Step 1:  Create a blank 400px by 400px document and fill it with a solid black colour. Run the Filter > Render > Difference Clouds command from the main menu and keep re-running it until you end up with a satisfactory cloud (the clouds themselves are randomly generated each time). Then run  Filter > Pixelize > Mosaic with a size setting of 12 or 15 pixels, depending on how large you want the circuits.

Step 2: Now select Filter > Blur > Radial Blur and duplicate the settings on the left.  Keep the quality as high as possible, or you'll get pixelation, which is definitely NOT desired in the next few steps.

Step 3: Press OK to render the blur effect, and then run Filter > Stylize > Emboss with an angle of 135 degrees, a height of 2 pixels, and a strength of 200%. It doesn't resemble a circuit yet, but the next filter will change all that!   Choose  Filter > Brush Strokes > Accented Edges from the menu, and input a width of 2px, a brightness  of 50, and a smoothness of 5.

Step 4: You can finish off the effect by selecting Filter > Stylize > Find Edges, which will pick out all the edges and make the circuits far more visible. Now just select Image > Adjustments > Invert to reverse the colours, and there you have it - a circuit board of your very own!

Step 5: You should, of course, attempt to personalize this effect a little before you add it to your own creations.  To alter the colours, just navigate to  Image > Adjustments > Hue / Saturation, click on the colorize checkbox, and vary the Hue setting until you find a colour of your liking.   Skynet has never looked so plausible...