Issue link: https://iconnect007.uberflip.com/i/1470111
66 DESIGN007 MAGAZINE I JUNE 2022 At the beginning of the design process, we should have built the footprints with a compo- nent courtyard size that has been agreed upon with the assembler, to prevent parts from being placed too close to each other. e soware will also have the capability of adding rules to check the component spacing using the court- yards for the same reason. Courtyards are an important part of the footprint—they not only prevent parts from butting up against each other but will also prevent placing short parts too close to tall parts, which makes it impos- sible to rework the shorter parts. We also add heights to the footprints to enable us to check that the parts are within a particular height envelope and prevent cards that mount next to each other from colliding. As PCB placement nears completion, we like to engage with the assembler to have them review the placement data for manufac- turability. Components that are too close to one another or to a board edge may not meet their DFM requirements or may inhibit the parts from being reworked should that become necessary. Model Citizens Designers can generate 3D models of the PCB to provide analysis of the placement to assure that components fit appropriately and cables have the required room to be installed. Checking the CAD models of the component placements of adjacent PCBs in a card cage is also recommended to assure they can be inserted and removed without issue. Some PCBAs require conformal coating to pro- tect them from harsh environments. is will require input and review by the conformal coating provider and may require additional documentation to identify keep-out areas. Circuit reuse has become an increasingly popular practice. Circuit reuse enables a designer to use existing, "proven" circuits, such as a power supply or memory circuit, which can be huge time-savers when the designs have the space and same stackups to use them iden- tically, as intended. However, they can become less proven and less cost-effective when they can't be used identically due to space con- straints or stackup variations. We use Siemens' Valor NPI soware to per- form a DFM analysis to assure that the design will release to PCB fabrication seamlessly. Other soware tools can perform similar DFM analyses. We generate the "deliverables" file from Valor to assure the deliverables match the Valor analysis. Some PCBs are intended to be assembled one-up and others are intended to be multi- ple-up in arrays. It's important to identify this during the design process so that the process is supported. In some cases, rails are added to the PCB to facilitate the assembly process and then they will be removed aerward. Commu- nications between the design engineer, layout designer, and assembler are critical to stream- lining the assembly processes. Early and regular communication is the common theme in our approach to DWM. While we've focused this article on the pro- cesses related to PCB design, you can easily adapt a DWM approach to other design activi- ties. Integrating with all major stakeholders to understand the impact of your process on their processes is critical to designing with manu- facturing. DESIGN007 Scott Miller is chief operating officer for Freedom CAD Services, Inc. Circuit reuse has become an increasingly popular practice.