Study On Embedded Copper Heat Dissipation Technology And Process Of Micreowave Printed Circuit Board

Internal heat of printed circuit board (PCB) sharply increases due to developmentdirection of communication electronic products to high-speed, high-frequency,high-density-integration and miniaturization. High working temperature not onlydirectly threats the PCB dielectric material, hole plating and surface solder points, butalso indirectly affects the transmission quality of high-frequency signal. The heatproblem of microwave PCB with a high-frequency signal transmission inevitablybecomes one of the hot-points for microwave PCB designers and manufacturers.A comprehensive summary and discussion was proposed on the heat dissipation ofmicrowave PCB. The cooling technology of embedded small piece metal with highthermal conductivity in multilayer microwave PCB has good advantage in thedevelopment of electronic products miniaturization.Several major experiments on embedded copper technology were carried outthrough experiments of optimization design and whole manufacturing process. Theflatness, the width of plastic flow, the depth of pit, the reliability at the hybrid junctionof the embedded copper and were studied as well as the machining production on theembedded copper by the reference to technology indicators of the embedded copperhybrid platen. For the flatness, the matching plate thickness of prepared embeddedcopper was determined by theoretical calculation and optimal relationship betweenactual copper thickness and its matching plate thickness was obtained. The resultshowed good flatness when the actual copper thickness was the theoretical thicknessplus0.07mm. For the plastic flow and the pit,23full factorial experiment method wasused to look for the best cushioning material at the juntion and the most appropriatemilling slot size of prepreg. The minimun plastic flow width and the pit depth wereobtained when the milling slot size of prepreg was the copper size unilateral plus0.330mm and the cushioning material was a combination of aluminum and copper foil.The comprehensive influence of drilling parameters on hole wall quality of theembedded copper, production efficiency and production costs was also studied by usingmultiple indicators orthogonal experiment method and orthogonal assistant software. The experiment results showed that drill rotation speed of40krpm, entering speed of20ipm, exit speed of100ipm and drill setting life of90are the best conditions under themultiple indicators and the rank of factors importance was drill rotation speed>drillsetting life>exit speed>entering speed. In addition, The production capacity of steppedslot in embedded copper area was also assessed by statistical software Mintab15. Theresult showed that the length CPK of1.47, the width CPK of1.60, the first depth CPKof1.38and the second depth CPK of1.79met the requirements of CPK>1.33.The process of embedded copper to dissipate heat was studied through12-layerPCB hybrid lamination with high and low frequency substrates for communicationstation. The alignment of low-frequent substrates with dissymmetric hybrid laminationstructure was enhanced through the method of compensation according to thecoefficient of expansion and shrinkage. Before the enhancement of alignment, thedimensional change of the top substrate and the base substrate reached up to0.416mmand other inner substrates were up to0.127mm. However, the dimensional change of allsubstrates were less than0.0762mm after compensation. In addition, for the alignmentdegree between high-frequent substrate and low-frequent substrate, a contrapuntal edgeof the two different substrates was added to solve deviation problem on overturningoperation to improve interlamination alignment.The semi-metalized slot of the embedded copper area of microwave hybrid PCBwas also studied from four aspects of cutter type, cutting direction, productionparameters and production process. The results showed flat bottom cutter and inversewalking could effectively reduce the burr of semi-metalized slot wall and the bestproduction parameters were the ratation rate of35krpm, the feed rate of7ipm and thesetting life of6m and a new production process could enhance the quality ofsemi-metalized slot wall.Finally, the products reliability of twelve layers embedded copper microwave PCBwas tested from drift tin and reflow experiment by the reference of Huawei unleadedstandard. The results showed that the target area was no stratificating, foaming, resinmicro-cracks and other undesirable phenomena.