Laser depaneling can be executed with extremely high precision. This makes it extremely useful in situations where areas of the board outline demand close tolerances. It also becomes appropriate when tiny boards are participating. As the cutting path is very narrow and can be located very precisely, PCB Depanelizer can be placed closely together on the panel.
The reduced thermal effects suggest that despite the fact that a laser is involved, minimal temperature increases occur, and for that reason essentially no carbonization results. Depaneling occurs without physical connection with the panel and without bending or pressing; therefore there exists less chance of component failures or future reliability issues. Finally, the positioning of the cutting path is software-controlled, which suggests changes in boards could 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 having a thickness of 800µm (31.5 mils). Only few particles remained and consisted of powdery epoxy and glass particles. Their size ranged from typically 10µm to a high of 20µm, and a few could 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 basic cleaning process might be included in remove any remaining particles. This kind of process could consist of the usage of just about any wiping having a smooth dry or wet tissue, using compressed air or brushes. You can also employ any kind of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid just about any additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path within these test boards (slot in the middle of the exam pattern), the boards were put through 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
Cutting path location. The laser beam typically uses a galvanometer scanner (or galvo scanner) to trace the cutting path inside the material spanning a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to get 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 merely a very limited time, which minimizes local heating.
A pattern recognition system is employed, which can use fiducials or some other panel or board feature to precisely get the location in which the cut has to be placed. High precision x and y movement systems can be used as large movements together with Pneumatic PCB Depanelizer for local movements.
In these sorts of machines, the cutting tool is definitely the laser beam, and features a diameter of approximately 20µm. What this means is the kerf cut through the laser is about 20µm wide, as well as the laser system can locate that cut within 25µm with regards to either panel or board fiducials or some other board feature. The boards can therefore be placed very close together in a panel. For any panel with lots of small circuit boards, additional boards can therefore be put, leading to cost savings.
Since the laser beam may be freely and rapidly moved within both the x and y directions, cutting out irregularly shaped boards is simple. This contrasts with a few of the other described methods, which is often limited to straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and in some circumstances require extremely precise cuts, for example when conductors are close together or when ZIF connectors must be reduce . These connectors require precise cuts on both ends from the connector fingers, as the fingers are perfectly centered involving the two cuts.
A possible problem to take into consideration will be the precision from the board images on the panel. The authors have not even found a business standard indicating an expectation for board image precision. The nearest they may have come is “as necessary for drawing.” This problem may be overcome with the help of a lot more than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. Shows in a sample board reduce in Figure 2 the cutline may be placed precisely and closely lmuteg the board, in cases like this, near the outside of the copper edge ring.
Even though ignoring this potential problem, the minimum space between boards on the panel may be as low as the cutting kerf plus 10 to 30µm, depending on the thickness from the panel plus the system accuracy of 25µm.
Inside the area covered by the galvo scanner, the beam comes straight down in the middle. Even though a sizable collimating lens is utilized, toward the sides in the area the beam has a slight angle. This means that depending on the height from the components nearby the cutting path, some shadowing might occur. Since 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 challenge.
Stress. As there is no mechanical exposure to the panel during cutting, in some instances each of the depaneling can be carried out after assembly and soldering. This implies the boards become completely separated from the panel in this particular 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 near the fringe of the board are not subject to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed. This also signifies that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity without any pallets are essential.
A typical production technique is to pre-route the panel before assembly (mechanical routing, utilizing a ~2 to 3mm routing tool). Rigidity will then be based on the dimensions and volume of the breakout tabs. The last depaneling step will generate even less debris, and making use of this method laser cutting time is reduced.
After many tests it is now clear the sidewall in the cut path can be quite clean and smooth, whatever the layers within the FR-4 boards or Laser Depaneling. If the requirement for a clean cut will not be very high, like tab cutting of a pre-routed board, the cutting speed could be increased, resulting in some discoloration .
When cutting through epoxy and glass fibers, there are no protruding fibers or rough edges, nor are there gaps or delamination that will permit moisture ingress with time . Polyimide, as utilized in flex circuits, cuts well and permits for extremely clean cuts, as seen in Figure 3 and in the electron microscope picture.
As noted, it is essential to maintain the material to get cut by the laser as flat as possible for maximum cutting. In some instances, like cutting flex circuits, it can be as easy as placing the flex on a downdraft honeycomb or even an open cell foam plastic sheet. For circuit boards it could be more difficult, particularly for boards with components for both sides. In those instances it could be desirable to make a fixture that may accommodate odd shapes and components.