Micro mechatronics 1part 6: soldering and glueing

Prof. Fritz J. NeffDirector of the Laboratory for Micro mechatronics and Hybrid integrated thick film circuitSat the University of AppliedSciences Karlsruhe (FH), 16. August 2004

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Introduction

After the thick film structures havebeen manufacturedAnd controlledThe Surface-Mount-Technology SMT occurs

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Characteristics of soldering

Remove of disturbing layers on thesurfaceWetting of the surfaces and spreadingof the solder(with flux)Interdifusion and establishing of alloysystemsCrystalisation of solder

Prof. Fritz J. Nef, Steinbeis TZ Mechatronik-Karlsruhe 4

Soldering process

main requirements:- connection between substrate, solder and SMD- no damage of SMDs- live long reliability of the soldered product

Two different methods:- bringing liquid solder to the point of connection- soldering paste dispensed on the soldering pad

and then treated by reflow soldering

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Soldering temperature

ca. 260°C

ca. 183°C

group

solders

225°C205°C

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Temperature problems

260 °C: Maximal on electronic groups235 °C: Maximal on BGA (Ball Grid Array)225 u. 235 °C: Minimal necessary for leadfree

solders205 °C: Minimal necessary on electronic group

examples:- SnAg3,8Cu0,7-alloys, melting temperatures at

216°C – 221°C - Sn63Pb37-alloys, melting temperature at 183°C

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Problems with/without lead

Restriction On Substances(ROS-guideline)

of EU-commissionlast day for solders with lead

01.01.2008Japanese electro industrie has changed yet also for

consumer goods!

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Soldering technologies for printedcircuit boards (PCB)

local soldering technologies:- with soldering hammer, by LASER

automated soldering process for groups(PCBs):- wave soldering (1 wave, double wave)- Reflow soldering (Infra red)- Convection soldering (need of gaz)

Problem: small elements become earliermax. of temperature than big elements

- vapour phase soldering

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Parameters for soldering

solderflux

combination of materials withsolder

thermal energyphase of increasing temperature

soldering phasecooling phase

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Process steps

selection of soldering pastestencil printing or dispensing of

solder pasteFine-Pitch-assembly

Soldering process- Reflow or- vapour phase

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Application of soldering pastes•Dispensing•Stencil Printing Technologie•Screen Printing

Granular size of soldering pastes10 µm < d < 45 µm

Granular size for microdots5 < d < 25 µm.

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Stencil manufacturing

by LASER cutting or by etchingaccuracy < 0,1µm

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SMT-sideA

SMT-sideB

THT

Siemens

Soldering line forelectronic groups

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Vapour phase soldering

also known as condensation solderingtransfer of thermal energy according to second law of thermodynamics

the more is the temperature difference themore ist the energy transfertemperature increases more if the thermal capacity is small

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Vapor phase solderingtransfer time for thermal energyτ = c x m / (A x h)mit A = contact arear and h = coefficient of thermal conduction(Wm-2 K-1)end temperature Te

TD = vapour temperature, T0 = surface temperature,

⟩−⟩⟨−⟨+=−

eTTTTt

Deτ100

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Vapour phase soldering

Gesättigter Dampf215 °C

Medium

Sensor

FBG >20 °CFBG >20 °C

FBG >20 °C (< 215 °C)

FBG ≤ 215 °C

FBG < 215 °C

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Characteristics of vapor phase soldering

Homogenous heating of group (PCB)small ΔT on the PCB in peak temperatureContinuous condensating processO2-free conditionsLowest possible energy transfer to the PCBExceeding of peak temperature is not possibleBoiling point of perfluorised Polyether 230°C

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Convection soldering

Important parameters:- control of the different heating zones- control of processing time

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BGA-soldering

Examples for Ball Grid ArraysBGA: 560 connections, pitch: 1,27mmBGA: 480 connections, pitch: 1,27mmBGA: 728 connections, pitch: 1,00mmBGA: 400 connections, pitch: 1,27mm

