21st Century Manufacturing Part 10 potx

Reflection on a concurrent design methodology: A case study in wearable computer design.. 6.8 CASE STUDY ON COMPUTER MANUFACTURING' 6.8.1 Overview This case study presents the product de

6.6.15 Printed Circuit Board Assembly (or Printed Wiring

6.6.18 Surface Mount Technology (SMT)

The process of attaching components directly to the surface of a PCB Increasingly,SMf is replacing the older pin-in-hole method

6.6.19 Tape Automated Bonding

A process in which precisely etched leads (supported on a flexible tape or plastic rier) are interconnected to the chip or a substrate by a heated pressure head Thisprocess simultaneously creates a bond for all leads at once

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Brodersen, R W.I997 The network computer and its future In Proceedings of the IEEE national Solid-State Circuits Conference. San Francisco, CA

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'95, 159-162

Cho, T., G Chien, F Brianti, and P R Gray 1996.A power-optimized CMOS baseband channel

filter and ADC for cordless ••applications VI W Cirruil Confl'rl'lIre nigl',~r 96, June Clark, R.H.1985.Handbook of printed circuit manufacturing. New York: VanNostrand Reinhold

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Curry, I, and M Kenney 1999 Beating the clock: Corporate responses to rapid changes in the

PC industry.California Management Review 42 (1): &-36.

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Economist 1994.A survey of the computer industry, 17 (suppl.): 1-22

Economist. 1999 A bad business, July, 53-54

Finger, S.,I Stivoric, and CAmon, et aI.1996 Reflection on a concurrent design methodology:

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Gupta, R., et al 1989 An object-oriented VLSI CAD framework: A case study in rapid

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Le, M, T., F Burghardt, S Seshan, and J Rabaey 1995 InfoNet: The networking infrastructure

Leicht, H W.1995 Reflew soldering and repair of BOAs In 10th European Microelectronics Conference, 508-520.

Long, A.c,S Narayanaswamy, A Burstein, R Han, K Lutz, B Richards, S Sheng, R W.Brodersen, and 1 Rabaey 1995 A prototype user interface for a mobile multimedia terminal

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Mitt,M •G Murakami, T Kumakura, and N Okabe.1995.Advanced interconnect and low costmicro stud BGAIn The 1995 JEEF.lCPMT Electronics Manufacturing Symposium, 428-521.

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by C F Coombs Jr.,3.1-3.14 New York: McGraw-HilI

Narayanaswamy, S., S Seshan, E Brewer, R Brodersen, F Burghardt, A Burstein, Y-C,Chang,A Fox,I Gilbert, R Han,R Katz,A C Long,O.Messerschmitt,1 Rabaey.1996.Appli~cation and network support for InfoPad IEEE Personal Communications Magazine, March.Norman, D A 1998 The invisible computer. Cambridge, MA; MIT Press

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6.8 CASE STUDY ON COMPUTER MANUFACTURING'

6.8.1 Overview

This case study presents the product development process of the InfoPad shown inFigure 6.22 TheInfoPad is a portable, wireless computer aimed at an approximateselling price of $300 It provides text and graphics, pen input, limited speech input,

Fipn (j.2Z The InfoPad~a wireless "information appliance" (see

<www.ua.bwu.be.-keJey.edu»

>zhe InfoPadWlilla large collaborative project, and particu.lar acknowledgmenuare made to thefollowing colleagues: Professor Robert Brodersen,Professor Jan Rabaey, Dr Frank Wang, Brian Richards,

audio output, and full-motion color video In a restricted classroom or home ronment it can be used as a mobile communication device and a sketch pad(Brodersen, 1997) Twenty prototypes were produced as evaluation kits for mar-keting purposes and user testing in a college classroom.

envi-6.8.2 Goals of the Case Study

Some key points that may be learned in the case study include the following:

