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Finding the Right Manufacturing Partner
Test Expert software helps in designing for test.

Having grown into a major tier-two EMS provider over the last 25 years, SMTC has built a strong reputation based on the strength of performance for its OEM clients. As a recognized EMS provider, SMTC is driven by delivering customized and flexible design, engineering and manufacturing services in its chosen markets. SMTC's primary North American headquarters are in Toronto, Canada and San Jose, California, with a global footprint of manufacturing and technology centers, together totaling close to 600,000 square feet of capacity with more than 40 manufacturing and assembly lines. It has manufacturing operations on the ground in Canada, the United States, Mexico and China.

Founded in 1985, the company's services include printed circuit board assembly, systems integration and comprehensive testing services, enclosure fabrication, product design, engineering and supply chain management services. These services span product life cycles all the way from development and introduction through growth, maturity, post-production services and end-of-life phases.

Higher Engineering Level
SMTC understands the changing dynamics of the industry and markets it serves. More so now than in the past, companies like SMTC require an in-house staff with a higher level of engineering capabilities because design engineering support has become so crucial and important today. This is why SMTC is deeply involved with its customer design teams at the early stages of product development to ensure a smooth process from prototyping to a full turnkey solution.

Design for Excellence
Early involvement in the design cycle can lead to products which are more cost-effective, more manufacturable, of intrinsic higher quality, better time to market and have longer product life-cycles. Design reviews focusing on key areas throughout the design cycle provide critical feedback to address potential problems, thus ensuring a successful new product introduction, along with high quality, high production yield and a highly manufacturable product. Design reviews can be categorized as material (design for supply chain), test (design for testability), fabrication (design for fabrication) and assembly (design for manufacturability).

Design for Supply Chain (DFSC). Very early in the design cycle, component selection and technology can have the single greatest impact on success of the end product. Early partnership with strategic manufacturing partners can provide insight during this selection process. Minimum information is approved manufacturer listing which can be uploaded and cross-indexed to part databases to provide information on process, lifecycle, regulatory, alternates, PCN (Product Change Notification), and supply. Does your supplier have strategic preferred manufacturers and suppliers? Aligning your component selection with preferred suppliers can have long-term cost advantages.

Technology maturity, market acceptance and lifecycle. It is very tempting to embed the latest technology and small form factor into your design, but is it truly necessary, and does this limit your options for suppliers capable of manufacturing and providing quality product?

Regulatory compliance and process compatibility. These are typically not major criteria for component selection, but can have the single biggest impact on manufacturability, chemistry and future redesign requirements.

Design for Testability (DFT). Once component selection and inherit functionality is finalized, interconnects and schematics are developed. During this time, best practices for isolating circuits, providing sufficient net access, considerations for JTAG/Boundary Scan and testability should be reviewed prior to layout.

Preliminary test access can be determined early with BOM/AML and schematics where test violations and required test point and access can be identified early on. It is important to focus on testability to provide JTAG chains for embedded and pull-down to support testability. Regardless of your test strategy, incorporating maximum net access and testability will ensure your design can support and is ready for test as you ramp to production.

Once the design is finalized, formal DFT reports using automated software can provide complete test access reports and provide a comprehensive listing of access violations, additional test point requirements or mechanical spacing constraints providing a net access percentage and feedback on how to increase the coverage.

Net Access
It is important not to confuse net access with testability, as a design with 100 percent net access can provide have limited testability if proper JTAG chain, pull-downs and early design for test review are not done or implemented.

Even the best designs do not guarantee 100 percent testability and is it important to consider both structural and electrical when reviewing DFT. A good test strategy considers both. Test strategies such as AOI, X-Ray (2D/3D) provide coverage on components (placement, presence and correctness), solderability (fillet, ground plane, defects, solder fill). Flying probe, ICT, JTAG/Boundary Scan, Functional Test provide coverage on component (value, tolerance, function) and system level functionality.
Flying prober is one of many available test platform options.

Simulations of test coverage determine total test coverage and provide feedback on redundant coverage to optimize the test strategy to further reduce test times and cost.

Reliability and Quality testing such as Hi-pot, Burn-in, and ESS will depend on your design; temperature, duration and voltage should be based on end product requirements, component industrialization, and design capabilities and considerations. When introducing such tests, a well defined sampling and functional testing (both before and after stress testing) and statistical confidence performance review will determine if sampling and reduction of duration can be considered.

Design for Fabrication (DFF). DFF is focused on the printed circuit board fabrication itself and typically needs a minimum of gerber information, drill and fabrication details. Design rules based on the suppliers capabilities, process tolerances and material specifications are applied to provide feedback on issues which may prevent high quality and repeatable fabrication. Component selection, design requirements and complexity dictate the fabrication requirements. Laminate performance, layer count, and copper weight via technology and regulatory considerations quickly determines the complexity of fabrication and can define capability requirements, surface finish, stackup. Layout reviews are important to identify and address potential issues prior to fabrication.

Finish Requirements
Key considerations: minimum pitch of components can define surface finish requirements to achieve co-planarity and can be a large cost driver. Other considerations include shelf life, solderabilty and availability.

Technologies such as blind/buried vias, via in pad, and embedded passives all need to be carefully considered based on supplier capability, design stability and quality (process robustness and repeatability). Poor PCB quality or consistency can create significant costs in re-spin and drive yield issues both with the PCB and manufacturer.

PCB panelization can drive significant costs if not taken into consideration. A properly designed panel should be developed between the PCB board manufacturer and the assembly house to ensure highest possible master panel yield.

Design for Manufacturing (DFM) or Design for Assembly (DFA). A preliminary DFM can be performed with component layer placement files to provide initial feedback on layout prior to internal layer connections. This can save significant re-layout time from feedback that comes later in the design cycle. Once the final layout, BOM, Gerbers, CAD and assembly drawings are completed, automated software can apply preset design rules to the provided design to categorize violations into high, medium, low and acceptable classifications.

Areas of review are primarily focused on reviewing PCB design considerations, SMT compatibility and automation, PTH thermal, wave and selective soldering compatibility, as well as mechanical consideration such as poke-yoke, press-fit, swage, torque and fixturing, etc.

Focusing on DFM spotlights process step/thermal cycle reduction through technology consolidation and simplification (i.e. THR to SMT, 0402 to 0603, etc.); automation (supply and process compatibility); and thermal balancing (ground plane, SMT/PTH relief).

Risks vs. Benefits
Various design reviews can be provided at various stages of the design cycle and the risks vs. benefits need to be evaluated to determine the best time to involve the manufacturer in your design reviews. It is important to align with strategic manufacturing partners early on to provide relevant design feedback on all aspects of the design and lifecycle — not just prototype — as the design decisions made early on affect the long term viability and cost of the product for its total lifecycle.

SMTC Corporation, founded in 1985, is a mid-size provider of end-to-end electronics manufacturing services (EMS) including PCBA production, systems integration and comprehensive testing services, enclosure fabrication, as well as product design, sustaining engineering and supply chain management services. SMTC facilities span a broad footprint in the United States, Canada, Mexico, and China, with more than 1,875 full-time employees. SMTC services extend over the entire electronic product life cycle from the development and introduction of new products through to the growth, maturity and end-of-life phases.

SMTC offers fully integrated contract manufacturing services with a distinctive approach to global original equipment manufacturers (OEMs) and emerging technology companies primarily within industrial, computing and communication market segments.

Contact: SMTC, 635 Hood Road, Markham, Ontario, L3R 4N6 Canada 905-479-1810 fax: 905-479-1877 In USA: 408-934-7100 E-mail: Web:

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