Halogen-Free Electronics 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.

The IPC J-STD-004 committee met at APEX last month. They are planning on releasing an updated specification. One positive change that is being made is that titration is being eliminated as an acceptable method for quantitative halide analysis. That means that ion chromatography is the only acceptable test method for quantitative halide analysis per J-STD-004. You can find this test method on the IPC website at: Ion Chromatography Test Method 2.3.28.1

The J-STD-004 requires that a flux be less than 500 ppm of total halide (Cl+Br+Fl+I) to be classified as L0 (which is often used synonomously with halide-free). The challenge is that only ionic halides are detected with ion chromotography. As I have stressed before, L0 or halide-free per J-STD-004 is not necessarily halogen free.

The committee agreed to include a note in this revision of J-STD-004 that this test method should not be used to test for total halogen content. Although I would have preferred replacing the current test method with the oxygen bomb combustion & IC method for detection of halogens, I feel this is a step in the right direction.

We are getting closer to the goal of everyone undertanding what “halogen-free” really means! Baby steps!

When testing a solder paste or flux for halogen content, it is still up for debate as to whether or not the sample should be reflowed prior to testing. Those looking to assemble halogen-free electronics are interested in what remains on the board. Therefore, it makes sense to test the residue for halogen content.

Unfortunately, reflowing the material does make the testing more difficult. The reflow profile used could impact the halogen content. Leaving this open for interpretation may allow for the use of an unrealistic profile to make the halogen content of a material appear better or worse. Also, the process of scraping up the residue to prepare for testing allows for contamination.

Indium Corporation would prefer to see a standard developed to be able to perform a halogen test on the raw flux rather than residue. However, this would require some correlation between the raw flux and what would actually appear in the residue. The adjacent figure shows testing of a flux before and after reflow. As expected, after reflow the halogen content appears higher because all of the solvents in the flux have volatilized. In the coming weeks, we will try to correlate the before and after reflow halogen values to the volatility of the flux (through TGA analysis). If a correlation exists, then we will test it on other materials to attempt to validate this correlation.

I was at the IPC APEX convention last week and attended the IPC J709 Halogen-Free Electronics Task Group meeting on Monday March 31st. There were well over 100 people attending this meeting. That is almost an order of magnitude more than what I typically see at an IPC Task Group meeting (just another confirmation that this halogen-free thing is the real deal). The two biggest challenges facing the group are (1) how to define “halogen-free” and (2) what are the maximum acceptable limits of those halogens.

Does halogen-free include all of the halogens or just Cl and Br? Should it just include CFR’s (chlorinated flame retardants), BFR’s (brominated flame retardants), and PVC (polyvinyl chloride) because these are the compounds being targeted by environmental organizations? Are the 900ppm Br, 900ppm Cl, and 1500 ppm total limits that are established for PCB’s suitable for all electronics parts and materials? These are some of the questions that the large group discussed (and often disagreed on) as the group looks to create a clear message for the industry.

In the end, the most notable accomplishment was the agreement to develop a tiered approach to defining and testing for halogens. Initially, there will probably be four groups (or classes) of halogen-free which will become increasingly more accurate and difficult to comply with. The fundamental approach is something like this:

Class 1 (easiest): Restriction of PVC, BFR, and CFR using the already established 900/900/1500 limits.
Class 2: Restriction of elemental Br and Cl using the already established 900/900/1500 limits. However, there will be an exempted list of materials.
Class 3: Same as Class 2 without any exemptions.
Class 4: Restriction of all halogens (Br, Cl, Fl, I) using a maximum of “none detected” as defined by equipment capabilities

Of course, this is all subject to change based on the input of the group!

Folks,

In my blog posting of December 1, 2005, I asked PC Magazine’s “Cranky Geek” John Dvorak about his knowledge of RoHS. He admitted to being unaware at that time. Well PC Magazine has now gone “green” and is knowledgeable not only on RoHS, but also other green metrics, such as recycling, and carbon footprints. Their April 2008 issue is labeled The Green Issue. The most shocking statistic from the issue: All of the obsolete computers in the US would make a 22 story mountain that would cover the entire 472 square miles of greater Los Angeles. Yikes! WEEE, RoHS and Green are here to stay.

Interest in halogen free solders and assembly continues to grow, even in spite of the controversy of whether or not it is a valid green issue for solder. Many of us think that halogen free will be the topic of this year in electronic assembly materials. Due to this interest Tim Jensen of Indium is starting a Halogen Free Blog.

The image above is from the January 2008 edition of National Geographic….as I said, the need for recycling is now mainstream.

Cheers,

Dr. Ron

There is a significant push in the electronics industry to produce “halogen-free” products in order to be more environmentally friendly. The industry has begun to adopt the definition of halogen-free as less than 900ppm of Cl (Chlorine) and less then 900ppm of Br (Bromine). If a product contains both Br and Cl, then it must have less than 1500ppm total. In the world of solder pastes and fluxes, the term “halide-free” is typically used. The question has arisen as to whether halogen-free and halide-free are synonymous and what is the difference between a halogen and a halide. I will try to explain using as little chemistry as possible.

The term halogen refers to any element in the Group 17 of the periodic table (see www.webelements.com). The elements in this group include Cl, Br, Fl (Fluorine), I (iodine), and At (Astatine). Therefore, halogen-free should technically mean “does not contain any F, Cl, Br, I, or At.” Easy enough so far, but things will get a bit more cloudy as we move to the term halide. Using my trusty dictionary (which is actually www.dictionary.com), a halide is defined as any compound containing a halogen. For example, table salt (NaCl) is a halide. What has happened in the electronics industry is that the use of the term halides is actually referring to “halide ions.” A halide in the ionic form, such as Br- or Cl-, reacts with metals in the presence of moisture to cause corrosion and dendritic growth. In terms of electrical reliability, the use of ionic halides in a no-clean flux creates a greater long-term reliability risk.

The differentiation between halogen-free and halide-free has created some confusion in the industry. If you are truly looking to eliminate all Br and Cl, then you cannot only eliminate the ionic halides. Buying a solder paste that is “halide-free by titration” or “halide-free by ion chromatography” confirms that there are no ionic halides in the material, but may not be completely free of all Cl, Br, and the other halogens. If you want a truly halogen-free solder paste or flux, be sure your supplier runs an oxygen bomb combustion followed by ion chromatography on that material. This method is effective at identifying the total halogen content of a flux.