• Designing and fabricating a complex system like the InfoPad require ration between many engineering disciplines Specifically, most consumer elec-tronic products are electromechanical systems They consist of mechanicalcomponents such as structures, enclosures, and mechanisms, combined with(harnesses), and switches In spite of the advancements within each field-

collabo-namely, the electrical CAD tools (BCAD) shown in Figure 5.9 and themechanical CAD tools (MCAD) shown in Table 3.2-a gap still exists todayfor good communicationbetween BCAD and MCAD The cartoon of Figure 6.23captures this struggle

• An environment called the domain unified computer aided design ment (DUCADE) has thus been developed to address this need It is a con-current engineering system for ECADIMCAD The links from (a) conceptualdesign to (b) detail design to (c) fabrication are smooth and deterministic, cre-ating a fast link from the initial design to a fabricated product This integrationimproves product quality and time-to-market

environ-Flpre 6.13 DUCADE has the goal of reducing the wall between ECAD and

• A specific focus is on constraint resolution between electrical and mechanical

issues A central virtual-white-board environment is created to share and

com-municate coupled design issues during the design process.

• Various electrical and mechanical subsystems can be designed for modularityand reused in successive design generations This further accelerates the design

The detailed designs for the InfoPad subsystems were conducted by various designmultimedia network group, the user interface group, and the mechanical design group.Each group used its own domain design tools to perform specific design tasks.However, at certain critical junctures predetermined design data within eachteam's domain were shared with other teams in a collaborative way For example,Figure 6.25 illustrates the collaboration between the "pad group" and "mechanicaldesign group." The PCB of the pad was designed using the Racal PCB layout tools,and the InfoPad casing was designed using theMSCIARIES mechanical designpackage

The domain unified computer aided design environment (DUCADE) thenprovided concurrent access to all the design tools of each team Importantly, at crit-issues that were predetermined as being coupled between design teams.Commercial CAD packages that were encapsulated in the DUCADE system

AutoCAD, 5 ProEngineer,6 ACIS, 7 Finesse,8and RacaWisula 9 ARIES and AutoCADI

ProEngineer were primarily used for mechanical component design and mechanicalkernel and package for solid modeling Racal/ Visula was the major electrical designtool for PCB layout design

4MSCIARIESTMis a trademark of MacNeal Schwendler Corporation

5AlltocADTh< is a trademark of Autodesk Inc

6ProEngineerTl.t is a trademark of Parametric Technology Corporation

7ACISn< is a trademark of Spatial Technology Inc

8Finesse™ is a trademark of Harris EDA Inc

~calIV'ISUalTM is a trademark of Racal-Redac

Flcure 6.24 Designarchitecture of the InfoPad system.

Readers who are interested in the electrical system design can refer to the ture for radios in wireless communication development (Sheng et aI., 1994; Cho etaI., 1996), mobile multimedia networking and applications (I.e etal,1995; Amir etel.,

litera-Proxim/Plessy radics

XLink radio controls

antenna

-Plastic (ABS)casing

- Color display module

- Ribbons/connectors-Screws

- 9V battery set (Sx9V)

Mechanical subsystem

-Enclosure-Structure

InfoPad system design

System specification

Backbone network

Protocols

IBase station IRadio

Flpre 6.25Detailed design of mechanical casing and PCB.

interface applications (Long et al., 1995),and design tools and framework (Guerra et aI.,1994;Rabaey et el., 1995;Wang et al., 1996).Table 6.3 summarizes the implementation.6.8.5Coupled Design Constraints

Figure 6.26 shows some of the coupling constraints that occurred between the tionship between the locations/orientations of the electronic components and theenclosure's shape This coupling relationship usually required iterative design taskscompact packaging Because the lnfoPad was designed to be a low-power device,manyconstraints focused on the compact packaging of ICs, devices, and displays.6.8.6 Coupling Constraints Originating in the Mechanical

engi-TABLE 6.3 Major Electrical Subsystems and Components of InfoPad

Majorsubsystenu Functionality Major parts Source/part No

PAL Commercial part/ATV 2500LEPROM Commercial part/AM27COlOArm subsystem Central control Octal buffer Commercial partlHCfS74

