Halogen-Free Assembly Blog

By Tim Jensen

On July 16th and 17th, the IPC has organized a 2-day event in Boston to discuss the challenges with environmentally friendly electronics assembly. A significant portion of this event will revolve around halogen-free. This is a follow up from a similar meeting held in Arizona in January. That January meeting had over 200 attendees and the IPC had to turn down people at the door who wanted to attend. It was an awesome event with tons of useful information. Looking at the list of presenters, I suspect the one in Boston will be just as good.

You can check out the details at IPC Boston Meeting. I will be taking part in a panel discussion on the second day in which I will provide Indium Corporation’s perspective on what halogen-free means for solder pastes and fluxes.

I will see you there as we save the environment on chloride ion at a time!

No vulgarity here, but there is a lot of questions in the electronics industry as to whether the term “halogen-free should include Fluorine (F). Most activity only references chlorine (Cl) and bromine (Br) as being restricted. As the adjacent cartoon notes, there are conditions in which fluorine can be dangerous (despite the fact that we put it in our toothpaste and drinking water).

So, why not add fluorine to the electronics definition of “halogen-free?” The main reason is that the environmental organizations such as Greenpeace are only targeting Cl and Br. Therefore, the electronics giants are simply making it easier for themselves. Why restrict an item that is not likely to give them bad press? It would be tough to argue that Fluorine is more enviromenmentally safe than the other halogens.

The concern with excluding fluorine from the halogen-free specification is that it is possible to use this as a substitute activator (rather than Cl or Br). F may make the flux more prone to corrosion and SIR issues.

I say add fluorine and make it more complete but that’s just my two cents!

One of the primary concerns with halogen-free solder pastes and fluxes revolves around the wetting and coalescence. The reason that halogens (usually in the form of covalently bonded halides) are used in the flux is because they are very effective at oxide removal. The halogen-free alternatives just aren’t as efficient.

So, what is head-in-pillow and what is the correlation to halogen-free? Head-in-pillow is an assembly defect in which the bumps from a BGA or CSP don’t coalesce with the solder paste on the PCB pad. The root cause of this defect is typically from component warpage. However, there is experimental evidence that suggests that solder pastes with better activity (ability to remove oxides) are less prone to this defect. There is the link to halogen-free. If a halogen-free solder paste is not as effective at oxide removal, there is a potential for an increased occurance of this head-in-pillow defect.