Lead Free Soldering Technology

Transcription

1 Lead Free Soldering Technology Chung-Ang University Young-Eui Shin

2 Trend of Package Small, Light, High performance High speed, Large capacity High integrity, High density

3 Comparison of package size 45mm 30mm PKG QFP (Quad Flat Package) BGA (Ball Grid Array) AREA 2025mm 2-100% 900mm 2-44% 18mm 12mm In case of 304 pins CSP (0.8mm Pitch) (Chip Size Package) CSP (0.5mm Pitch) (Chip Size Package) 324mm 2-16% 144mm 2-7%

4 Individual utilization of internet (%) In 1997 In Japan U.S Korea Singapol Sweden

5 Principle of Soldering PCB Solder Materials Electronic devices Materials Properties wetting melting Heat diffusion Soldering Machine Principle of Soldering Solder Joints Quality, Reliability wetting Solder Joining temperature The state of surface Cu Solder Cu Surface treatment flux Coated layer Reaction layer (IMC) Solder materials Lead materials Joining temperature Interface Reaction of Solder Joints

6 Joining Process and Requirement Interface of Multi-layers Joining interface application operation Interface reaction Interface reaction layer Diffusion Defect formation Grain growth Phase transformation Property, Joints Reliability Electric property Optical property Mechanical property (bonding strength) Properties of Interface Nuclear phase, Composition, Crystal structure, Interface shape, Defect Prediction of Optimal Interface Structure Properties Kinetics of interface dx = dt f ( T ) g ( x )

7 Lead Free Solder Materials and Reflow Condition Temp Low Property Temperature range out of heat-resistance Sn-Zn 199 Sn-Ag-Cu Sn-Ag-Bi 210 Bonding Strength Reliability 220 Sn-Pb 183 High Sn/3.5Ag/0.75Cu Temperature variation of PCB during reflow Heat-resistance temperature of device - Melting point (liquidus temperature) Sn/3Ag/2.5Bi/2.5In Sn/8Zn/3Bi Sn/37Pb MP( ) Liquidus temp Solidus temp Tensile Strength(MPa) Room temp Elongation(%) The first stage Considerations in Reflow conditions atmosphere Temperature Air,N2 - Air,N2 - N2,(Air) Oxidation(Time, Temp) Air,N2 -

8 Reflow Technology of Lead Free Solders Solder Joints Quality Wettability Manhatan Solder ball Bridge Void Bonding strength Temp Subject of profile Preheat temp (flux activity) wetting solder ball void bonding strength = Solders Sn-Ag-Bi Sn-Ag-Cu Sn-Zn Sn-Pb Over shoot Preheat time (flux activity) wetting solder ball void bonding strength Device (lead coating) Sn-Pb Sn-Bi Pd Sn Au etc Heating rate solder ball void device Time (sec) Reflow Profile Preheat (temp, time) Reflow peak (heating rate, temp, time) Cooling (cooling rate) Temperature out of heat-resistance T Heating time(at 200 ) device Soldering atmosphere Concentration of oxygen Reflow peak device Solder melting temp holding time wettability bonding strength(reliability) (joining interface state) Cooling rate bonding strength(reliability) (compound property, joining interface state) Temperature variation needs to be Smaller (Max-Min= T) Improvement of heating ability

9 Diffusion Melting X 1 Sn(L) Cu(S) Melting depth KD (X)Kt1= 1QDexp()= 01 60Sn-40Pb : Sn>Au>Ag>Cu>Pd>Pt>Ni 1RTDiffusion Average moving distance of atom (X 2 (X2)2Dt= 4D110D)s Moving distance in a liquid over meting point : 10mm/h Moving distance in a solid under meting point : 0.1mm/h Thickness of reaction layer Thickness of reaction layer 3= 3Q3K3DD0exp( ) = (X)KQ 3 : Activation energy of compound layer growth trt

