What Causes Solder Icicles During Wave Soldering

Phil
Welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting, the Assembly Brothers. Today we are coming to you from the through-hole soldering laboratory at ITM.

We are here high atop Mount Rialto. We are here to talk about electronic assembly, materials, equipment, components, practices and procedures, among other things.

As a matter of fact, I think we are in the right place for once, which is unusual for Jim and myself. We actually have a wave soldering question today Jim. The question is from R.J.

He is asking why are we getting solder icicles on some leads when we run boards in our wave solder machine? Where should be look first to change our process?

As I get close to standing astride my soap box, I guess the first thing is let's answer the question with regard to process. Certainly the first thing that comes to my mind is lead protrusion.

That might be a variable you have there. In some cases you may be exceeding what may be the ideal lead protrusion considering the immersion through the wave.

Then there are other questions in terms of your pot temperature, which would certainly lead to icicles.

Jim
If your pot was too cool. The solder is too viscous and it can't fall off as it comes out of the wave.

Phil
And you would probably see more bridging that way too. Right Jim?

Jim
Either one, the solder doesn't flow properly. It can bridge, or it can stick to the leads and cause an icicle.

Phil
Possibly fluxing too. If you are getting it really through the holes and everything.

Jim
Right. You are counting on some flux being still present on the surfaces to help the solder flow and fall off of the leads, and once again bridges is another similar problem.

It could be not enough flux, or you overheated the flux during pre-heat and burned it off, so there is none left when you come out of the wave and icicles are forming.

Phil
And you know Jim, this is something that you and I have talked quite a bit about. Wave soldering is almost considered an ancient technology as opposed to the process.

Jim
This is like wave soldering 001, very basic stuff.

Phil
Right, but I certainly don't blame R.J. A lot of the old-timers are gone now and to some it is a new technology, even though wave soldering has been around for at least seventy years now.

Jim
That is older than you are Phil.

Phil
You are right it is. That is scary, talk about fossil technology. It is interesting, there is just this void of engineers that have experience in wave soldering.

A couple of us old fossils kicking around. It is kind of like new technology to a lot of people, including R.J. here. Everything old is new again and this is the epitome of it.

But anyway R.J., we hope that we gave you and some other people some guidance. Good luck.

Jim
Yes, understand that wave soldering is a highly inter-related process with fluxing, heat and molten solder. There are lot of things that can go wrong and you really need to understand this.

So if you are new to a machine because the expertise is gone search out some text books and articles and so forth, or someone who really knows the process to get some of these fundamental down. Make your life a lot easier.

Phil
Well good, thank you for listening to Board Talk with Phil and Jim. Again nine out of ten Board Talk listeners are current, the other one just impedes. Whether you are current or impeding, whatever you do...

Jim
Don't solder like my brother.

Phil
No, don't solder like my brother.

All hints so far are very helpful. You can also check if the solder pump is not impeded by dross and working fine driving enough solder flow. This wave soldering process is very old, but some of the materials like lead-free solder and fluxes are new and create some challanges.

Boy you guys are old. Check the flux, be careful of low solid content flux, it may burn off as stated and also check the conveyor speed and the conveyor angle to verify the solder is peeling off the bottom side as the leads are existing the wave. As mentioned check the solder alloy to verify it meets the solder alloy requirements and is not contaminated. A viscosity change in the molten solder will create icicles. Good luck from an old timer.

Thanks Jim and Phil for your comment regarding the Icicles. I agreed and suspect about the high temperature of FLux during the pre-heat but not sure what should be ideal temperature or at least the possible range.

Another potential cause is copper dissolution in the solder alloy. Have your solder supplier test for Cu content. If it above 1,000 PPM, low or no copper bar solder additions can help.

Let's also consider heatsinking in the mix. If the leads are trying to be soldered to a large copper plane or if the components are larger, higher mass parts then look to your pre-heat settings as a possible solution. R.J. mentioned that not all the leads are icicling which would warrant a check of the thermal mass of the leads that are.

Surface mount is great but through hole isn't dead yet! So many boards still have through hole components so wave soldering is still necessary. The two are complementary.

The wave soldering patent was issued in 1958 to Electrovert. The technology is "only" 60 years old.

Most probably cold solder issue. Check temperature in pot. Are you seeing excessive bridging as well?

Another question to ask is if this suddenly occurred to an otherwise defect free assembly or problems right from the start. If it was fine before look for a change in process.

It it's a new product that is causing you grief look to design such as lead protrusion.