SRAM CommercialpartffC551001 BFL-85ARM60 Commercial partlGPS-P60ARMPRARM interface chip Custom designed and fabricatedPlesseydownlink Commercial part/GEC.DE6003Proxirn uplink Commercial partlRDA.l00f200Radio subsystem Wifeless Xilinix Commercial partlXC-4008

communications RXchip Custom designed and fabricated

TXSRAM Commercial partffC551001 BFL·85Antenna f x 2) Commercial partlEXC-VHF 902

SMJEXC-UHF 2400Text/graphics LCD Commercial part/Sharp LM64k83display

Color video LCD Commercial partlSharp LQ4RAOIdisplay

Text/graphics chip set Custom designed and fabricatedMultimedia Multimedia110 (x 5)

subsystem Color video chip set l.'ustomdesignedandfabricated

(x 5)Audio control chip set Custom designed and fabricated(x5)

Gazelle pen board Commercial part

Speaker Commercial partPower subsystem Power supply 9VbatteryX 5 Commercial pan

• Given the standard mechanical/UI features on the terminal casing-forexample, the window for the LCD display on the top case, the access windowfOTthe battery set-again, the shapes, dimensions, and positions of the PCBsand their components were limited to certain values

• Given the fact that the casing needed mechanical supporting structures lation grids, and antenna positioning relative to the user's body, certain restric-tions on placement of ICs were inevitable

venti-To display these fOTthe electrical designers, DUCADE provided a simple ered" view of the(em> • ,)mechanical constraints This was because the electricaldesign teams were familiar with 2.5~D layout tools (rather than 3-D tools) for ICs

"lay-Flture 6.26 Coupling mechanical/electrical design constraints,

Figun- 6.27Layout of the mechanical constraints,

Powerconstraints

Electromagneticconstraints

Proximityconstraints.Routing area

Etec.comp.

loc and orienl

ShieldingPower

~

internal height for the electrical subsystems is 0.78 inch Special features on thebottom case are the circular busses fur mounting the PCB, the through window forthe battery set, and various mechanical dimensions and shapes of electrical switches.Such features needed to be compatible with the work of the electrical design team.6.8.7 Coupling Constraints Originating in the Electrical

Domain IC.>ml

Other constraints originated on the "electrical side" and had to be accommodated

on the "mechanical side." They are given the symbolC~>m'They were as follows:

•The "z-height" of certain large devices on the PCBs were flagged and veyed to the mechanical designers for consideration Often this exchangeresulted in more favorable packaging and overall space saving

con-• Various switches,volume control knobs, and other 110 were of course mounted

on the side of PCBs and their precise dimensions were conveyed to theplastic casing's boundary with user-friendly dimensions These componentswere a power connector, a power switch,serial/parallel ports, audio 110jacks,

a keyboard jack, two volume control knobs, and a connector for an attachablecolor display

• Certain devices, such as the power supply,required electromagnetic shielding.Once the sites for these devices were determined their dimensions were sharedwith other teams

• The locations and sizes of the mounting holes that attached the PCB to thebottom casing were also the product of a dialogue between electrical andmechanical designers

Figure 6.28 shows the PCB layout of the InfoPad terminal with these electricalconstraint features highlighted To present these electrical constraints to mechan-ical designers in the DUCADE environment electrical constraints along with theanalysis.The approach captured only the geometric aspects of the electrical designunder development

6.8.8 Resolving the Coupling and Constraints(C.<>m)

After several iterations between the mechanical and electrical design teams, factory compromises were achieved TIley are given the symbolCe<>m' The evi-dence in firms such as Hewlett-Packard and Sony is that, over many productrevisions, these couplings can be further refined and the product gets more efficientand compact (Cole, 1999) In fact, an interesting exercise for students is to "dissect"several generations of the familiar Sony Walkman and see how the engineers have

satis-invented new ways of resolving the constraints (Ce<>m)' For a first prototype there

Flpre 6.28 PCB layout and some electrical constraints.

is a limit to how much can be achieved in the first few iterations Nevertheless forthe InfoPad the main constraints were resolved, leading-to the following newaspects of the "final" design:

•The PCB design was changed to a customized "U shape." It provided a smallerform factor for the new specification and allowed access to the selected battery set

