MOUNTING OF SURFACE MOUNT COMPONENTS - National Semiconductor

Mounting of Surface Mount Components

Introduction

Over the past few year, electronic products, and especially

those which fall within the category of Consumer Electronics,

have been significantly reduced in physical size and weight.

Products such as cellular telephones, lap-top computers,

pagers, camcorders, etc., have been reduced by as much as

3/4 of their original introductory size and weight. The most

significant contributing factor to this reduction has been the

inclusion of fine pitch, Surface Mount (SM) components. The

larger, thicker and heavier leaded Through-Hole (TH) pack-

ages consumed far too much power, too much space and

contributed significantly to the total weight of the final prod-

uct.

Product manufacturers were listening when the customer

said ″Make it smaller, lighter and less expensive″.

A second phase to this continued reduction in package size

and weight is currently being experienced. A new family of

sub-miniature surface mounted packages known under the

industry’s generic name of Chip Scale Packages (CSP) have

recently been introduced. CSP size components are cur-

rently the basis of a new series of consumer products. CSP

components are currently being supplied in two (2) package

configuration, both of which will be a maximum of 1.2 X of

the die size. One incorporates planar or bumped pad inter-

connections on the peripheral of the package underside. The

other package is in the form of a reduced scale ball grid array

either in a partially or fully populated I/O condition.

The increasing availability of the CSP significantly impacts

the ability of product designers to design hand-held products

of a size and weight not previously possible. The new CSP

allows a higher density of components to be placed into an

increasingly smaller portion of an existing printed circuit

board, or that the printed circuit board may be reduced with

an accompanying reduction in product size, weight and cost.

Chip Scale Packages incorporating high I/O dies, along with

discrete passive components are currently used in the de-

sign of the palm-sized camcorders. As a residual benefit,

with components in closer proximity the signal propagation

time is reduced thus producing a series of faster circuits.

Accompanying the benefits of smaller size, reduced weight,

higher density and increased performance, the individual

Methods, Technologies and Techniques used to assemble

printed circuit board assemblies have been impacted.

Component Size Comparison

The Surface Mount (SM) package was developed to provide

the customer with increased component density and perfor-

mance over the larger Dual-Inline-Package (DIP). The SM

package also provides the same DIP high reliability.

The Chip Scale Package (CSP) was developed to provide

the customer with an additional increase in component per-

formance and density over the SM package. The CSP also

provides the same high reliability as the DIP and SM pack-

age.

CSP and SM packages at National were internally qualified

for production under the condition that they be of compa-

rable reliability performance to a standard dual in line pack-

age under all accelerated environmental tests.

Molded Dip, SOIC, CSP - 24 Pin

MS101138-1

Molded Dip, SOIC, micro-SMD-8Pin

MS101138-2

TSSOP & CSP - 24 pin

MS101138-3

August 2000

Mounting of Surface Mount Components

Accelerated Bias Moisture Test

DIP, SO’s, & CSP

Figure 1

is a summary of accelerated environmental bias

moisture test performance on 15V CMOS and 30V BIPO-

LAR product assembled in SM and DIP (control) packages.

PCB Assembly Flows

Through-Hole (TH) Technology

Insert Leaded Packages on

side #1

↓

Wave solder the leads on side

↓

Aqueous Clean PCP

↓

Inspect & Rework PCB

↓

Test PCB

Mixed Technologies - TH Side 1 & Passive SM Side 2

Insert Leaded Packages on

side #1

↓

Reverse board to side #2

↓

Apply adhesive

↓

Attach passive SMT

components

↓

Cure adhesive

↓

Reverse board to side #1

↓

Wave solder leaded & SMT

components

↓

Aqueous Clean PCB

↓

Inspect & rework PCB

↓

Test PCB

Thermal Stress - Side 2 Surface Mount

During the wave solder operation, the side 1 TH components

are subjected to significantly less thermal stress than the

side 2 bottom side SM mounted components. Only the TH

leads come in contact with the molten solder, compared to

the entire SM package being immersed in molten solder.

Figure 2

illustrates a comparison of package temperature

versus wave soldering dwell time for TH components

mounted on side 1, with SM packages mounted on side 2.

