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 Lothar Weitzel 2007 Seite 2
Solder Surfaces WE in house solder surfaces HASL Lead-free SnPb ENIG Immersion Sn Immersion Ag Lothar Weitzel 2007 Seite 3
Lead-Free HASL thickness variations very thin areas Lothar Weitzel 2007 Seite 4
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 Lothar Weitzel 2007 Seite 5
Solder Surfaces WE in house solder surfaces HASL Lead-free SnPb ENIG Immersion Sn Immersion Ag Lothar Weitzel 2007 Seite 6
Immersion Tin Ref1 Ref2 Ref3 Ref4 Ref2a Ref3a Ref5 Growth of intermetallic phase between Cu and Sn k [nm/sqrt(sec)] 100 225 C 10 125 C 60 C RT 1 0,1 0,01 0,001 0,002 0,0025 0,003 0,0035 1/T [1/ K] @ 125 C SAC lead free reflow process Sn thickness [µm] 1,1 1 0,9 0,8 0,7 0,6 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 Sn thickness [ µm] 1 0,8 0,6 0,4 0,2 0 0x 1x 2x t [h] number of cycles Lothar Weitzel 2007 Seite 7
Immersion Tin growth of intermetallic phase between Cu and Sn IMP 50min @175 C FIB cut through immersion tin layer Lothar Weitzel 2007 Seite 8
wettability with SAC solder 9,0 8,0 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0,0 Silver Tin Lothar Weitzel 2007 Seite 9 0h = fresh board 2h 120 C 4h 120 C 4 h 155 C 2x Reflow N2 240 C + 2w 3x Reflow vapor phase wetting time 2/3 Fmax [sec] 2x Reflow air 220 C 2x Reflow air 240 C + 2w Comparison Immersion Ag vs Sn preconditioning measurements done by ISIT
wettability with SAC solder 8,0 6,0 4,0 2,0 0,0 Lothar Weitzel 2007 Seite 10 0h = fresh board 2h 120 C 4h 120 C 4 h 155 C 2x Reflow N2 240 C + 2w 3x Reflow vapor phase wetting time 2/3 Fmax [sec] 2x Reflow air 220 C 2x Reflow air 240 C + 2w Comparison lead free solder surfaces Silver Tin ENIG Lead free HAL preconditioning measurements done by ISIT
Solder Surfaces ENIG Straylight can lead to solder resist deposits in PTHs Drill Ø Clearance 100 µm Immersion Sn Immersion Ag difficult to process Clearance in solder resist layout End Ø Drill Ø Lothar Weitzel 2007 Seite 11
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 Lothar Weitzel 2007 Seite 12
Requirements element melting point [ C] possible alloys melting point/range of alloy [ C] process requirement : due to the higher melting points of lead-free solders higher process temperatures and longer solder processes necessary Lothar Weitzel 2007 Seite 13
Requirements Comparison of several reflow temperature profiles (SnPb and lead-free process) reflow temperature profiles customer SnPb customer lead-free 250 200 T [ C] 150 100 50 0 0 1 2 3 4 5 6 t [min] Lothar Weitzel 2007 Seite 14
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 2.1.1 350 300 SAC profile solder shock 288 C comparison : solder shock vs SAC reflow-temperature profile T [ C] 250 200 150 100 50 0 Peak ~240 C 0 1 2 3 4 5 6 t [min] Lothar Weitzel 2007 Seite 15
Requirements Lothar Weitzel 2007 Seite 16
Requirements standard was developed for components warm/hot air component printed circuit board solder joint refers to the question whether a component will survive the temperatures used for lead-free soldering Lothar Weitzel 2007 Seite 17
Requirements max. temperature profile according to JEDEC J-STD-020C T [ C] 300 250 200 150 100 50 0 T s = 150-200 C t L = 60-150 sec 0 100 200 300 400 t [sec] 260 C Peak! longer process times and higher process temperatures (peak and preheat) Lothar Weitzel 2007 Seite 18
Material Parameters Di- / Multifunctional epoxy resin T 260 Delamination Dicyandiamideor Novolackcuring heat up phase (TMA curve) Isola AG! 10-15 min for standard FR4 higher values for Novolak or halogen free systems Lothar Weitzel 2007 Seite 19
Material Parameters T D 5% weight loss = T D (Decomposition) Isola AG! 310-320 C for standard FR4 higher values for Novolak or halogen free systems Lothar Weitzel 2007 Seite 20
Material Parameters Dynamical Mechanical Analysis Thermal Mechanical Analysis Tg Differential Scanning Calorimetry Isola AG Tg(DMA)>Tg(DSC)>Tg(TMA) also depends on measuring parameters! Lothar Weitzel 2007 Seite 21
