| High density interconnect (HDI) rigid-flex board as an advanced printed circuitboard (PCB) is developed to match with the miniaturization, high frequency, high speedand multifunction of electronic products. HDI rigid-flex board exhibits a goodagreement with design and manufacture of high integration-density and intelligentelectronics due to the compatibility of the advantages of HDI board and rigid-flex board.HDI rigid-flex board has been widely applied for high-performance electronics inastronautic technology, medical equipment and consumer products. Blind holes for layerconnection, are one of key processes of HDI rigid-flex board. The manufacture of blindholes for HDI rigid-flex board was investigated based on the practice of industry.Laser technology for manufacturing blind holes performs the effects of highefficiencies and precision, compared to mechanical process. The key factors of drillingblind holes with UV laser were investigated. The parameters with UV laser which affectthe drilling depth were optimized through orthogonal experiments. The relationshipbetween the parameters of UV-laser process and drilling depth exhibited the result ofdrilling efficiencies as laser power>laser frequency>processing speed>height of z-axis.The best parameters and method in manufacturing first-step, second-step blind holeswith the diameter at200μm were successfully obtainedPlasma can be applied for the manufacture and desmear of blind holes. Thetechnology parameters of plasma which affected the etching depth of polyimide (PI)were optimized via the orthogonal experiment. The etching depth of PI wassignificantly affected by dealing time and was increased with the increment of dealingtime. Blind holes with diameter at100μm on a double side flexible printed circuit (FPC)were obtained through process with plasma parameters as RF at2500W, proportion ofgas at12:5, total gas at1000ml/min and dealing time at25min. The etching rates ofdifferent materials during plasma process were got via plasma desmear of the blindholes, resulting in the etching rates as acrylic resin>polyimide>epoxy resin.The purpose of black holes is to form thin conductive layer via physical absorption. The effects of black holes for the microvias of epoxy resin and polyimide substrates,respectively, were discussed through the experiments on dealing times, temperatures,concentrations of black-hole solution, the times of black holes. The rates of materialsadsorbed with carbon were discussed, resulting in that the adsorption rate of carbon onepoxy resin was faster than that of polyimide substrate and broken holes of PI inlayerwith rigid-flex board could be prevented with double treatment of black holes.A novel method on making two-step blind holes was invented. The trends ofdeformation in holes were got by analyzing the effects of the adhesive epoxy resin filmafter lamination. The second-step blind holes with diameters at100μm, which werelaminated by double-side FPC, epoxy resin and copper, were finally obtained. Themethod showed a good agreement with efficiency, simplification, low cost andmatching with materials.Base on above researches, eight layer HDI rigid-flex with second-step blind holeswere successfully achieved by optimizing whole processes during manufacture and ledto a function for industrialization of such board. |
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