Under ideal conditions, the rate of thermal expansion of

package lead frame and plastic encapsulant would be the

same. When both materials expand at the same rate during

thermal excursions, bonds between metal and plastic main-

tain a mechanical integrity. Because it is difficult and costly to

tailor an epoxy encapsulant material to meet the Coefficient

of Thermal Expansion (CTE) of the metal lead frame, a mis-

MS101138-4

MS101138-5

Mounting of Surface Mount Components

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PCB Assembly Flows (Continued)

match at some point in the thermal excursion will occur, pos-

sibly producing an opening by which contaminants may en-

ter.

Normally, thermal expansion rates for epoxy encapsulant

and metal lead frame materials are linear and remain fairly

close at temperatures approaching 160 Deg C displayed in

Figure 3

. At lower temperatures the difference in expansion

rate of the two materials is not great enough to cause inter-

face separation.

However, when the package reaches the glass-transition

temperature (Tg) of epoxy (typically 160 - 165 Deg C), the

thermal expansion rate of the encapsulant increases sharply,

and the material undergoes a transition into a plastic state.

The epoxy begins to expand at a rate three times or more

greater than the metal lead frame, causing a separation at

the interface.

Mixed Technologies - TH & SM Side1&SMonSide 2

Screen print solder paste on

side #1

↓

Attach SMT components

↓

Reflow solder paste

↓

Insert leaded packages on side

↓

Reverse PCB to side #2

↓

Apply adhesive

↓

Attach passive SMT

components

↓

Cure adhesive

↓

Reverse PCB to side #1

↓

Wave solder leaded and SMT

components

↓

Aqueous clean PCB

↓

Inspect & rework PCB

↓

Test PCB

TABLE 1. Surface mount packages recommended for Wave Solder Immersion.

Package Type Lead Count

34568141620

SC-70 X

SOT-23 X X X

SOT-223 X X

SOIC - NARROW X X X

SOIC - WIDE XXX

•

Please verify through device specific application notes.

•All other packages and lead types are not recommended.

MS101138-6

FIGURE 3. Immersion in 360˚C Solder

Mounting of Surface Mount Components

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Surface Mount Technology - Single Sided PCB

Screen print solder paste on

side #1

↓

Attach SMT components

↓

Reflow solder paste

↓

Aqueous clean PCB

↓

Inspect & rework PCB

↓

Test PCB

Surface Mount Technologies - Double Sided PCB

Screen print solder paste on

side #1

↓

Apply adhesive on side #1

↓

Attach SMT components on

side #1

↓

Cure adhesive on side #1

↓

Reverse PCB to side #2

↓

Screen print solder paste on

side #2

↓

Attach SMT components on

side #2

↓

Reflow solder paste (both

sides)

↓

Aqueous clean PCB

↓

Inspect & rework PCB

↓

Test PCB

Changing Assembly Techniques &

Technologies

Combined Wave Solder and Solder Reflow

More mature products incorporating printed circuit boards

designed with Through-Hole (TH) semiconductors in a Dual-

In-Line (DIP) package and with TH axial leaded components,

require bottom side board wave soldering for component to

pad interconnection.

Specified packages (see

Table 1

) may be mounted on the

underside (side 2) of the board using this same solder at-

tachment technique. This assembly technique allows better

utilization of the PCB underside, thus freeing up top side real

estate for high lead count active components.

Securement of the bottom side (side 2) SM components is

achieved through the use of a cured adhesive applied prior

to the wave soldering application. Component Engineers re-

sponsible for components selected for bottom side SM

mounted components had to take into consideration that

these components were subjected to the same time and

temperature wave soldering profile experienced by only the

leads of leaded TH components and selected these SM

components accordingly.

Fine Pitch SM Solder Reflow Side 1 and Side 2

Fine pitch SM components are routinely mounted both on

side 1 and side 2 with no use of adhesive. The one exception

to this rule is when the component possesses a larger body

mass in relation to the strength of the total volume of solder

paste incorporated in the component interconnection.

Purpose of Solder Paste

Solder paste provides both the metals and the cleaning

agent used to produce the pad interconnection of package

lead to printed circuit board pad.

The purpose of the fluxing system within the paste is to pro-

vide clean, positive wettable surfaces to which the metal sol-

der bonds, thus allowing the electrical interconnection to be

produced. The fluxing system operates as the cleaning

agent required to remove potential oxides from both the

package lead/pad and the board pad. The fluxing system

also provides protection of the newly cleaned metal surfaces

from re-oxidation during the soldering operation while the

lead and pad is at their highest temperature.

