Punching/die cutting. This procedure needs a different die for each new circuit board, which happens to be not much of a practical solution for small production runs. The action might be PCB Depaneling, but either can leave the board edges somewhat deformed. To lower damage care must be taken to maintain sharp die edges.
V-scoring. Often the panel is scored for both sides into a depth of approximately 30% from the board thickness. After assembly the boards might be manually broken out of your panel. This puts bending strain on the boards that can be damaging to a number of the components, in particular those close to the board edge.
Wheel cutting/pizza cutter. An alternate approach to manually breaking the world wide web after V-scoring is to apply a “pizza cutter” to slice the other web. This requires careful alignment in between the V-score as well as the cutter wheels. Additionally, it induces stresses within the board which could affect some components.
Sawing. Typically machines that are employed to saw boards from a panel work with a single rotating saw blade that cuts the panel from either the very best or maybe the bottom.
Each of these methods is restricted to straight line operations, thus simply for rectangular boards, and each one to a few degree crushes and/or cuts the board edge. Other methods will be more expansive and can include the following:
Water jet. Some say this technology can be done; however, the authors are finding no actual users of this. Cutting is conducted using a high-speed stream of slurry, which happens to be water with an abrasive. We expect it should take careful cleaning following the fact to remove the abrasive portion 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 easier to interrupt the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be quite a significant lack of panel area to the routing space, since the kerf width normally takes around 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 is going to be required for the routed traces.
Laser routing. Laser routing provides a space advantage, as being the kerf width is just a few micrometers. For example, the little boards in FIGURE 2 were initially laid out in anticipation how the panel would be routed. This way the panel yielded 124 boards. After designing the layout for laser depaneling, the volume of boards per panel increased to 368. So for every 368 boards needed, just one panel should be produced as an alternative to three.
Routing can also reduce panel stiffness to the level a pallet may be required for support during the earlier steps inside the assembly process. But unlike the last methods, routing is just not limited by cutting straight line paths only.
Many of these methods exert some degree of mechanical stress in the board edges, which can cause delamination or cause space to produce around the glass fibers. This can lead to moisture ingress, which actually can reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components in the board and after soldering, the ultimate connections between your boards and panel must 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 near areas that ought to be broken to be able to take away the board through the panel. It is therefore imperative to take the production methods into mind during board layout as well as for panelization to ensure certain parts and traces will not be placed in areas regarded as susceptible to stress when depaneling.
Room is additionally needed to permit the precision (or lack thereof) with which the tool path can be placed and to take into consideration any non-precision in the board pattern.
Laser cutting. One of the most recently added tool to PCB Router and rigid boards is really a laser. Inside the SMT industry various kinds of lasers are increasingly being employed. CO2 lasers (~10µm wavelength) can provide quite 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. These two laser types produce infrared light and could be called “hot” lasers as they burn or melt the material being cut. (As being an aside, these are the basic laser types, particularly the Nd:Yag lasers, typically used to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the flip side, are used to ablate the information. A localized short pulse of high energy enters the best layer of your material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
Choosing a 355nm laser is founded on the compromise between performance and cost. To ensure that ablation to happen, the laser light has to be absorbed through the materials being cut. Within the circuit board industry these are generally mainly FR-4, glass fibers and copper. When examining the absorption rates of these materials (FIGURE 4), 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 from a relatively wide beam with an extremely narrow beam and after that continuous in a reverse taper to widen again. This small area the location where the beam is at its most narrow is referred to as the throat. The perfect ablation occurs when the energy density applied to the material is maximized, which takes place when the throat of your beam is merely within the material being cut. By repeatedly exceeding the same cutting track, thin layers in the material will be removed till the beam has cut right through.
In thicker material it can be required to adjust the focus from the beam, as the ablation occurs deeper into the kerf being cut in the material. The ablation process causes some heating from the material but could 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 power to depanel flex circuit panels. Present machines acquire more power and may also be used to depanel circuit boards around 1.6mm (63 mils) in thickness.
Temperature. The temperature surge in the material being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quick 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 find the optimum mix of settings to ensure a clean cut free from burn marks. There is no straightforward formula to ascertain machine settings; they may be influenced by material type, thickness and condition. Based on the board as well as its application, the operator can select fast depaneling by permitting some discoloring as well as some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing has demonstrated that under most conditions the temperature rise within 1.5mm from your cutting path is below 100°C, way below what a PCB experiences during soldering (FIGURE 6).
Expelled material. Inside the laser utilized for these tests, an airflow goes across the panel being cut and removes the majority of the expelled dust into an exhaust and filtering method (FIGURE 7).
To test the impact of any 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 consisted of powdery epoxy and glass particles. Their size ranged from around 10µm into a high of 20µm, and a few could have consisted 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 possibly be added to remove any remaining particles. Such a process could comprise of using just about any wiping having a smooth dry or wet tissue, using compressed air or brushes. You can also employ any sort of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any type of additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path in these test boards (Figure 7, slot in the midst of the test pattern), the boards were subjected 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 utilizes a galvanometer scanner (or galvo scanner) to trace the cutting path within the material spanning a small area, 50x50mm (2×2″). Using this type of scanner permits the beam being moved in a very high speed over the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is within the same location only a very small amount of time, which minimizes local heating.
A pattern recognition system is employed, which can use fiducials or any other panel or board feature to precisely discover the location the location where the cut must be placed. High precision x and y movement systems can be used as large movements in conjunction with a galvo scanner for local movements.
In these sorts of machines, the cutting tool is definitely the laser beam, and contains a diameter of approximately 20µm. This simply means the kerf cut by the laser is approximately 20µm wide, as well as the laser system can locate that cut within 25µm with respect to either panel or board fiducials or another board feature. The boards can therefore be placed very close together inside a panel. For a panel with a lot of small circuit boards, additional boards can therefore be put, creating saving money.
As being the laser beam could be freely and rapidly moved both in the x and y directions, eliminating irregularly shaped boards is easy. This contrasts with some of the other described methods, which may be confined to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and sometimes require extremely precise cuts, as an example when conductors are close together or when ZIF connectors must be remove (FIGURE 10). These connectors require precise cuts on both ends from the connector fingers, while the fingers are perfectly centered involving the two cuts.
A possible problem to take into account is definitely the precision of the board images around the panel. The authors have not even found a marketplace standard indicating an expectation for board image precision. The nearest they already have come is “as required by drawing.” This problem may be overcome by adding over three panel fiducials and dividing the cutting operation into smaller sections making use of their own area fiducials. FIGURE 11 shows within a sample board eliminate in Figure 2 how the cutline can be placed precisely and closely round the board, in this instance, near the away from the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards around the panel could be as low as the cutting kerf plus 10 to 30µm, dependant upon the thickness in the panel 13dexopky the system accuracy of 25µm.
Throughout the area covered by the galvo scanner, the beam comes straight down in between. Despite the fact that a big collimating lens is used, toward the sides from the area the beam carries a slight angle. Consequently based on the height of your components nearby the cutting path, some shadowing might occur. Because this is completely predictable, the space some components need to stay removed from the cutting path can be calculated. Alternatively, the scan area can be reduced to side step this issue.
Stress. While there is no mechanical connection with the panel during cutting, in some instances all the FPC Cutting Machine can be executed after assembly and soldering (Figure 11). This implies the boards become completely separated through the panel in this particular last process step, and there is no need for any bending or pulling in the board. Therefore, no stress is exerted on the board, and components close to the side of the board usually are not at the mercy of damage.
In your tests stress measurements were performed. During mechanical depaneling a substantial snap was observed (FIGURES 12 and 13). This also implies that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity without any pallets are needed.