Punching/die cutting. This method demands a different die for each new circuit board, which is not really a practical solution for small production runs. The action may be PCB Depaneling, but either can leave the board edges somewhat deformed. To lessen damage care must be taken up 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 from the panel. This puts bending strain on the boards which can be damaging to a few of the components, especially those near to the board edge.
Wheel cutting/pizza cutter. A different technique to manually breaking the web after V-scoring is to use a “pizza cutter” to cut the remaining web. This requires careful alignment in between the V-score along with the cutter wheels. Furthermore, it induces stresses inside the board which might affect some components.
Sawing. Typically machines that are used to saw boards away from a panel work with a single rotating saw blade that cuts the panel from either the best or perhaps the bottom.
Every one of these methods is restricted to straight line operations, thus just for rectangular boards, and each of them to a few degree crushes and cuts the board edge. Other methods are more expansive and may include the following:
Water jet. Some say this technology can be achieved; however, the authors have found no actual users of this. Cutting is carried out having a high-speed stream of slurry, which is water having an abrasive. We expect it should take careful cleaning following the fact to eliminate the abrasive area of the slurry.
Routing ( nibbling). Usually boards are partially routed before assembly. The other attaching points are drilled using a small drill size, making it easier to break the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant reduction in panel area to the routing space, because the kerf width normally takes approximately 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This simply means a lot of panel space will be necessary for the routed traces.
Laser routing. Laser routing supplies a space advantage, as being the kerf width is simply a few micrometers. For example, the tiny boards in FIGURE 2 were initially organized in anticipation that this panel will be routed. In this fashion the panel yielded 124 boards. After designing the design for laser depaneling, the volume of boards per panel increased to 368. So for every single 368 boards needed, just one single panel should be produced as opposed to three.
Routing also can reduce panel stiffness to the level that a pallet is usually necessary for support through the earlier steps inside the assembly process. But unlike the earlier methods, routing will not be limited by cutting straight line paths only.
Most of these methods exert some extent of mechanical stress around the board edges, which can cause delamination or cause space to produce across the glass fibers. This may lead to moisture ingress, which is effective in reducing the long-term reliability of the circuitry.
Additionally, when finishing placement of components around the board and after soldering, the ultimate connections between your boards and panel must be removed. Often this is accomplished by breaking these final bridges, causing some mechanical and bending stress about the boards. Again, such bending stress may be damaging to components placed close to areas that should be broken to be able to eliminate the board from the panel. It can be therefore imperative to accept the production methods into account during board layout as well as for panelization in order that certain parts and traces will not be placed into areas considered to be at the mercy of stress when depaneling.
Room is additionally expected to permit the precision (or lack thereof) which the tool path can be put and to look at any non-precision within the board pattern.
Laser cutting. Probably the most recently added tool to PCB Depaneling Router and rigid boards is a laser. Inside the SMT industry several types of lasers are now being 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 might be called “hot” lasers while they burn or melt the content being cut. (As an aside, these are the basic laser types, especially the Nd:Yag lasers, typically utilized to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are employed to ablate the content. 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 (FIGURE 3).
The option of a 355nm laser will depend on the compromise between performance and cost. In order for ablation to take place, the laser light has to be absorbed from the materials to become cut. Within the circuit board industry these are mainly FR-4, glass fibers and copper. When examining the absorption rates for these materials (FIGURE 4), the shorter wavelength lasers are the most appropriate ones to the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, as it is focused from a relatively wide beam with an extremely narrow beam and then continuous in the reverse taper to widen again. This small area where the beam reaches its most narrow is known as the throat. The perfect ablation happens when the energy density put on the fabric is maximized, which occurs when the throat of the beam is definitely in the material being cut. By repeatedly groing through a similar cutting track, thin layers in the material will likely be removed till the beam has cut right through.
In thicker material it may be necessary to adjust the focus from the beam, because the ablation occurs deeper into the kerf being cut to the material. The ablation process causes some heating from the material but could be optimized to have no burned or carbonized residue. Because cutting is performed gradually, heating is minimized.
The earliest versions of UV laser systems had enough power to depanel flex circuit panels. Present machines convey more power and can also be used to depanel circuit boards up to 1.6mm (63 mils) in thickness.
