The last few decades have brought several new challenges for manufacturing companies. Technology and improvements in transportation of goods has enabled companies to source parts globally. This has also resulted in more manufacturers having entered the market place.
Competition for business is fierce. Manufacturing companies in the developing world market are able to offer products at lower prices. In an effort to maintain business and achieve growth many manufacturers are continually developing new products to widen their customer base. They must be quick to market with a high-quality product or be left behind.
New Product Introduction (NPI) is the process that takes an idea from an initial working prototype to a thoroughly refined and reproducible final product. A New Product Introduction process can consist of various phases or gates.
The Develop Phase activities are focused on advancing the product design features and characteristics into a more defined form while assessing risk in the design. A validation plan is also developed during this phase. A comprehensive review of the design is performed to evaluate the robustness of the design and its ability to meet customer and performance requirements.
DFM/A activities are initiated prior to design completion or design freeze. In addition, the process required for production is being evaluated, including location, space requirements, equipment and preliminary process mapping.
Design for Manufacture and Assembly (DfMA) is a design approach that focuses on ease of manufacture and efficiency of assembly. By simplifying the design of a product it is possible to manufacture and assemble it more efficiently, in the minimum time and at a lower cost. This combination enables a product design to be efficiently manufactured and easily assembled with minimum labor cost.
DfMA combines two methodologies – Design for Manufacture (DFM) and Design for Assembly (DFA). Through the effective use of Design for Manufacturing and Assembly (DFM/DFA) best practices, products are designed with the process in mind. Both DFM and DFA seek to reduce material, overhead, and labour costs.
In the electronics product design lifecycle, mass manufacturing is done at the final stage of product release. There are several factors such as good design, minimum PCB assembly re-operations & iterations, less material overhead and labor cost to consider in this stage to manufacture valued products for OEMs and enterprises.
Through the use of DFM/A, a company can prevent, detect, quantify and eliminate waste and manufacturing inefficiency within a product design. DFM/A is a break from tradition. With DFM/A, the Design and Manufacturing Engineers work together as a team in developing the product’s manufacturing and assembly methods simultaneously with the design.
With DFM/A, the Design and Manufacturing Engineers work together as a team in developing the product’s manufacturing and assembly methods simultaneously with the design. It is applicable to PCB fabrication or PCB assembly or product assembly.
Traditionally, DfMA has been applied to sectors such as the design of automotive and consumer products, both of which need to efficiently produce high-quality products in large numbers. More recently, construction contractors have begun to adopt DfMA for the off-site prefabrication of construction components such as concrete floor slabs, structural columns and beams, and so on.
DFT is the method of design to ensure PCBA level operational & functional testing facilitated by test points on the board. Once the physical manufacturing process is finished, DFT helps to validate the board’s assembly and ensure product hardware is manufactured defect-free.
Adopting Design for Excellence (DFx) upfront as an integral part of the product development process produces higher quality products, lower product cost, and shorter product development cycles. A DFx team engages with the customer early on to assist designing sources of potential issues out of the product.
DFM techniques are focused on individual parts and components with the goal of reducing or eliminating expensive, complex, or unnecessary features which would make them difficult to manufacture. It is concerned with selecting the most cost-effective materials and processes to be used in production and minimizing the complexity of the manufacturing operations.
Design for Manufacturing (DfM) concentrates on minimizing the complexity of manufacturing process operations by:
- Determining the cost of fabricating individual components
- Reducing machined component features to control production costs, increase quality and assembly time efficiencies, and improve DfA outcomes
- Like DfA, the DfM process works to optimize product development, ensure smooth prototyping, and maximize ease of manufacturing.
Eliminate expensive, complex or unnecessary features for easy manufacturing
- Avoid tight tolerances, and accommodate within manufacturing process capabilities (e.g. PCB stackups, trace width-spacing, thickness & via/hole/cutout toolings)
- PCB panelization is very important factor in PCB fabrication cost
- Good to avoid parts with sharp edges & points, better to use radial chamfering
- Try to avoid bulky parts in design to reduce fatigue and lifting challenges
- Avoid rigid-flex PCB design if not mandatory
- Avoid uneven pads & irregular shapes in footprints for better etching
- Minimize solder-mask offsets for sufficient solder-joints in reflow process
- Use more thermal vias (instead of bigger Via holes)
Design for Assembly (DfA) Guidelines
DFA techniques focus on the reduction and standardization of parts, sub-assemblies, and assemblies. The goal is to reduce the assembly time and cost. It is concerned with reducing the product assembly cost and minimizing the number of assembly operations.
