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SEPTEMBER 2024 I PCB007 MAGAZINE 49 per and the electroless copper. Solving a par- ticular issue requires looking at different pro- cess steps than previously looked at in Type 1 ICD. It is important to stress Type 2 ICD is not an electroless copper/direct metallization/ desmear problem. e electroless deposit in Figure 2 is firmly on the interconnect. e elec- trolytic copper has separated from the electro- less copper. e root cause of such a defect is the lack of adhesion of the electrolytic copper to the elec- troless copper. When encountering this prob- lem, the first order of business is to determine if the PCB was panel- or pattern-plated. If it's pattern-plated, did developer or photoresist residues remain on the interconnect? Was the developer solution at proper concentration, temperature, and pH? Is there resist lock-in? ese problems will prevent the electrolytic copper from adhering to the electroless. Other potential sources of Type 2 defects include: • Oxidation at the interconnect • Poor adhesion of electroplated copper to the electroless Long hold times or rinsing with excessively hot water cause oxidation between operations. To improve adhesion, enough copper must be micro-etched. Typically, a 15–20 micro-inch etch is sufficient. e concern arises when 10 or fewer microinches of copper are removed. is is an insufficient amount of copper removal to provide enough anchoring sites for the cop- per electroplate. Since many PCB fabricators have reduced electroless copper plating thick- ness to reduce costs, they have been reluctant to be aggressive on the microetch. e result is insufficient anchoring of the electrolytic cop- per to the electroless. e solution is simple: If your electroless copper process cannot stand up to a microetch that removes 15–20 micro- inches, then find one that does. Perhaps a less common ICD is a cohesive failure of the electroless copper deposit (Fig- ure 4). Essentially, the copper deposit sepa- rates from itself. In Figure 4, the copper is both on the post and the electro-deposited copper, clearly separating from itself. ere are several causes for Type 3 defects: • Excessively thick electroless copper deposits • Lack of epitaxial copper deposit growth • Excessive catalyzation • Operating parameters favoring excessive copper deposition rates All of these will interfere with the orderly growth of the electroless copper crystals. Figure 3: Type 2 ICD: Electrolytic copper separates from the electroless copper. Figure 4: Type 3 ICD: Cohesive failure of the electroless copper deposit.