Lead free Solder Paste troubles !!!!

We're just getting started in lead free, but the solder balling and poor wetting sounds like what we saw in some early experiments where we were investigating whether we needed nitrogen. Without nitrogen inerting we got just the kind of things you've described. Other factors played into it, but lack of nitrogen was the big driver.

Take this with a grain of salt though - we aren't in production yet.

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EMS-Engineer,

Lead free alloys have a very low wetting creep. You probably will not ever get the same type of weting with a LF as opposed to SN 63/37. The question is if it is acceptable. Lead free solder joints cannot be inspected to the same criteria as leaded joints. They will be dull and grainy and have little to no spread. There is no official document like IPC-610 for lead free (yet) but everything you are experiencing is what I've been told would happen.

I believe that Kester and some of the other major manufacturers should have information that may help on thier web page.

Good Luck

Chris

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Pb free pastes do not wet out like 63/37. Their are no claims from any manufacturers that I am aware of that say it will. Your "little solder balls" are likely caused from oxidization during reflow. What type paste are you using 3,4,5? What are the other temps and durations in reflow? You may want to try Alpha OM338 paste. I have used Indium and others and I find it odd that you say it is "stiff" The Indium and other manufacturers I have used is very "thin". Are you sure that you have good paste? It seems like it is garbage. No-Cleans tend to release and print much better than W.S. pastes from my experiences. We have never experienced the need for nitrogen atmosphere using lead free.

Russ

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The LF pastes will have virtually NO wetting spread. This is normal. LF mobilities are virtually non-existant with SAC alloys. However, the addition of varrying amounts of silver can (and does) improve mobility but, this comes with a price (paste price increases and Silver related platelette formations which affects reliability).

Paste release is a function of your paste, stencil aperature design rules and your stencil material.

Solder balls may be an indication you need an extended drying period in your profile and/or reduced ramping rate.

As you're finding out LF is not a drop-in solution. Nitrogen is an excellent way to hide your real problems and drive up your manufacturing costs (all at the same time). Is your product consumer, Hi-REL, aerospace, what?

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Your problem is easy. Lead free solder is like 63/37 solder paste when it was started. We make things complicated. We believed before that lead free has high melting temp and will not produce good fellet so on....

The only thing you must do is to look for solder paste manufacturer which can provide minimal cost at a low melting point. No nitrogen needed, no expensive reflow oven or even your old reflow oven can be use. I suggest you ask the supplier of solder paste. If you can not find the right supplier, please feel free to come back to me and I will show you.

Arman

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Hi all ! I have a very simple ( maybe stupid ) question : Can we mix the lead-free components with 'Pb components' ? I mean, some component would lead-free, but it is only 5% of the whole. Will I have problems on wave and on reflow ?

Thanks for help. I am a beginner in this issue... habba

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Well Thanks for all the good advise. Lots of different opinions on this one. I took the advise to contact my current supplier of solder paste. They sent in one of their tech people along with a sales guy and we ran without much trouble. Other than a slight increase in the soak zone and a recommendation to get rid of the standard reductions on my stencil, except for homeplates on 1206 and 805 parts, we were golden. Boards came out pretty well all things considered. I guess next time I have a problem I will call my supplier first. Kudos to aim solder for their help.

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