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70 PCB007 MAGAZINE I OCTOBER 2022 In a future column, I will take a deeper dive into the various surface preparation methods. PCB007 Michael Carano is VP of quality at Averatek. To read past columns, click here. adhesion and the conforma- tion of the resist. ere is less reliance today on the chemis- try of the resist for adhesion. Topography matter s. How- ever, a non-uniform rough- ened surface can present its own set of issues for the adhe- sion of the film. e actual pro- file of the copper surface may be due to excessive mechani- cal brush pressures, defective brushes, lack of pumice effec- tiveness, and over- or under- a g g r e s s i v e c h e m i c a l t r e a t - ments. This invar iably leads to areas on the copper sur- face where there may be deep gouges and depressions as well as areas where the roughening is inadequate (Figure 2). When the copper surface is non-uniform with areas of deep crevices, as well as areas where little topography is seen, dry film resist adhesion is compromised. Depending on the particular unit operation in the fabrication process, this can lead to dish-downs, nicks in the copper circuitry, signal integrity loss, poor impedance matching, and non-unform dielec- tric thickness within the bondline. Figure 2: Excessive roughness in copper surface preventing dry film adhesion.