Quality and reliability of high aspect-ratio blind microvias formed by laser-assisted seeding mechanism in PCB
The laser-assisted seeding (LAS) mechanism should be able to plate microvias with a high aspect ratio that may not be feasible by conventional electroless plating due to the small via geometry. In particular, the plating of microvias with a high aspect ratio close to one is difficult due to the limited accessibility of chemical solution to the via internal wall surface in conventional plating technology. LAS is a promising alternative. The objectives of this paper are to report the deposition mechanism of a thin copper film layer (laser-assisted seeding) on printed circuit board (PCB) microvias dielectric and to study the quality and reliability of the microvias produced by this mechanism. Results find that the microvias produced by LAS have acceptable quality and are as reliable as that formed by conventional electroless plating technology. The hole wall of the microvia was covered with deposited copper, and the thickness of which was found related to some LAS parameters. A set of experimental best LAS processing conditions is also given.
CO2 Laser Induced Blind-Via for Direct Electroplating
Blind-via plays a crucial role in interlayer interconnection of printed circuit board. To get the blind via metallized a direct electroplating process has been put forward by the way of a inducing CO2 laser beam irradiating the copper in the bottom of blind via. The method for direct electroplating of copper onto a non-copper platable layer has been investigated in blind via metalization. The regression analysis was used to discuss the laser beam energy in different parameters. The results of electroplated blind via showed that the copper in the bottom of blind via can be induced by CO2 laser, and the induced copper particles ejected to the hole wall plays a role of the conductive film layer that mainly composed of copper by electroless plating or carbon black conductive film during electroplating, plasma used in cleaning blind via can promote the sorption of induced copper particles onto the via wall.
Flow in a branching open channel: a review
Branching channel flow refers to any side water withdrawals from rivers or main channels. Branching channels have wide application in many practical projects, such as irrigation and drainage network systems, water and waste water treatment plants, and many water resources projects. In the last decades, extensive theoretical and experimental investigations of the branching open channels have been carried out to understand the characteristics of this branching flow, varying from case studies to theoretical and experimental investigations. The objectives of this paper are to review and summarise the relevant literatures regarding branching channel flow. These literatures were reviewed based on flow characteristics, physical characteristics, and modeling of the branching flow. Investigations of the flow into branching channel show that the branching discharge depends on many interlinked parameters. It increases with the decreasing of the main channel flow velocity and Froude number at the upstream of the branch channel junction. Also it increases with the increasing of the branch channel bed slope. In subcritical flow, water depth in the branch channel is always lower than the main channel water depth. The flow diversion to the branch channel leads to an increase of water depth at the downstream of the main channel. From the review, it is important to highlight that most of the study concentrated on flow characteristics in a right angle branch channel with a rigid boundary. Investigations on different branching angles with movable bed have still to be explored.