Laser depaneling can be executed with extremely high precision. This will make it extremely valuable in situations where elements of the board outline demand close tolerances. In addition, it becomes appropriate when very small boards are involved. Since the cutting path is extremely narrow and can be located very precisely, individual boards may be placed closely together on the panel.
The reduced thermal effects mean that despite the fact that 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 positioning of the PCB Router is software-controlled, meaning alterations in boards can be handled quickly.
To test the impact of 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 around 10µm to your high of 20µm, and a few might have was made up of burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components on the board. If so desired, an easy cleaning process could be included in remove any remaining particles. Such a process could include the usage of just about any wiping having a smooth dry or wet tissue, using compressed air or brushes. You could also employ any type of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any type of additional cleaning process, especially a costly one.
Surface resistance. After cutting a path within these test boards (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., as well as 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 within the material more than a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to get moved in a extremely high speed over the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is within the same location merely a very short time, which minimizes local heating.
A pattern recognition product is employed, which may use fiducials or other panel or board feature to precisely get the location in which the cut needs to be placed. High precision x and y movement systems can be used for large movements together with a galvo scanner for local movements.
In these sorts of machines, the cutting tool is the laser beam, and it has a diameter of around 20µm. What this means is the kerf cut from the laser is all about 20µm wide, as well as the laser system can locate that cut within 25µm regarding either panel or board fiducials or other board feature. The boards can therefore be placed very close together in a panel. For a panel with many small circuit boards, additional boards can therefore be put, ultimately causing cost savings.
As the Desktop PCB 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 can be limited to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and in some instances require extremely precise cuts, for example when conductors are close together or when ZIF connectors need to be eliminate . These connectors require precise cuts on ends of the connector fingers, while the fingers are perfectly centered in between the two cuts.
A potential problem to consider is definitely the precision in the board images on the panel. The authors have not found a niche standard indicating an expectation for board image precision. The nearest they lsgmjm come is “as necessary for drawing.” This problem may be overcome with the help of greater 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 around the board, in this instance, next to the outside of the copper edge ring.
Even though 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 of the panel in addition to the system accuracy of 25µm.
Within the area included in the galvo scanner, the beam comes straight down at the center. Even though a large collimating lens is utilized, toward the sides of the area the beam includes a slight angle. Which means that depending on the height in the components nearby the cutting path, some shadowing might occur. As this is completely predictable, the distance some components need to stay removed from the cutting path can be calculated. Alternatively, the scan area may be reduced to side step this issue.
Stress. As there is no mechanical contact with the panel during cutting, in some instances all the depaneling can be carried out after assembly and soldering. What this means is the boards become completely separated from your panel in this particular last process step, and there is no requirement 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 certainly not subjected to damage.
Within our tests stress measurements were performed. During mechanical depaneling a significant snap was observed. This implies that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity without any pallets are essential.
A common production technique is to pre-route the panel before assembly (mechanical routing, employing a ~2 to 3mm routing tool). Rigidity will then be dependant on the size and style and amount of the breakout tabs. The final PCB Separator step will generate much less debris, and by using this method laser cutting time is reduced.
After many tests it is clear the sidewall from the cut path can be extremely clean and smooth, no matter the layers within the FR-4 boards or polyimide flex circuits. If the requirement for a clean cut is not high, like tab cutting of a pre-routed board, the cutting speed could be increased, leading to some discoloration .
When cutting through epoxy and glass fibers, you will find no protruding fibers or rough edges, nor are available gaps or delamination that would permit moisture ingress with time . Polyimide, as used in flex circuits, cuts well and permits for extremely clean cuts, as seen in Figure 3 as well as in the electron microscope picture.
As noted, it really is required to keep your material to get cut through the laser as flat as is possible for optimum cutting. In particular instances, as with cutting flex circuits, it may be as easy as placing the flex on the downdraft honeycomb or even an open cell foam plastic sheet. For circuit boards it could be harder, specifically for boards with components for both sides. In those instances still it could be desirable to prepare a fixture that will accommodate odd shapes and components.
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