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PCBD-Apr2015

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16 The PCB Design Magazine • April 2015 organic Solderabilty Preservative (oSP) IPC Specification (NONE) OSPs are organic coatings that form a com- plex organo-metallic complex with the copper surface of the PWB. This complex preserves the solderability of the copper surface through as- sembly. A wide variety of OSPs have evolved with the increasing complexity of the PWB. Initial- ly, all that was required was a single thermal excursion for soldering leads into component holes, Then came surface mount that required at least two thermal excursions (one per side); add on top of that the need to hand solder an occasional rework. The biggest relevant evo- lution is lead-free assembly. LF assembly tem- perature at 260 ° C is approximately 35 ° C higher than eutectic soldering (225 ° C). The manufac- turers of OSP have developed new OSPs to meet the market demands. These have a greater abil- ity to withstand increasing number of thermal excursions and higher temperature, as needed for LF. OSP products include benzotriazoles, imid- azoles, benzimidiazoles and phenyl benzimid- azoles. Some of the newer OSPs have additives occasionally referred to as "oxygen scavengers." These additives can stretch the performance window of the specific OSP. The more ther- mally robust coatings have significantly higher decomposition temperatures than the peak as- sembly reflow temperature. They require con- tact with appropriate flux and/or molten solder to penetrate the coating. They have longer shelf life, survive multiple reflow cycles and are more lead-free assembly compatible. After more than one year of struggling with a specification for OSP, no consensus was reached, and no specification was set forth. This was due to the wide assortment of organic products that were used for solderability pres- ervation for the various applications, each with its own thickness recommended values. Acknowledgement To date, all committee activities have been voluntary and acknowledgement is in order for the members and equally important for their respective companies that allow for the time in- vested by their employees. PCBDESIGN IPC SURFACE FINISH SPECS UPDATE continues feature The eu-funded NANoReG project is developing the next generation of reliable and comparable ex- perimental data on the environmental, health and safety aspects of nanomaterials. NANoReG, which began in March 2013, has already successfully es- tablished the basic conditions for its R&D work and will now move on to deliver on its key objectives. Nanomaterials are chemical sub- stances or materials that are manu- factured at an incredibly small scale (down to 10 000 times smaller than the diameter of a human hair). ex- perts believe they have the potential to contribute significantly to europe's industrial competitiveness, and are already used in hundreds of products. in order to fully capitalise on this potential mar- ket however, the safety of nanomaterials must be beyond reproach. As these nanomaterials are of- ten unique and have never been on the market before, assessments must be done on a case-by- case basis using globally recognised and approved methods. Regular meetings have also been set up with policy makers in partner countries, along with glob- al standardisation institutions in countries like the us, Canada, Australia, Japan and Russia. The long term objective of NANoReG is to ensure that the in - novative and economic potential of nanomaterials is not put at risk sim- ply because health and safety issues have not been fully addressed. Removing Risk to Unleash the Full Potential of Nanomaterials George Milad is the national accounts manager of technology at uyemura international Corporation. he may be reached by clicking here.

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