Types Of Solder Paste Fluxes

The fluxing system is composed of a flux and binder system

used in solder paste, and is generally divided into the cat-

egories of Rosin-based, Water Soluble and No-Clean.

Rosin-based fluxes are designated

R Rosin, non-activated

RMA Rosin, mildly activated

RA Rosin, fully activated

Water Soluble fluxes are designated

WS Water-soluble

No-Clean fluxes are designated

NC No-Cleaning required

Mounting of Surface Mount Components

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Comparison of Particle Size / Shape of Various Solder Pastes

200 x Alpha (62/36/2)

MS101138-7

200 x Kester (63/37)

MS101138-8

Solder Paste Screened on Pads

MS101138-9

200 x ESL (63/37)

MS101138-10

Mounting of Surface Mount Components

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Solder Paste For Standard SM

Packages

Consistency and uniformity is the key for any successful sol-

der paste material. The basic requirement is a stable and ho-

mogeneous blend of atomized metal alloy combined with a

flux, binder, and solvent system which eliminates the possi-

bility of later separation of the respective materials. These

qualities are required to ensure a predicable screening and

stenciling printing operation producing the required pattern

definition.

The selected solder paste should be formulated so as to

eliminate potential breakdown of the metal, flux, binder, and

solvents combination, or the premature drying of the solder

paste on the printer. Both of the previously cited qualities

should be in addition to providing a minimum of 48 hours

tack time. The selected solder paste should be formulated so

as to prevent slump and provide over 8 hours of screen

working life, with no presence of skipping, scooping and

clumping during printing.

For screen printing of standard pitch SM packages, the

metal alloy powders should be spherical is shape with a

minimal oxide content and screened to 45-75 micron particle

size. The paste should contain a minimum of 88% to 90%

metal content, and have a viscosity of 500,000 to 600,000

centipoise.

For stencil printing of standard pitch SM packages, the metal

alloy powders shape, size and content should remain the

same but the viscosity should be increased to 700,000 or

800,000 centipoise.

In most cases, R, RMA and RA rosin-based fluxes will nor-

mally be removed using an aqueous de-ionized heated wa-

ter cleaning system, augmented with a saponifier or another

surfactant additive. The resultant cleaning water should pro-

duce biodegradable saponified products.

Solder Paste For Fine Pitch SM Packages

Those solder pastes specifically designed for high lead

count, fine pitch packages with lead spacing of 0.015″re-

quire a unique formulation for stenciling, screening and auto-

matic point to point dispensing.

Solder pastes specifically formulated for fine pitch SM com-

ponents should incorporate all of the previously cited quali-

ties, plus a flux system developed specifically to ensure that

no slumping while still in the wet stage. Fine pitch solder

paste should not produce bridging, shorting or solder balling

when the paste experiences the reflow.

As is in the case of Standard Pitch SM components, R, RMA

and RA rosin-based fluxes will normally be removed using

hot de-ionized water, augmented with a surfactant or other

additive.

Water Soluble Solder Paste For Fine Pitch Surface

Mount Packages

Water soluble solder pastes should display all of the stencil

or screen printing qualities displayed by conventional rosin-

based pastes, but should also eliminate the need for chlorof-

luorocarbons, chlorocarbons or other solvent blends some-

times used for rosin-based flux residue removal.

Although they are soluble in water, water soluble pastes

should not be hygroscopic and should be formulated to pro-

vide up to 8 hours of screen working life and 48 hours of tack

time similar to rosin-based pastes.

Water soluble, fine solder pastes should be halogen-free.

The water-soluble residues should be capable of being

cleaned to the extent that they are equivalent in perfor-

mance, water extract resistivity and SIR values to standard

RMA fluxes. Flux residues should be able to be removed

with a cool presoak followed by a 140 Deg. F spray.

Stencil Thickness

SM Lead Pitch

inch mm

0.050 1.27

0.025 0.63

0.015 to 0.020 0.4 to 0.5

Recommended Stencil Thickness

inch mm

0.008 to 0.010 0.20 to 0.25

0.006 to 0.008 0.15 to 0.20

0.004 to 0.006 0.10 to 0.15

Stencil Materials

Stainless Steel is the most prevalent material used to pro-

duce stencils, but brass, Alloy 42, molybdenum and nickel

plated brass are also used.

Squeegee

Metal is the most common material used to produce squee-

gees. The justification for the use of metal is that it produces

a uniform surface across the top surface of the stencil with-

out scooping down into the just deposited solder paste.

