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Question about leaded parts used in leadfree soldering process

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#40871

Question about leaded parts used in leadfree soldering process | 7 April, 2006

Hi, i tried to search but am hving trouble finding discussions on leaded parts being used in leadfree soldering process. So, i need some inputs from expert members here.

Will it work if a component plated with SnPb will be used in a lead free soldering process?

thank you!!

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#40880

Question about leaded parts used in leadfree soldering process | 7 April, 2006

Technically speaking, most likely yes it will work, unless possibly it is a BGA. There are issues surrounding BGA's. Here are some of the general issues: On any type of component, if the Pbfree solder you are using contains bismuth, then the Pb in the component termination plating could possibly cause low melting point tertiary alloy intermetallics with the bismuth which will be weak. For BGA's, a SnPb solder ball should melt and mix completely by the time the higher temperature Pbfree paste melts, so there shouldn't be incomplete mixing of the alloys. However, some people claim there will be much greater voiding in the balls, possibly due to them being heated higher and longer than they normally would need to be? I know you didn't ask about this, but the opposite situation for BGA's also has issues. If a Pbfree BGA is used with SnPb solder, the BGA ball will tend not to melt completely or thoroughly mix with the SnPb paste, causing zones of different intermetallics which will significantly weaken the long term reliability of the joint. It may look good and act good right off the line, but if it goes through any temperature cycling in its life it will tend to fail much earlier. Technical issues aside, unless you can claim a Pb exemption for the product you are considering this for, your product will no longer meet RoHS, if you do this.

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#40882

Question about leaded parts used in leadfree soldering process | 7 April, 2006

Is it safe to assume that you're only talking about SMT reflow here?

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#40883

Question about leaded parts used in leadfree soldering process | 7 April, 2006

Yes, sorry, I have no detailed experience with wave-soldering.

Probably if you use Pb components with Pbfree wave, you risk contaminating your wave solder pot. I don't know how much it would take or what all the dangers of that are, other than the still valid - non-compliance with RoHS. Which could then be transferred to other products, as well.

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#40951

Question about leaded parts used in leadfree soldering process | 13 April, 2006

Thank you! sorry, i just realized my posted question was not very specific.. no, it's not a BGA part, it's just a standard surface mount device and the only leaded part are the leads.

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#40952

Question about leaded parts used in leadfree soldering process | 13 April, 2006

yep, only SMT reflow.

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RDR

#40959

Question about leaded parts used in leadfree soldering process | 13 April, 2006

If your part will withstand the higher pbfree reflow temp you should be fine. We have done this on limited basis in pbfree transistion with no reported reliability issues.

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#40978

Question about leaded parts used in leadfree soldering process | 14 April, 2006

Hi russ, I am in the process of developing a "hybrid" reflow profile to solder a board that has LF BGAs and leaded solder. Have you encountered a similar situation before? if so what was the "safe" top side temp for the leaded components that was set in your profile?. I am aiming for a joint temp of little over 220 deg C for about 45-60 sec.

any pointers?

Thanks in advance

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#41107

Question about leaded parts used in leadfree soldering process | 20 April, 2006

thanks! yes, the package has been qualified using 260deg max pk temp for the reflow at precon

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#41109

Question about leaded parts used in leadfree soldering process | 20 April, 2006

Amol,

I thought I answered your question in another thread, dude! Anyway, to re-iterate. Yes, I was able to pull it off a hybrid profile. The LF BGA passed tensile testing, but no, it wasn't thermally cycled or stressed first to expose any latent IMC formation.

I achieved around a 230*C peak temperature on my BGA Ball, but suffered too high of a peak on a smaller component, namely a 0805 chip component. The joint on that component looked slightly charred and "de-wetted" up the component termination. And again, I used a "transitional" Leaded paste that has a similar flux to LF paste.

Raquel, you should do fine with a (non-BGA) Sn/Pb part in a Pb-Free paste. That's practically a no-brainer especially if your end product does not have to be 100% ROHS compliant. The Sn/Pb plating comprises a negligible part of the overall joint, so yes, as Amol says, just make sure you're over your LF Paste's eutectic point for sufficient time.

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#41112

Question about leaded parts used in leadfree soldering process | 21 April, 2006

yes! i though this thread looked familiar! looks like it has been repeated....even the response from muse is very very familiar...that, or i am have a serious attack of deja vu!

thanks for the requote though.......by doing some research I decided to go with a peak of 220 degrees with a TAL (above 217) of 30 sec. i have yet to run the profile to measure, but theoritically it should work.(the MP of SAC solder changes anywhere from 213 to 220 dec C depending on the ratio of SAC solder ball volume and SnPb solder volume)

Amol

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