically machines that are used to saw boards from a panel utilize a single rotating saw blade that cuts the panel from either the best or the bottom.
Each one of these methods is limited to straight line operations, thus just for rectangular boards, and each of them for some degree crushes and 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 of this. Cutting is performed 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 get rid of the abrasive area of the slurry.
Routing ( nibbling). Most of the time boards are partially routed just before assembly. The remaining attaching points are drilled having a small drill size, making it easier to interrupt 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 towards the routing space, since the kerf width typically takes approximately 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 be needed for the routed traces.
Laser routing. Laser routing supplies a space advantage, because the kerf width is just a few micrometers. For instance, the tiny boards in FIGURE 2 were initially laid out in anticipation the panel could be routed. In this manner 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 every 368 boards needed, just one single panel needs to be produced rather than three.
Routing could also reduce panel stiffness to the level which a pallet may be required for support during the earlier steps within the assembly process. But unlike the earlier methods, routing is not really limited 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 around the glass fibers. This can lead to moisture ingress, which can reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the last 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 can be damaging to components placed close to areas that ought to be broken to be able to remove the board through the panel. It is actually therefore imperative to take the production methods into consideration during board layout as well as for panelization in order that certain parts and traces are certainly not put into areas known to be susceptible to stress when depaneling.
Room can also be needed to permit the precision (or lack thereof) that the tool path can be placed and to take into account any non-precision inside the board pattern.
Laser cutting. By far the most recently added tool to delaminate flex and rigid boards is really a laser. In the SMT industry several kinds of lasers are employed. CO2 lasers (~10µm wavelength) can provide 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. Both these laser types produce infrared light and could be called “hot” lasers as they burn or melt the material being cut. (As being an aside, they are the laser types, especially the Nd:Yag lasers, typically utilized to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are used 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 relies on the compromise between performance and price. In order for ablation to take place, the laser light has to be absorbed from the materials to get cut. Inside the circuit board industry these are generally mainly FR-4, glass fibers and copper. When looking at the absorption rates for these particular materials, the shorter wavelength lasers are the best 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, because it is focused from a relatively wide beam with an extremely narrow beam and after that continuous in a reverse taper to widen again. This small area in which the beam is at its most narrow is known as the throat. The perfect ablation occurs when the energy density applied to the material is maximized, which occurs when the throat from the beam is just within the material being cut. By repeatedly going over the identical cutting track, thin layers in the material will likely be vboqdt until the beam has cut all the way through.
In thicker material it could be essential to adjust the main focus in 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 could 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 capacity to Motorized PCB Depaneling. Present machines get more power and could also be used to depanel circuit boards as much as 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 for the same location) is dependent upon the way length, beam speed and whether a pause is added between passes.
An educated and experienced system operator can select the optimum mixture of settings to ensure a clean cut free of burn marks. There is no straightforward formula to determine machine settings; they are 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 perhaps some carbonization, versus a somewhat slower but completely “clean” cut.