Rubber of an 80 to 90 Durometer reading is also used.

Print Speed

Printing speeds of 0.5 to 2.5 inches (15 to 65 mm) per sec-

ond are normally used, depending on type and capabilities of

the solder printing machine.

Print Pressure

During the solder paste printing operation, sufficient down-

ward pressure should be exerted by the squeegee against

the stencil surface to wipe the stencil clean. Although the

printing pressure will vary with the type of printer, typically a

pressure of 1.25 to 2.5 lbs per inch of squeegee length is ac-

ceptable.

Off And On Contact

Both contact and non-contact techniques are used success-

fully. If non-contact is used, a snap-off of up to 0.005 is rec-

ommended.

Temperature And Humidity

The screen printing of solder paste should be performed be-

tween a temperature of 68˚ to 78˚ F (20˚ to 26˚ C). The rela-

tive humidity of the application area should be kept between

35% to 65%. Solder paste not applied to printed circuit

boards should not be returned to the container from which it

was taken.

Stencil And Screen Cleaning

Stencils and screens should be cleaned of unused solder

paste using water heated to a minimum of 140 Deg F in con-

junction with a pressure spray. Although the initial water

need not be deionized, it is recommended that a final rinse

be performed using deionized water, followed by an isopro-

Mounting of Surface Mount Components

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Solder Paste For Standard SM

Packages (Continued)

panol rinse. This same procedure should also be followed for

any hand tools and the squeegee used to apply the solder

paste.

At no time should the stencil, screen or tools which have

come in contact with unreflowed solder paste be cleaned in

equipment used to clean printed circuit boards of reflowed

solder paste residues.

Component Placement System

System Configuration and Specifications

Product designs continue to demand continued down-sizing

of the component package, accompanied by higher board

densities. The component placement system must accom-

modate these trends by employing a highly accurate, com-

puter controlled, camera directed placement nozzle that is

responsible for constraining the component during pick-up

through push-off after placement.

Following are some of the more significant elements devised

by the system vendors there by enabling the placement sys-

tem to produce high speed, high density accurate compo-

nent placements:

•Computer controller

•Windows or vendor software

•Vision correction system

•Component body height adjustment

•Z-Axis placement programmability

•Single Head - Multiple programmable nozzles

•Dual Head - Multiple programmable nozzles

•Dual Head - 6 nozzles per head

•Dual Work Table - 12 heads with 3 nozzles per head

Placement System

Placing Heads

Componet Types

The types of components which may be placed are generally

only restricted by the types of feeders that may be may be in-

terfaced to the placement system. Following are some repre-

sentative component types which are being automatically

picked and placed by placement systems of the latest de-

sign:

1. Chips

2. CSP

3. QFP

4. TAB

5. BGA

6. MELF

7. SOIC

8. PLCC

9. TSOP

10. TSSOP

11. Flip Chip

Component In-Feeding Systems

With the introduction of the embossed (pocketed) tape, more

package types are being supplied in this format due to in-

creased end-user demand. The embossed tape provides the

end-user the ability to maintain an improved quantity and

quality control through the use of the see-through tape and

the rigid cardboard sidewalls of the shipping reel. Paper tape

is normally only used to provide the smallest types and val-

ues of discrete, passive components.

•8 mm paper tape

•8 mm embossed tape

•12 mm embossed tape

•16 mm embossed tape

•24 mm embossed tape

•32 mm embossed tape

•48 mm embossed tape

•Stick in-feeding

•Tray in-feeding

•Ultra-small chips up to 4.5 mm

•Medium-sized odd form components up to 28.0 mm

•Large odd form components up to 38.0 mm

MS101138-11

MS101138-12

Mounting of Surface Mount Components

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Component Placement System

(Continued)

•Extremely large odd form components up to 74.0 mm

Printed Circuit Board Dimensions

Current placement systems are designed to provide the end

user with the maximum printed circuit board size in both the

X and Y axis. Most of the current designs will allow a change

in the conveyor rail width to be automatically executed by

servo motors by program commands conveyed through the

computer controller.

•Min. 80 x 50 mm (3 x 2″)

•Max. 508 x 457 mm (20 x 18″)

Vision Assisted Component Placement

The vision system should include as a basis element of the

design, an ability to process (establish X/Y/Theta) the com-

ponent location on the pick-up head and match the compo-

nent to the respective component pads. To achieve the re-

quired placement accuracy, the following is necessary:

•Gray scale vision processing.

