Punching/die cutting. This process needs a different die for every single new circuit board, which happens to be not a practical solution for small production runs. The action could be PCB Depaneling, but either can leave the board edges somewhat deformed. To lessen damage care should be taken up maintain sharp die edges.
V-scoring. Usually the panel is scored for both sides to a depth around 30% from the board thickness. After assembly the boards may be manually broken out of the panel. This puts bending force on the boards that may be damaging to several of the components, in particular those near the board edge.
Wheel cutting/pizza cutter. A different approach to manually breaking the world wide web after V-scoring is to apply a “pizza cutter” to reduce the other web. This requires careful alignment involving the V-score along with the cutter wheels. Additionally, it induces stresses from the board which might affect some components.
Sawing. Typically machines that are used to saw boards away from a panel utilize a single rotating saw blade that cuts the panel from either the very best or perhaps the bottom.
Every one of these methods is limited to straight line operations, thus just for rectangular boards, and all of them for some degree crushes and/or cuts the board edge. Other methods are definitely more expansive and include the following:
Water jet. Some say this technology can be carried out; however, the authors are finding no actual users of it. Cutting is carried out with a high-speed stream of slurry, which can be water by having an abrasive. We expect it will require careful cleaning after the fact to get rid of the abrasive area of the slurry.
Routing ( nibbling). Usually boards are partially routed ahead of assembly. The remainder attaching points are drilled by using a small drill size, making it simpler to break the boards out of your panel after assembly, leaving the so-called mouse bites. A disadvantage could be a significant reduction in panel area towards the routing space, as the kerf width often takes approximately 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. What this means is a significant amount of panel space will be required for the routed traces.
Laser routing. Laser routing gives a space advantage, as the kerf width is simply a few micrometers. For instance, the tiny boards in FIGURE 2 were initially outlined in anticipation how the panel can be routed. In this way the panel yielded 124 boards. After designing the design for laser depaneling, the number of boards per panel increased to 368. So for each and every 368 boards needed, merely one panel should be produced rather than three.
Routing could also reduce panel stiffness to the level a pallet may be required for support in the earlier steps from the assembly process. But unlike the earlier methods, routing is not really restricted to cutting straight line paths only.
The majority of these methods exert some degree of mechanical stress about the board edges, which can lead to delamination or cause space to build up throughout the glass fibers. This may lead to moisture ingress, which can reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components about the board and after soldering, the very last connections in between the boards and panel really need to be removed. Often this really is accomplished by breaking these final bridges, causing some mechanical and bending stress around the boards. Again, such bending stress might be damaging to components placed in close proximity to areas that need to be broken so that you can get rid of the board in the panel. It is therefore imperative to accept the production methods into consideration during board layout and for panelization in order that certain parts and traces will not be positioned in areas considered subjected to stress when depaneling.
Room is likewise expected to permit the precision (or lack thereof) in which the tool path can be put and to consider any non-precision in the board pattern.
Laser cutting. Probably the most recently added tool to PCB Router and rigid boards can be a laser. Within the SMT industry various kinds lasers are increasingly being employed. CO2 lasers (~10µm wavelength) can provide 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 can be called “hot” lasers because they burn or melt the fabric being cut. (For an aside, these are the laser types, especially the Nd:Yag lasers, typically accustomed to produce stainless-steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are used 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 (FIGURE 3).
Choosing a 355nm laser is dependant on the compromise between performance and expense. To ensure ablation to happen, the laser light needs to be absorbed by the materials to become cut. Within the circuit board industry these are typically mainly FR-4, glass fibers and copper. When examining the absorption rates for these particular materials (FIGURE 4), 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 carries a tapered shape, since it is focused coming from a relatively wide beam for an extremely narrow beam and after that continuous in a reverse taper to widen again. This small area where beam is at its most narrow is called the throat. The ideal ablation happens when the energy density placed on the information is maximized, which occurs when the throat in the beam is merely inside the material being cut. By repeatedly groing through the same cutting track, thin layers of your material is going to be removed before the beam has cut all the way through.
In thicker material it might be essential to adjust the main objective of the beam, since the ablation occurs deeper into the kerf being cut to the material. The ablation process causes some heating of your material but can be optimized to go out of no burned or carbonized residue. Because cutting is carried out gradually, heating is minimized.
