抄録
レーザ発振器の特性, 結像光学系の回折, 試料の熱物性, レーザ照射条件を総合的に考慮して実験に即したモデルを構築し, プリント基板の樹脂除去解析を行った. 単一照射, 繰り返し照射による樹脂除去における除去深さ, 加工穴の底面形状, 側壁の勾配といった加工結果が, 光学系の回折で生じる加工点でのレーザ強度分布と樹脂のレーザ吸収に強く依存することを定量的に明らかにした.
Two-dimensional axisymmetric non-steady heat conduction was analyzed considering the laser diffraction in the image formation optical system and resinous evaporation. The validity of analysis was confirmed comparing with the experimental results. Main results obtained are as follows : (1) When the resin is relatively thick, the shape of via hole reflects the laser intensity distribution because the thermal conductivity of resin is not so large. (2) As the thickness of remained resin becomes thinner than the absorption length of resin by repetitive irradiation, the removal quantity rapidly decreases and the smear remains on the substrate. (3) Less the removal quantity, less the reflection of the laser intensity distribution to the bottom shape of via hole although the side angle of via hole hardly changes. (4) Two- or three-dimensional non-steady heat conduction analysis considering the diffraction of the optical system is necessary for estimating the shape of via hole. (5) The one-dimensional analysis proposed in the previous paper is useful enough to estimate the removal depth although the removal depth by the second shot would be a little deeper than expected because heat is transferred in the radial direction.