Material Parameters Standard-FR4 z-axis Cu at room temperature z-axis [µm] 70 60 50 40 30 20 10 0 25 50 75 100 125 150 175 200 225 250 T [ C] solder process annular ring is bent outwards tensile stress in Cu barrel pad lifting at peak temperature Lothar Weitzel 2007 Seite 22
Material Parameters Moisture Intake 1 Adsorption of water molecules onto laminate surface 1 H2O 2 dθ = k ad ph O N ( 1 θ ) 2 dt p H 2 O H2O 3 Diffusion of water molecules into the laminate j D = D c 3 H2O 2 Desorption of water molecules from laminate surface dθ = kdes N dt E E k T k k T des = A e = D 0 e k des θ des = 96kJ / mol( H 2O Metal) Lothar Weitzel 2007 Seite 23
Material Parameters Moisture Intake storage @ 40 C 92% r.f. 0,8 HTg Board moisture intake [wt-%] 0,6 0,4 0,2 0 critical threshold 0 25 50 75 100 125 150 175 200 225 250 delamination t [days]! diffusion constants are in the range of 10-8 cm 2 /sec Lothar Weitzel 2007 Seite 24
Material Parameters Critical threshold depends on : material used layup of multilayer layout soldering profile drying of boards might be necessary depending on the above mentioned parameters Lothar Weitzel 2007 Seite 25
1 5 0 1 4 0 1 3 0 1 2 0 1 1 0 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 Material Parameters Moisture Desorption of laminate rel. kdes 50 75 100 125 150 175 T [ C] at higher temperatures the desorption is limited by the diffusion process or water molecules motion in the laminate respectively k des Desorption of water molecules from laminate surface dθ = kdes N dt k des = A e E k T θ des = 96kJ / mol( H 2O Metal) Diffusion of water molecules in the laminate j = D = D 0 D c e E k T Lothar Weitzel 2007 Seite 26
Material Parameters Moisture Desorption of laminate 150 C-1 150 C-2 125 C-1 125 C-2 100 C 80 C 1 rel. moisture content 0,8 0,6 0,4 0,2 0 0 20 40 60 80 100 120 140 t [h] 125 C is a very effective temperature regarding pcb drying Lothar Weitzel 2007 Seite 27
Material Parameters Moisture Characteristics of laminates; corresponding publications Lothar Weitzel 2007 Seite 28
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 Lothar Weitzel 2007 Seite 29
Materials/IPC 4101B RoHS max. allowed contaminations (referred to the homogeneous material ) Substance limit [wt %] Lead 0,1 Mercury Cadmium 0,1 0,01 not used in pcb material nor in pcb processes Chromium VI 0,1 PBB PBDE 0,1 0,1 flame retardants Lothar Weitzel 2007 Seite 30
Materials/IPC 4101B Formation of Dibenzodioxin and Dibenzofuran Polybrominated-Biphenyl(PBB) Brominated Dibenzodioxin O Br x Br y combustion Br x O Br y Polybrominated-Diphenyl-Ether(PBDE) Brominated Dibenzofuran O Br x Br y Br x O Br y Lothar Weitzel 2007 Seite 31
Materials/IPC 4101B PBB and PBDE have not been used in FR4-laminates for many years! TBBA is standard halogenated flame retardant Br CH 3 Br C C CH 2 O C O CH 2 CH CH 2 O O Br CH 3 Br n TBBA amount of bromide in standard laminate ~10 weight-% halogen free materials use flame retardants on Nitrogen/Phosphorous basis Lothar Weitzel 2007 Seite 32
Materials/IPC 4101B Group 99 (in total 55 different groups) Lothar Weitzel 2007 Seite 33
Materials/IPC4101B T 260 ~10-15min T D ~ 310-320 C DICY cured systems DICY cured systems in combination with halogen free flame retardant T 260 ~30-60min T D ~ 340-350 C Novolak cured systems Standard FR4 Tg135 HTg 150 HTg 170 HTg150 filled HTg 170 filled Standard FR4 Tg135 filled HTg 150 filled HTg 170 HTg170 filled Lothar Weitzel 2007 Seite 34
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 Lothar Weitzel 2007 Seite 35
Solderability Tests examination of temperature resistance for all materials necessary! base material screen printing paste solder mask via-filling paste carbonpaste blue mask Lothar Weitzel 2007 Seite 36
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 Lothar Weitzel 2007 Seite 37
Solderability Tests Tests of different layout/multilayers necessary Materials : Standard FR4 High Tg High Tg (Novolak) halogen free Lothar Weitzel 2007 Seite 38
