Laser depaneling can be carried out with very high precision. This will make it extremely useful in situations where parts of the board outline demand close tolerances. It also becomes appropriate when really small boards are involved. Since the cutting path is very narrow and may be located very precisely, individual boards may be placed closely together on the panel.
The reduced thermal effects mean that even though a laser is involved, minimal temperature increases occur, and thus essentially no carbonization results. Depaneling occurs without physical exposure to the panel and without bending or pressing; therefore there is certainly less chance of component failures or future reliability issues. Finally, the position of the PCB Router is software-controlled, which means alterations in boards may be handled quickly.
To check the impact for any remaining expelled material, a slot was cut in a four-up pattern on FR-4 material with a thickness of 800µm (31.5 mils). 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 some may have was comprised of burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components on the board. In that case desired, a simple cleaning process might be included in remove any remaining particles. Such a process could contain the use of any kind of wiping having a smooth dry or wet tissue, using compressed air or brushes. You can also use any type 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 within these test boards (slot in the middle of the exam pattern), the boards were subjected to a climate test (40?C, RH=93%, no condensation) for 170 hr., and the SIR values exceeded 10E11 Ohm, indicating no conductive material is
Cutting path location. The laser beam typically utilizes a galvanometer scanner (or galvo scanner) to trace the cutting path within the material over a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to be moved at a high speed across the cutting path, in the range of approx. 100 to 1000mm/sec. This ensures the beam is in the same location just a very short period of time, which minimizes local heating.
A pattern recognition method is employed, which may use fiducials or some other panel or board feature to precisely discover the location where cut needs to be placed. High precision x and y movement systems can be used as large movements in combination with a galvo scanner for local movements.
In these types of machines, the cutting tool is the laser beam, and features a diameter of approximately 20µm. This means the kerf cut by the laser is about 20µm wide, as well as the laser system can locate that cut within 25µm regarding either panel or board fiducials or any other board feature. The boards can therefore be put very close together in a panel. For any panel with a lot of small circuit boards, additional boards can therefore be put, resulting in cost benefits.
Since the PCB Depaneling Router can be freely and rapidly moved in both the x and y directions, cutting out irregularly shaped boards is straightforward. This contrasts with a number of the other described methods, which is often 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 have to be reduce . These connectors require precise cuts for both ends in the connector fingers, while the fingers are perfectly centered involving the two cuts.
A possible problem to consider will be the precision from the board images on the panel. The authors have not yet found a business standard indicating an expectation for board image precision. The closest they lsgmjm come is “as necessary for drawing.” This issue can be overcome by adding more than three panel fiducials and dividing the cutting operation into smaller sections using their own area fiducials. Shows in a sample board cut out in Figure 2 that the cutline may be placed precisely and closely round the board, in this instance, next to the outside of the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards on the panel could be as low as the cutting kerf plus 10 to 30µm, depending on the thickness from the panel in addition to the system accuracy of 25µm.
Within the area protected by the galvo scanner, the beam comes straight down at the center. Even though a big collimating lens is used, toward the edges from the area the beam includes a slight angle. This means that depending on the height in the components close to the cutting path, some shadowing might occur. Because this is completely predictable, the distance some components must stay taken off the cutting path could be calculated. Alternatively, the scan area can be reduced to side step this problem.
Stress. Because there is no mechanical connection with the panel during cutting, in some instances each of the depaneling can be carried out after assembly and soldering. What this means is the boards become completely separated from the panel in this last process step, and there is not any necessity for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components nearby the fringe of the board are not subject to damage.
In our tests stress measurements were performed. During mechanical depaneling a significant snap was observed. This means that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity and no pallets are required.
A standard production method is to pre-route the panel before assembly (mechanical routing, employing a ~2 to 3mm routing tool). Rigidity is then based on the dimensions and volume of the breakout tabs. The final PCB Depaneler step will generate much less debris, and by using this method laser cutting time is reduced.
After many tests it is clear the sidewall of the cut path can be quite clean and smooth, no matter the layers within the FR-4 boards or polyimide flex circuits. If the need for a clean cut will not be extremely high, as in tab cutting of the pre-routed board, the cutting speed may be increased, leading to some discoloration .
When cutting through epoxy and glass fibers, you can find no protruding fibers or rough edges, nor are available gaps or delamination that would permit moisture ingress over time . Polyimide, as utilized in flex circuits, cuts well and permits for extremely clean cuts, as observed in Figure 3 as well as in the electron microscope picture.
As noted, it is required to keep the material to become cut by the laser as flat as you can for optimum cutting. In certain instances, as with cutting flex circuits, it may be as basic as placing the flex over a downdraft honeycomb or perhaps an open cell foam plastic sheet. For circuit boards it might be harder, especially for boards with components on both sides. In those instances it still could be desirable to get ready a fixture that will accommodate odd shapes and components.