Vortrag Dr. Weitzel, Firma Würth-Elektronik - FED-Wiki

LEAD FREE

HALOGENFREE

Würth Elektronik

PCB Design Conference 2007

Lothar Weitzel 2007 Seite 1

Content

• Solder surfaces/Overview

• Lead free soldering process requirements/Material parameters

• Different base materials/IPC4101B

• Solderability tests

• Moisture sensitivity

• Link between lead free and halogen free

• Summary


Solder Surfaces

WE in house solder surfaces

HASL

Lead-free

SnPb

ENIG Immersion Sn Immersion Ag


Lead-Free HASL thickness variations very thin areas


Lead-Free HASL solder bridges between SMD pads with pitch smaller or equal 500µm higher Cu leaching

!

lower reliability of board due to high thermal stress


Solder Surfaces

WE in house solder surfaces

HASL

Lead-free

SnPb

ENIG Immersion Sn Immersion Ag


Immersion Tin

Growth of intermetallic phase between Cu and Sn

@ 125°C

1,1

1

0,9

0,8

0,7

0,6

0,0 1,0 2,0 3,0 t [h]

4,0 5,0 6,0 7,0

1

0,8

0,6

0,4

0,2

0

0x

100

225°C

Ref1 Ref2 Ref3 Ref4 Ref2a Ref3a Ref5

125°C 60°C RT

10

1

0,1

0,01

0,001

0,002 0,0025 0,003 0,0035

1/T [1/°K]

SAC lead free reflow process

1x number of cycles

2x


Immersion Tin growth of intermetallic phase between Cu and Sn

IMP

50min @175°C

FIB cut through immersion tin layer


Comparison Immersion Ag vs Sn

wettability with SAC solder

9,0

8,0

7,0

6,0

5,0

4,0

3,0

2,0

1,0

0,0 preconditioning

Silver

Tin measurements done by ISIT


Comparison lead free solder surfaces

wettability with SAC solder

Silver Tin ENIG Lead free HAL

8,0

6,0

4,0

2,0

0,0 preconditioning measurements done by ISIT


Solder Surfaces

Straylight can lead to solder resist deposits in PTHs

ENIG

Immersion Sn

Immersion Ag difficult to process

►

Clearance in solder resist layout

Drill Ø

Clearance ≥ 100 µm


Content







• Summary


Requirements process requirement : due to the higher melting points of lead-free solders higher process temperatures and longer solder processes necessary element melting point [°C] possible alloys melting point/range of alloy [°C]


Requirements

Comparison of several reflow temperature profiles

(SnPb and lead-free process) reflow temperature profiles customer SnPb customer lead-free

250

200

150

100

50

0

0 1 2 3 t [min]

4 5 6


Requirements example :

IPC 6012 rigid pcbs thermal stress test according to IPC TM650 2.6.8 (solder shock test) max. 288°C 10sec floating (after drying) investigation using micro section according to IPC TM 650 2.1.1

SAC profile solder shock 288°C comparison : solder shock vs

SAC reflow-temperature profile

350

300

250

200

150

100

50

0

0 1

Peak ~240°C

2 3 t [min]

4 5 6


Requirements


Requirements standard was developed for components warm/hot air component solder joint printed circuit board refers to the question whether a component will survive the temperatures used for lead-free soldering


Requirements max. temperature profile according to JEDEC J-STD-020C

300

250

200

150

100

50

0

0

T s

= 150-200°C t

L

= 60-150 sec

260°C Peak

100 200 t [sec]

300 400

!

longer process times and higher process temperatures (peak and preheat)


Material Parameters

Di- / Multifunctional epoxy resin heat up phase

(TMA curve)

©Isola AG

T

260

Delamination

Dicyandiamideor Novolackcuring

!

10- 15 min for standard FR4 higher values for Novolak or halogen free systems



T

D

5% weight loss = T

D

(

Decomposition)

©Isola AG

!

310-320°C for standard FR4 higher values for Novolak or halogen free systems



D ynamical M echanical A nalysis

T hermal M echanical A nalysis

D ifferential S canning C alorimetry

Tg

©Isola AG

Tg(DMA)>Tg(DSC)>Tg(TMA) also depends on measuring parameters !


