Resolving Inter Site Fabrication Discrepancies in Automated Module Packaging Files
Containerize module fabrication data in IPC-2581C to lock CAM modifications, enforce netlist parity, and eliminate inter-site geometry discrepancies.
Solder Dam Width
Meaning
Strips of solder resist material between adjacent surface mount pads isolate the wet solder during assembly. Specifying the solder dam width prevents electrical shorts from forming between closely spaced component pins. This narrow strip of polymer mask must remain intact on the board surface after exposure and development.
Ensuring sufficient width prevents the mask from peeling off and allowing molten solder to bridge the gap.
Solder Bridging
Molten solder can flow between adjacent pads if there is no physical barrier to contain it during the reflow process. In high density packages like fine pitch quad flat packs, the pins are so close together that even a small amount of runout can create a bridge. A sufficient solder dam width acts as a physical dam that keeps the solder on its designated copper pad.
This isolation is critical for preventing assembly defects that require manual rework or cause component damage.
Fabrication Capability
Limits on the resolution of the imaging equipment and the adhesion of the photoresist material determine the minimum dimension that a fabricator can reliably produce on a board. If the designer specifies a solder dam width that is narrower than the capability of the factory, the material will lift off during development and leave the traces exposed. This failure often occurs during the washing phase when the fine strips of mask are stripped away by the chemical spray.
Design Rule
CAD software enforces minimum spacing rules during the layout phase to ensure that the board conforms to the manufacturer’s requirements. When laying out fine pitch components, designers must balance the pad size and the solder mask clearance to ensure that the solder dam width is sufficient. If the gap between the mask clearances is too small, the software will generate a design rule violation that must be resolved before releasing the design for fabrication.
This automatic check prevents layout configurations that are impossible to manufacture with standard processes. By resolving these violations early, engineers can avoid delivery delays and reduce the cost of board re-spins.