solder-mask web must be present between pads.Minimum LPI solder-mask pad clearance is 2.5 mil.Here is the IPC-7351 standard for QFN packages: IPC-7351 Nominal land-pattern for QFN packageīelow we describe how the footprint is created, when we take both the IPC-7351 criteria and the capabilities of PCB Fabrication and PCB Assembly vendors into consideration. In addition, the heatsinking provided by the thermal pad makes them difficult to rework. The downside is that QFNs are also notoriously difficult for PCB assembly, due to their fine pitch and flat bottom. Each component has toe, heel, and side solder fillets, as illustrated below. Regardless of your choice in software, it’s best to take a close look at how the design rules are set up and make sure they’re in line with the DFM guidelines from your fab and assembly vendors.Īn SMT footprint is IPC-7351 compliant if the calculated solder fillets meet the component-specific criteria in the standard. At Nuvation Engineering we use an IPC-7351 compliant layout tools, meaning that the formulas and methodology in IPC-7351 for calculating land-pattern geometry are built in. The IPC standard pertaining to SMT footprints is IPC-7351, Generic Requirements for Surface Mount Design and Land Pattern Standard. There are various schematic capture and EDA tools that can be used for PCB layout, including Altium Designer, Cadence Allegro, and Mentor Graphics Expedition. In addition to DFM Guidelines, there are a number of industry standards provided by the Association Connecting Electronics Industries (IPC). Whether you’re designing a prototype PCB or a high-volume product, following DFM guidelines will reduce the number of manufacturing defects you encounter, saving money by improving yield and eliminating debug time. The first step in designing a perfect PCB footprint is contacting your chosen fabrication vendor and contract manufacturer, and understanding their specific Design for Manufacturing (DFM) guidelines. The quality of a PCB footprint directly impacts the performance, reliability and quality of the PCB assembly. To create robust and cost-effective printed circuit boards, layout designers need to follow best practices for PCB footprint generation.
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