What is a PCB Array?
What do you think of when you hear the word “array”? Perhaps you think of an antenna array, or possibly some type of mathematical array or maybe even Video Graphics Array (VGA like the adapter connection from your PC to your Monitor). It is one of those words in the English language that can mean something different to almost anyone who hears it. In PCB manufacturing, questions about PCB arrays are very common. This post will provide a better understand of what they are, why they are needed and how to specify them.
Simply put, a PCB array is when a single PCB is replicated multiple times to make a larger array of connected boards or a “matrix” so to speak.
This process is also referred to as “stepping out” the individual boards or referred to as “step and repeat”. Other terms used to describe a PCB array include: panelized, stepped out, palletized and rout and retain.
Why would someone want a PCB array?
The reason a manufacturer would want their PCB in an array is to help them with the manufacturing assembly process. An array enables the ability to load the parts at a much faster rate because an entire array consisting of multiple PCBs can be loaded with components all at once instead of one at a time. The boards are loaded using automated equipment referred to as a “pick and place” machine. This equipment simply picks up parts (normally surface mount devices) and places the part down on the board.
From a bare PCB fabrication perspective, arranging boards in an array will typically increase the cost of the individual boards because you will get fewer boards on a production panel due to the spacing between the individual boards and borders around the individual boards. However, this increase in cost is more than offset by the efficiency gained in assembly and reduction in overall assembly cost.
Additional PCB Array Terms
To allow for easier handling during the assembly process, extra PCB material is added to the sides of the array, called rails. The rails could be on all four sides of the array or only on two sides. If the rails are only designed to be on two sides then you may get a few more pieces up on the panel which will help the PCB unit cost.
Typically, three fiducials are needed on an array and they usually go on the rails. The ideal size is .050”. A fiducial is a circle that is a copper pad with the same surface finish as the rest of the board. This provides alignment targets for the automated assembly equipment. Some manufacturers may require fiducials on each individual board as well. However, for the most part there are pads or other features on the individual boards that can be used to provide additional alignment targets.
Tooling holes in the four corners of the PCB array somewhere in the rails is fairly common as well. Again, these are used to aid in alignment and orientation when assembling the board. The typical size is .125” and they are non-plated.
Scoring is making a small “V” groove along the length of the board where they will later be separated. The groove is typically 1/3rd on top, 1/3rd on bottom leaving 1/3rd of the material remaining in place to hold the boards together. When scoring, there should not be any parts placed within .250” of the edge of the board. If they are closer than that, there is the possibility that the parts could come loose during the depaneling process. If the board thickness is more than .062” and the score line is a long score line it can require a significant amount of force to separate the boards.
Tab Rout arrays will leave a small tab on all four sides of the board attached to the other boards or the rails. This type of array is not as stiff as the scored array but can be easier to break apart.
That covers some of the basics of PCB Arrays. Be sure to work with your PCB manufacturer to determine the best array for your next project. Your PCB manufacturer should be able to assist with array development but there are also software tools available to assist.
Need assistance arranging a PCB array? Try our free, online PCB Array Calculator