This process is called "evicting" a single board. It is often referred to as "step-by-step repetition". Other terms used to describe arrays are: paneling, stepping, palletizing, and collapse and retention.
Why would anyone want an array?
The reason manufacturers want their circuit boards to be arranged is to help them complete the manufacturing process. It allows them to load parts at a faster speed because they can load the entire array at once instead of loading one board at a time. The circuit boards are loaded using automated equipment called "pick and place" machines. The device simply picks up parts (usually surface mount devices) and places them on the board.
Arranging circuit boards usually increases the cost of a single circuit board. This happens because when they are in the array, you can get fewer boards on the production panel instead of when running as separate boards. Although the cost of a single board will rise, the cost of assembling the board is lower due to the array configuration.
Every electronic assembler and manufacturer has their own specific guidelines on how they want to set up the array for manufacturing. These guidelines provide some fairly common general practice ideas.
The size of the array
The array size ranges from 8 x 10 inches to 10 x 12 inches, as the overall maximum size. If the PCB manufacturer uses an 18×24 production panel size and 16×22 available space, the best fit for the largest array will be 7.8 x 10.8 inches. This will allow at least four arrays on the panel. If the array size is greater than this value, you will only be able to add two arrays, and the cost per board will increase significantly. The smaller array size can be used for a smaller single circuit board, and each panel still has a good yield.
Rails are additional PCB material that is added to the sides of the array for easier handling during assembly. The rails can be located on all four sides of the array or only on both sides. If you only have it on both sides, you can usually put a few more pieces on the panel, which will help reduce the cost of each board.
Generally, three reference points are required on the array and placed on the guide rail. The ideal size is 0.050 inches. The benchmark is a copper pad circle with the same finish as the rest of the circuit board. This provides alignment targets for automated assembly equipment to align things. Some manufacturers may also require benchmarks on each individual board. However, in most cases, there are pads or other features on a single board that can be used to provide additional alignment targets.
Tool holes in the four corners of the array (in the guide rail) are also common. Again, these are used to aid alignment and orientation when assembling the circuit board. The typical size is 0.125 inches, and they are non-plated.
The pitch will depend on whether the array is scored or wired. For tab routing, the spacing is 0.100 in most cases. By scoring the circuit boards and placing them next to each other, no spacing is required. There are two options for the "split board" we just mentioned-that is, how to separate the boards after assembly. The options are scoring or tab rout.
Notching means making a small "V" shaped groove along the length of the board where they will separate. The groove is usually at 1/3 of the top and 1/3 of the bottom, leaving 1/3 of the material in place to hold the board together.
When scoring, no parts should be placed within 0.250 inches from the edge of the board. If they are closer than this, the parts may loosen during the splitting process. If the board is thicker than 0.062 inches and the scribe line is long, it may require a lot of force to separate the board.
The Tab rout array will leave a small label on all four sides of the board connected to other boards or rails. This type of array is not as rigid as the scored array, but it is easier to separate.
The label usually has one on each side of each board and is usually 0.050 inches wide. They usually drill small holes on the edge of the label on the outside of the board. These small holes are called "rat bites" or "piercings." I even heard that they are called "rat bites." Either way, they can break the label from the board more easily. They do leave rough edges, so some additional sanding or grinding may be required to smooth them.
X output means that one of the individual boards on the array failed the test and is marked with a mark. Some manufacturers allow a certain percentage of X output in the order, while other manufacturers may require no X output on any array. Since there is no X output, this will make the circuit board more costly, because PCB manufacturers may need to manufacture a larger number of arrays to meet their output order requirements.
How do you calculate the size of the array?
Many people use the Kwickfit program to calculate arrays, which is a very convenient tool. If you have Kwickfit, here are the steps to get the best fit array:
Panel size is set to 18 x 24, margin is 1 inch
Select the best fit array
Enter the size of a single board
Maximum size 7.8 x 10.8
The minimum quantity is 1 and the maximum quantity is 100
If you don’t have kwickfit, you can also do this manually. Of course, a spreadsheet or calculator makes this easier.
Suppose the largest X dimension is 7.8, and the largest Y dimension is 10.8. Use the smallest size of a single board as the X size.
1. The first step is to determine your rail size
Rail size = _______
If your rail size is 0.5, you double it (the rails on both sides) and then subtract that size from the total available size of the X dimension.
Then subtract 1 inch from 7.8” = 6.8” inches. This is the "available" space of your array now in the x dimension.
2. The second step is to add your spacing to the size of the board.
X size = _______
Spacing = __________
For example, your circuit board is 1 inch and the pitch is 0.1. Add them together and you have 1.1 inches.
3. The third step is to determine how much is suitable.
Divide 6.8 by your individual board size and add spacing. In this case, 6.8 divided by 1.1 = 6.1 Therefore, you will be able to install 6 1" size boards in the x dimension using 0.1 pitch and 0.5 rails.
4. Add them together in the fourth step
Note: Since there is space on both sides of the board, you must add 0.1 to the total number of boards to get the correct overall size.
So here is the total number of X dimensions.
6 pcs * 1.1 = 6.6 + .1 (for extra space) = 6.7 + 1 (for guide rail) = 7.7" in X dimension Then perform the same process for Y dimension 10.8-1 = 9.8" Available space 9.8 / 1.1 = 8.9 (must be rounded down) so on the Y dimension it is equal to 8 width 8 * 1.1 = 8.8 + .1 = 8.9 + 1 (for the rail) = 9.9" on the Y dimension. Therefore, you will get 6 x 8 ( 48), the overall size is 7.7 x 9.9, with 0.500 inch rails and 0.100 inch spacing.
Now you can do this manually as I show here. Or, you can visit our website and try our array calculator. It will do all the mathematical operations for you and make a beautiful graphic image for you.