Pcb Array’s Definition of Terms
PCB Array – What is it?
Also take a look at our new PCB Array Calculator 1.01.
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 definitely 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 array’s are very common. This post will provide a better understand of what they are, why they are needed and how to specify them.
An pcb array is combining a single PCB multiple times to make a larger array of connected boards, a “matrix” so to speak.
This process is referred to as “stepping out” the individual boards. It is often referred to as “step and repeat.” Other terms used to describe an pcb array are: panelized, stepped out, palletized and rout and retain.
Why would someone want a PCB array?
The reason a manufacturer would want their board in a pcb array is to help them with the manufacturing process. It gives them the ability to load the parts at a much faster rate because they can do the whole array at one time instead of loading one board 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.
Arraying the boards will typically raise the cost of the individual boards. This happens because you will get fewer boards on a production panel when they are in an array versus when they are run just as individual boards. Even though the individual board cost will go up, the cost of assembly of the boards is less because of the pcb array configuration.
Here are some of the key terms:
To allow for easier handling during the assembly process, extra PCB material is added to the sides of the array, these are called rails. The rails could be on all four sides of the array or only on two sides. If you only have it on two sides then you can usually get a few more pieces up on the panel which will help the per board 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 finish as the rest of the board on it. This provides alignment targets for the automated assembly equipment to get things lined up. 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 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 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.
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.
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.
That covers some of the basics of PCB Array. In the next post I will talk about how you calculate dimensions and the best way to specify them to your PCB Manufacturer.
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. For example, take a look at our new PCB Array Calculator that lets you easily calculate a best fit array.
Please post your questions and comments about PCB Array’s below.
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