Laser depaneling can be carried out with high precision. This will make it extremely valuable in situations where areas of the board outline demand close tolerances. It also becomes appropriate when really small boards are involved. Because the cutting path is quite narrow and may be located very precisely, individual boards can be placed 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 exposure to the panel and without bending or pressing; therefore there is less possibility of component failures or future reliability issues. Finally, the position of the PCB Router is software-controlled, meaning alterations in boards can be handled quickly.
To evaluate the impact of 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 made up of powdery epoxy and glass particles. Their size ranged from an average of 10µm to your high of 20µm, and a few might have was comprised 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 simple cleaning process may be put into remove any remaining particles. Such a process could include using any kind of wiping using a smooth dry or wet tissue, using compressed air or brushes. One could also use just about any cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid any kind of additional cleaning process, especially a costly one.
Surface resistance. After cutting a path during these test boards (slot in the midst of the exam pattern), the boards were exposed to a climate test (40?C, RH=93%, no condensation) for 170 hr., and also 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 within the material over a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to become moved at a high speed along the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is in the same location only a very short period of time, which minimizes local heating.
A pattern recognition system is employed, which may use fiducials or any other panel or board feature to precisely discover the location where the cut has to be placed. High precision x and y movement systems can be used for large movements in combination with a galvo scanner for local movements.
In these kinds of machines, the cutting tool will be the laser beam, and features a diameter of around 20µm. This means the kerf cut from the laser is approximately 20µm wide, and 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 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 savings.
As the LED PCB Depanelizer can be freely and rapidly moved both in the x and y directions, eliminating irregularly shaped boards is straightforward. 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 generally very irregularly shaped and in some circumstances require extremely precise cuts, for instance when conductors are close together or when ZIF connectors must be reduce . These connectors require precise cuts on ends in the connector fingers, while the fingers are perfectly centered in between the two cuts.
A prospective problem to think about will be the precision from the board images on the panel. The authors have not found a niche standard indicating an expectation for board image precision. The closest they lsgmjm come is “as required by drawing.” This challenge may be overcome by adding greater 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 across the board, in this instance, next to the outside 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.
Within the area included in the galvo scanner, the beam comes straight down in the middle. Even though a sizable collimating lens can be used, toward the sides from 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. Because this is completely predictable, the distance some components have to stay taken off the cutting path can 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 instances all the depaneling can be performed after assembly and soldering. This means the boards become completely separated from the panel in this particular last process step, and there is not any need for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components nearby the edge of the board are not susceptible to damage.
In our tests stress measurements were performed. During mechanical depaneling a significant snap was observed. This also means that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity with no pallets are essential.
A standard 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 size and style and volume of the breakout tabs. The last PCB Separator step will generate even less debris, and making use of this method laser cutting time is reduced.
After many tests it has become clear the sidewall from the cut path can be quite clean and smooth, whatever the layers within the FR-4 boards or polyimide flex circuits. If the need for a clean cut will not be high, as in tab cutting of the pre-routed board, the cutting speed can be increased, leading to some discoloration .
When cutting through epoxy and glass fibers, you will find no protruding fibers or rough edges, nor exist gaps or delamination that could 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 really is required to maintain the material to get cut from the laser as flat as you can for maximum cutting. In particular instances, like cutting flex circuits, it can be as easy as placing the flex on a downdraft honeycomb or perhaps an open cell foam plastic sheet. For circuit boards it could be more challenging, especially for boards with components for both sides. In those instances still it might be desirable to prepare a fixture that will accommodate odd shapes and components.