Many solutions are practiced for depaneling printed circuit boards. They consist of:
Punching/die cutting. This method needs a different die for PCB Depaneling, which is not really 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 minimize damage care has to be come to maintain sharp die edges.
V-scoring. Often the panel is scored on sides to your depth of approximately 30% in the board thickness. After assembly the boards can be manually broken out of the panel. This puts bending strain on the boards that can be damaging to some of the components, especially those close to the board edge.
Wheel cutting/pizza cutter. An alternate strategy to manually breaking the web after V-scoring is to apply a “pizza cutter” to reduce the rest of the web. This requires careful alignment involving 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 used to saw boards out of a panel make use of a single rotating saw blade that cuts the panel from either the best or perhaps the bottom.
Each one of these methods has limitations to straight line operations, thus only for rectangular boards, and all of them to a few degree crushes and cuts the board edge. Other methods are definitely more expansive and can include the subsequent:
Water jet. Some say this technology can be carried out; however, the authors are finding no actual users of it. Cutting is performed using a high-speed stream of slurry, which is water with an abrasive. We expect it will require careful cleaning right after the fact to get rid of the abrasive part of the slurry.
Routing ( nibbling). Most of the time boards are partially routed prior to assembly. The rest of the attaching points are drilled having a small drill size, making it simpler to interrupt the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant loss of panel area towards the routing space, since the kerf width often takes as much as 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies a lot of panel space will be required for the routed traces.
Laser routing. Laser routing provides a space advantage, because the kerf width is just a few micrometers. For example, the little boards in FIGURE 2 were initially organized in anticipation the panel would be routed. In this way 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 must be produced as opposed to three.
Routing can also reduce panel stiffness to the level that a pallet is usually necessary for support during the earlier steps inside the assembly process. But unlike the earlier methods, routing will not be restricted 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 build up across the glass fibers. This can lead to moisture ingress, which often can reduce the long term reliability 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 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 close to areas that need to be broken so that you can eliminate the board from your panel. It is actually therefore imperative to accept the production methods into consideration during board layout and for panelization in order that certain parts and traces are not put into areas regarded as subject to stress when depaneling.
Room is additionally needed to permit the precision (or lack thereof) in which the tool path can be put 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 actually a laser. In the SMT industry several types of lasers are employed. CO2 lasers (~10µm wavelength) can offer extremely high power levels and cut through thick steel sheets and in addition 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 because they burn or melt the material being cut. (Being an aside, these are the basic laser types, especially the Nd:Yag lasers, typically employed to produce stainless-steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the contrary, are used to ablate the fabric. A localized short pulse of high energy enters the best layer from the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust.
The choice of a 355nm laser relies on the compromise between performance and expense. In order for ablation to occur, the laser light must be absorbed from the materials to become cut. In the circuit board industry they are mainly FR-4, glass fibers and copper. When looking at the absorption rates for these materials, the shorter wavelength lasers are the best ones for that ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam includes a tapered shape, as it is focused coming from a relatively wide beam with an extremely narrow beam and then continuous in a reverse taper to widen again. This small area in which the beam are at its most narrow is referred to as the throat. The ideal ablation occurs when the energy density placed on the fabric is maximized, which happens when the throat in the beam is just within the material being cut. By repeatedly groing through the same cutting track, thin layers of the material is going to be vboqdt until the beam has cut all the way through.
In thicker material it may be required to adjust the main objective of the beam, as the ablation occurs deeper into the kerf being cut in 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 capacity to Motorized PCB Depaneling. Present machines have more power and can also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature rise 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 to 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 should be able to pick the optimum mixture of settings to ensure a clean cut without any burn marks. There is not any straightforward formula to find out machine settings; they are influenced by material type, thickness and condition. Depending on the board along with its application, the operator can select fast depaneling by permitting some discoloring or perhaps some carbonization, versus a somewhat slower but completely “clean” cut.