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Formic Acid Soldering Processes
Conventional
soldering process
Formic acid
soldering process
3S enables 3 Free
soldering solutions:
• Flux Free
• Void Free
• Solder Splash Free
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• Assembly solution provider for high power devices
• 20 years experience in Die Attach, Clip Attach and Reflow process
• Over 500 installed bases for power devices with clip process all over
the world.
3S Silicon tech., Inc.
• 100 employees
• Worldwide technical support and
service
• Contact our representative or visit
www.sss-tech.com.tw
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Residue Free & Low Void — Formic Acid Vacuum Reflow Oven
Kuo-Liang, Yeh
Sept. 19th 2019 11:00-11:30
Location: 4F TechXPOT
Booth no: I2320
Email: kl.yeh@sss-tech.com.tw
3S Silicon Tech We are different and better
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Today
• Why is the formic acid process essential?
• How can soldering problems be solved by formic
acid?
• What breakthrough has 3S Silicon tech made?
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Why is the formic acid
process essential?
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Package Void rate Solder Reflow Oven Application Power Devices
Stereo
package >30% Preforms
Convection reflow
oven
Consumer
electronics
Flattened
design (SMT) 10-30%
High flux
contained
solder
paste
convection reflow
oven/ 2008 3S
launched snap
oven
Household
appliances
charger
Mobile phone power
management
Flattened and
matrix design 2-5%
Low
residue
solder
paste
2015 3S launched
vacuum reflow
oven
Vehicle electronics
Server
Smart Appliances
Flattened and
matrix design <2%
Flux free
solder
paste
2019 3S launches
formic acid
vacuum reflow
oven
High-end automotive
electronics
High-end IC
Military and aviation
diodes
Evolution of Power Devices
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Power Device Packaging Process
Below
Dispensing Die Bond
Upper
Dispensing Reflow Oven Clip Bond
Top view Side view
Assembly of components
TO lead frame TO appearance
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Drawbacks of Voids
As a result of voids:
• Increase resistance
• Decrease thermal conductivity
• Corrosion solder joint
• Lower reliability
• Shorter lifetime
Chip
Lead Frame
Solder
Joint Macro-voids
Planar micro-voids
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How can soldering problems
be solved by formic acid?
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Formic Acid Soldering Process
Metal Metal
oxide
RCOOH
R’4NX
+ M(COOR)
Metal
HCOOH
+ H2O + CO2
Ideal formic acid soldering solution :
Traditional soldering process
Formic acid soldering process
Solder Paste
Flux Solder alloy
Rosin Tackifier Activator Rheology
Modifiers Solvent
R’4NX RCOOH
• Flux Free
• Void Free
• Solder splash Free
Metal Metal
oxide
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Applications of Formic Acid Soldering Process
Copper Pillar Bumping
Formic
Acid
DBC to baseplate
A. Wafer bumping B. Flux free preforms
Bump size: 50um Preform size: 55mm
Commercialized applications
Metal oxide
Clip
FA (formic acid)
C. Flux free Solder Paste
Not yet commercialized application
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Key Issues
Challenges of solder paste:
a. Larger surface area, more metal oxide
b. Penetration depth of FA
c. Slow reaction rate of formic acid
r r/2
Surface area
6r2 Double Surface area
[ 6(r/2)2 ] * 8 = 12r2
a
FA
Metal oxide
Clip
Melting solder
FA
Temperature
Reaction time
b
c
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What breakthrough has
3S Silicon tech made?
