Several methods are practiced for depaneling printed circuit boards. They involve:
Punching/die cutting. This technique needs 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 must be come to maintain sharp die edges.
V-scoring. Often the panel is scored on sides to a depth of around 30% of the board thickness. After assembly the boards could be manually broken from the panel. This puts bending strain on the boards that may be damaging to some of the components, particularly those close to the board edge.
Wheel cutting/pizza cutter. A different strategy to manually breaking the net after V-scoring is by using a “pizza cutter” to slice the other web. This involves careful alignment in between the V-score and also the cutter wheels. Additionally, it induces stresses in the board which can affect some components.
Sawing. Typically machines that are utilized to saw boards from a panel use a single rotating saw blade that cuts the panel from either the top or perhaps the bottom.
Each 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 more expansive and can include the subsequent:
Water jet. Some say this technology can be achieved; however, the authors have found no actual users of it. Cutting is performed with a high-speed stream of slurry, that is 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). More often than not boards are partially routed before assembly. The rest of the attaching points are drilled with a small drill size, making it simpler to break the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant loss in panel area for the routing space, since the kerf width often takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies lots of panel space will be needed for the routed traces.
Laser routing. Laser routing provides a space advantage, because the kerf width is simply a few micrometers. As an example, the tiny boards in FIGURE 2 were initially presented in anticipation that this panel could be routed. In this way 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 each 368 boards needed, only one panel needs to be produced rather than three.
Routing could also reduce panel stiffness to the stage that a pallet may be needed for support during the earlier steps inside the assembly process. But unlike the prior methods, routing will not be confined to cutting straight line paths only.
Many of these methods exert some degree of mechanical stress on the board edges, which can cause delamination or cause space to build up around the glass fibers. This can 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 final connections involving 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 near areas that should be broken in order to remove the board through the panel. It really is therefore imperative to accept production methods into consideration during board layout as well as for panelization to ensure that certain parts and traces are certainly not put into areas considered to be susceptible to stress when depaneling.
Room is also needed 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. By far the most recently added tool to delaminate flex and rigid boards is really a laser. In the SMT industry various kinds lasers are now being employed. CO2 lasers (~10µm wavelength) can offer 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 can be called “hot” lasers because they burn or melt the content being cut. (As an aside, they are the laser types, specially the Nd:Yag lasers, typically employed to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are utilized 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 has to be absorbed from the materials to become cut. Within the circuit board industry these are generally mainly FR-4, glass fibers and copper. When looking at the absorption rates for such 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 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 reaches its most narrow is known as the throat. The optimal ablation takes place when the energy density applied to the fabric is maximized, which happens when the throat from the beam is merely in the material being cut. By repeatedly going over the identical cutting track, thin layers from 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 objective from the beam, as the ablation occurs deeper to the kerf being cut into the material. The ablation process causes some heating in the material but could be optimized to leave no burned or carbonized residue. Because cutting is performed gradually, heating is minimized.
The earliest versions of UV laser systems had enough capability to Motorized PCB Depaneling. Present machines have more power and may also be used to depanel circuit boards approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature surge in the material being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns towards the same location) is dependent upon the road length, beam speed and whether a pause is added between passes.
A knowledgeable 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 not any straightforward formula to determine machine settings; they may be influenced by material type, thickness and condition. Depending on the board and its application, the operator can select fast depaneling by permitting some discoloring or even some carbonization, versus a somewhat slower but completely “clean” cut.