Circuits Assembly - April 2008 - (Page 70)

Getting Lean Dfx for Lean Designers unfamiliar with Lean can actually add process steps – and cost. n EMS provider’s facility can completely in terms of unit price may actually be on par with embrace Lean manufacturing principles, but if with a slightly higher priced SMT component when the OEM customers’ products aren’t designed throughput costs are considered. Not all product can for them, the result is inefficiency and missed costbe designed as 100% SMT, of course. However, when reduction opportunities. only one or two through-hole parts are involved, the Optimizing designs for Lean manufacturing benefits of selecting SMT options should be considrequires designers to balance their goals for functionalered. ity, material cost and long-term product enhancement Any design element that drives manual processing flexibility against throughput cost and logistics effiadds significant throughput cost and may reduce qualciency. Here, we focus on key elements in optimizing ity. For instance, hand insertion vs. automatic placedesign to minimize throughput and logistics costs. ment triples the labor cost. Hand soldering vs. wave or A basic premise of Lean is to eliminate non-value reflow soldering results in triple the cost of automated added activity. Unfortunately, many designers actusoldering multiplied by the number of leads being ally add non-value activity in the form of additional hand soldered. process steps in their quest to reduce component cost Improperly sized through-hole pads and holes or fully use PCB real estate. Much of what is discussed will result in unacceptable solder joints, which means here involves the basis of added inspection and toutheir contribution to better chup. Lack of fiducials, production quality. Howimproperly placed fiduever, the (added) cost of cials, or fiducials in the inefficient throughput is wrong shape or size affect equally important. In some SMT component placecases, design constraints ment accuracy. may drive tradeoffs that SMT parts on the impact throughput; howassembly bottom-side that ever, many of the examples cannot be wave soldered below illustrate issues that drive the need for a doucan be avoided simply by ble-sided reflow process. following industry design While the process does standards, such as those not impact overall product published by IPC. Adher- Figure 1. Vias should not be placed in pads as they may quality, it adds the cost of ence to EMS provider contribute to void formation when trapped gases become selective solder pallets and design guidelines is also heated and try to escape. additional solder paste. important, as these guideBottom-side SMT pads lines are more specifically aligned to the manufacturthat will be wave soldered require modified (larger/ ing processes used. exposed) lands. Minimizing the number of process steps and stanIncorrect orientation of the bottom-side SMT dardizing processes to minimize changeover time components can increase the frequency of opens and are key drivers of efficient throughput. Single-sided shorts, resulting in lower quality and added inspecassemblies and assemblies that are either 100% SMT tion and touchup. Likewise for incorrect SMT land or 100% through-hole are most efficiently processed. patterns, which can cause opens, shorts, tombstoning, Assemblies that place mixed technology on both sides etc. of the board typically drive additional automated and Simple steps, such as specifying that component manual processing time, additional tooling costs and fastening hardware exposed to the bottom side (solder a greater potential for handling or thermal shockside) should always be stainless steel, can minimize related defects. Standard designs or panelizations also cost. This is because zinc-plated hardware attracts reduce costs in terms of driving better PCB pricing solder and requires masking. and minimizing setup and changeover time. Specifying preformed component packages, such PCBs that are 100% SMT are typically more effias reels, instead of individual components, simpliciently processed than their mixed-technology counfies processing. Wires are not a preferred wave solder terparts. A through-hole part that appears cheaper option and generally require a special offline assembly A Chris Munroe is director of engineering at EPIC Technologies (epictech.com); chris. munroe@epictech. com. His column appears bimonthly. 70 Circuits Assembly APRIL 2008 circuitsassembly.com http://epictech.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - April 2008

Circuits Assembly - April 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Screen Printing Better Manufacturing Design and Modeling of High-Speed, High-Density 3-D CSPs and Memory Modules The ‘Big Brush Off’ Revisited Impact of Soldering Atmosphere on Solder Joint Formation Beyond Moore’s Law ESD Control For Class 0 ESDS Devices Growing Your Brand This Year’s Model Tech Tips Reflow Soldering Process Doctor Pb-Free Lessons Learned Getting Lean Equipment Advances Apex Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - April 2008

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