The embedded products consist of integration of hardware board PCBA (Printed circuit board assembly), firmware code developed in the integrated development environment (IDE) tools and mechanical enclosure. As embedded system products are becoming more and more complex and innovative with multiple new technologies the role of system engineer and hardware board designers are becoming more and more challenging to produce the error free system design at first attempt.
Listing out the priorities
All hardware, firmware and mechanical design related risks should be brought out and discussed with all team members before starting the design and mitigation steps should be planned as part of project planning.
We begin with Software
The Design rule check (DRC) of schematic and layout files should be done before releasing any design files to the PCB (Printed circuit board) fabricators, DRC rules should not be waived off and exception of DRC rules should be reviewed carefully with all design and manufacturing team members. Netlist verification steps helps hardware system designer to verify each and every nets connectivity, open, short and unconnected nets in the design.
Considering Design for test (DFT) analysis at schematic and layout phase eliminates board spin due to identifying lack of testability (test coverage) related issues. Designing the manual or automated manufacturing test system at the time of schematic and board layout phase helps designers to find the overall test time and test coverage related issues.
Designing as per components
Feasibility for rework of fine pitch components like ball grid array (BGA) and chip scale package (CSP) should be done at the time of board layout phase to eliminate rework issues in the production build also at the time of customer returns for failure analysis.
Implementing reusable schematic and layout blocks in the design helps to eliminates the repeating errors in the design files.
Circuit, layout and mechanical simulation tools helps designer simulate critical signals and produce error free design. Using 3D simulation tool feature of layout tool the designer can verify high Z height components on the board and integration with mechanical enclosures. System engineers can also use “Development kits” to test and simulates few of the features of embedded products.
Power matters too
Estimating proper power budget of the entire system and designing different power and ground planes helps hardware system designer to design the boards operating on multiple voltages and handling power sequencing.
By implementing polarized user interface connectors and providing over voltage, over current, short circuit protection for on-board input-output connectors, external interface related issues can be eliminated.
The most of the Design for Manufacturing (DFM) and Design for Assembly (DFA) related issues are occurred due to the electronics component footprint creation issues or PCB layout standards. The electronics component footprint should be created as IPC-7351 Class A-B or C standards (Based on the application of final product) and validation of footprint should be done before releasing the final Gerber file (using verification tools) to the PCB fabricator.
Moving on to hardware
By Implementing IPC based reference designators, Polarity markings and implementing IPC based design guidelines for schematic and layout design the component assembly related issues are eliminated.
By providing all board fabrication related details it includes special fabrication instructions, PCB materials with Glass transient (TG) level with required finish (Matt or Glossy finish)), layer stack up, soldermask and silkscreen color and all tolerance levels in the fabrication drawing of Gerber files helps PCB fabricator to build error free board multiple times.
Reviewing Gerber files with board fabrication and assembly vendors and implementing all manufacturing and assembly feedback in the design before releasing the final Gerber files avoids extra time spent to get error free boards in hand.
DFM reports and test coupons from manufacturing vendors helps to identify manufacturing related issues and occurrence at production build.
Selection of components
Electronics component ordering should be done much in advance before releasing the Gerber for the production build and all active and passive components should be placed and checked by taking 1:1 pinout of assembly file before releasing the final Gerber to the production house to eliminate the future assembly related issues. The electronics component part number selection should be done by taking final assembly process into the account for Example the pick and place data like tape and reel packaging property should be taken into the consideration. Verification of regulatory information of electronics component should be done directly with component manufactures instead of going through distributors for getting correct and error proof information.
By implementing proper version control and design file release to manufacturing mechanism helps error free transfer of all hardware files to the manufacturing location.
By reviewing the production assembly flow and production process at the advance stage of design helps to reduce the issues in the production build.
In case of mechanical enclosure based systems, use of 3D printers and 3D models in the design phase helps designers to build proto mechanical available much in advance cycle of project and to integrate with PCBA and overall system.
How it helps
By implementing integration of Product lifecycle management (PLM) used by production manufactures with layout tool helps designers to use the common parts and certified layout footprint across all the designs, it also provides End of life (EOL), Restriction of Hazardous Substances (ROHS), UL and all other information for all electronics components. Re-using common electronic component data base in all design helps designer to use common parts across the design, reduce the bill of material (BOM) cost and it helps to find EOL for the electronics component in the design.
