Once a board design is complete and it is time to start manufacturing the board must be panelized. This process involves adding board features that provide the necessary hooks to allow a pick and place machine to handle the board for automated assembly. Panelizing includes adding grip rails (for conveyor support), tooling holes (for mechanical alignment and fastening) and global fiducials (optical marks for machine vision detection).
Figure 1: Panelized board in a pick and place assembly machine
These features are added in a way that allows removal after manufacturing is completed. Another major component of panelizing is determining how many individual boards should be included into the given panel. A lot of factors come into play when considering how to panelize a design and this series of blog posts will discuss the issues. While fab companies will often panelize a board for you and this service is often included in the setup charge, it makes sense to thoughtfully consider the way it should be panelized and then provide them with the directions and let them do the work.
Communicating with the Fab Shop and the Contract Manufacturer (CM)
The fab shop makes actual bare PCB and the CM assembles and solders the components on. When considering efficient panelization of a project it is key to understand the fab and CM requirements to ensure your design fits within their abilities (including tooling, process, capability). To reduce costs it is important to understand what panel size your fab shop considers their standard process as that will be the cheapest even if they can accommodate unusual requests. The next step is to determine what features the CM needs on the board for assembly such as grip rails, tooling holes etc. Both these steps are important when optimizing for cost as we will show. If the panel design sticks to reasonable conventions then assumptions could be made about capabilities but it is always good to check.
Choosing the Panel Size
As a designer you determine the size of the board and then determine how many boards to include in a panel. This panel design gets sent to the fab shop and they may put it on another panel which is what they actually manufacture, confused yet? You should be, and the first point to make is that the nomenclature used by designers and fab shops differ – it’s probably best to clear this up. When a design firm says a panel they mean the array of boards that go into the pick and place machine for assembly, when a fab shop says panel they mean the raw size of the board before cutting down into ‘panels’ as known by design firms. Sometimes the term pallet is used interchangeably for panel or in some cases a design firm says ‘pallet’ which means the array of panels that the fab house makes. So context is key here. It’s recommended to speak in fab lingo when speaking to the fab shop where figure 2 shows a ‘9-up array’ and where two of these arrays can fit on a 12”x18” ‘panel’ use for manufacturing. We’ll stick to this convention from now on (except that when we say panelize a design like in the title of this post we mean to make an array).
Figure 2: A 7″x10″ 9-up array of 2″x3″ boards.
So we can typically assume that 12”x18” or 18”x24” panels will fit into the standard process of a fab shop. So if we design for a 12”x18” panel then two of them will fit on the 18”x24” panel. That means if we design for 12”x18” we’ll be good for both these processes. A standard size for an array is no bigger than 7.8”x10.8” which gives the fab shop room for their required tooling and impedance control test coupons etc. when two of these are placed within a 12”x18” panel. So figure 2 shows the optimal size of the array given a 2”x3” board with the CM required features which include grip rails, the tooling holes and fiducial features on them.
In the next post we’ll discuss the CM requirements for assembling the boards and how that may impact the efficiency in panelization. As a teaser, let us consider figure 3 where the panelization used only two grip rails instead of four. Normally only two grip rails are required by the CM and this gives us 10 boards for the exact same size array, a 10% increase in efficiency.
Figure 3: A 7″x10″ 10-up array of 2″x3″ boards.
You may ask, “Why not just let the fab shop choose the array size for most efficiency?” The truth is that a lot of factors come into play when determining the array size and it can come back to the actual design of the board in certain circumstances. This is most clear if slightly changing the board size by 5mm, which can often be accommodated, could impact the panel efficiency and this could mean serious savings especially in high volume designs.
As with any design you need to need to weigh non-recurring engineering costs (NRE) such as efficient panelization against the cost of the manufacturing process. If you are doing 3 prototypes of a one-off board then it may not matter how efficiently the design is panelized. While some companies change the panelization for production to optimize for cost and pay less emphasis on this during the prototype phase, additional tooling and PCB form factor changes can drive up the design costs. Certainly if you are going into production then close attention should be paid to the process.
Fidus Systems provides design support services for low to high volume customers. Contact us if you have questions about increasing the efficiency of your electronic manufacturing process and our expert team can help you increase efficiency and decrease manufacturing costs.
Trevor Smouter – Fidus Hardware Designer