Design For Manufacturing (DFM)

If the designer is looking at getting the board automatically assembled with a pick-and-place machine, then it pays you to get as many boards onto the one "panel" as you can. A panel is simply a large PCB containing many identical copies of your board. It takes time to place a board into position on a pick and place machine, so the more boards you can load at once, the more cost effective your manufacturing will be. The procedure is named panelisation.

A panel will also contain tooling strips on the top and bottom, to allow for automated handling of the panel. Different manufactuers may have different maximum panel sizes they can produce. Each individual board can be "routed out" and joined with "breakout tabs", or simply butted together and scoured out with a "V groove". A V groove is a score mark placed on your board that allows you to easily "snap" the board along the groove. A breakout tab is a small strip of board perhaps 5-10mm long joining your board to your panel. Small non-plated holes are also drilled along this strip, which allows the board to be snapped or cut out of the panel after assembly.

Tooling strips are strips of blank board down the top and bottom side of your board. They contain tooling holes, fiducial marks, and other manufacturing information if required. Standard tooling holes are required for automated handling of your board. 2.4mm and 3.2mm are two standard hole sizes. Four tooling holes per panel is sufficient, one in each corner. The tooling trips connect to your board(s) with breakout tabs or V Grooves.

Fiducial marks are visual alignment aids placed on your PCB. They are used by automated pick and place machines to align your board and find reference points. A video camera on the machine can identify the center of fiducial marks and use these points as a reference. On a panel there should be 3 fiducial marks, known as global fiducials. Bottom left/right and top left corners. They should be at least 5mm away from the board edges. They can be mounted on the tooling strips. The fiducial mark should be a circular pad on the copper layer of diameter 1.5mm typically. The fiducial should not be covered with solder mask, and the mask should be removed for a clearance of at least 3mm around. The pad can be bare copper or coated like a regular pad. Two local fiducial (one in opposite corners) is also required next to each large fine pitch surface mount device package on your board.

If the user solidly connects a surface mount pad to a large copper area, the copper area will act as a very effective heat sink. This will conduct heat away from your pad while soldering. This can encourage dry joints and other soldering related problems. In these situations a thermal relief connection, which comprises several (usually 4) smaller tracks connecting the pad to the copper plane. Thermal relief options can be set automatically in many packages.