Four factors influencing the surface thickness of PCB treated by OSP

OSP is the abbreviation of Organic Solderability Preservatives. With the development of Surface Mount Technology (SMT Technology), the copper surface organic solder coating process has been more and more widely used.


The main factors influencing the film thickness in OSP surface treatment are PCB:


1, OSP concentration of main components: alkyl benzene imidazole or similar components (imidazole) is the main component of OSP liquid, its concentration is the basis of determining the thickness of OSP film.


2, pre immersion: pre immersion can prevent harmful ions such as chlorine ion damage to the OSP cylinder solution. And the pre infusion solution with copper ion amount, can promote the formation of complex protective film, shorten the coating time. Generally speaking, because of the presence of copper ions, the imidazolium imidazole has a certain degree of complexing with copper ions in the pre flux solution. When the complex with a certain degree is deposited on the surface of copper to form a complexing film, a thicker protective layer can be formed in a relatively short period of time, thus acting as a complexing promoter. But alkylbenzimidazole or similar components in presoak (imidazole) amount. And excess copper ion, the pre infusion solution of premature aging, need to be replaced.


The main function of the OSP prepreg is to accelerate the formation of OSP film thickness and to deal with the effects of other harmful ions on the OSP cylinder. It is recommended that the liquid medicine be well changed, as far as possible, without pre dipping the cylinder as a routine process. This will reduce the cost.


3, dipping time: in the OSP of the bath composition, determine the temperature and pH conditions, complex formation of the protective film thickness will increase as the dipping time increased linearly, and with the extension of time and slow, after more than a certain time, basically no increase in film thickness.


4 organic acids: the addition of organic acids can increase the solubility of alkyl benzene imidazole in aqueous solution. Promote the formation of complexing protective films. The amount of excess will lead to the dissolution of the protective film deposited on the surface of copper, thus controlling the added value of organic acids (PH) is critical. When the pH value is too high, the solubility of the alkyl benzene imidazole decreases, and the oily substance precipitates, which is harmful to the dip coating. When the pH value is well controlled, a dense, homogeneous and moderately thick complex film can be obtained. When the pH value is too low, the solubility of the complex film increases, so that the complex deposited on copper can not be dissolved to form a film with a required thickness.


 

(Source: internal information)

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