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12 The PCB Magazine • February 2015 by Michael Carano OMG ELECtrOnIC ChEMICALS LLC OSP and Selective Electroless Nickel for Mixed-Metal Finish PWBs and BGA Substrates Introduction The documentation relating to the require- ments for alternative surface finishes have been well publicized at many industry forums. Pres- sure to eliminate lead in electronics assemblies is forcing fabricators and OEMs to reevaluate their surface finish and joint attachment pro- cedures. Many of the requirements, in fact, are obvious. Regardless, the PWB fabrication indus- try needs to work closely with contract manu- facturers and end users to fully appreciate the true impact of technology trends. These trends are significant and include: 3 Surface mount continues to increase at the expense of through-hole with finer and fin- er features. 3 The use of non-tin/lead coatings and sur- face finishes will increase. Surface finishes such as electroless nickel/immersion gold, OSP and immersion tin will be utilized. 3 With political movements toward ban- ning lead in all electronic assemblies gaining significant momentum, lead-free solder pastes and wave solder materials will be adopted. 3 The need for more robust solderable fin- ishes under extreme environmental conditions including corrosive atmospheres. 3 The alternative surface finishes must per- form through multiple thermal cycles with less active pastes and fluxes. 3 The use of multiple metal finishes on the same bare board will place new emphasis on the compatibility of coating with each other, and the actual assembly module. 3 Increased I/O demand and reduced lead pitch will require much tighter controls over the processes used to fabricate the bare board. feature