Surface Mount Surface Mount TechnologyTechnology

Research and Presentation:Research and Presentation:

Amy HoppAmy Hopp

Sept. 4, 2003Sept. 4, 2003

CIM ~ Period 2CIM ~ Period 2

Automation/Programmable Processes inAutomation/Programmable Processes in

Table of ContentsTable of Contents

What is SMT?What is SMT?Screen PrintingScreen PrintingAffects of AutomationAffects of AutomationThrough Hole TechnologyThrough Hole TechnologySolderingSolderingComponentsComponentsSurface Mount ComponentsSurface Mount ComponentsOther Main IssuesOther Main IssuesLimitationsLimitationsEquipmentEquipmentThe FutureThe FutureCitationsCitations

What is SMT?What is SMT?

SMT is a process for populating circuit boards.

This is done by mounting components directly to the surface of the substrate.

Then a layer of solder paste is screen printed onto the pads and the components are attached by pushing their leads into the paste.

When all of the components have been attached, the solder paste is melted using either reflow soldering or vapor-phase soldering.

Screen PrintingScreen Printing

Polyester or stainless steel Polyester or stainless steel woven wire mesh is woven wire mesh is stretched over an stretched over an aluminum frame with a aluminum frame with a glued-on photosensitive glued-on photosensitive emulsion.emulsion.

Stencils have etched Stencils have etched openings to match the land openings to match the land patterns on the substrate patterns on the substrate (PCB). (PCB).

Affects of AutomationAffects of Automation

Screens are used mainly because of its lower Screens are used mainly because of its lower cost, faster delivery and reusability.cost, faster delivery and reusability.

Usually the stencil design is a programmed Usually the stencil design is a programmed process for better efficiency and time.process for better efficiency and time.

Hand printing is almost impossible with screens. Hand printing is almost impossible with screens. it is very difficult to align the screen on the work area it is very difficult to align the screen on the work area

which is due to the poor visibility due to the presence which is due to the poor visibility due to the presence of the screen mesh in the openings. of the screen mesh in the openings.

Through Hole Technology Through Hole Technology

Electronic components are inserted through Electronic components are inserted through holes in the PCB prior to soldering. holes in the PCB prior to soldering.

The insertion may be done manually or by The insertion may be done manually or by machine. machine.

SolderingSoldering

Wave soldering was a “drag-and-dip” process.Wave soldering was a “drag-and-dip” process.

Reflow soldering is usually done by reheating Reflow soldering is usually done by reheating the solder (1 method: infra-red soldering).the solder (1 method: infra-red soldering).

BenefitsBenefits CleanerCleaner Much better qualityMuch better quality Less waste of materialsLess waste of materials

ComponentsComponents

In THT, In THT, size of the component is limited size of the component is limited by the packaging requirement.by the packaging requirement.

Leads must rugged enough to survive the Leads must rugged enough to survive the insertion process without damage.insertion process without damage.

Lead diameters, drilling and imaging Lead diameters, drilling and imaging tolerances puts a limit on how closely tolerances puts a limit on how closely leads are spaced, which in turn limits the leads are spaced, which in turn limits the size of component packages.size of component packages.

Surface Mount ComponentsSurface Mount Components

The solder joint is all the more important as it The solder joint is all the more important as it imparts both electrical and mechanical imparts both electrical and mechanical connections unlike the through hole connections unlike the through hole components.components.

Also see much higher temperatures during Also see much higher temperatures during soldering. soldering.

Because of their smaller size, it is sometimes Because of their smaller size, it is sometimes not possible to provide part markings not possible to provide part markings on them.on them.

Other Main IssuesOther Main IssuesFrequency response Frequency response Surface mount packages has reduced component Surface mount packages has reduced component

related parasitic reactants because of shorter related parasitic reactants because of shorter component leads. component leads.

Parasitic reactants affect the performance of high Parasitic reactants affect the performance of high frequency circuits.frequency circuits.

Package Propagation DelayPackage Propagation Delay(time required for an electrical signal to propagate from the (time required for an electrical signal to propagate from the input to the output of the IC)input to the output of the IC)

In surface mount packages there are fewer parasitic In surface mount packages there are fewer parasitic reactants (primary cause of propagation delay) and reactants (primary cause of propagation delay) and they are smaller and more uniform.they are smaller and more uniform.

Other Main IssuesOther Main Issues

Electromagnetic interference Electromagnetic interference

Through hole component leads serve as tiny Through hole component leads serve as tiny antennas that radiate and receive undesirable antennas that radiate and receive undesirable signals. signals.