•Component placement algorithms.

•Fiducial (local and global) camera.

•Component pad/lead recognition camera.

Placement Speed

Although placement speed is typically quoted at approxi-

mately 0.1 second per placement, Flip Chip components can

take as long as 3.5 to 5.0 seconds per shot (placement).

Component placement speed is dependent upon such fac-

tors as distance which the placement head must travel be-

tween component pick-up and placement location, and the

requirement to view the component leads/pads for

component-to-pad alignment prior to placement

•Min. 0. 09 sec. per component

•Max. 0. 12 sec. Per component

Placement Accuracy

The accuracy to which the component is aligned and placed

on the solder pads is contingent upon several factors, such

as use of local fiducial marks; datum point location; size of

printed circuit board; flatness of printed circuit board; etc.

•Min. ±0.025 mm (using local fiducial marks)

•Max. ±0.1 mm

Component Pick-Up Head Types

The most favored technique of component pick-up is via the

vacuum nozzle due to the system’s ability to create a nega-

tive pressure instantly upon making contact with the top sur-

face of the component with the soft rubber nozzle contact,

and then reverse the process by producing a positive pres-

sure to ″blow″the component off the nozzle upon placement.

Mechanical chucks, although favored for some time, are ex-

pensive to maintain and do present some mechanical diffi-

culties in their operation.

•Vacuums Nozzles

•Mechanical Chucks

Component Placement Pressure

Programmable placement pressure can be specified for

each component, enabling placement of very delicate parts.

Convection Reflow Furnace

Techniques of Solder

Interconnection

Solder interconnection of Through-Hole and Surface Mount

components to printed circuit boards may be classified as

using the following two (2) categories:

Local Component Heating

Local heating can be divided into the following methods:

•Hot plates with solder paste or flux.

•Hand solder iron with solder and flux.

•Hot bar (pulsed heater) using solder paste or flux.

•Hot air gun using solder paste or flux.

•Directed laser energy using solder paste or flux.

Global Board Heating

Global heating is divided into the following methods:

•Solder submersion.

•Directed IR reflow using solder paste.

•Hot air furnace reflow using solder paste.

•Vapor phase reflow using solder paste.

•Convection furnace reflow using solder paste.

As is displayed by the various soldering techniques above,

solder paste is the dominant method of attaching electrical

components to printed circuit boards.

Thermal Processing (Reflow) System

In a similar fashion as in the case of the component place-

ment system, the specifications for thermal processing sys-

tem will be developed based upon the anticipated reflow sol-

dering requirements throughout the life of the oven. This

statement is true for not only the type and configuration of

the components currently being soldered, but also any adhe-

sive which would require curing.

Taken into consideration will be whether the components of

a surface mount design are leaded or leadless the physical

size and robustness of the component to withstand reflow

temperatures. Because most components being designed

into today’s products are of a reduced mechanical configura-

tion and located in close proximity to each other on smaller

printed boards, the selection of the technology used within

the reflow system becomes even more critical.

Following are only some of the more critical decisions which

will be made concerning the more pertinent parameters of

the thermal processing system selection:

MS101138-13

Mounting of Surface Mount Components

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Techniques of Solder

Interconnection (Continued)

Product Throughput

Is the reflow oven ″sized″for the current and anticipated pro-

duction requirements. This will require not only a determina-

tion as to the number of boards the oven will process, but

also how the boards will be conveyed through the oven.

Thermal Uniformity and Accuracy

The reflow system should provide a uniform heat transfer

from the heating source, distributing it evenly over the prod-

uct surfaces under process in an accurate manner so that all

of the board surfaces receives an equal temperature rise.

The same criteria is required for cooling.

Nitrogen Consumption

The infusion of nitrogen immediately prior to and during the

solder paste reflow operation is mandated by the process

and materials being assembled. Specifically, bare-copper

circuit boards, and no-clean solder pastes benefit from the

inclusion of the nitrogen atmosphere.

Certain No-Clean solder paste with a metal alloy content of

greater than 98% will often require the use of Nitrogen be-

cause the remaining 2% (by weight) or less will contain an in-

sufficient amount of flux material available to prevent oxida-

tion of the soldered elements if reflowed in an air

environment.

Should the process and materials being assembled require

nitrogen, features within the oven design should be present

which minimizes nitrogen consumption during preheat, soak,

reflow, and cool.

