High Temperature Reflow Soldering

Phil
Welcome to Board Talk. This is Jim Hall and Phil Zarro, the Assembly Brothers, also known as ITM Consulting, and we're here to attempt to answer your process and SMT-related questions. Let's see, what do we have today, a reflow question.

Jim
Phil, this one is very interesting. "You mentioned that vapor-phase soldering uses temperatures of 235 to 240 C for lead-free soldering. We use a 0.8 millimeter RoHS BGA that states, it is recommended to apply a soldering temperature higher than 250 C.

Could we use vapor-phase system for this part? Do you have any idea why the part recommends temperatures higher than 250?"

The answer is, “No!”

I don't know anybody who makes a vapor-phase fluid higher than 250 C, and I have no idea why a component manufacturer would specify a soldering temperature of over 250 C.

I don't know of any solder ball alloy that requires 250 C to collapse.

Phil
I'm surprised the component manufacturer would want to subject their component to such sustained temperature. Unless they want to sell you a lot of components.

Jim
The answer to the question is get back to this component manufacturer, and if you can find intelligent life there, which is the first challenge, and we'll give you points for that – you can ask them why. Low silver alloys melt at 227 C. So, maybe you want to take them up to 240 C.

What about the package? If you warp the package and create a bunch of head and pillow, is the vendor going to cover for you and help you out? I would really look at that part, talk to the people who are making it and be sure that that's what's required, because most of the other things on the board aren't going to allow you to go to that temperature - even if you had a vapor-phase fluid. What else on the board wants to go up to that temperature?

Phil
I have to say, this is not the first time Jim and I have encountered application notes from component manufactures that were way out in space somewhere. So, you're very right to question this. Trying to find intelligent life among those component people - lots of luck.

Phil
Thanks for asking the question, it's a good question. Beyond that, whether using vapor-phase or convection reflow or even a laser, don't solder like my brother.

Jim
And don't solder like my brother.

You guys are quite a duo. The peak temperatures being seen by many smaller parts on complex cards are in the order of 250-260 deg C when lead free alloys are being used and convection is the process of choice. The component manufacturers are probably happy with it, but as an industry we live with it because the predominant convection reflow technology cannot isolate the thermal characteristics of the process and keep the lower mass parts cooler - so they ramp faster and to a higher peak.

260c is an off the shelf VP fluid. But the more important point is that like all Vapor Phase Fluids - this is a MAX, not a desired point of process heating being terminated. Show me that in a convection oven.

Gentlemen, when it comes to vapor phase, Solvay Solexis offers the Galden HS260 with a boiling point/vapor temp of 260 C. This fluid is used regularly for circuit boards in the oil exploration down hole industry as well as several others.