Study Of Organic Solderability Preservatives On Copper Surface

As one of the final surface fnishing technologies for PCB board, OrganicSolderability Preservatives(OSP) process is low cost, simple in operation,environmentally friendly to meet the RoHS and the requirements of lead-freesoldering with increasingly wide application in the PCB industry. This paper aims todevelop a technology of OSP process which has better performance than themainstream products on the domestic market.The compositions and optimum technologic parameters of OSP andpretreatment are researched. The factors which influence the thickness of OSP filmare also studied. The performance of OSP which is prepared by using alkyl phenylimidazole is analyzed by testing instruments. It is found that its properties of heatresistance, oxidation resistance and weldability are better than the commercializedOSP products on the domestic market. The concentration of alkyl phenyl imidazoleis selected for2.5g/L, the content of organic acids is3.5mol/L, The content oflong-chain acid is0.3wt%. The pH value is maintained at about3.0, the temperatureis40℃, and processing time is60s. But for the OSP which uses diaryl imidazole asthe active ingredient, the thickness of its film is always less than0.2μm. The abilityto protect the copper surface is comparatively poor, and needs further study.Meanwhile, two kinds of pretreatments are studied to determine the optimumcompositions and technologic parameters. Both of the pretreatments can acceleratethe generation of the OSP film, and make the imidazoliumcompounds only depositon copper. The first pretreatment uses benzimidazole as the active ingredient, andthe concentration of benzimidazole is1.0g/L, pH of the solution is maintained atabout8, processing time is60s. Hydroxyquinoxaline is used as the activeingredient in the second pretreatment. The concentration is3.0g/L, pH of thesolution is maintained at about12.5, processing time is60s.The OSP film formation process is summarized in this paper. The mechanismof factors which affect the thickness of OSP film is explained. The mechanism ofpretreatment is studied. Before the copper surface immerses to OSP solution, aprecoat can be formed on the copper surface by the pretreatment. The existence ofthe precoat can accelerate the generation of the OSP film. So, the OSP solution canbe avoided to add excess copper ion, and in this way the discoloration of goldsurface is prevented.