PCB requirements

LitePlacer does not require anything special from your PCB design apart from industry standard SMD design – but you have to do those!

Fiducials

There should be alignment marks on the PCB. (These are called “fiducials”.) The industry standard fiducial (according to IPC-7351) is a 1mm diameter round dot. There should be a 2mm solder mask opening and no circuitry or markings within this feature. The machine will use optical recognition for the marks, measure their position and calculate the component positions from these, adjusting for displacement, rotation and possible scale and shear errors.

There must be at least three fiducials; four or more is preferred. The location accuracy decreases for components outside the area enclosed by the fiducials, therefore three might not be enough, while four in the corners of the PCB is. If there are more than four, the algorithm will use them. However, the advantage is theoretical, since the accuracy of the transform with four fiducials is already well within the machine movement tolerances.

The fiducials placement is free, there is no need to have them perpendicular or square to each other, just spread them out.

In case your board does not have standard fiducials, rectangular features can be used as well. In case your board has no fiducials, you can use vias or pads as such; you need to put the CAD coordinates of the them to the pick and place file using the same format as “real” components.

The fiducial setup box looks like this:

You can select if the algorithm accepts round rectangular or both shapes for targets. If you use existing board features instead of real fiducials, you might have other items close by. For this, you can set the tolerance, how close to the nominal position a feature needs to be and still get accepted. For real tricky cases, you can request manual “OK” for the optical recognition, to be sure the intended target got selected.

If you name your fiducials as FI1, FI2, … or FID1, FID2, … the program automatically recognizes these (case insensitive).

The Pick and Place File

Your PCB must be designed with a computer using a program designed for SMD layout. All of these are able to produce a pick and place file. For the file format requirements, please see the Input File Format page.

Organized CAD Library

Although it is not strictly required, having your CAD library well organized towards automated placement will make your life so much easier, that you should have it. This means components with reference points in the physical center, component rotations in a consistent manner (such as all ICs with reference pin to upper left), and so on. You shouldn’t need to refer to your CAD data when you look at a part to figure out which way is 0 rotation!