9

Lead-Free Reflow Profile Recommendation (IPC/JEDEC J-STD-020C)

Reflow Parameter

Lead-Free Assembly

Averageramp-uprate(LiquidusTemperature(T

3°C/secondmax

Preheat

TemperatureMin(T

150°C

TemperatureMax(T

200°C

Time(mintomax)(t

60-180seconds

Ts(max)toTLRamp-upRate

3°C/secondmax

Timemaintainedabove:

Temperature(T

217°C

Time(t

60-150seconds

PeakTemperature(T

260+0/-5°C

Timewithin5°CofactualPeaktemperature(t

20-40seconds

Ramp-downRate

6°C/secondmax

Time25°CtoPeakTemperature

8minutesmax

Note1:Alltemperaturesrefertotopsideofthepackage,measuredonthepackagebodysurface

25

Time

Tp

tp

t 25

Ramp-up

ts

Ramp-down

Preheat

Critical Zone

Figure 26. Surface Mount Assembly Profile.

SMT Assembly

Reliable assembly of surface mount components is a

complex process that involves many material, process,

and equipment factors, including: method of heating

(e.g.,IRorvaporphasereflow,wavesoldering,etc.)cir-

cuit board material, conductor thickness and pattern,

type of solder alloy, and the thermal conductivity and

thermalmassofcomponents.Componentswithalow

mass,suchastheSOTpackage,willreachsolderreflow

temperaturesfasterthanthosewithagreatermass.

AvagoTechnologies’diodeshavebeenqualifiedtothe

time-temperatureprofileshowninFigure26.Thisprofile

isrepresentativeofanIRreflowtypeofsurfacemount

assemblyprocess.

After ramping up from room temperature, the circuit

board with components attached to it (held in place

withsolderpaste)passesthroughoneormorepreheat

zones.The preheat zones increase the temperature of

the board and components to prevent thermal shock

and begin evaporating solvents from the solder paste.

The reflow zone briefly elevates the temperature suffi-

cientlytoproduceareflowofthesolder.

Theratesofchangeoftemperaturefortheramp-upand

cool-downzonesarechosentobelowenoughtonot

causedeformationoftheboardordamagetocompo-

nentsduetothermalshock.Themaximumtemperature

inthereflowzone(T

Theseparametersaretypicalforasurfacemountassem-

blyprocessforAvagoTechnologiesdiodes.Asageneral

guideline,thecircuitboardandcomponentsshouldbe

exposedonlytotheminimumtemperaturesandtimes

necessarytoachieveauniformreflowofsolder.