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PCB-Mar2017

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68 The PCB Magazine • March 2017 Introduction The process of forming a reliable solder joint between the component and the printed circuit board is paramount with respect to the manu- facturing of robust circuit board assemblies. For example, an electronic connection between cir- cuits using a through-hole is typically carried out by coating the through-hole walls and oth- er conductive surfaces of a printed wiring board with hot, molten solder to make electrical con- nections by wetting and filling the spaces be- tween the conductive through-hole surfaces and the leads of electrical components which have been inserted through the through-holes. Soldering inconsistencies (e.g., inconsistent or weak adherence to the conductive surfaces) are often the result of difficulties in keeping the conductive surfaces of the printed circuit board clean and free of tarnishing and corrosion prior to and during the soldering process. There are several techniques to protect the solderability of the printed circuit board and prevent solder- ing inconsistencies which have been developed. The most common involves the deposition of a coating of metal or a combination of metals on the conductive surfaces of the printed cir- cuit board. The deposited metal coatings are often referred to as "final finishes." Common final finishes include, for example, electroless nickel (EN), electroless palladium (EP), electro- less nickel/immersion gold (ENIG), electroless nickel/electroless palladium/immersion gold (ENEPIG), immersion silver, and electroless nickel/electroless palladium (ENEP). However, there has been new research with respect to pro- tecting solderable finishes from corrosion and in the preservation of solderability. Several pub- lished research reports detail the issue of creep by Michael Carano RBP CHEMICAL TECHNOLOGY Improving Solderability and Corrosion Resistance for Final Finishes, Part 1 TROUBLE IN YOUR TANK

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