Effect of molecular structure of phenolic resin on solder dip resistance and peel strength of printed circuit adhesives

Phenolic resins were synthesized by using various kinds and amounts of catalyst and changing the mole ration of formaldehyde and phenol. The solder dip resistance and the peel strength were measured for two-component printed circuit adhesives mixed with poly(vinyl acetal) resin, and the relation between these properties and the molecular structure of the phenolic resins were studied. Catalysts such as ammonia, amines having low boiling points, and alkaline earth metal oxide and hydroxides give resins with good properties. When the mole ratios of ammonia to phenol and formaldehyde to phenol are respectively 0.05–0.10 and 1.5, the resins obtained have good characteristics. The solder dip resistance is improved by aging the resin solution at moderate temperature.