Issue link: https://iconnect007.uberflip.com/i/1503998
56 PCB007 MAGAZINE I JULY 2023 think like a semiconductor company: tighter controls, cleanrooms, minimal human han- dling, etc. Let's face it: ings go wrong. Conventional electroless copper has been used in the fabri- cation of printed circuit boards for more than 50 years. You would think that because we've experienced everything that can go wrong, history will never repeat itself. at is simply not an accurate statement. Chemical processes are dynamic, not static. Ever-changing con- centrations, specific gravity, additive break- down products, etc., influence process and deposit quality. In turn, these affect reliability and should not be taken lightly. Desmear It's important to understand the material properties of the resin systems you are using to build your boards. Not all FR-4 materials are created equal. Pay close attention to the Tg and Td of the material sets in question. Review the IPC slash sheets and supplier data packages for further information. Resin blends, the type of cross-linking agents used, and other addi- tives such as fillers, will influence the degree at which resin smear is formed and can be removed by the desmear process. e SEMs in Figure 1 show the surface con- ditions of the blind vias as well as the properly filled/plugged via. Figure 2 shows the results Figure 1: With alkaline permanganate desmear (top row), SEMs for 140° Tg material, and (bottom row) 170° Tg material. Note the difference in the topography of the two resin materials under the same desmear conditions.