PCB Assembly Services - Screaming Circuits: Basic Layout - Aligning Components


Basic Layout - Aligning Components

Not long ago, I designed an Arduino compatible clock board. The board has twelve NeoPixel (digital addressed RGB LEDs) arranged around the board to act as hour hands. The minutes and seconds are represented by an external ring of 60 NeoPixels.

Clock with layers
How did I go about positioning the twelve NeoPixels, and what does it matter? For aesthetic reasons, I do want each NeoPixel in the proper place. If any are off a bit, I'll notice every time I look at the clock.

I created a triangle, with all of the correct distances, and drew in in my CAD software’s Document layer. The Document layer looks just like a silk screen layer, when visible, but it won’t be printed on the board. You can use this layer to put in extra information for yourself, or for the manufacturer.

Call out with tDocu layer
You’ll notice that I also wrote, in the document layer “No tabs here.” That’s an instruction to the PC board fabrication house to not put a panel tab where the micro USB connector goes. If they did, the board wouldn’t be buildable when panelized.

Some people create a fabrication document layer and an assembly document layer. An example might pertain to reference designators. If the board is too compact for reference designators, of if, for esthetic reasons, you want to leave them off the finished board, You can put the reference designators in an Assembly Documentation layer. Then be sure to let your assembly house know what you’ve done.

The other things I did here, is keep all of the LEDs aligned with the baseline of the PC board. In theory, you can place a component at any rotation angle you want. But, like any system, manufacturing works better when there are fewer variables.

You reduce the probability of error if you keep your components aligned at factors of 90 degrees. It also helps to keep polarities oriented the same way, as much as possible. For example, if you can, have all of the diode polarities facing the same direction.

Duane Benson
Time flies like an arrow; fruit flies like a banana


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