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AUGUST 2019 I PCB007 MAGAZINE 83 The common palladium catalyst deposition is a water-based process. Even the palladium ion to metal deposition makes particles during the process because of a water phase reaction. As a result, the palladium deposition over the substrate surface is sporadic particles. In con- trast, this LMI process allows the palladium to deposit atomically. This deposited palladium forms an ultra-thin layer that is a few nanome- ters thick depending on the LMI coated condi- tions, and the deposited palladium is atomical- ly aligned. The copper atom deposition during electroless plating is also atomically aligned from the beginning when this palladium layer is used for the plating catalyst (Figure 4). The novel catalyst LMI allows electrolytic copper plating starting with less than 300 nm of the electroless copper thickness because of this mechanism. This extremely thin copper can be etched in a very short time and main- tains the circuit's three-dimensional structure very well when it is applied to this SAP circuit formation. This also minimizes the isotropic etching influence on the trace formation. Figure 5 shows a TEM image of the palla- dium layer by LMI (in red). The LMI layer is deposited over a glass substrate (bottom side) and potted with epoxy resin (top side) during the sample preparation. The cross-section im- age indicates a very consistent thickness fol- lowing the glass substrate topography. The LMI ink and process parameters set 8.3 nm palladi-um deposition for this test sample and this sec-tion image indicates around 8 nm of the layer thickness. The thickness control needs minor adjustment to hit the target. The organo-metal ink concentration and the coated ink thickness can control 1/10 accuracy (±10%) of this test, then the metal deposition thickness is possibly controlled Parameters Palladium ink concentration: 1% (by weight as Pd) Coated ink thickness (wet): 10 microns Palladium density: 12.0 g/cm3 Estimated palladium thickness (metal) = 1 x 10-2 x 10 x 10-7 / 12.0 = 8.3 x 10-10 cm = 8.3 nm Figure 4: Electroless copper deposition using LMI. Figure 5: TEM/EDS image showing the palladium layer by LMI (red). within 0.1 nm or better accuracy as nominal thickness. Also, the thickness can be down to sub-nanometer thick. This thickness range is very close to gas phase processes such as MOCVD and sputter technology [3] . Here are the coating parameters used for the calculation for the estimated palladium layer thickness: Figure 6: Flex circuit by SAP with LMI copper.