Happy’s Essential Skills: Design for Manufacturing and Assembly, Part 2

Estimated reading time: 9 minutes

Layout Efficiency is the percentage of capacity from design rules and structure that a designer can deliver on the board^[4]. Layout efficiency is the ratio of the actual wiring on a layer that was used to wire up a schematic versus the maximum wiring that could be used on that layer (totally full) or Wd divided by Wc. Layout efficiencies, typically, for ease of calculations are assumed to be 10%. Table 2 provides a more detailed selection of efficiencies

Example of DFMA Metrics

Three examples I have from my early days of using DFM/A metrics was the design of HP’s first and second inkjet printer, the Thinkjet™ and Quietjet™, and the design of the next generation of standard paper color inkjet printer, the Deskjet™. The Dewhurst & Boothroyd Methodology was applied to the first prototype Deskjet (bb). This prototype evolved from the two earlier inkjet printers, only more complex because now the paper was cut-sheet and not fan-folded with sprocket holes and was color with two heads. In all aspects it was more complex, with complex assembly and consequently, a lower ‘Ease of assembly’ rating. As a comparison, HP evaluated competing IBM PROprinter and OKI 182 printers even though these were more expensive printers. The resulting redesign and optimization using DFMA principles and seen in Table 4 and the rating on the final Deskjet (lb)

Table 4: Results of DFM/A analysis of printer prototypes.

Figure 12: DFM/A analysis of three HP inkjet printers and two competitors.

REFERENCES

1. Boothroyd, G., and P. Dewhurst, "DESIGN FOR ASSEMBLY", Dept. of Mechanical Engineering, University of Massachusetts, Amherst, Massachusetts, 1983.
2. General Electric, "Review of DFM Principles", Internal DFM Conference Paper, Charlottesville, VI, 1982
3. Hawiszczak, Robert, "Integrating  Design For Producibility Into A CAE Design Environment", NEPCON EAST, June 1989. pp 3-14.
4. Holden, H., The HDI Manual, published by PCB007, June 2008, a free download at http://hdimanual.com.
   

Further Reading

1. Boothroyd, G., and P. Dewhurst, "Design for Assembly", Dept. of Mechanical Engineering, University of Massachusetts, Amherst, Massachusetts, 1983.
2. Daetz, Douglas, "The Effect of Product Design on Product Quality and Product Cost," Quality Progress, June 1987, pp. 63-66.
3. Hume,H.; Komm,R.; and Garrison,T., IBM, "Design Report Card: a Method for Measuring Design for Manufacturability," Surface Mount International Conference, Sept, 1992, pp 986-991.
4. John Berrie and Andy Slade, “Knowledge Based Design Analysis for EMC,” Publication of Zuken-Redac Systems Ltd., Tewkesbury, Gloucestershire, UK, 1995.
5. O’Sullivan, Barry, “The Design Advisor: Capturing Design Practices and RFI / EMI Concerns,” The Board Authority, Vol.2, No.4, December 2000, pp. 47-52.
6. Hanus, Robynne,” HDI DFM and Physical Design Verification,” The Board Authority, Vol.2, No.4, December 2000, pp. 42-46.
7. L. Moresco, "Electronic System Packaging: The Search for Manufacturing the Optimum in a Sea of Constraints," IEEE Transactions on Components, Hybrids and Manufacturing Technology, 1990, Vol. 13, 1990, pp. 494-508.

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