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26 PCB007 MAGAZINE I NOVEMBER 2025 Understanding Interconnect Defects, Part 2 by Michael Carano, C onsultant, Global Ele ctronics Asso ciation T RO U B L E I N YO U R TA N K Part 1 of this two-part series presented a more detailed look at the underlying causes of intercon- nect defects (sometimes known as interplane sepa- ration), with these three modes of interplane sepa- ration: • Type 1: Separation of the electroless copper deposit from the interconnect • Type 2: Separation of the electrolytic copper deposit from the electroless copper deposit, but the electroless remains on the post • Type 3: Cohesive failure of the electroless, whereby the electroless copper deposit actu- ally separates from itself Type 1 ICDs are the most common and often diffi- cult to troubleshoot since many process variables affect it (as discussed in detail in Part 1). In this column, the focus is on Type 2 and Type 3 ICDs. Type 2 ICDs It is important to stress that a Type 2 ICD is not an electroless copper/direct metallization/desmear problem. The electroless deposit in Figure 2 is firmly on the interconnect. The electrolytic copper has separated from the electroless copper. The root cause of such a defect is lack of adhesion of the electrolytic copper to the electroless copper. When encountering this problem, we must first determine whether the printed wiring board was panel- or pattern-plated. If pattern-plated, did devel- oper or resist residues remain on the interconnect? Was the developer solution at the proper concen- tration, temperature, and pH? Is there resist lock-in? These problems will prevent the electrolytic copper from adhering to the electroless. Other potential sources of Type 2 defects: • Oxidation at the interconnect • Poor adhesion of electroplated copper to the electroless • Dry film residues remaining after incomplete development Long hold times or rinsing with excessively hot water cause oxidation between operations. To improve adhe- sion, a sufficient amount of copper must be micro-etched. Typically, a 15–20 microinch etch is sufficient. Concern arises when 10–15 or fewer microinches of copper are removed. This is generally an insufficient amount of copper removal to provide enough anchoring sites for the copper plate. Since many printed wiring board fabricators have reduced electroless copper plating thickness to reduce costs, they are reluctant to be aggres- Figure 1: In a Type 2 ICD, electrolytic copper separates from the electroless copper. ⊲