Laser depaneling can be executed with extremely high precision. This will make it extremely useful in situations where areas of the board outline demand close tolerances. In addition, it becomes appropriate when really small boards are involved. Because the cutting path is very narrow and may be located very precisely, individual boards can be placed closely together on the panel.
The reduced thermal effects mean that even though 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 possibility of component failures or future reliability issues. Finally, the position of the Inline PCB Router is software-controlled, meaning alterations in boards may 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 consisted of powdery epoxy and glass particles. Their size ranged from typically 10µm to some high of 20µm, plus some might have consisted of burned or carbonized material. Their size and number were extremely small, without any conduction was expected between traces and components on the board. If so desired, a basic cleaning process could be included in remove any remaining particles. This type of process could contain using just about any wiping with 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 any kind of additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path during these test boards (slot in the center of the test 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 in the material over a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to be moved with a high speed over the cutting path, in the plethora 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 product is employed, which may use fiducials or any other panel or board feature to precisely discover the location in which the cut has to be placed. High precision x and y movement systems are used for large movements together with a galvo scanner for local movements.
In these types of machines, the cutting tool is the laser beam, and it has a diameter of approximately 20µm. This means the kerf cut through the laser is approximately 20µm wide, and also the laser system can locate that cut within 25µm with regards to either panel or board fiducials or other board feature. The boards can therefore be placed very close together in a panel. To get a panel with many small circuit boards, additional boards can therefore be placed, leading to cost savings.
Because the LED PCB Depanelizer can be freely and rapidly moved within both the x and y directions, removing irregularly shaped boards is simple. This contrasts with a few of the other described methods, which can be confined to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and in some instances require extremely precise cuts, for example when conductors are close together or when ZIF connectors have to be eliminate . These connectors require precise cuts for both ends from the connector fingers, as the fingers are perfectly centered in between 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 niche standard indicating an expectation for board image precision. The nearest they lsgmjm come is “as necessary for drawing.” This challenge may be overcome with the addition of more than three panel fiducials and dividing the cutting operation into smaller sections making use of their own area fiducials. Shows in a sample board reduce in Figure 2 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 may be as little as the cutting kerf plus 10 to 30µm, depending on the thickness in the panel plus the system accuracy of 25µm.
In the area covered by the galvo scanner, the beam comes straight down in the center. Even though a sizable collimating lens is utilized, toward the sides in the area the beam features a slight angle. This means that depending on the height from the components near the cutting path, some shadowing might occur. Since this is completely predictable, the distance some components need to stay taken off the cutting path could be calculated. Alternatively, the scan area can be reduced to side step this issue.
Stress. Because there is no mechanical exposure to the panel during cutting, in some circumstances all of the depaneling can be performed after assembly and soldering. What this means is the boards become completely separated from the panel in this particular last process step, and there is absolutely 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 not subject to damage.
Within our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed. This implies that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity with no pallets are needed.
A common production method is to pre-route the panel before assembly (mechanical routing, utilizing a ~2 to 3mm routing tool). Rigidity is then determined by the dimensions and volume of the breakout tabs. The ultimate PCB Depaneler step will generate much less debris, and by using this method laser cutting time is reduced.
After many tests it has become remove the sidewall in the cut path can be very clean and smooth, regardless of the layers in the FR-4 boards or polyimide flex circuits. If the need for a clean cut is not really high, like tab cutting of the pre-routed board, the cutting speed can be increased, causing some discoloration .
When cutting through epoxy and glass fibers, you can find no protruding fibers or rough edges, nor exist gaps or delamination that could permit moisture ingress as time passes . Polyimide, as found in flex circuits, cuts well and permits for extremely clean cuts, as observed in Figure 3 and in the electron microscope picture.
As noted, it is actually essential to maintain the material to be cut through the laser as flat as is possible for maximum cutting. In some instances, as with cutting flex circuits, it can be as simple as placing the flex on the downdraft honeycomb or even an open cell foam plastic sheet. For circuit boards it might be more challenging, specifically for boards with components on sides. In those instances it could be desirable to make a fixture that will accommodate odd shapes and components.