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The electronics industry continues to strive to provide more environmentally friendly products. This movement is partly due to legislation from various countries, partly due to public outcry from well publicized Third World recycling practices, and partly due to non-government organizations (NGOs) testing and publishing information on electronic devices regarding their content of various toxic materials. One set of materials targeted for reduction and eventual elimination are halogenated compounds. Halogens are found in plastics for cables and housings, board laminate materials, components,and soldering fluxes. Challenge 1: Defining halogen free
In its simplest defi nition, halogen free means does not contain any of the elements in Group 7 (17) of the periodic table (figure 3). Those elements are chlorine (Cl), bromine (Br), fluorine (F), iodine (I), and astatine (At). Relative to the electronics industry, the primary halogens used are Cl and Br. Fluorine is occasionally used in fluxes for soldering, but is currently not receiving much attention. Therefore, the electronics definition of halogen free is typically defined asCl and Br free. 
The differences in the standards (table 1) are the source of much of the confusion on what halogen free actually means. The IPC is developing the J-STD-709 which is designed to better provide guidance on low halogen electronics. As of December 2008, the J-STD-709 specification is still not complete. There is interest in changing the 900 ppm limits up to 1000 ppm to mesh with the RoHS legislation. It will also likely only focus of Br and Cl from flame retardants and PVC. However, once Br or Cl is identified, it is very difficult to say with any certainty where that halogen is coming from. Therefore, electronics companies will likelyrestrict halogens from all sources making their life easier. 
Challenge 2: Halogen free PCBs
Brominated flame retardants have been commonly used in the fabrication of printed circuit boards. There are now some halogen free alternatives that are readily available on the market today. There is still a great deal of concern as to how these materials will affect the assembly process and since halogen free still represents less than 10 percent of the laminate market, the industry still lacks production experience to defi ne process and reliability windows. Prices of the halogen free PCBs are higher than that of their halogenated counterparts. A great deal of this cost difference is just economies of scale. However, there is also a key challenge that PCB fabricators face. Halogen free materials tend to be more rigid. The drilling process of PCB fabrication suffers from this physical property. It is estimated that the drill life could be compromised by as much as 25 percent. This is by no means insignificant and will likely mean the halogen free PCBs will always cost more to manufacture. That cost will probably be reflected in selling prices to the PCB assembler. The good news is that many of the halogen free board properties that are of concern to the assembler are as good as or better than comparable halogenated boards. By comparing data sheets from a number of suppliers, it is easy to see that the halogen free boards generally have lower CTE. They have longer T-260 and T-288 times and a higher Td temperature. These all mean that the board will be better suited for multiple reflow processes and will be able to withstand higher reflow temperatures. From a reliability perspective, there is a significant amount of differing information relative to CAF resistance. A CAF (conductive anode filament) is an electrochemical failure in which a filament grows between inner layers of the PCB. This usually happens when some type of inner layer delamination occur allowing space for the filament to grow. This delamination is a result of the CTE mismatch between the epoxy resin and glass fibers. Work done by Nan Ya suggests that the halogen free boards exhibit a greater resistance to CAF formation. Another study performed by CALCE shows that halogen free boards aremore prone to CAF formation. This conflicting data should be very concerning for anyone producing high reliabilityassemblies. As more independent work becomes available,it will become clearer as to whether CAF formation is asignificant concern or not. Challenge 3: Halogen free vs. halide free fluxes
By definition, a halide is any compound containing a halogen. Table salt (NaCl), for example, is a halide. By this defi nition, halide free would mean a product does not contain any halogenated compounds. However, that is not exactly how the term is used for soldering fluxes. A flux that is classified as halide free by the IPC/J-STD-004 is actually only free of ionic halides. Classifying fluxes based on their halide content is not a new concept. IPC, as well as other standard bodies such as IEC and JIS, has classified electronic soldering fluxes for decades to determine their potential corrosiveness if left unclean on an electronics assembly. The classification method categorizes fluxes as L, M, or H based on their level of corrosiveness. In addition, the fluxes are rated for halide content as 0 or 1. The difference between these terms is critical because those seeking halogen free electronics should not assume that a halide free flux complies with their halogen free requirements. The test method that the IPC recommends for halide content of fluxes is ion chromatography. The challenge with ion chromatography when used alone is that it only identifies the ionic variant. Covalently bonded halides have bonds that are more difficult to break and are not detected. In addition, there are chemicals that have similar retention times to Cl and Br which can result in non-halides being misidentified as halides. Ion chromatography preceded by oxygen bomb combustion (EN 14582) is a more accurate way of testing for the presence of halogens as all forms are detected, both ionic and covalent species. This test method involves subjecting a sample of material to an oxygen bomb combustion in which the all of the organic material is burnt off at very high temperatures. Halogenated compounds are converted into fluoride, bromide or chloride ions. The remaining ash consists of the halogens and other inorganic materials and is dissolved into an absorption solution. That solution is then run through ion chromatography in which a true reading of the halide content can be determined. All halogen bonds, including any covalently bonded halides are broken through the oxygen bomb process and are detected by ion chromatography. The simplified test method used in IPC J-STD-004 for halide content creates confusion for those attempting to assemble halogen free electronics. It is not sufficient to simply accept terms such as “halide free by ion chromatography” or “L0 per JSTD-004.” To be halogen free, one must requiretesting on the paste or flux to follow the EN14582 test method. It is expected that the J-STD-004 will eventually beupdated to include this more accurate test method. However,the updating process can take a year or more. Challenge 4: Assembly process implications
Without a doubt, the removal of halogens from solder pastes and fluxes will have the greatest potential impact to the board assembly process. Halogens are used in these products to aid in the soldering performance by providing powerful oxide removal capabilities to enhance wetting. Combine that with the fact that the industry is in the middle of a lead free transition in which they are required to use alloys that don’t wet as well as their leaded predecessors. In a solder paste, halogen removal has the potential to negatively impact wetting and coalescence. This will be most evident in applications that require long profiles or those which require very small deposits of solder paste. Because of this, two relatively new defects can become more prevalent. The first is what is called “the graping phenomenon.” Graping is essentially an incomplete coalescence of the solder paste leaving a rough uneven surface as seen in figure 4. 