Material Parameters at room temperature solder process annular ring is bent outwards

Standard-FR4 z-axis Cu

40

30

20

10

0

70

60

50

25 50 75 100 125 150

T [°C]

175 200 225 250 tensile stress in Cu barrel pad lifting at peak temperature



Moisture Intake

1

Adsorption of water molecules onto laminate surface d

θ dt

= k ad

⋅ p

H

2

O

⋅

N

⋅

( 1

− θ

)

⇒ ∝ p

H

2

O

1

3

Diffusion of water molecules into the laminate j

= −

D

⋅ ∇

c

D

=

D

0

⋅

E e

− k

⋅

T

3

2

2

Desorption of water molecules from laminate surface d

θ dt

= − k des

⋅

N

⋅ θ k des

=

A

⋅

e

−

E k

⋅ des

T k des

=

96 kJ / mol ( H

2

O

−

Metal )



Moisture Intake storage @ 40°C 92% r.F.

HTg Board

0,8

0,6

0,4

0,2

0

0 critical threshold

25 50 75 100 125 150 175 200 225 250 t [days]

!

d iffusion constants are in the range of 10 -8 cm 2 /sec delamination



Critical threshold depends on :

• material used

• layup of multilayer

• layout

• soldering profile

► drying of boards might be necessary depending on the above mentioned parameters



Moisture Desorption of laminate

5 0

4 0

3 0

2 0

1 0

0

9 0

8 0

7 0

6 0

1 5 0

1 4 0

1 3 0

1 2 0

1 1 0

1 0 0

50 75 100

T [°C]

125 150 175 at higher temperatures the desorption is limited by the diffusion process or water molecules motion in the laminate respectively

Desorption of water molecules from laminate surface d

θ

= − k des dt

⋅

N

⋅ θ k des

=

A

⋅

e

−

E des k

⋅

T k des

=

96 kJ / mol ( H

2

O

−

Metal )

Diffusion of water molecules in the laminate j

= −

D

⋅ ∇

c

D

=

D

0

⋅

E e

− k

⋅

T



Moisture Desorption of laminate

150°C-1 150°C-2 125°C-1 125°C-2 100°C 80°C

1

0,8

0,6

0,4

0,2

0

0 20 40 60 t [h]

80 100 120 140

125°C is a very effective temperature regarding pcb drying



Moisture Characteristics of laminates; corresponding publications


Content







• Summary


Materials/IPC 4101B

RoHS max. allowed contaminations (referred to the „homogeneous material“)

Substance limit [wt %]

Lead

Mercury

Cadmium

Chromium VI

PBB

PBDE

0,1

0,1

0,01

0,1

0,1

0,1 not used in pcb material nor in pcb processes flame retardants



Formation of Dibenzodioxin and Dibenzofuran

Polybrominated-Biphenyl(PBB) Brominated Dibenzodioxin

O

Br x Br y combustion

Polybrominated-Diphenyl-Ether(PBDE)

O

Br x Br y

Brominated Dibenzofuran

O

Br x Br y

Br x

O

Br y



PBB and PBDE have not been used in FR4-laminates for many years

!

TBBA is standard halogenated flame retardant

C

O

C CH

2

O

Br

CH

3

C

CH

3

Br

O CH

2

CH CH

2

O

Br Br n

TBBA amount of bromide in standard laminate ~10 weight-% halogen free materials use flame retardants on Nitrogen/Phosphorous basis



Group 99 (in total 55 different groups)


Materials/IPC4101B

T

260

T

D

~10-15min

~ 310-320°C

DICY cured systems

Standard FR4 Tg135

HTg 150

HTg 170

T

260

T

D

~30-60min

~ 340-350°C

DICY cured systems in combination with halogen free flame retardant

Novolak cured systems

HTg150 filled

HTg 170 filled

Standard FR4 Tg135 filled

HTg 150 filled

HTg 170

HTg170 filled


Content







• Summary


Solderability Tests examination of temperature resistance for all materials necessary !

screen printing paste base material solder mask via-filling paste blue mask carbonpaste


Solderability Tests parameters which affect the thermal stability of a printed circuit board

• pcb thickness/PTH diameter

• base material (T

260

, T

D

, CTE-z...)

• Cu-thickness

• fill material of vias

• number of layers (resin content)

• layout

• etc


Solderability Tests

Tests of different layout/multilayers necessary

Materials :

Standard FR4

High Tg

High Tg

(Novolak) halogen free


Solderability Tests used temperature profile according to IPC/JEDEC standard J-STD-020C very extreme profile and not recommended for solder process !

