Pb-Free 8/9/ Reliability of Pb-free Solder Alloy Study NEPP FY02 Harry Shaw at NASA-GSFC Jong Kadesch at Orbital Science Corp./GSFC

Pb-Free 8/9/ Objectives Identify a candidate of Pb-free alloys based on a literature search Validate Hand-soldering assembly process: soldering process, usage of flux, selection of soldering guns temp. Compare the solder joints between Sn/Pb solder vs. Pb-free solder alloys: optical solder joint comparison after cross- section.

Pb-Free 8/9/ Schedule and Cost Q1-FY02$10,000 –Identifying Pb-free candidates –Procurement of test boards, components, solder alloy Q2-FY02 $10,000 –Board assembly Q3-FY02 $10,000 –Visual and X-ray inspection –Cross-section analysis Q4-FY02 $10,000 –Final report

Pb-Free 8/9/ Pb-free Alloy Evaluated by the Organization Sn96.5/Ag3.5 GSFC Selection for Hand-Soldering

Pb-Free 8/9/ Core Wire Solid Wire No Clean Flux Water Soluble Flux Rosin Base Flux

Pb-Free 8/9/ Cost Comparison Note: cost generally driven by the metal market, not by Pb-free solder alloy demand

Pb-Free 8/9/ Sn/Pb –cost: relatively low –rosin base flux –easily available –lead time: within 2-3 days –core wire available Sn/Ag –2.2 to 2.7 times higher* –rosin base flux (2%) –easily available – days –core wire available Solder Alloy Comparison * [source from Kester]

Pb-Free 8/9/ Flux Type No Clean Convenient Corrosion problems in room temp. Rosin Base –RA –RMA Reliable solder joints if cleaned well. CFC cleaning solvent phase- out. Corrosion problem in high temp exposure if not cleaned well. Water Soluble No solvent needed for cleaning. Additional time required for bake out

Pb-Free 8/9/ Test Boards Used existing board design - High Voltage Power (HVP) Board requires two component types Dimensions: 4” x 5.5” Board surface finish –Eutectic Sn/Pb –Electroless Ni/Immersion Gold (ENIG)

Pb-Free 8/9/ Component Finish (as available) Diodes (SGB10UFSMS) –Pb/In finish (not available in Pb-free alloys) Capacitors (1515) –Pt/Ag finish Predicted failure* –1206 chip resistors: 2P mean life is 2014 cycles from -55C to 160 C –0805 chip resistors: 2P mean life is 4725 cycles from -55C to 160 C –1515 chip capacitors: no data available *Data from NCMS

Pb-Free 8/9/ Component Mounting Matrix Additional two (2) boards are sent to JPL for their evaluation using reflow soldering technique. Current Work Future Work

Pb-Free 8/9/ Hand Soldering Process Use MetCal soldering gun 600 series: soldering iron temperature at 350 °C –the actual temperature at the board is less than 350 °C and the exact temperature is not measurable. It is therefore, critical to control the time of heat exposure to the components Observations: –Sn/Pb soldering process is easier and quicker than Sn/Ag –Sn/Pb has well established core solder wire and various diameters It is always not the case for Pb-free solder alloys –wetting of Sn/Ag is more difficult than Sn/Pb, flux definitely required to improve the wetting –longer time to work on the components with Sn/Ag

Pb-Free 8/9/ Inspection Visual inspection using optical microscope –solder appearance: color or brightness/dullness, graininess –wetting appearance: shape of solder –burning or melting of components X-ray inspection –voids Cross-section inspection –voids –intermetallic formation

Pb-Free 8/9/ Visual Inspection of Solder Joints no difference in coloration between Sn/Pb and Sn/Ag most Sn/Pb solder joints are shiny, some Sn/Ag solder joints are shiny and some are appear to be dull smooth surface of Sn/Pb versus rough surface of Sn/Ag more irregular shape of solder joints in Sn/Ag solder, perhaps due to difficulty in wetting

Pb-Free 8/9/ Sn/Pb Solder Joints

Pb-Free 8/9/ Sn/Pb vs. Sn/Ag Sn/Pb Sn/Ag

Pb-Free 8/9/ Sn/Ag Solder Joints

Pb-Free 8/9/ Sn/Ag Solder Joints

Pb-Free 8/9/ X-ray Inspection No voids detected in solder joints both Sn/Pb & Sn/Ag Some solder joints shows poor workmanship –missing solder on one termination of the capacitor (02A1- C14) –spot solder on one termination of the capacitor (04A1-Cxx) Insufficient solder fillet due to poor pad design of the board –poor placement of the component (03A1-C12, & 04A1-Cxxx)

Pb-Free 8/9/ X-ray Images of Missing Solder 02A1-C14 04A1-Cxx

Pb-Free 8/9/ X-ray Images of Poor Placement 04A1-Cxxx 03A1-C12

Pb-Free 8/9/ Cross-section of Sn/Pb

Pb-Free 8/9/ Sn/Pb

Pb-Free 8/9/ Cross-section of Sn/Ag

Pb-Free 8/9/ Sn/Ag

Pb-Free 8/9/ Conclusions Sn/Ag has marginal wetting –Sn/Ag requires flux to improve wetting –Sn/Ag may require longer process time (x2) Sn/Ag solder joints appears to be somewhat different than Sn/Pb solder joints –Sn/Ag appear to be less shinier due to grainy surface Over all, the same soldering process for Sn/Pb can be adopted for Sn/Ag without major difficulties.