SMC leads do not penetrate the board and SMC leads do not penetrate the board and thus reduce this problem. Hence sensitive thus reduce this problem. Hence sensitive circuits can often be combined onto a single circuits can often be combined onto a single board, simplifying shield design.board, simplifying shield design.

Other Main IssuesOther Main Issues

Cost Cost Though assembly costs for an automated Though assembly costs for an automated

SMT line are not appreciably different SMT line are not appreciably different from that for an automatic through hole from that for an automatic through hole line, significant cost reduction occurs at line, significant cost reduction occurs at the overall system level. the overall system level.

Quality Quality The higher level of automation in SMT The higher level of automation in SMT

results in improved quality and more results in improved quality and more consistent output.consistent output.

LimitationsLimitations

Mechanical Strength Mechanical Strength The solder joints of surface mount The solder joints of surface mount

components become both the electrical and components become both the electrical and mechanical contacts to the board. mechanical contacts to the board.

The amount of solder available is generally The amount of solder available is generally much less than at a through hole joint; so its much less than at a through hole joint; so its mechanical strength is less. mechanical strength is less.

Since leads do not penetrate the board, they Since leads do not penetrate the board, they cannot reinforce the joint. cannot reinforce the joint.

LimitationsLimitations

CTE Mismatch CTE Mismatch The coefficient of thermal expansion for The coefficient of thermal expansion for

ceramic component body is less than that of ceramic component body is less than that of the organic printed wiring board.the organic printed wiring board.

The difference in expansion over temperature The difference in expansion over temperature must be entirely absorbed within the solder must be entirely absorbed within the solder joints. joints.

For leadless components, over the full For leadless components, over the full product temperature range, large stresses product temperature range, large stresses can be built in the joints, causing eventual can be built in the joints, causing eventual failure. failure.

EquipmentEquipmentVitronics XPM Series Reflow OvensVitronics XPM Series Reflow Ovens

Maximum Operating Temp. 350º C Maximum Operating Temp. 350º C Windows 98® Operating System Windows 98® Operating System Data Logging Data Logging Cell Fan Speed ControlCell Fan Speed Control Nitrogen Reduction Apertures Nitrogen Reduction Apertures Individual Zone and Controlled Exhaust Individual Zone and Controlled Exhaust Closed Loop Conveyor Speed Closed Loop Conveyor Speed Over-temperature Switches Over-temperature Switches Swing Arm for Computer Swing Arm for Computer Pentium Computer w/ VGA Monitor Pentium Computer w/ VGA Monitor Auto Start/Stop Auto Start/Stop 2000 (+) Recipe Storage 2000 (+) Recipe Storage Light Tower Four Color Light Tower Four Color Electromechanical Power Hood Lifts Electromechanical Power Hood Lifts Closed Loop Temperature Control Closed Loop Temperature Control

EquipmentEquipmentDEK 265 Horizon Screen PrinterDEK 265 Horizon Screen Printer

Windows NT operating system with touch Windows NT operating system with touch screen monitor screen monitor

Programmable telecentric single-camera Programmable telecentric single-camera vision alignment system vision alignment system

Motorized stencil alignment Motorized stencil alignment Automatic rail width adjust with Automatic rail width adjust with

programmable board stop programmable board stop Magnetic board support tooling pins: 19mm Magnetic board support tooling pins: 19mm

& 4mm diameter & 4mm diameter Software controlled closed loop squeegee Software controlled closed loop squeegee

pressure pressure On board event loggingOn board event logging SPC data collection capability SPC data collection capability SMEMA machine interfaceSMEMA machine interface Operator/maintenance documentation on Operator/maintenance documentation on

CD-Rom with on-board help CD-Rom with on-board help 1 year machine warranty (parts and labor) 1 year machine warranty (parts and labor)

The FutureThe Future

Most aims towards the future in SMT is Most aims towards the future in SMT is geared towards:geared towards:

To evolve solder, to create a newer, better To evolve solder, to create a newer, better alloy composition to improve performance. alloy composition to improve performance.

the capability to create PCBs smaller and the capability to create PCBs smaller and lighter (eventually to the nano scale).lighter (eventually to the nano scale).

CitationsCitations

http://www.tutorialsweb.com/smt/smt.htmhttp://www.tutorialsweb.com/smt/smt.htm

http://http://www.engr.iupui.edu/~solaiyap/smt/radhika/smtintwww.engr.iupui.edu/~solaiyap/smt/radhika/smtintro.htmlro.html

http://smt.pennnet.com/Articles/Article_Display.cfhttp://smt.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICm?Section=Articles&Subsection=Display&ARTICLE_ID=183179LE_ID=183179

http://http://www.uic.comwww.uic.com//

http://smtinfo.net/http://smtinfo.net/