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3S’ Novel Formic Acid Reflow Oven
A. Formic Acid
Gas Supply
System
D. Plasma
Assisted
Exhaust Gas
Treatment
B. Double- Chamber Formic
Acid Design
C. Smart
Machine
Performance
EHS Policy
Features:
• Shorter cycle time
• Higher throughput
• Lower void rate
• Stronger bonding strength
• Safer FA supplied system
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Operation of Formic Acid Reflow Oven
Double-Chamber Formic Acid Reflow Oven (patented by 3S)
Zone 1
2 3
4 5
Cycle time 45 - 90 sec
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Formic
Acid
FA Gas
Vacuum
/Plasma
1 2 3 4 5 6 7 8 9 10 11
Evaporator
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Profile of Formic Acid Chamber
Zone
3
Zone
4
Zone
5
Zone
6
Zone
7
Zone
8
Zone
9
Atmosphere
(760torr)
(1 torr)
Cycle time 45-90s
(700 torr)
N2
FA
℃
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Double-Chamber Formic Acid Reflow Oven
“Double-Chamber” design is required
1. Each chamber provides optimized
conditions for different metal oxides
2. Shorten cycle time
Standard Electrode Potentials
Sn2+(aq) + 2e- Sn -0.14
Cu2+(aq) + 2e- Cu 0.34
E0/V
Chamber no. Function
1-4 Preheat zones
5 Copper oxide reduction
6 Heating zone
7 Tin oxide reduction
8 Precooling
9-11 Cooling zones
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Reduction of
CuO SnO
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FA FA
FA
FA
N2
N2
N2
N2 N2
N2 FA
FA FA
FA
N2
Formic
Acid
N2 /FA
Metal oxide
Clip
Metal oxide
Clip
Under vacuum
Deeper penetration Under 1 atm
Poor penetration
Passive
diffuse
Active
drive in
N2
N2
N2 N2
N2
Penetration Depth
Slow Faster
3S pure FA gas Traditional FA/N2 mix gas
N2 N2
N2
N2
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Top view
FA
FA
Penetration
depth: ca. 2mm
Penetration Depth Between Pure FA Gas and FA/N2 Mix Gas
Side view
Depth: 100um
glass
vacuum
PFA: 40 torr
10 sec
Normal pressure
PFA:PN2 = 40 : 720 torr
10 sec
Penetration
depth: ca. 11mm
Before reflow
3S Pure FA gas Conventional
FA/N2 Mix gas
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tape
340℃ 340℃ FA FA
Solder
powder
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• Improve penetration
• Enhance reactivity
Pure FA Gas
(patented by 3S) FA/N2 Mix Gas
Poor reactivity Higher reactivity
Metal oxide
FA FA
FA
FA
N2
N2
N2
N2 N2
N2
FA
FA FA FA
Metal oxide
N2
Formic
Acid
N2 /FA
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Reactivity Between Pure FA Gas and FA/N2 Mix Gas
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Reactivity Between Pure FA Gas and FA/N2 Mix Gas
Reaction time:
PFA: 40 torr@ 340℃ PFA:PN2 = 40 : 720 torr @ 340℃
1000 msec 1000 msec 5000 msec
Metal oxide
FA FA
FA
FA
N2
N2
N2
N2 N2
N2 FA
FA FA FA
Metal oxide
3S pure FA gas supply system is 5 times faster than FA/N2 mix gas.
Pure FA Gas
(patented by 3S)
FA/N2 Mix Gas
Each FA is surrounded
by 18 N2.
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EHS Policy
Healthy Safety
EHS
• Closed FA supplied system no CO, FA leakage
• Plasma enhances FA decomposition
• Smart safety control
2HCOOH + O2 2CO2 + 2H2O
2CO + O2 2CO2
Plasma oxidation
Environment
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HCOOH + heat CO + H2O
Formic acid decomposition
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3S Perfects Your Soldering Process
• Formic acid soldering process is a non-clean process with Flux Free, Void
Free , Solder Splash Free.
• 3S enhances FA penetration depth up to 5 times deeper.
• 3S enhances FA reaction rate by 5 times faster.
• 3S provides safer, non-toxic gas leakage and environment-friendly soldering
process.
• 3S provides an open innovation platform lab for product verification.
Formic Acid / Vacuum
Reflow Oven
Die/Clip Bonder Dispenser Screen Printer
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Thank you for Your Kind Attention
3S Silicon Tech We are different and better
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Contact information:
•Booth no: I2320 • Tel: 886-3-5577-668
• Mail: sales@sss-tech.com.tw
• 3F, 169-2, Sec. 1, Kang-Le Road, Hsin-Feng Shiang, Hsin-Chu County, Taiwan
304440
Q & A
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