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Comparisionvapour phase - convection

BGA-Ball soldered in vapor phase BGA-Ball soldered

in convection oven

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Parameters leading to decision

quantity of heat during liquidus timethermal mass of elementsused solder

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Intermetallic phase

smallintermetallicphaseCu/Sn

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steps of soldering SMDs

Dispensing or screen printing of solder

surface mount technology(Fine-Pitch-Placement)

soldering process(Reflow-, convection-, or vapour phasesoldering)

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Pick-and-place with reflow soldering

Solderapplication,Pick-and-place,Thermal treatment

LotkugelnFlußmittel

AgPd-Lötpad

Keramiksubstrat

Geschmolzenes Lot

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Preparation of soldering

Mounting plan for the controlwith amplifier of an elctrocardiographicsystem made on Al2O3-ceramic-substrate

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Dispencing and SMD-fine-pitch-placement

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placementVacuum gripper withSMD-elementoverhead theLanding positionElectronic elementsor devices (SMD)

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Temperatur profile reflow soldering

260

240

220

200

180

160

140

120

100

80

60

40

20

Temperatur / °C

10 20 30 40 50 60 70 80 90 100 110

15s 25s 25s 8s 47s

73s65s

1.Phase 2.Phase 3.Phase Vorheiz-phase

Schmelzen der Lotpaste

Vorheizen Lötphase

Zeit / s

Aufheizen des Ofeninnenraumes Erwärmen der Bauelemente

Preheat-Time(Timer)

Soldering-Time (Timer)

Abkühl-phase

120

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Reflow oven in the LMHS

Beschickungsseite

Reflowprozessprotection of sensibel elementswith ceramic hut

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basics of glueing

soldered- Peak temperature 220°C- energy for melting anddiffusion necessary

Lot Kleber

Bauelement

a.) b.)

glued- Peak temperature 170°C- energy for hardening ofth glue

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Types of gluesgeneraly:

Single component, Two components, Containing solvents, Without solvents,Activated by light,Theraml activation.

Important for micro technicsinsulating,isotrop electric conducting,anisotrop electricconducting,thermal conducting.

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Advantages of conducting glues

Low temperature treatment of the electronic devicesno fluxerOptimal comportment by temperature change stressSimple handling and using by dispensing or screen printingOptimal for systems with very small dimensionsGood electrical conductors are also good thermal conductors

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Isotropic conducting glues

61

0,60,2

0

1

2

3

4

5

6

7

8

9

10

72 74 76 78 80 82 84

Ag - Anteil in %

spez

.Wid

erst

and

in 1

0-3

Ohm

cm

Spezific resistant is depending ofthe relative amount of conducting

particles within the mass of the glue

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Silver ion migration

Ag is hydrolisatingby warm and humid climate to Ag+-Ionsby migration to theanodes in theneigbourhoodfollows the short cut

+ -

Silberdentriden

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Anisotropic conducting glues

lower contact pad on substrate

upper contact ball of electronic device

Conducting particles

By compression deformed buttherefore, conducting particles

Particle-diameter 6,5µm

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Possibility with Flip-Chip-Bonding

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Decision aidEpo-Tek-Kleber E2101 E3116 E3116

-5H20E-PFC

H70E-4

SMD X X X

Flip-Chip X X

Dispenser X X

Siebdruck X X X X X

Stempeldruck X

Scherfestigkeit (N/cm²) 1050 970 >1030 830 790Wärmeleitfähigkeit

(W/m*K) 2,1 2,0 2,0 1,64 1,43

Max. Dauerbetriebs-temp. (°C) 150 175 175 200 150

Isotrop X X X

Anisotrop X XSpez. el. Vol.widerstand

(Ù*cm) 1-4*10-4 1-5*10-4 1-5*10-4 1-4*10-4 1*1014