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JULY 2019 I PCB007 MAGAZINE 55 The supplier tech team, however, performed its own investigation. The team asked for data on laser via formation used at this facility and examined materials immediately after laser via formation. As the results showed (Figure 6), the wedge or gap already existed. Moving back further into the process, the team noted that gap existed on certain flexible materials supplied by a third party. When the chemical supplier tech team ob- tained flex materials from a second supplier, examination showed no gap or wedge exist- ed either before or after chemical process- ing. Of course, chemicals such as those used in desmear or micro-etching, could have led to this defect. But in this situation, this was not the case. Conclusion Lesson learned: Don't assume it is the chem- istry. Fabricators, in many instances, may not want to take any responsibilities. As a process troubleshooter, stick to your guns and conduct a thorough upstream and downstream inves- tigation. Ensuring a quality copper deposit in the vias with electroless copper or alternatives, such as carbon-based direct plate processes to the vias, depends on process control, equip- ment design, and chemical parameters. When these are not in control, defects arise. PCB007 Michael Carano is VP of technology and business development for RBP Chemical Technology. To read past columns or contact Carano, click here. Figure 5: SEM view of the via in the flexible circuit (note the gap). Figure 6: Two views of the gap after via formation and before any further processing.

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