Vapor Phase and Backward Compatibility

Vapor Phase and Backward Compatibility
We use lead-free solder paste with a melting point of 217 degrees C, along with 230 degree C Galden. We have a new project that uses tin-lead solder. The Assembly Brothers, Phil Zarrow and Jim Hall, offer their suggestions.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
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Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.


And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers, coming to you from ITM Consulting. Jim, this is exciting. We have a vapor phase question. Who better to answer this question but Dr. Vapor Phase, Mr. Jim Hall himself?

What is vapor phase, Phil?

Blow the cobwebs from your mind there.

Oh yeah, I used to do that.

Yes, you’re responsible because I have seen your name on some of the patents. Not getting off that easy, old-timer. This is from S.O. S.O. writes, for our surface mount boards, we solder with a vapor phase soldering machine. We usually use lead-free solder paste that has a melting point of 217 degrees C, along with 230 degree C Galden, which is the medium that we use these days. In this case, they are using the Galden LS 230.

We can mention Galden by name because I think they are the only ones that make this stuff these days. We have a new project that wants us to use tin-lead solder. Obviously, he is talking SN 63. This paste has a lower melting point of 183 degrees C. Presumably, we should also change the Galden down to a 200 degrees C Galden LS 200 to suit the tin-lead solder paste. What is the correct approach here? Also, most components these days are tinned with lead-free solder. How does that work out with our tin-lead solder?

Let’s talk about vapor phase and backward compatibility. We actually have covered backward compatibility using lead-free parts in tin-lead solder. Go into the Board Talk crypt and you will find at least one session that addresses that backward compatibility issue. You are certainly right. You want to use a lower temperature fluid if you are going to solder tin-lead.

As I always say, you never want to get the board any hotter than you have to. The only reason you have to get it hot is to promote good wetting. We’re going back thirty-five, forty years ago when I worked in vapor phase. The only game in town was 3M’s SC 70, which boiled at 215 C, which gave us very good soldering. 200 is kind of low for general tin-lead soldering. If you look at the spec sheets of your tin-lead solder paste you will see that most of them have a minimum temperature like 205, 210. You want to check with the manufacturer and do some of your own testing.

Speaking theoretically, we have certainly soldered tin-lead at 200 degrees C on specific applications. The question is are you going to get adequate wetting and adequate flux activation and adequate flux deactivation if you are using a no-clean. You want to check with your manufacturer.

Looking at it from the theoretical side, Dr. Lee of Indium tells us that in ideal conditions you can solder seven or eight degrees above the full liquidous temperature of your alloy. Well as you pointed out, your full liquidous is 183 for tin-lead. So, 200 is above that. I could argue that vapor phase is a pretty ideal soldering situation because there is very uniform heating and it is oxygen free. I think you have a pretty good chance of getting good success with that.

But again, you want to confirm with your solder paste vendor and do some of your testing. On the really positive side, it may be very advantageous to go to 200 degrees for soldering it because you can limit warping of the board and components and minimize head-in-pillow and non-wet open defects. If you look at the literature that is being published on low temperature solders now, a number of published papers talk about keeping reflow below 200 degrees because below those temperatures your warpage of components and PCBs is reduced to the point where you can eliminate or minimize head-in-pillow and non-wet open defects. So, I think there are some positive reasons to go to 200 degrees.

But as Jim emphasized, you have to check with your solder paste manufacturer. Specifically ask what their experience is going to this temperature, or any temperature, using vapor phase. Vapor phase has been around long enough that it has an established base, so they should have that kind of data for you.

All of the major solder manufacturers have very competent, well-trained, experienced people to help you. Any of your issues relating to your solder paste, you should be contacting them and taking advantage of that knowledge which they all will share very enthusiastically with you.

Thanks for your questions S.O. And to all of your out there, you have just wasted some of your apparently not all that valuable time listening to Board Talk with Jim Hall and Phil Zarrow. We thank you. Believe me, whatever you are doing whatever temperature your using, please don’t solder like my brother.

And please don’t solder like my brother.


The discussion completely skips over whether the components on the assembly can all be exposed to the condensation vapor. This needs to be checked thoroughly, as some components may not be able to undergo VPS at any temperature. As far as the dual IMC argument, Ike does have a point. However, component leads finished in SAC305 are very common today, and they have been soldered with Sn63 solder with no issues seen for many years. You are soldering to the SAC solder where it covers the lead, and where it doesn't you are forming a standard IMC between the plated copper and the Sn63 solder. Both are very reliable. This does not include BGAs, however. That is a completely different scenario.
Richard Stadem, General Dynamics Mission Systems
A critical point not discussed is the dual Intermetallic boundary or layer that will be formed in this application. If the components are tinned in Lead-Free (SAC105 or something like that) the tinning will not reflow if the temp is only 200C. This will create solder caps over the tinned ends not homogeneous Intermetalics so the chance for fractures and partials is increased exponentially.
Ike Sedberry, ISEDS
Using the Galden 230 is no issue. I use the 235 in mine. Most machines have multiple depths for the board, the deeper you go the greater the density of the vapor, the greater the heat transfer. The profile would be done with either less time at the deeper setting or not going so deep.

Easily switching between SAC alloy and Sn63. Just adjust your profile/time and depth setting accordingly.
Alan Woodford, NeoTech

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