performance of pb free solder pastes at different reflow
DESCRIPTION
TRANSCRIPT
Performance of Pb-free Solder pastes at different
reflow profiles
Primary Objective
To analyze the defects of Pb-free solder pastes from two different manufacturers, subjected to three different reflow profiles, viz.,
In-Spec Profile Above-Spec Profile Below-Spec Profile
Secondary Objective
To come up with the above said reflow profiles based on the two different solder paste manufacturer’s specification sheets.
The two solder pastes selected were, Alpha OM-338-T Pb-free Indium 5.1 Pb-Free
Alpha Pb-free Specification
Ramp Rate : 0.8°C to 1.7oC/SecondSoak Temp : 130°C to LiquidusTAL : 35 - 90 sec Peak Temp : 232-250oC
Indium 5.1 Pb-free Specification
Ramp Rate : 0.5°- 2.0°C/SecondSoak Temp : 200°-210°CTAL : 30 - 90 sec Peak Temp : 229-260oC
Project Description
The above mentioned Pb-free solder pastes are subjected to three different profiles.
The performance of each paste is analyzed by examining the possible defects.
The defects are then superimposed on the reflow profile explaining the reasons for their occurrence.
Profiling Procedure
The paste and the reflow specification are collected from the paste manufacturer specification document.
The three different reflow recipes for the Pb-free solder pastes are then generated.
The zone temperature and the conveyor speed for each specification of each paste are noted down.
The thermocouple-attached copper coupons are used for profiling.
Alpha Reflow Statistics
Profile Ramp Rate(°C/Sec)
Soak Temperatur
e
TAL(Seconds)
Peak Temp (°C)
Alpha Above-Spec
2.8130°C to
217°C134.7 270.5
Alpha In-Spec
1.2130°C to
217°C64.3 241.4
Alpha Below Spec
1.1130°C to
217°C19.6 220.2
Zone Temperatures for Alpha Paste
Profile Conveyor
Speed Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone
6 Alpha
Above-Spec 38 153 187 212 249 268 281Alpha
In-Spec 36 86 116 148 193 235 256Alpha
Below Spec 35 65 94 124 164 201 240
Alpha Reflow Profiles
Indium Reflow Statistics
Profile Ramp Rate(°C/Sec)
Soak Temperatur
e
TAL(Seconds)
Peak Temp (°C)
Indium Above-Spec
1.7200°C to 210°C
124.5 268.1
IndiumIn-Spec
1.3200°C to 210°C
62.5 239.7
Indium Below-Spec
1.1200°C to 210°C
7 218.2
Zone Temperatures for Indium Paste
Profile Convey
or Speed Zone 1 Zone 2 Zone 3 Zone 4 Zone 5
Zone 6
Indium Above-Spec 29 125 166 205 211 257 282
Indium In-Spec 31 104 139 173 217 201 254Indium
Below-Spec 35 84 110 130 161 190 240
Indium Reflow Profiles
Reflow Procedure
The Pb-free solder paste is pasted on the copper coupons using a 0.25 in diameter stencil aperture.
The first printed copper coupon was subjected to reflow with a Above-Spec profile recipe for both pastes.
The second printed copper coupon was subjected to reflow with an In-Spec profile recipe for both pastes.
The third printed copper coupon was subjected to reflow with a Below-Spec profile recipe for both pastes.
Reflow Procedure
The images of the copper coupons are taken after reflow.
The performance of the solder paste in all the three profiling conditions are analyzed by examining the possible defects using, Magnifying scope X-Ray
The images of the defects are captured and further analyzed.
Defects Analysis
Anticipated Defects
Solder Balling Colder Solder Voiding Blow Holes Non-Wetting De-Wetting Poor Wetting
Pin holes Porous Solder Disturbed Solder Solder Spatter Scratches Oxidation
Solder Balling
Small spheres of solder that remain on the board after reflow soldering adhering to the board.
