Fluid Mechanics and Mass Transfer of the Rotating Screw Electrode Process for Plating Through-Holes in Multilayered Printed Circuit Boards

美国伊利诺伊州皮尔斯坦大学CTS-9422770制造多层印制电路板的一个关键问题是在电镀“通孔”的内表面快速而均匀地沉积铜。对于传统电路板(其中所有互连都是通过通孔的方式)以及也使用表面贴装技术的电路板，在电镀速度、均匀性和沉积延展性之间进行权衡，只有以降低速度为代价才能获得可接受的良率，这需要大量的资本投资和过程中的库存成本。对于未来电路板中高深宽比的孔，对现有工艺的增量修改将不能在可接受的处理速度下提供所需的一致性。本项目包括对一种全新的高深宽比镀孔方法的流体力学和传质的基础研究。其关键思想是在浸没板的通孔中操作旋转螺旋电极(RSE)。RSE产生径向、方位和轴向流动，导致与传统技术相比，在孔内和孔内进行更有效的传质。实验表明，所得铜层的厚度比常用的振动板技术获得的轴向均匀度要大得多，振动板技术在孔洞中建立了时间周期的泊松耶流动。还将考虑轴向压力梯度对流动的修正，其大小将被选择以提供流动反转。这将在相反方向的流动部分之间提供逆流传质，并抑制孔中央部分阳离子耗尽边界层的形成。这种方法将为工业评估和开发目前正在开发的大高宽比通孔的改进电镀工艺奠定基础。研究结果对其他应用领域的强化传热传质也有一定的借鉴意义。

ABSTRACT CTS-9422770 PEARLSTEIN UNIVERSIRTY OF ILLINOIS A key problem in manufacture of multi-layered printed circuit boards is rapid and uniform deposition of copper on inner surfaces of plated "through-holes." For conventional boards (in which all interconnects are by means of through- holes) as well as boards also using surface-mount technology, the trade-off between plating speed, uniformity, and deposit ductility is such that acceptable yields are achievable only at the cost of reduced speed, requiring large capital investment and in-process inventory costs. For holes of higher aspect ratio in future boards, incremental modification of the existing process will be incapable of providing the desired uniformity at acceptable processing rates. This project consists of a fundamental study of the fluid mechanics and mass transfer of a radically new approach to plating high aspect ratio holes. The key idea is to operate rotating screw electrodes (RSEs) in through-holes of submerged boards. The RSE generates radial, azimuthal, and axial flow, leading to much more effective mass transfer into and within the hole than is possible using conventional technology. Experiment shows the thickness of the resulting copper deposit has much greater axial uniformity than is achieved using the popular oscillating board technique, which establishes time-periodic Poiseuille flow in the hole. Flow modification by an axial pressure gradient, whose magnitude will be chosen to give flow reversal, will also be considered. This will provide countercurrent mass transfer between oppositely directed portions of the flow and suppress formation of cation-depleted boundary layers in the central section of the hole. This approach will lay the foundation for industrial evaluation and development of an improved plating process for high aspect ratio through-holes currently being developed. The results will also have implications for enhancing heat and mass transfe r in other applications.