Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs (English)
Post on 07-Jul-2015
1490 Views
Preview:
DESCRIPTION
Transcript
Low Voiding Reliable
Solder Interconnects for
LED Packages on Metal
Core PCBs
PRIVILEGED AND CONFIDENTIAL MATERIALS
Outline/Agenda
• Introduction
• Assembly
• Components
• Materials
• Process
• Results of Experiments
• Conclusions
• Q & A
PRIVILEGED AND CONFIDENTIAL MATERIALS
Introduction – LED Packages
• Lumen maintenance requirement for LED
packages used in commercial & outdoor
residential lighting is 70% lumen maintenance for
50% of population after 35,000 hours and 3 year
warranty (Energy Star A; IESNA LM-80)
• Good thermal management is key to long term
stability of light output (brightness) and color
temperature of LED lights
– Solder joints with low voiding for low thermal
resistance
PRIVILEGED AND CONFIDENTIAL MATERIALS
Package Assembly
• For this study used commercially available LED
package, metal core boards and solder pastes
– Luxeon Rebel LED
– Metal Core PCB substrate w/ Aluminum core, Copper
circuitry and 2 dielectric types
– 4 solder pastes – Pb-free; no clean; zero halogen; 4
alloy types
PRIVILEGED AND CONFIDENTIAL MATERIALS
LED Package
• Surface mount package w/ ceramic substrate & metal interconnect
• Solderable to next level substrate - bottom side with thermal pad under LED, and (2) pads for electrical connections
• Hard silicone lens
over LED
PRIVILEGED AND CONFIDENTIAL MATERIALS
Metal Core PCB (MCPCB) • Aluminum core; Copper
circuitry and (2) Dielectric types
– Dielectric A: High thermal
conductivity for good conduction of heat into metal core
– Dielectric B: Low modulus for reducing solder joint strain, especially for assemblies w/ large CTE mismatch between package and board
PRIVILEGED AND CONFIDENTIAL MATERIALS
Solder Pastes • All with Type 3 lead-free solder powder; no-clean; zero
halogen
ID Alloy Attribute
A SAC305 Broad application range
B Maxrel Superior creep resistance,
temp cycling / vibration
performance
C SACX Plus
0807
Reduced Ag for lower cost
D SnBiAg Low melting point (<140°C)
PRIVILEGED AND CONFIDENTIAL MATERIALS
Assembly Process & Testing
• Assembled 36 LEDs per board; (5) boards per
solder paste and dielectric type
• Standard SMT equipment – printing, P/P, reflow
• Solder paste printing: 5 mil stencil, on-contact
printing at 2.54 cm/sec; 268 gr/cm pressure;
0.051 cm/sec stencil release
• Reflow in air with high soak profiles
• % Voids by Xray; 50% solder joints per board
measured
PRIVILEGED AND CONFIDENTIAL MATERIALS
Reflow Profile Test • Pre-screening test with high soak & straight ramp
profiles, SAC305 paste & Type B dielectric MCPCB
board
Str RampHigh Soak
25
20
15
10
5
0
Profile
% V
oid
s
5.875.71
Boxplot of % Voids - MCPCB with Type B Dielectric; SAC305 Paste
PRIVILEGED AND CONFIDENTIAL MATERIALS
Reflow Profile – SAC & Maxrel Alloy Pastes
150-200°C, 115 sec soak; 240°C peak; 67 sec TAL
PRIVILEGED AND CONFIDENTIAL MATERIALS
Reflow Profile – SnBiAg Alloy Paste 100-110°C, 75 sec soak; 175°C peak; 60 sec TAL
PRIVILEGED AND CONFIDENTIAL MATERIALS
Test Results
PRIVILEGED AND CONFIDENTIAL MATERIALS
Main Effects Plot for Dielectric & Paste Alloy
BA
20.0
17.5
15.0
12.5
10.0
7.5
5.0SnBiAgSACX0807SAC305Maxrel
Board Dielectric
Me
an
Paste Alloy
Main Effects Plot for % VoidsData Means
PRIVILEGED AND CONFIDENTIAL MATERIALS
% Voids vs Board Dielectric
BA
35
30
25
20
15
10
5
0
Board Dielectric
% V
oid
s
10.80510.465
Boxplot of % Voids
PRIVILEGED AND CONFIDENTIAL MATERIALS
% Voids vs Paste Alloy & Dielectric
Paste Alloy
Board Dielectric
SnBiAgSACX0807SAC305Maxrel
BABABABA
35
30
25
20
15
10
5
0
% V
oid
s 20
Boxplot of % Voids
PRIVILEGED AND CONFIDENTIAL MATERIALS
Void Sizes
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% o
f J
oin
ts
ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20%
Void Size as % of Joint Area
LED Assembly Voids Sizes
B Diel/ SAC305
A Diel/ SAC305
A Diel/ SnBiAg
B Diel/ SnBiAg
A Diel/ Maxrel
B Diel/ Maxrel
A Diel/ SACX0807
B Diel/ SACX0807
PRIVILEGED AND CONFIDENTIAL MATERIALS
Average Void Sizes
LED Assembly Average Void Size
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
SAC305 Maxrel SACX0807 SnBiAg
Paste Alloy
Averg
e V
oid
Siz
e (
% jo
int
are
a) Dielectric A
Dielectric B
PRIVILEGED AND CONFIDENTIAL MATERIALS
Maximum Void Sizes
LED Assembly Max. Void Size
0.0
5.0
10.0
15.0
20.0
25.0
30.0
SAC305 Maxrel SACX0807 SnBiAg
Paste Alloy
Ma
x. V
oid
Siz
e (
% jo
int
are
a) Dielectric A
Dielectric B
PRIVILEGED AND CONFIDENTIAL MATERIALS
Typical Xray Voids Images
Paste Alloy/
Dielectric Type
SAC305 Maxrel SACX
0807
SnBiAg
MCPCB
Dielectric A
%Voids 9.3 15.8 10.0 11.6
MCPCB
Dielectric B
% Voids 7.2 12.6 12.3 12.3
PRIVILEGED AND CONFIDENTIAL MATERIALS
Summary/Conclusions • (4) different metal alloy solder pastes were evaluated for % voids in
the reflowed joints formed between a LED surface mount package
and MCPCB substrates having (2) different dielectric types
• Overall, the board dielectric type had little effect on the solder joint %
voids, whereas the solder alloy had a more significant effect
• The Type A dielectric boards resulted the lowest average and
maximum void sizes, for all pastes, and the SnBiAg paste resulted in
the smallest void sizes
• Overall, >90% of the solder joints had void sizes ≤4% of the solder
joint area and less than 20% voids on average
• The SAC305 alloy paste combined with the Type B board dielectric
resulted in the lowest % voids (<8.5%)
• The boards from this study will be subjected to further tests including
electrical/optical, die shear, thermal cycling/shock, and solder joint
characterization by cross-sectioning
PRIVILEGED AND CONFIDENTIAL MATERIALS
For More Information Please Contact:
Ravi Bhatkal – VP, Energy Technologies
Rbhatkal@cookson.com
+1-908-791-3013
Amit Patel – Technology Analyst
Apatel@cookson.com
+1-908-791-3051
top related