Temperature. The temperature increase in the content being cut is dependent upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns to the same location) depends upon the path length, beam speed and whether a pause is added between passes.
An experienced and experienced system operator are able to find the optimum mix of settings to guarantee a clean cut free from burn marks. There is absolutely no straightforward formula to figure out machine settings; they are affected by material type, thickness and condition. Dependant upon the board along with its application, the operator can decide fast depaneling by permitting some discoloring and even some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing indicates that under most conditions the temperature rise within 1.5mm from your cutting path is less than 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. In the laser employed for these tests, an airflow goes all over the panel being cut and removes most of the expelled dust into an exhaust and filtering method (FIGURE 7).
To test the impact of the remaining expelled material, a slot was cut inside a four-up pattern on FR-4 material using a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and was comprised of powdery epoxy and glass particles. Their size ranged from typically 10µm to your high of 20µm, and a few could possibly have was made up of burned or carbonized material. Their size and number were extremely small, with no conduction was expected between traces and components in the board. In that case desired, a straightforward cleaning process could be included with remove any remaining particles. Such a process could contain the usage of any type of wiping using a smooth dry or wet tissue, using compressed air or brushes. You could likewise use any sort of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any sort of additional cleaning process, especially an expensive one.
Surface resistance. After cutting a path in these test boards (Figure 7, slot during the test pattern), the boards were exposed to a climate test (40°C, RH=93%, no condensation) for 170 hr., along with the SIR values exceeded 10E11 Ohm, indicating no conductive material is present.
Cutting path location. The laser beam typically works with a galvanometer scanner (or galvo scanner) to trace the cutting path within the material more than a small area, 50x50mm (2×2″). Using this sort of scanner permits the beam to be moved at a high speed along the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is in the same location merely a very short time, which minimizes local heating.
A pattern recognition technique is employed, that may use fiducials or any other panel or board feature to precisely obtain the location where cut needs to be placed. High precision x and y movement systems can be used for large movements in combination with a galvo scanner for local movements.
In most of these machines, the cutting tool is definitely the laser beam, and possesses a diameter of approximately 20µm. This means the kerf cut by the laser is all about 20µm wide, along with the laser system can locate that cut within 25µm with respect to either panel or board fiducials or some other board feature. The boards can therefore be put very close together in the panel. For the panel with lots of small circuit boards, additional boards can therefore be put, leading to cost benefits.
Because the laser beam can be freely and rapidly moved both in the x and y directions, eliminating irregularly shaped boards is not difficult. This contrasts with a number of the other described methods, which can be confined to straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and in some instances require extremely precise cuts, for instance when conductors are close together or when ZIF connectors need to be reduce (FIGURE 10). These connectors require precise cuts for both ends of your connector fingers, while the fingers are perfectly centered involving the two cuts.
A potential problem to consider is definitely the precision of your board images on the panel. The authors have not even found an industry standard indicating an expectation for board image precision. The closest they may have come is “as required by drawing.” This challenge can be overcome by adding a lot more than three panel fiducials and dividing the cutting operation into smaller sections using their own area fiducials. FIGURE 11 shows in a sample board reduce in Figure 2 that this cutline may be put precisely and closely round the board, in such a case, near the beyond the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards about the panel can be as low as the cutting kerf plus 10 to 30µm, based on the thickness of your panel 13dexopky the machine accuracy of 25µm.
In the area covered by the galvo scanner, the beam comes straight down in the middle. Even though a huge collimating lens is utilized, toward the sides of the area the beam features a slight angle. Consequently based on the height of the components near the cutting path, some shadowing might occur. Because this is completely predictable, the distance some components have to stay taken from the cutting path can be calculated. Alternatively, the scan area can be reduced to side step this challenge.
Stress. Because there is no mechanical contact with the panel during cutting, in some circumstances all the FPC Cutting Machine can be executed after assembly and soldering (Figure 11). This means the boards become completely separated from your panel in this last process step, and there is absolutely no requirement for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components close to the edge of the board are not susceptible to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a tremendous snap was observed (FIGURES 12 and 13). This means that during earlier process steps, for example paste printing and component placement, the panel can maintain its full rigidity with out pallets are needed.