10 Experimental materials Sn-Ag Lead Free Solder (mass%) Sn-3.5Ag Sn-3Ag-5Bi Sn-3.5Ag-0.7Cu Sn-3.5Ag-2.5Bi-2.5In Sn-37Pb (Ref) Device FR-4 QFP (500µm pitch) Cu lead Surface treatment size : mm thickness : 0.8mm Cu pad (electro plating) Sn-10Pb coating (10 µm) Au/Pd/Ni coating (0.01/0.08/0.3 µm ) Surface treatment Heat-resistance preflux

11 Experimental method Experimental materials Air reflow 90sec preheating in 170 Max temp at QFP joints : 230 (30sec over 220 ) Reliability test 1. Aging test (125, 0 to 2000 hour) 2. TC test (-40 30min~125 30min, 0 to 2000 cycles) Observation of joining structure 45 tensile test Observation of fracture surface Evaluation of solder joint in QFP Examine effect on joining strength by structure

12 Joining Strength after Aging Test Strength (N SnAg SnAgBi SnAgCu SnAgBiIn SnPb Strength (N SnAg SnAgBi SnAgCu SnAgBiIn SnPb Holding time(hour) Holding time(hour) Coated Sn-Pb Coated Au/Pd/Ni

13 Joining Strength after Temperature Cycling Test Dept. of Mechanical Engineering Strength (N SnAg SnAgBi SnAgCu SnPb Strength (N SnAg SnAgBi SnAgCu SnPb Number of cycles Number of cycles Coated Sn-Pb Coated Au/Pd/Ni

14 Sn-8Zn-3Bi solder joints after aging test(coated Sn-Pb) coated Sn-Pb Strength(N) Sn-3.5Ag Sn-8Zn-3Bi Air Sn-8Zn-3Bi N Holding time(hour) Joining Strength after Aging Test (a) Air (b) N2 Cross section of Sn-8Zn-3Bi solder joints(coated Sn-Pb)

15 Sn-8Zn-3Bi solder joints after aging test(coated Pb) coated Pd Strength(N Sn-3.5Ag Sn-8Zn-3Bi Air Sn-8Zn-3Bi N Holding time(hour) Joining Strength after Aging Test (a) Air (b) N2 Cross section of Sn-8Zn-3Bi solder joints(coated Pb)

16 Strength of Sn-8Zn-3Bi solder joints according to lead coating Fracture load (N) After reflow soldering Aging 2000hour in 398K 0 Sn-Pb coating Au/Pd/Ni coating Sn-Ag coating Sn-Bi coating Sn-Cu coating Sn-8Zn-3Bi solder Sn-3.5Ag- 0.7Cu solder Sn-Pb solder

17 Structure and Mechanical properties of BGA Bonding wire Chip Mold resin Signal via Properties of BGA PWB (Printed wiring board) Thermal via Structure of BGA Solder bump Small size due to peripheral arrangement of pad Self Alignment effect Excellent electric characteristics

18 Coated Sn/Ag multi-layer Cu core ball Sn/Ag Sn/Ag/Sn/Ag Sn Coated Solder Au (0.7 µm) Ni (7 µm) Sn Ag About 740 µm Plating thickness (µm) 670 µm Sn Ag (coated from left side of Cu core) Plating thickness Cu core Cu (30 µm) Pad

19 Sn-Ag solder ball after Reflow Sn/Ag coated Cu core ball Sn-3.5Ag paste Cu core ball Sn-3.5Ag ball

20 Growth of Reaction Layer (Sn-Ag solder, Cu core Sn-Ag solder) As reflow Ag 3 Sn Phase (Ag, Co,Ni)Sn 3 layer Heat treated at 150 Cu core (Au,Cu) 6 Sn 5 layer (Au,Co,Cu,Ni) 6 Sn 5 layer direction of diffusion of Ni,Co direction of diffusion of Au,Sn direction of diffusion of Cu Void Heat treated at 150 for 500 hours (a) Sn-3.5Ag solder ball (b) Cu cored Sn-3.5Ag solder

21 Future Trends of Micro Joining The Joining Reaction-Layer Control Technology The Joining Interface Analysis Technology Low Temperature Joining Technology Materials Development The Establishment of Evaluation Technology