Solder Balling was seen in Alpha Above-Spec Alpha Below-Spec Indium Above-Spec Indium Below-Spec
Indium Above-SpecIndium Above-Spec Alpha Above-SpecAlpha Above-Spec
Solder Balling
Solder Balling
Solder Balling
Alpha Below SpecAlpha Below Spec Indium Below-SpecIndium Below-Spec
Solder Balling
Solder Balling
Solder Balling
Solder Balling
The possible reasons for Solder Balling could be Preheat temperature too low / high Preheat ramp up rate high Excessive heating rate Solder paste viscosity too low Solder paste oxidation
Cold Solder
A solder joint with poor wetting and a grayish porous appearance is called as Cold Solder.
Cold Solder was seen in Indium Below-Spec
Indium Below-SpecIndium Below-Spec Indium Below-SpecIndium Below-Spec
Cold Solder
Soldered Region Cold SolderCold Solder
Cold Solder
The possible reasons for Cold Solder could be Insufficient heat In adequate cleaning Excessive impurities in solder Poor fluxing action Low cooling rate
Non-Wetting
A condition whereby a surface has contacted molten solder , but the solder has not adhered to all surface leaving the base metal exposed is called as Non-Wetting
Non-Wetting was seen in Indium Above-Spec Alpha Above-Spec
Indium Above-SpecIndium Above-Spec Alpha Above-SpecAlpha Above-Spec
Non-Wetting
Non-Wetting
Non-Wetting
The possible reason for Non-Wetting is Preheat temperature high Reflow Temperature too low Presence of physical barrier between surfaces to be
joined Solder paste oxidation
Dewetting
Dewetting is a condition that results when molten solder coats a surface and then recedes to leave irregularly-shaped mounts of solder and has an appearance of water on greasy surface.
Dewetting was seen in Indium Above-Spec Alpha Above-Spec
Indium Above-SpecIndium Above-Spec Alpha Above-SpecAlpha Above-Spec
Dewetting
Dewetting
Dewetting
The possible reason for Dewetting is Excessive Reflow temperature Excessive heating rate Board contamination
Flux Splatter
Flux Splatter is a condition where we find the flux is splattered around the solder, creating aesthetic issues.
Flux Splatter was seen in Indium Above-Spec Alpha Above-Spec
The possible reason for Flux Splatter is Improper process parameter (Heat / Moisture)
Indium Above-specIndium Above-spec Indium Above-SpecIndium Above-Spec
Flux Spatter
Flux Spatter
Craters
Craters are formed due to the out gassing of various volatile substances and moisture present in the solder paste, creating aesthetic issues.
Craters were seen in Alpha Above-Spec Alpha In-Spec Alpha Below-Spec
The possible reason for Crater formation is Out Gassing of volatile substances and moisture.
Alpha Above-SpecAlpha Above-Spec Alpha In-SpecAlpha In-Spec
Craters
Crater Craters
Alpha Below-SpecAlpha Below-Spec Alpha Below-SpecAlpha Below-Spec
Craters
Crater Crater
Flux Charring
Due to excessive heat, the flux starts charring and gets deposited on to the board and also blackening of the board occurs, creating aesthetic issues.
The Flux Charring is seen in Indium Above-Spec Alpha Above-Spec
The possible reason for Flux Charring is Excessive heat
Alpha Above-SpecAlpha Above-Spec Indium Above-SpecIndium Above-Spec
Flux Charring
Flux charring
Flux charring
Scratches
Scratches are formed on the surface of the solder surface due to poor handling of components during cleaning and other processes, causing aesthetic issues.
Scratches were seen in all the specifications due to poor handling occurred during cleaning.
Uneven Surfaces
Uneven surfaces are formed due to the out gassing of various volatile substances and moisture present in the solder paste, creating aesthetic issues.
Uneven Surfaced were seen in Alpha Above-Spec Alpha In-Spec
The possible reason for Uneven surface formation is Out Gassing of volatile substances and moisture.
Alpha In-SpecAlpha In-Spec Alpha Above-SpecAlpha Above-Spec
Uneven Surfaces
Oxidation
Oxidation of solder occurs due to the excessive heat in the oven, which is seen outside as a blackened surface causing aesthetic issues.
Oxidation is seen in Indium Above-Spec Indium In-Spec
Indium Above-SpecIndium Above-Spec Indium In-specIndium In-spec
Oxidation
Por
Comparison of three specification
In-Spec Below-SpecAbove-Spec
While comparing the three profiles, The In-Spec solder is too shiny than the other two profiles.