250

200

150

Printed circuit boards were run 3* through the reflow process. Some boards were also tested afterwards using accelerated thermal cycling

100

50

0

0 1 2 3 4 t [min]

5 6 7 8


Solderability Tests visual check

(delamination)

PTH micro section before

JEDEC-020C temperature profile after

Lp after reflow and ATC cycles surface 1 surface 2

7

6

5

2

1

4

3

0

-5 -4 -3 -2 -1 0 1

DeltaR/R [%]

2 3 4 5


Solderability Tests before

Standard FR4 (Dicy cured) after 3x reflow cycles



Standard FR4

Delamination after 4 reflow cycles alternative material HF-FR



Standard FR4 - 8 and 12 layer after 500 cycles -45/125°C


Solderability Tests printed circuit boards with a high layer count

(copper; resin content) show severe pad lifting which leads to cracks in the solder mask cracks in solder mask after reflow cycles

12 layer ML 1,6mm thick standard FR4


Solderability Tests at room temperature due to the different expansions of base material and copper barrel the solder mask is being stretched soldering process annular ring is bent outwards tensile stress in Cu barrel at peak temperature



Comparison Standard FR4 vs halogen free material

Standard FR4 cracks in solder mask after reflow processes alternative material HF-FR same layout, same solder mask etc.



12 layer multilayer thickness 1,6mm layup using 100µm cores

(2116 Prepreg) and

106 or 1080 prepregs

8 layer multilayer thickness 1,6mm layup using 100µm cores

(2116 Prepreg) and

0,71µm core (4*7628) as well as 1080 prepregs



Halogen free material after 3 lead-free solder processes and

1000 cycles -45/125°C


Content







• Summary


Moisture Sensitivity

High Tg (Novolak cured) 3* Reflow dried stored (moisture) delamination


Moisture Sensitivity before reflow

Halogen free material after storage in climatic chamber and 4x reflow cycles



Halogen free material



Solderability test with different peak temperatures after storage for several months

275

250

225

200

175

4 4,5 profile 1 profile 2

275

250

225

200

175

150

125

100

75

50

25

0

0 1 2 3 4 t [min]

5 6 7 8

T

Peak

=260°C profile 1 profile 2

5 t [min]

5,5 6 6,5

T

Peak

=250°C



Halogen free material after several months storage run 3 times through profile 2 without drying



Halogen free material after several months storage run 3 times through profile 1 without drying or profile 2 after drying


Content







• Summary


Lead-free vs Halogen-free

T

260

T

D

~10-15min

~ 310-320°C

DICY cured systems

Standard FR4 Tg135

HTg 150

HTg 170

T

260

T

D

~30-60min

~ 340-350°C

DICY cured systems in combination with halogen free flame retardant

Novolak cured systems

HTg150 filled

HTg 170 filled

Standard FR4 Tg135 filled

HTg 150 filled

HTg 170

HTg170 filled



Material parameters

• Decomposition Temperature

T

D

[°C]

• Time to delamination @ 260 °C

T

260

[min]

• CTEz

Coefficient of Thermal Expansion

[ppm/K]

• Moisture Intake

370

360

350

340

330

320

310

300

DICY

Standard FR4

• Tg

Novolak

DICY halogen free

15 30 45

T

260

[min]

Time to Delamination @260°C

60


Materials/IPC4101B

©Nanya


Content







• Summary


Summary

Assumption : process using temperature profile according to JEDEC J-STD-020

• Standard FR4 materials can be used for multiple lead-free soldering processes within a certain thickness range; with the extreme profile used here up to 3 reflow cycles are possible; pad lifting and cracks in SM appear depending on board thickness/layer count

• thick boards or boards with thick copper layers require a material with a lower Z-CTE, high thermal resistance and low moisture intake

• depending on storage conditions (moisture intake) different materials showed different effects

• best results so far including processability : halogen free material


Summary

12

10

8

18

16

14

6

4

2

HF TG 150°C higher copper thicknesses plugged vias more than 3 solder processes

Standard FR4 TG 135°C up to 3 lead-free solder processes

1

HF TG 170°C

2 3 board thickness [mm]

4


Thank you very much for your attention


Vortrag Dr. Weitzel, Firma Würth-Elektronik - FED-Wiki

LEAD FREE

HALOGENFREE

Würth Elektronik

PCB Design Conference 2007

wettability with SAC solder

wettability with SAC solder

= −

⋅ ∇

=

⋅

=

⋅

=

⋅

= −

⋅ ∇

=

⋅

Thank you very much for your attention

Related documents

Products

Support

Vortrag Dr. Weitzel, Firma Würth-Elektronik - FED-Wiki

LEAD FREE

HALOGENFREE

Würth Elektronik

PCB Design Conference 2007

wettability with SAC solder

wettability with SAC solder

= −

⋅ ∇

=

⋅

=

⋅

=

⋅

= −

⋅ ∇

=

⋅

Thank you very much for your attention

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