The earliest versions of UV laser systems had enough capability to depanel flex circuit panels. Present machines acquire more power and could also be used to depanel circuit boards around 1.6mm (63 mils) in thickness.
Temperature. The temperature boost in the information being cut is dependent upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how rapidly the beam returns to the same location) is dependent upon the way length, beam speed and whether a pause is added between passes.
An informed and experienced system operator will be able to find the optimum mixture of settings to make sure a clean cut without any burn marks. There is not any straightforward formula to determine machine settings; these are influenced by material type, thickness and condition. Based on the board and its application, the operator can pick fast depaneling by permitting some discoloring or 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 the cutting path is below 100°C, way below exactly what a PCB experiences during soldering (FIGURE 6).
Expelled material. Within 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 filtration system (FIGURE 7).
To evaluate the impact associated with a remaining expelled material, a slot was cut in a four-up pattern on FR-4 material having a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and was made up of powdery epoxy and glass particles. Their size ranged from around 10µm into a high of 20µm, plus some may have contained burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components in the board. If so desired, a basic cleaning process might be put into remove any remaining particles. This type of process could contain using any type of wiping by using a smooth dry or wet tissue, using compressed air or brushes. You can likewise use any sort of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any kind of additional cleaning process, especially a costly one.
Surface resistance. After cutting a path during these test boards (Figure 7, slot during the test pattern), the boards were put through a climate test (40°C, RH=93%, no condensation) for 170 hr., and also the SIR values exceeded 10E11 Ohm, indicating no conductive material is present.
Cutting path location. The laser beam typically uses a galvanometer scanner (or galvo scanner) to trace the cutting path inside the material over a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam being moved at the quite high speed along the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is with the same location simply a very short time, which minimizes local heating.
A pattern recognition product is employed, which can use fiducials or some other panel or board feature to precisely obtain the location where cut has to be placed. High precision x and y movement systems are used for large movements together with a galvo scanner for local movements.
In most of these machines, the cutting tool is the laser beam, and features a diameter of around 20µm. This means the kerf cut with the laser is about 20µm wide, and the laser system can locate that cut within 25µm with respect to either panel or board fiducials or other board feature. The boards can therefore be put very close together in a panel. For any panel with many different small circuit boards, additional boards can therefore be put, leading to saving money.
As being the laser beam can be freely and rapidly moved within both the x and y directions, removing irregularly shaped boards is simple. This contrasts with a number of the other described methods, which may be limited to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and in some instances require extremely precise cuts, by way of example when conductors are close together or when ZIF connectors have to be eliminate (FIGURE 10). These connectors require precise cuts for both ends of the connector fingers, whilst the fingers are perfectly centered between the two cuts.
A potential problem to take into consideration may be the precision of the board images about the panel. The authors have not really found a marketplace standard indicating an expectation for board image precision. The nearest they 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 because of their own area fiducials. FIGURE 11 shows inside a sample board remove in Figure 2 that this cutline can be put precisely and closely across the board, in such a case, near the beyond the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards in the panel can be as low as the cutting kerf plus 10 to 30µm, depending on the thickness from the panel 13dexopky the system accuracy of 25µm.
Within the area protected by the galvo scanner, the beam comes straight down in between. Though a big collimating lens can be used, toward the sides of the area the beam features a slight angle. This means that based on the height of your components close to the cutting path, some shadowing might occur. Because this is completely predictable, the distance some components need to stay pulled from the cutting path can be calculated. Alternatively, the scan area may be reduced to side step this issue.
Stress. While there is no mechanical exposure to the panel during cutting, sometimes each of the FPC Depaneling Machine can be carried out after assembly and soldering (Figure 11). What this means is the boards become completely separated in the panel within this last process step, and there is absolutely no need for any bending or pulling around the board. Therefore, no stress is exerted in the board, and components close to the edge of the board are certainly not at the mercy of damage.
In our tests stress measurements were performed. During mechanical depaneling an important snap was observed (FIGURES 12 and 13). This also signifies that during earlier process steps, including paste printing and component placement, the panel can maintain its full rigidity with no pallets are needed.