Graping occurs when oxide forms on the outside of the printed paste deposit and the activators are not able to remove it. The smaller the deposit, the more surface area exposed to oxidation relative to total flux. Therefore, small deposits such as 0201s put a very high demand on the flux activator. Halogen free materials will likely be more prone to graping. The second defect likely to become more common during the halogen free transition is the head-in-pillow defect. Head-in-pillow happens during the reflow process when using a BGA component or PWB that is prone to warping. As the BGA or PWB warps, it creates separation between the ball and the solder paste deposit. At the reflow stage, both the solder paste and the ball go molten, but are not in contact with each other. An oxide layer will build up on the molten solder making it less likely to coalesce togetherwhen they come back into contact with one another during cool down. The resultant open solder joint will look like theillustration shown in figure 5. 
As a result of graping and head-in-pillow solder joints, solder paste manufacturers will have a challenge formulating halogen free solder pastes that perform as well as the current halogen contained materials. Improving the reflow performance isn’t that simple though. As the activator is modified it can adversely affect the print performance, stencil life, and shelf life. Therefore, when evaluating the halogen free materials, it is essential to carefully examine the reflow performance, but don’t skimp on the print portion of the evaluation. Summary
As the industry is moving toward promoting environmentally friendly or “green” electronics, there continues to be a rapid minimization and/or elimination of halogenated compound use. This can have an adverse effect on material costs, product reliability, and process yields. Understanding the halogen-free material properties is key to successfully assembling more environmentallyfriendly electronics. ------------------------------------------------------------------------- ----------------------------------------------------- “Green” trends The enactment of RoHS on July 1, 2006 prohibited the use of two halogenated flame retardants: Polybrominated biphenyls (PBBs) and Polybrominated diphenyl ethers (PBDEs). Although there may be some remaining controversy, it appears there is general agreement that PBBs and PBDEs are environmentally unfriendly. Such compounds tend to bioaccumulate and can be found in humans, animals and the environment. In addition, when products containing these flame retardants are recycled, they place workers at risk. Early in 2008 the OKO institute published and additional list of more than 40 substances to be considered for RoHS inclusion. RoHS was always intended to be a “living” document and hence will be modified with time. This proposed modification has been dubbed by some as RoHS 2. Tetrabromobisphenol A (TBBPA) and Hexabromocyclododecane (HBCD or HBCDD) were included in the above list of 40 or so substances. TBBPA is one of the most important flame retardants for PCBs. HBCDs are used in thermal insulating foams, so they are not of much interest to the electronics industry. Back in mid-December 2008, the EU announced that no new substances will be banned under RoHS at that time. However, tens of thousands of substances will be evaluated under the EU’s REACH law including TBBPA. REACH (Registration, Evaluation, Authorisation and restriction of CHemicals), at 849 pages, is the “largest” law ever enacted by the EU. In comparison RoHS has only six pages. REACH requires that any chemical imported or manufactured by a company in the EU in quantities over one metric ton must be registered. After registration, the companies importing or producing each material must participate in cooperative evaluation of the material to demonstrate its safety. It is expected that this work will take decades to accomplish. However, 16 substances will likely be designated as substances of very high concern (SVHC). These substances will require early evaluation and disclosure in any product where they are used. TBBPA is noton the list, but its flame retardant cousin HBCDD is. Non-government organizations (NGOs) such as Greenpeace will likely have a growing influence on the “Greenness” ofelectronics. Their “Guide to Greener Electronics”, see figure 1 is an example. One of the features of REACH is that individualscan query companies about the substances in their products.Companies must respond in 45 days. Greenpeace, the WorldWildlife Fund and other NGOs are encouraging consumers tomake such queries by publishing form letters on their websitesfor consumers to send in. We believe that the combination ofRoHS, REACH and the NGOs will continue to create interestby electronics companies to be halogen free, in a sense justto avoid any hassles. This is evidenced by outside packagingon a Sony Home Theater receiver in which their halogen freeproclamation is listed as part of their “eco info” as shown infigure 2. 
----------------------------------------------------- References
1. Aghazadeh M.; “Halogen Free…A Global Perspective;” IPC Halogen Free Symposium; Scottsdale, AZ; January 2008
2. Lee FY; “Halogen-Free Materials Manufacturing and Supply Chain Challenges;” IPC Halogen Free Symposium; Scottsdale, AZ; January 2008
3. Sood B; “Comparison of Halogen Free and Halogenated Printed Circuit Board Laminate Materials Subjected to Pb free Soldering Conditions;” IPCIt’s Not Easy Being Green; Boston, MA, July 2008 About the authors
Timothy Jensen can be reached at tjensen@indium.com and Dr Ron Lasky can be reached at rlasky@indium.com Copyright: IPC APEX 2009 | 