Infrared Radiation (I.R) Reflow Soldering

Radiant I.R. is a direct, focused heat source and was the ini-

tial heating technique used by the electronics industry to re-

flow solder paste. This technique, when not properly ad-

justed in relation to the board distance, could allow

excessive amounts of directly focused heat to be delivered

to the surface of the board producing a scorching effect to

the board and the components under reflow.

This technique is no longer commercially viable.

Natural Convection Reflow Soldering

Natural convection of the heat required to reflow the solder is

normally obtained through the use of a non-focused I.R.

source, without the benefit of a forced air circulation. This de-

sign is often referred to as ″non-focused″, with the efficiency

capability rated lower than the forced convection design due

to the ability of larger components to shield smaller compo-

nents from the available heat source.

Forced Convection Reflow Soldering

Heat require to reflow the solder paste is achieved by direct-

ing I.R. energy towards a metal or ceramic surface and utiliz-

ing the convected (radiated) energy from the opposite sur-

face to produce the reflow.

The heat is circulated within the reflow zones by strategically

located fans. By use of a non-directed, convected heat circu-

lated via strategically located fans, hot spots on the boards

can potentially be eliminated.

Fixed Convection Reflow Soldering

Fixed Convection reflow soldering utilizes much of the same

technology as Forced Convection with the exception of the

use of strategically located fans.

Heating Zones

The number of heating zones required will be determined by

current and anticipated product throughput requirements,

product size and physical mass, product orientation within

the oven while on the conveyor, and requirements dictated

by the particular solder paste reflow profile. Reflow ovens

are typically offered in ranges from four to 12 heating zones.

Active Cooling Zones

Active cooling zones should be positioned immediately adja-

cent to the heating zones and should be ideally provided to

meet the reflow requirements specified by the solder paste

manufacturer.

The amount of cooling required may also be dictated by

product handling or subsequent assembly operations follow-

ing reflow.

Depending on the system requirements and vendor capabil-

ity, the number of cooling zones which may be incorporated

into the system may range from one to 12.

Pcb Assembly Cleaning

If the printed circuit boards were assembled using a rosin

based or other flux system which requires removal from the

board surface after reflow, the subsequent cleaning opera-

tion should be performed as shortly after reflow as possible.

The timely initiation of the cleaning operation is dictated by

the ability of the flux to collect and harden with additional

residues under and around traces and the bodies of compo-

nents. The lack of attention to the timely removal of this resi-

due present additional and unneeded removal difficulties,

with the possibility that some contaminates may be trapped

in flux and remain on the surface of the board to potentially

compromise qualities for the finished product.

Pcb Cleaning Test

Upon completion of the solder reflow operation the surface

mount assembly should be tested for ionic and other con-

taminates using recognized specification, such as IPC-6012.

If the printed circuit board is to have a permanent solder

mask coating applied, the bare uncoated board should be

also tested for ionic and other contaminates prior to perma-

nent coating.

SM Reflow Soldering Reliability

More recently designed products utilizing the low profile,

high lead count, fine pitch SM components, when combined

with Chip Scale Packages present additional challenges to

the techniques and technologies of high reliability compo-

nent interconnection.

The potential obstacles of high reliability fine pitch SM and

reduced size CSP component interconnections are contin-

gent upon a number of parameters, with the most prevalent

being:

•Technology and package construction.

•Quality and repeatability of the reflow process.

•Metallurgy and uniformity of both the solder paste and in-

terconnection pad plating.

•Individual board design, both internally and externally.

Mounting of Surface Mount Components

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SM Reflow Soldering Reliability

(Continued)

•Conditions in which the product will be used.

•What is the intended product life.

Reliability level demands are higher for products using the

new low profile, fine-pitch, high lead count miniature IC pack-

ages, such as CSP and reduced size BGA over assemblies

built around older, more conventional packages with their

longer and more compliant leads.

Thermal Characteristics of SM

Components

Both Chip Scale Packages and SM components are typically

fabricated using a combination of either a metal lead frame;

laminated substrate; ceramic substrate, or flexible film sub-

strate as a base on which a die is adhesively attached. Gold

wires are bonded from die to lead frame/substrate, and the

unit is encapsulated, with a thermoset epoxy.

Because each material has different rate of thermal expan-

sion, the thermal characteristics of the materials generally

correspond to a Thermal Mechanical Analysis (TMA) graph.

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whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

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Tel: 1-800-272-9959

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Mounting of Surface Mount Components

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.