PCB Panelization In Design For Manufacturing
During PCB production, PCB must be panelized according to suitable dimensions and shapes in order to bring the production costs and durations down. Let's see the effects of a suitable PCB panelization design on production times, and therefore costs, with an example.
Let's try to sample the Loading/Unloading times for the same single PCB, which is panelized as a Single, 2x3 and 4x4. The table shown in Figure-1 specifies the estimated times for single and panelized PCBs.
As it can be seen from the table above, when we manufacture the same card as a single, it takes 270 seconds for it to go through the Wave Solder machine, when we panelize it as 2x3 (6 pcs.), the duration per card is reduced to 45 seconds, and when we panelize it as 4x4 (16 pcs.), the duration per card is further reduced to 16,88 seconds. While it takes 8 seconds for it to go through the Cream Solder machine, if we panelize it as 2x3 (6 pcs.), the duration per card is reduced to 1,33 seconds, and if we panelize it as 4x4 (16 pcs.), the duration per card is further reduced to 0,50 seconds. This will give us a time reduction of 83 % 2x3 (6 pcs.) panelized cards and 94 %
for 4x4 (16 pcs.) panelized cards in terms of loading/unloading times. While there is no significant reduction of time or cost in low production volumes, the reduction of time and cost in daily productions or high volume PCB production will not be negligible.
Before we begin panelization, we have to know the minimum and maximum dimensions of the machinery and conveyors to be used in the processes and act accordingly. A panelization application that exceeds the dimensions of the conveyor will cause a panelized card to not fit in the machine. (For instance, the Optical Inspection (AOI) machine only allows a minimum card size of 50x60mm and a maximum card size of 460x510mm.)
If possible, the panelization must have a rectangular shape and preferably not exceed the dimensions of 200x200mm. During the card manufacturing processes, panelization must be done so that the card is carried on its longer edge and the breakaway tab application must be designed accordingly.
Even if the PCB has fiducial points, it is useful to place fiducial points on the breakaway tab as well. If the width of the breakaway tab is 5mm or shorter, the fiducials will be left at the bottom of the Conveyor Clamps, so they must be positioned at a distance of 5mm from the Board Edge along the card's transverse axis.
If the materials or legs on the side of the longer edge according to the direction of flow on the PCB, are not located within 5mm of the board edge, a 5mm breakaway tab must be included to the side of the edge on which the card will be carried. If this tab is not included, conveyor clamps or fingers will touch the material or lift the legs up.
If axial or radial inserters are to be used in the production process, the tab on the side of the longer edge must be 8 mm in length and located on the longer edge.
During panelization, taking into account the weights of components such as transformers, coolers, coils on the PCB, the bending of the card on the conveyors or the deflection / breakage of the V-CUTS as a result of panelization must be prevented.
During panelization, if Manual Installation is to be performed, it must be ensured that all cards are facing the same direction. If the cards in the panelization are positioned to be facing different directions, there will be a possibility that the operators who will perform the Manual Installation may install directional components in the wrong direction.
There may be materials located at a distance of 5mm or closer from one board edge of the PCB. In this case, one inverted/one regular panelization method may be implemented in order to reduce the costs of the PCB material. The directions are adjusted by aligning the edges within which the materials are located, with the conveyor clamps or fingers.
During panelization, overhanging components of the PCB (e.g. Socket, Header, LED, Switch, Button, Cooler) (if any) must be taken into consideration while designing the edge strips. If a strip that has the same dimensions as the overhanging parts of the components of the PCB is not included, these components will be hooked on or stuck to the conveyors or the edges of the machinery.
During panelization, an internal strip must be applied so that the overhanging components of the PCB (e.g. Socket, Header, LED, Switch, Button, Cooler) cannot touch the components on the other card. If this strip is not used, the overhanging components will overlap with the other components, it will not be possible to attach the component or solder it due to the fact that it is hanging in the air.
If the edges of the PCB that are placed on the conveyors are flat or have a design that is not the same length as the PCB, PCB edges on the side of the conveyors must correspond to the card's length with breakaway tabs. If the card edges have variable lengths or are shorter than the card's length, the machine's Conveyor Clamps or Conveyor Fingers will be unable to hold or advance the card or will be stuck on the joints of the conveyors.
During PCB panelization, gaps may be left between cards that are not rectangular or square-shaped. If the gaps inside the panelized card are bigger than a Few cm, during Wave Soldering, the solder material may overflow from the gaps and spread over the card. In order to avoid this issue, the gaps must be sealed with breakaway tabs.
With variable PCB edges or in cases where there should be no burr formations as the PCB will be placed in a very sensitive box mould, Mouse Bite breakaway tabs can be applied. In these applications, the weight of the card must be taken into account so that the tabs are not broken or the card is not bent. Another point to consider must be the position, number and thickness of the tabs to be placed according to the card's weight. The holes to be drilled on the tab must start from the outside of the tab. The holes must be positioned along the edge of the PCB.