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does copper wire become thinner when it dip to leadfree solder?

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arnold

#37530

does copper wire become thinner when it dip to leadfree solder? | 2 November, 2005

we are encountering a problem on our production. after dipping a copper wire AWG#30 to a leadfree solder the wire becom thinner and easily to break. does the leadfree soler has the capability to weaken the wire (lessen the diameter)after dipping to leadfree solder?

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#37531

does copper wire become thinner when it dip to leadfree solder? | 2 November, 2005

Hello Arnold, Yes, by definition of joint formation, copper will dissolve in lead free solder in order to form the connecting intermetallic layer. There is a distinct difference in the copper dissolution rates of the major alloys being considered with SAC305 being the fastest in dissolving copper and SN100C being the slowest. Test data is available by contacting me below: Bgilbert@fctassembly.com

One option is to use a high copper content solder alloy such as SN100C4 (contains 4% copper) which further slows the copper dissolution from a wire dramatically. It is recommended for use with magnet wires and for stripping insulation at elevated temperatures (400C).

Regards, Bob Gilbert

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Slaine

#37536

does copper wire become thinner when it dip to leadfree solder? | 2 November, 2005

I thought it was the tin content that leached the copper so presumed 100Sn would be more aggressive?

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KEN

#37575

does copper wire become thinner when it dip to leadfree solder? | 2 November, 2005

Copper wire will become thinner when dipped in tin/lead or lead free solder. The copper is disolved off of the bulk wire. This is one reason rework on solder pots must be restricted. Eventually, after repeated cycles you will have smaller and smaller annular rings (and leads) on your through-hole components. I have seen rework done where the opeator says hey, the solder won't stick to the board. Duh. Where are your pads? Disolved away into the pot after 4-5 attempts are soldering the device.

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#37576

does copper wire become thinner when it dip to leadfree solder? | 2 November, 2005

Slaine, our intuition is the same as yours [that 100Sn should dissolve the copper faster than other solders]. Bob Gilbert's FCT data shows otherwise. Look here: http://www.fctassembly.com/newsltr/2004/0804/Aug04.htm

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arnold

#37584

does copper wire become thinner when it dip to leadfree solder? | 3 November, 2005

davef, how can you convince me that 100Sn dissolved copper much faster?

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#37586

does copper wire become thinner when it dip to leadfree solder? | 3 November, 2005

arnold: I did not say that Sn100 dissolved copper faster. The graph of dissolution rates [from the link above] shows that Sn100 dissolves copper slower than many of the other solders.

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#37589

does copper wire become thinner when it dip to leadfree solder? | 3 November, 2005

Hello Arnold, Just to clarify the Sn100C discussion: Please note that SN100C is the Nihon Superior alloy composed of tin/.7copper/nickel. The key point in regard to SN100C is that Cu does not go directly into solution but first reacts to form an intermetallic layer. The rate of dissolution is then determined by how quickly that intermetallic dissolves and the Ni incorporated in that intermetallic in the SN100C stabilizes it and slows the dissolution rate.

Of course how close you are to saturation at a particular temperature is another factor. One of the factors in the high dissolution rate of SAC305 is that the Cu level is well below saturation. Increasing the Cu content or adjusting the Ag content to move the alloy towards a composition with a lower Cu saturation level does reduce the rate of dissolution a little but it is only when there is Ni present the rate of dissolution is brought to almost zero.

At higher temperatures the effect of the Ni is diminished and that is where the extra Cu in the SN100C3 and C4 plays a role.

Thanks, Bob

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Amol

#37616

does copper wire become thinner when it dip to leadfree solder? | 3 November, 2005

the copper forms intermetallics with tin to get Cu3Sn and Cu6Sn5. thus intermetallics formation consumes Cu and depends upon the cooling rate, faster the cooling rate, lesser the intermetallic formation

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