DEVELOPMENT OF NEW SURFACE-TREATMENT ON SMOBC FOR HIGH-DENSITY SMT, NEPS-90

In the application of Surface Mount Technology (SMT), the packaging de nsity is drastically increased by mounting on both sides of the Printe d Wiring Board (PWB). As a result, PWB has been required to improve re sistivity to greater thermal exposure to maintain good solderability e ven after multistage reflow soldering. NEC's new surface treatment sys tem on bare copper for SMOBC (Solder Mask On Bare Copper) PWB; ''NEPS- 90 (NEC Environment Preflux for SMT)'' has been developed to improve t he quality of soldering in the highly advanced SMT. The NEPS-90 has ve ry thin protective coating selectively deposited on copper surface by chemical bonding. Even though the thickness of coating film is 0.2 to 0.5 mum, it is enough to inhibit the oxidation reaction of copper duri ng reflow soldering. So the NEPS-90 shows much more excellent solderab ility than conventional rosin-based surface treatment. At the same tim e, the NEPS-90 is also able to remove the Ozone Depleting Compounds (O DC) from assembly process with the elimination of the cleaning operati on after soldering by appropriate choice of soldering postflux.