A lot of approaches are applied for depaneling printed circuit boards. They involve:
Punching/die cutting. This method needs a different die for PCB Depaneling, which 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 has to be taken to maintain sharp die edges.
V-scoring. Usually the panel is scored on both sides to a depth of approximately 30% of the board thickness. After assembly the boards can be manually broken out from the panel. This puts bending strain on the boards that may be damaging to a number of the components, especially those close to the board edge.
Wheel cutting/pizza cutter. A different strategy to manually breaking the internet after V-scoring is by using a “pizza cutter” to cut the rest of the web. This requires careful alignment in between the V-score as well as the cutter wheels. In addition, it induces stresses within the board which may affect some components.
Sawing. Typically machines that are employed to saw boards out of a panel make use of a single rotating saw blade that cuts the panel from either the very best or perhaps the bottom.
Each one of these methods is limited to straight line operations, thus only for rectangular boards, and each of them to some degree crushes and/or cuts the board edge. Other methods are definitely more expansive and can include the following:
Water jet. Some say this technology can be achieved; however, the authors have found no actual users of it. Cutting is conducted having a high-speed stream of slurry, that is water with the abrasive. We expect it should take careful cleaning after the fact to eliminate the abrasive part of the slurry.
Routing ( nibbling). Most of the time boards are partially routed just before assembly. The remaining attaching points are drilled using a small drill size, making it easier to get rid of the boards from the panel after assembly, leaving the so-called mouse bites. A disadvantage could be a significant lack of 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. This means lots of panel space is going to be required for the routed traces.
Laser routing. Laser routing supplies a space advantage, as the kerf width is just a few micrometers. For instance, the little boards in FIGURE 2 were initially organized in anticipation that the panel could be routed. In this manner the panel yielded 124 boards. After designing the design for laser Laser PCB Depaneling, the quantity 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 may also reduce panel stiffness to the level that a pallet may be required for support during the earlier steps inside the assembly process. But unlike the prior methods, routing is not confined to cutting straight line paths only.
The majority of these methods exert some extent of mechanical stress on the board edges, which can lead to delamination or cause space to develop round the glass fibers. This might lead to moisture ingress, which is able to reduce the long-term reliability of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the ultimate 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 eliminate 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 so that certain parts and traces usually are not put into areas known to be subject to stress when depaneling.
Room can also be required to permit the precision (or lack thereof) with which the tool path can be placed and to take into consideration any non-precision within the board pattern.
Laser cutting. Probably the most recently added tool to delaminate flex and rigid boards is really a laser. In the SMT industry several types 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 could be called “hot” lasers since they burn or melt the fabric being cut. (As an aside, these are the laser types, particularly the Nd:Yag lasers, typically used to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the contrary, are utilized to ablate the fabric. 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.
Deciding on a a 355nm laser is based on the compromise between performance and cost. To ensure that ablation to occur, the laser light needs to be absorbed from the materials to become cut. Inside the circuit board industry these are mainly FR-4, glass fibers and copper. When thinking about the absorption rates for these particular 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, because it is focused from the relatively wide beam with an extremely narrow beam and after that continuous in a reverse taper to widen again. This small area where the beam reaches its most narrow is known as the throat. The optimal ablation happens when the energy density placed on the material is maximized, which takes place when the throat of the beam is merely within the material being cut. By repeatedly going over exactly the same cutting track, thin layers from the material is going to be vboqdt till the beam has cut right through.
In thicker material it could be essential to adjust the focus in the beam, since the ablation occurs deeper into the kerf being cut in to the material. The ablation process causes some heating of the material but could be optimized to go out of no burned or carbonized residue. Because cutting is performed gradually, heating is minimized.
The earliest versions of UV laser systems had enough capacity to Motorized 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 surge in the content being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how fast the beam returns for the same location) is dependent upon the way length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator should be able to choose the optimum mixture of settings to make certain a clean cut without any burn marks. There is no straightforward formula to determine machine settings; these are 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 perhaps some carbonization, versus a somewhat slower but completely “clean” cut.