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April 26, 2018

Copper Dissolution Rate

Does anyone have data on the rate of copperdissolution in solder? Have any studies been done on time/temperature and amountof copper. It's easy to claim that SnPb dissolves Cu but everybody has adifferent opinion on the rate and amount.

B.W.

Expert Panel Responses

You'reright... everyone seems to have a different number for the rate. This is becausethe test methods used vary so widely. There are multiple factors that affectthe dissolution rate:
  • The solder alloy (we'll ignore this here since we are talkingspecifically about SnPb)
  • The solder temperature
  • The solder contamination levels (how much copper is alreadydissolved?)
  • The solder flow, including flow velocity and turbulence
  • The copper foil type (microstructure of the copper has ameasureable effect)
Severaldifferent test methods have been presented in the past decade, includingsurface trace dissolution, wire dissolution, and pad dissolution. All areworkable, though they may lead to systematic differences in results. As anexample, Hunt, et. Al (APEX 2009) reported a figure of 1.2um/s (0.047 mils/s)for SnPb solder at 255C, whereas my work with Denis Jean and Dale Lee reportedat SMTAI 2006 found a rate of 0.89um/s (0.035 mils/s) for a temperature of250C. Both rates were determined using foil dissolution from a PWB coupon,ours using a trace, and Hunt's using a pad. The rate differences found weremost likely due mostly to flow, but also may have been influenced by foil type.

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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

The High Density Packaging Users Group(HDPug) has just completed a copperdissolution study. The final report is still being written but all data iscollected. Potentially some of this data may be available to the industry.

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Jack Fisher
Chairman of the IPC Technology Roadmap Committee
Interconnect. Technology Analysis Inc.
Jack Fisher is a retired IBM executive, chairman of the roadmap since 1994, and member of IPC Hall of Fame.

The testing is done by dipping a metal cylinder into an infiniteamount of solder bath (no significant composition change). The radius reductionrate is used to indicate the dissolution of various elements in the solderbath. In real reflow process, the interfacial IMC growth and the solder jointcomposition variation due to surface material leaching may lead to a differentbehavior.

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Kay Parker
Technical Support Engineer
Indium Corporation
Kay Parker is a Technical Support Engineer based at Indium Corporation's headquarters in Clinton, N.Y. In this role she provides guidance and recommendations to customers related to process steps, equipment, techniques, and materials. She is also responsible for servicing the company's existing accounts and retaining new business.

Greatquestion on the dissolution rate: I've listed a few places where information isavailable for you to research.Therate of dissolution is based upon a variety of parameters of which, is theLead-Free alloy used, the temperature of the wave and the type of copper beingdissolved be it either copper foil or electroplated copper for the platedthrough holes and such. See more info at:

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

There are many factorswhich effect the rate of Cu dissolution such as solder flow rate, alloy type,copper type and of course soldering temperature and contact or dwelltime. As stated it was known that SnPb did dissolve copper, although at alow rate, and with the introduction of SAC alloys to address RoHS it was foundthese alloys had a much higher rate of copper dissolution than SnPb. There has been several studies performed on copper dissolution especially inrework mini-wave applications. Hamilton and Snugovsky of Celestica andKelly of IBM published a paper titled "A Study of Copper DissolutionDuring Lead Free PTH Rework Using a Thermally Massive Test Vehicle", SMTAi 2006which shows the comparison between copper dissolution rates of SnPb,approximately 0.007mils/sec and SAC, approximately 0.035mils/sec forrework process soldering temperatures. It was also found for lead-freealloys, the SnCu nickel modified alloy, SN100C has a copper dissolution ratesimilar to SnPb. The paper can be found on the SMTA website,www.smta.org.

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Mike Scimeca
President
FCT Assembly
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.