Many approaches are used for depaneling printed circuit boards. They consist of:
Punching/die cutting. This method demands a different die for PCB Depaneling, which is not 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. Usually the panel is scored for both sides to some depth of around 30% in the board thickness. After assembly the boards can be manually broken out from the panel. This puts bending strain on the boards which can be damaging to a number of the components, in particular those close to the board edge.
Wheel cutting/pizza cutter. Another method to manually breaking the web after V-scoring is by using a “pizza cutter” to reduce the rest of the web. This calls for careful alignment between the V-score and also the cutter wheels. Additionally, it induces stresses inside the board which might affect some components.
Sawing. Typically machines that are utilized to saw boards from a panel make use of a single rotating saw blade that cuts the panel from either the very best or the bottom.
All these methods is restricted to straight line operations, thus simply for rectangular boards, and each of them to a few degree crushes or cuts the board edge. Other methods are more expansive and can include these:
Water jet. Some say this technology can be carried out; however, the authors have found no actual users from it. Cutting is conducted with a high-speed stream of slurry, that is water with an abrasive. We expect it will need careful cleaning after the fact to get rid of the abrasive area of the slurry.
Routing ( nibbling). Usually boards are partially routed just before assembly. The other attaching points are drilled with a small drill size, making it simpler to break the boards from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant lack of panel area to the routing space, because the kerf width often 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 provides a space advantage, as the kerf width is only a few micrometers. For example, the small boards in FIGURE 2 were initially presented in anticipation that this panel would be routed. In this way the panel yielded 124 boards. After designing the layout for laser Laser Depaneling, the quantity of boards per panel increased to 368. So for each 368 boards needed, just one panel must be produced rather than three.
Routing may also reduce panel stiffness to the level that the pallet may be required for support through the earlier steps in the assembly process. But unlike the prior methods, routing is not really limited 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 produce round the glass fibers. This can lead to moisture ingress, which is able to reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the last connections between the boards and panel need to be removed. Often this really 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 close to areas that should be broken to be able to take away the board from the panel. It is therefore imperative to accept the production methods under consideration during board layout as well as for panelization so that certain parts and traces are certainly not put into areas known to be subject to stress when depaneling.
Room is also needed to permit the precision (or lack thereof) with which the tool path may be placed and to take into account any non-precision inside the board pattern.
Laser cutting. The most recently added tool to delaminate flex and rigid boards is a laser. Within the SMT industry various kinds lasers are being employed. CO2 lasers (~10µm wavelength) can provide very high power levels and cut through thick steel sheets as well as 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 as they burn or melt the content being cut. (Being an aside, these are the basic laser types, particularly 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 material. A localized short pulse of high energy enters the top 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 relies on the compromise between performance and price. To ensure ablation to take place, the laser light needs to be absorbed through the materials to get cut. Within 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 best ones for the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, since it is focused from the relatively wide beam for an extremely narrow beam then continuous in a reverse taper to widen again. This small area in which the beam is at its most narrow is called the throat. The ideal ablation happens when the energy density put on the fabric is maximized, which happens when the throat of the beam is simply in the material being cut. By repeatedly groing through the same cutting track, thin layers of the material will be vboqdt until the beam has cut all the way through.
In thicker material it could be required to adjust the main objective from the beam, since the ablation occurs deeper in to the kerf being cut in to the material. The ablation process causes some heating from the material but could be optimized to depart no burned or carbonized residue. Because cutting is performed gradually, heating is minimized.
The earliest versions of UV laser systems had enough power to Pneumatic 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 increase in the fabric 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 path length, beam speed and whether a pause is added between passes.
An educated and experienced system operator can pick the optimum blend of settings to make sure a clean cut without any burn marks. There is no 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 choose fast depaneling by permitting some discoloring or perhaps some carbonization, versus a somewhat slower but completely “clean” cut.