Design for Assembly (DfA) revolves around simplifying the product structure, focusing on:
- The designer should review the assembly design part by part and determine if any part can be eliminated or combined with another part. The designer should determine the theoretical minimum quantity of parts required for the assembly.
- Increasing ease of assembly by using keyed parts or components that can only go together in a certain orientation
- Ensuring ease of handling during assembly by measuring part size, weight, ease of dispensing, fragility, and flexibility
- Minimize the number of part count & types of parts to reduce inventory handling, sourcing, stock and assembly time
- Use parts with self-locating/aligning features & which can’t be installed incorrectly
- Design parts with self-fastening features to support mechanical challenges
- Use single side PCB for part placement
- Follow the ‘Top-Down’ assemblies approach for gravity advantage
- Do product design considering different parameters for a smooth assembly process like system partitioning, interconnection type and its assembly inside product, size and a package of parts, a minimum distance between assembly parts, etc.
- Provide parts enough clearance from PCB edges and also maintain minimum clearance between two components in a dense board considering the assembly process capability
- Arrange similar components symmetrically for easy installation
- Take care of mating connectors, cable orientation/height and area requirement
- Avoid using parts that are tangled prone & difficult to pick up/handle during assembly
- Avoid uneven pads & irregularities in footprint pads as it would require manual touch-up after surface mount technology to achieve optimum solderability
Using DfA and DfM in tandem forms the basis of Design for Manufacturing and Assembly (DfMA).
In simplest terms, DfMA is a set of guidelines for ensuring that a product is designed and revised so that it can be efficiently manufactured and assembled. It also has a positive effect on product quality.
DFM/DFA helps eliminate multiple revisions and design changes that cause program delays and increased cost. With DFM/A the design is often more comprehensive, efficient to produce and meets the customer requirements the first time.
DfMA facilitates dialogue and teamwork between designers and manufacturing engineers. Leveraging concurrent engineering lowers product costs, increases product reliability, and shortens time to market.
Other advantages of DfMA include:
Incorporating a modular design
Favoring standard parts over custom parts
Designing parts that are multi-functional and economical to fabricate
DFMA shortens assembly time by utilising standard assembly practices such as vertical assembly and self-aligning parts. DFMA also ensures that the transition from the design phase to the production phase is as smooth and rapid as possible.
Eliminating fasteners, etc., that reduce component cost and manufacturing time. DfMA increases reliability by lowering the number of parts, thereby decreasing the chance of failure.
Whether you plan to transfer a build-to-print or have engaged a manufacturer early in pre-production, the long-term value of DfMA activities impacts the complete product lifecycle.
Important DFM considerations
ENsure the fiducial markers and tooling strips are in place.
Take note of the designators for the components and be sure they are placed near the footprints and are clearly visible.
Try not to put components near the edge of the PCB.
Keep SMT components on the same layer, as it reduces stencil cost and assembly time.
Communicate clearly at the start of the project. It helps if you understand the requirements and constraints of the manufacturer before designing the PCB.
Provide accurate Gerber files and inform the assembler of any important instructions.
- Implement product testability starting from the development or prototype stage
- Cover all critical signals for testability
- Should have single side test points for added advantage on test set-up with Bed of Nail (BoN)
- Consider test points size and minimum pitch of test points right from the design phase to achieve Bed-of-nail (BoN) set-up within capabilities
- Ensure low skew between TAP signals (e.g xJTAG) & Buffer TAP signals with voltage level separations (inside TestFixture wiring)
- Consider testing multi-board panels as one unit
- Test points should have enough clearance to pad/component/PCB edge
- For full ICT (In-circuit test) coverage, every net of design should have test points
- Emphasize Test-flow to isolate issues related to component failures and manufacturing errors
- Choose correct spring-loaded probes (pins) to facilitate a proper electrical connection
- Avoid bulky & heightened components to use Flying probe testing
- Testing time per unit is crucial & target should be to achieve as minimum as possible
- Test automation should be driven from ease of testing, limited test-points, simple system feedback mechanicals
- Design test fixtures to cover functional validation either by semi OR full automation