Laser depaneling can be carried out with extremely high precision. It is then extremely useful in situations where areas of the board outline demand close tolerances. In addition, it becomes appropriate when really small boards are involved. As the cutting path is quite narrow and will be located very precisely, individual boards can be put closely together on the panel.
The low thermal effects mean that even though a laser is involved, minimal temperature increases occur, and therefore essentially no carbonization results. Depaneling occurs without physical connection with the panel and without bending or pressing; therefore there is certainly less possibility of component failures or future reliability issues. Finally, the positioning of the Inline PCB Router is software-controlled, meaning changes in boards can be handled quickly.
To evaluate the impact for any remaining expelled material, a slot was cut in a four-up pattern on FR-4 material using a thickness of 800µm (31.5 mils). Only few particles remained and was comprised of powdery epoxy and glass particles. Their size ranged from an average of 10µm to a high of 20µm, plus some may 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 you have desired, a basic cleaning process might be put into remove any remaining particles. This kind of process could consist of the usage of just about any wiping using a smooth dry or wet tissue, using compressed air or brushes. One could also have any kind of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid just about any additional cleaning process, especially a costly one.
Surface resistance. After cutting a path in these test boards (slot in the center 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 works with a galvanometer scanner (or galvo scanner) to trace the cutting path in the material over a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to get moved in a extremely high speed along the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is within the same location just a very short period of time, which minimizes local heating.
A pattern recognition system is employed, which may use fiducials or other panel or board feature to precisely get the location where cut needs to be placed. High precision x and y movement systems can be used for large movements in conjunction with a galvo scanner for local movements.
In these kinds of machines, the cutting tool is definitely the laser beam, and contains a diameter of around 20µm. What this means is the kerf cut by the laser is all about 20µm wide, and also 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 placed very close together in a panel. For any panel with lots of small circuit boards, additional boards can therefore be placed, ultimately causing cost savings.
Since the Desktop PCB Router can be freely and rapidly moved both in the x and y directions, cutting out irregularly shaped boards is easy. 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 can be very irregularly shaped and occasionally require extremely precise cuts, for instance when conductors are close together or when ZIF connectors have to be cut out . These connectors require precise cuts on both ends of the connector fingers, as the fingers are perfectly centered involving the two cuts.
A prospective problem to consider will be the precision of 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 lsgmjm come is “as required by drawing.” This challenge could be overcome with the addition of more than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. Shows in a sample board eliminate in Figure 2 that this cutline can be put precisely and closely around the board, in this case, next to the away from 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 as well as the system accuracy of 25µm.
Within the area included in the galvo scanner, the beam comes straight down in the center. Despite the fact that a big collimating lens is used, toward the edges from 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. As this is completely predictable, the space some components have to stay taken off the cutting path can be calculated. Alternatively, the scan area may be reduced to side step this challenge.
Stress. Because there is no mechanical connection with the panel during cutting, in some instances all the depaneling can be executed after assembly and soldering. What this means is the boards become completely separated from your panel within this last process step, and there is absolutely no need for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components near the edge of the board are not subjected to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed. This also means that during earlier process steps, including paste printing and component placement, the panel can maintain its full rigidity without any pallets are required.
A common production technique is to pre-route the panel before assembly (mechanical routing, employing a ~2 to 3mm routing tool). Rigidity is then determined by the dimensions and amount of the breakout tabs. The final PCB Depanel step will generate even less debris, and making use of this method laser cutting time is reduced.
After many tests it is remove the sidewall from the cut path can be very clean and smooth, regardless of the layers inside the FR-4 boards or polyimide flex circuits. If the necessity for a clean cut will not be high, as with tab cutting of the pre-routed board, the cutting speed can be increased, leading to some discoloration .
When cutting through epoxy and glass fibers, there are no protruding fibers or rough edges, nor are available gaps or delamination that could 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 really is necessary to keep your material to get cut by the laser as flat as you can for optimum cutting. In certain instances, as in cutting flex circuits, it could be as basic as placing the flex over a downdraft honeycomb or perhaps an open cell foam plastic sheet. For circuit boards it could be harder, particularly for boards with components on sides. In those instances still it could be desirable to get ready a fixture that can accommodate odd shapes and components.