Key Technology And Application Of Laser Formed Blind Via In HDI Printed Circuit Board

The high density interconnect （HDI） technology as one of the most fashionableprinted circuit board production technologies is widely used in the fields such ascomputer, communications, consumer electronics products, etc. Its main feature is theproduction of microvia. In this paper, the key production process of blind via formed bylaser in HDI board was studied, and the results research was applied to the production of10-layers’ free via stacked up structure （FVSS） HDI board. The experiments focused onthe main process of blind-via’s fabrication and metallization, and a new method forblind via metalization was explored. The achievements are as follows.The regression equations of energy, pulse width and collimation value in differentMASK diameters for laser drilling showed that the energy is linearly related with thepulse width and the collimation value. Fluctuations in the diameter of blind via fromedby CO₂laser direct drilling will be minimized when copper thickness is controlled in therange of8⁹μm with the selection of chemical method for copper reduction, and theinitially parameters of CO₂laser directly drilling blind via can be inferred. In the resultof orthogonal experiment, it was shown that the first thing should be the decision of thedielectric types, then the appropriate laser energy and pulse shots in dielectric layerablation. The laser parameters can be fine-tuned in this way. The blind via with0.13mmdiameter and the thickness to diameter ratio in one can be drilled in a good quality withthe parameters in2.2mm of MASK diameter,14μs of pulse width, one shot of17mJlaser beam for the first dirilling step and with the same collimation number in5μs ofpulse width,7shots for second dirilling step.During blind via filling process with copper plating, the quality of the filled via wasinfluenced by the plating solution, the diameters of blind via, and many other factors. Itwas derived by related experimental analysis that a higher copper sulfate with lowvitriolic acid plating solution, a smaller size of via, and a higher nozzle jet velocity canget a more perfect quality in blind via filling. Current density have a great impact onblind via filling in the process of plating.Considering the different copper growth rate ininside of the blind hole and the surface of plate, it can be regarded that a medium current density is most suited to filling the blind via in DC. The optimum parametersobtained for0.13mm blind via filling were220ml/L of copper sulfate,80ml/L ofsulfuric acid,2.0A/dm2of current density,85min of plating time and the280L/min of jetspeed.A method to direct plate blind via with CO₂laser assisted has been put forward,which can be achieved by seven steps:1). Etching mark target,2). Brown oxidation andLamination,3).CO₂laser direct drilling,4).Etching burr,5).Plasma desmear,6).Laserinducing,7).Blind via plating. And the rationality of mechanism was proved that CO₂laser sputtered copper particles to blind via wall in the inducing the bottom copperprocess of blind via. The samples of10-layers’ free via stacked up structure （FVSS）HDI board were produced in a small batch. With the optimization of the processparameters in experiments, the product yield was improved from the19%of trial boardsto the82.2%of samples for production.