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NOVEMBER 2020 I PCB007 MAGAZINE 27 ble, with no special treatments required. How- ever, the patten plate pre-clean process should be tested with the primary metallization process used. For example, the pre-clean mi- croetch should be determined by the thick- ness of the electroless or electroless plus flash copper. 7. Not all fabricators target the same markets. Common areas of specialization for fabricators might include, but aren't limited to, generalist prototypes, RF, high-speed, high layer count, very small feature size, exotic materials, flex, etc. Do you have particular chemistries that you recommend for these categories, and do chemistry capabilities overlap? Unfortunately, one chemistry cannot do it all, especially with such a large variation in board design, board thickness, types of features, fea- ture sizes, and the technical requirements of these features, especially as they continue to miniaturize. But there is definitely overlap. The market the fabricator services will have certain laminate materials and mixes of mate- rials that will affect the preferred choice of pri- mary metallization to make the holes or fea- tures conductive. High layer count panels with high aspect ratio holes classically start with electroless copper in the metallization process followed by periodic pulse reverse (PPR) elec- trolytic copper. These fabricators have the ca- pability for communication and infrastructure designs involving thick panels and on large formats. Fabricators for flex, rigid-flex, and exotic ma- terials like PTFE and LCP often use direct met- allization due to DM being a coating process that is not sensitive to material differences. It also offers a choice for environmentally con- scious fabricators or for use in regions of re- stricted water availability. Automotive PCB builders are set up for mass production with high automation. The plating processes are not complex, but process control and reliability are mandatory as the volumes are large. Automotive sees the number of mi- cro-processing units growing per car, including radar, vision, and RF conductivity. The implementation of HDI designs is rap- idly changing the automotive sector. Tradition- al mass production houses based on 4–6-lay- er technology are going to need to adapt to the demand for HDI with expanded plating ca- pacity. For single-level HDI, conformal fill can work, but copper via fill will be required for two-level HDI. EV cars with high voltage re- quirements are a new challenge. Aerospace/defense fabricators who run a high mix of materials and process sequences are at the other end of the spectrum from au- tomotive. A/D fabricators have facilities with flexible tooling to build designs, including rig- id, rigid-flex, and flex. Designers often use conventional multilayer cores with one to sev- eral layers of HDI. RF and high-speed materi- als are in demand and require plasma capac- ity for hole cleaning, but electroless and elec- trolytic metallization processes are suitable for today's materials. Mobile and IC substrates are made by a lim- ited number of specialized fabricators. The fea- ture sizes and L/S requirements require invest- ment in dedicated automation for handling, la- ser tools, and imaging and plating lines. The primary metallization is either electroless cop- per or direct metallization for HDI, and the DC copper via fill lines are in vertical contin- uous platers for both uniform plating control and productivity. Once the features have been rendered conductive, the choice of electrolyt- ic metallization will be driven by the types of features, their sizes, and performance require- ments. Conclusion As board designs become more complex in terms of materials used and features to be met- allized to address changing performance re- quirements, fabrication techniques and pro- cess chemistries must also adapt to enable these trends toward circuit miniaturization and densification and increased device functional- ity. The use of newer dielectric materials and mixes of materials in new applications requir- ing high signal speed and signal integrity will

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