Solderability Tests used temperature profile according to IPC/JEDEC standard J-STD-020C! very extreme profile and not recommended for solder process! 250 200 T [ C] Printed circuit boards were run 3* through the reflow process. Some boards were also tested afterwards using accelerated thermal cycling 150 100 50 0 0 1 2 3 4 5 6 7 8 t [min] Lothar Weitzel 2007 Seite 39
Solderability Tests visual check (delamination) before after JEDEC-020C temperature profile Lp after reflow and ATC cycles PTH micro section 7 6 5 4 3 2 1 0 surface 1 surface 2-5 -4-3 -2-1 0 1 2 3 4 5 DeltaR/R [%] Lothar Weitzel 2007 Seite 40
Solderability Tests before Standard FR4 (Dicy cured) after 3x reflow cycles Lothar Weitzel 2007 Seite 41
Solderability Tests Standard FR4 alternative material HF-FR Delamination after 4 reflow cycles Lothar Weitzel 2007 Seite 42
Solderability Tests Standard FR4-8 and 12 layer after 500 cycles -45/125 C Lothar Weitzel 2007 Seite 43
Solderability Tests cracks in solder mask after reflow cycles printed circuit boards with a high layer count (copper; resin content) show severe pad lifting which leads to cracks in the solder mask 12 layer ML 1,6mm thick standard FR4 Lothar Weitzel 2007 Seite 44
Solderability Tests at room temperature soldering process annular ring is bent outwards tensile stress in Cu barrel due to the different expansions of base material and copper barrel the solder mask is being stretched at peak temperature Lothar Weitzel 2007 Seite 45
Solderability Tests 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. Lothar Weitzel 2007 Seite 46
Solderability Tests 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 Lothar Weitzel 2007 Seite 47
Solderability Tests Halogen free material after 3 lead-free solder processes and 1000 cycles -45/125 C Lothar Weitzel 2007 Seite 48
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 Lothar Weitzel 2007 Seite 49
Moisture Sensitivity High Tg (Novolak cured) 3* Reflow dried stored (moisture) delamination Lothar Weitzel 2007 Seite 50
Moisture Sensitivity Halogen free material before reflow after storage in climatic chamber and 4x reflow cycles Lothar Weitzel 2007 Seite 51
Moisture Sensitivity Halogen free material Lothar Weitzel 2007 Seite 52
Moisture Sensitivity Solderability test with different peak temperatures after storage for several months T [ C] 275 250 225 200 profile 1 profile 2 profile 1 profile 2 175 4 4,5 5 5,5 6 6,5 t [min] T [ C] 275 250 225 200 175 150 125 100 75 50 25 0 0 1 2 3 4 5 6 7 8 T Peak =260 C T Peak =250 C t [min] Lothar Weitzel 2007 Seite 53
Moisture Sensitivity Halogen free material after several months storage run 3 times through profile 2 without drying Lothar Weitzel 2007 Seite 54
Moisture Sensitivity Halogen free material after several months storage run 3 times through profile 1 without drying or profile 2 after drying Lothar Weitzel 2007 Seite 55
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 Lothar Weitzel 2007 Seite 56
Lead-free vs Halogen-free T 260 ~10-15min T D ~ 310-320 C DICY cured systems DICY cured systems in combination with halogen free flame retardant T 260 ~30-60min T D ~ 340-350 C Novolak cured systems Standard FR4 Tg135 HTg 150 HTg 170 HTg150 filled HTg 170 filled Standard FR4 Tg135 filled HTg 150 filled HTg 170 HTg170 filled Lothar Weitzel 2007 Seite 57
Material Parameters Material parameters Decomposition Temperature T D [ C] Time to delamination @ 260 C T 260 [min] CTEz Coefficient of Thermal Expansion [ppm/k] Moisture Intake Tg T D [ C] Decomposition Temperature 370 360 350 340 330 320 310 300 DICY Standard FR4 Novolak DICY halogen free 15 30 45 60 T 260 [min] Time to Delamination @260 C Lothar Weitzel 2007 Seite 58
Materials/IPC4101B Nanya Lothar Weitzel 2007 Seite 59
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 Lothar Weitzel 2007 Seite 60
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 Lothar Weitzel 2007 Seite 61
Summary layer count 18 16 14 12 10 8 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 HF TG 170 C 1 2 3 4 board thickness [mm] Lothar Weitzel 2007 Seite 62
Thank you very much for your attention Lothar Weitzel 2007 Seite 63