• Some important electrical components were redesigned using different Iepackaging and different surface mounting techniques 1bis reduced the devicesizes and allowed them to fit into the smaller interior space of the mechanicalcasing

• The boundary features of the mechanical casing were changed for the addedaudio keyboard jacks, two serial ports, and the color video unit

• The interior contour of the mechanical casing was modified according to theshape of the new PCB Circular bosses were added and modified on the bottomcasing for mounting the newly designed PCB

• Curved, spline features were added to the two sides of the terminal casing toimprove the ergonomic and aesthetic design (Figure 6.29)

Two volume controls

iColor di~playconnttlor

Mounung holesPower connector

AUdio~

6.8.9 Fabrication

F'lgme6.29 CAD solid model of the

Tl'IfnPlld

The MOSIS service was used for the various ICs <www.mosls.org>,thePCBswere

"fabbed" at a local bureau <http://sierraprotoexpress.com> and the molds werefabricated on the CyberCut service <cybercut.berke1ey.edu> The design of themolds for plastic injections involved the precise specification of taper angles for sep-arating the mold halves, shrink factors for different materials, core design, runninggatedesign, and parting plane specification Prototype molds and casings are shown

in Figure 6.30

F1pre 6.30Top: the aluminum moldhalves; bottom; the injection moldedplastic casings,

METAL-PRODUCTS MANUFACTURING

7.1 INTRODUCTION

7.1.1 The "Garag.- Shop at www.start·up-eompany.com

The sepia photograph above, taken around 1917, shows William Woodland, one of mygrandfathers He was an aircraft mechanic He is sitting in the cockpit of a VickersVlJDIOYbiplane.My othergrandfather, Browett Wright, was arailroadengineer;specifically he was a "knocker." He walked around the stockyards at Watford Junction,

on the outskirts of London, carrying a small hammer By lightly knocking on thewheelsandaxlesofwagons, and listeningtu theresulting "ring,"hiswell-trainedearcould detecttheabsenceorpresenceofpotentially dangerous fatigue cracks.

As a hobby, these men and their friends often set up small machine shops intheir garages or basements where they would fabricate small personal projects.Sometimes, around the Christmasconsumer season, theyeven did small-batch man- ufacturing runs for localsuppliers/wholesalers

The garage shop allowed autonomy, custom fabrication, and reasonably gooddelivery times A wide variety of projects could be accomplished with a well-equipped tool chest and just two main machines: a small lathe and a medium-sizedthree-axis milling machine A drill press was an inexpensive addition that saved thesesuch as a bench grinder, a small sheet-metal press, and a weldingser-e-then they werereally in business

Many of today's famous figures in Silicon Valley and elsewhere also began theirstart-ups in a humble garage It is most likely that many of these garages containedthese basic tools in their early days

The most important point is this: these simple metal-cutting machines allow arange of parts to be made The same set of cutting tools can be used to make a widevariety of parts of rather complex geometry Machining is the most important metal-forming operation for this reason, despite the more glamorous appeal of FDM andother SFF processes In the last few decades, machining has endured a bad reputa-tion for being wasteful and for being a little slow, but it always bounces back infashion for these reasons of flexibility and good accuracy

7.'.2 The Origin of the Basic Machine Shop

From these humble origins emerges the job shop or machine shop-really just alarger version of the garage shop but with bigger machines, more specializedmachines, and perhaps several machinists However, in the end it all boils down toflexibility and specialized service with reasonable delivery

Machining is a powerful way of producing the outer structures of weird types that are just beginning the product development cycle or perhaps just enteringthe market: products located in the lower left comer of Figure 2.3 Also the job shopdesigns of mad inventors into reality

proto-All over the world, unusual start-up companies are being formed: computerstart-ups, biotech firms, in fact any new-product companies At some point thesepotential investors Most likely, the company will need to go to a machine shop to getthe prototype made For example, the first few Infopadcasings-c-see Chapter 6-

were readily machined with good tolerances of +1-0.002 inch (-50 microns) The

fabrication time was approximately three days from the moment the design wasfixed until a finished casing was fabricated by milling