1、PDF外文：http:/ An innovation in horizontal processing Peter Lymn and Ken Bishop CEMCO FSL Ltd, Waterlooville, UK Abstract Purpose The purpose of this paper is to detail an innovative new equipment enhancement for use in the horizontal processing of printed circuit boards (PCBs). Design/methodology/app
2、roach The paper describes a non-contact laminar or streamline flow process chamber. It also describes a transport and guiding method suitable for both thick and thin materials and expands on the mechanics and fluid dynamics that further reduce equipment length and operating cost. Findings The new pr
3、ocess chamber and its related enhancements result in a faster and more uniform chemical reaction than is obtainable with conventional flood chambers. This enables the equipment to have reduced length and to offer reduced operating costs. Originality/value The paper presents a new approach to horizon
4、tal processing that can offer reduced equipment footprints and reductions in operating costs. Keywords Process management, Printed circuits, Conveyors, Chemical technology process Introduction Printed circuit board (PCB) fabricators have used horizontal roller conveyers to transport copper cl
5、ad laminate through chemical spray treatment chambers for many years. These simple conveyorised spray processors have evolved over time to accommodate much thinner materials, but the complication of guiding and supporting them through spray jets generally means two types of machine are required； one
6、 for thick, rigid material and another longer, more complex system for very thin or flexible substrates. More recently, this type of equipment has been further adapted to incorporate immersion chambers for plating and other surface treatment processes where spray jets are not suitable. The need to c
7、ontain the static head above the roller transport system and the relatively long contact times required for immersion processes make these systems even longer and more complex. This paper describes a non-contact laminar or streamline flow process chamber that results in a faster and more uniform che
8、mical reaction than is obtainable with conventional flood chambers. It also describes a transport and guiding method suitable for both thick and thin materials and expands on the mechanics and fluid dynamics that further reduce equipment length and operating cost. 2 Chemical process chamber In
9、 conventional immersion chambers, fluid is pumped from a sump to a dammed roller conveyor chamber. The solution is typically re-circulated at a rate of five times the chamber volume per minute through manifolds positioned between conveyor rollers. Transportation is achieved by using roller wheels to
10、 avoid excessive masking of the panel being processed. This combination of flooded jet and roller wheel transport results in chaotic turbulent zones within a relatively stagnant bath and can lead to variable chemical reaction across the panel. The “Fluid Engine” immersion chambers, by contrast, prov
11、ide laminar flow up to 100 the chamber volume per minute or in excess of 11m per minute, resulting in faster, more uniform reactions. The engine comprises two plates closed at each side to form a narrow chamber. Fluid containment rollers, mounted at the entry and exit of the chamber, push and
12、pull both flexible and rigid materials through it. Fluid is injected at the centre of each plate producing a laminar flow towards the entry and exit ends of the chamber (Figure 1). This laminar flow results in steady boundary layers above and below the material being processed, helping to guide it t
13、hrough the process chamber. The leading and trailing edges of the plates are shaped to produce a Coanda effect, diverting the boundary layer diffusion point away from the panel entry and exit zones. This maintains the streamline flow and diverts fluid above the plates, preventing flooding and materi
14、al deflection. The Coanda effect was discovered by Henri-Marie Coanda, a Romanian born aeronautical engineer, and is named after him. The Coanda, or wall attachment, effect is the tendency for a moving fluid to attach itself to a surface and flow along it. When a fluid moves across a surface, a fric
15、tional force occurs between the fluid and the surface and slows it down. This resistance to the flow pulls the fluid towards the surface, causing the fluid to stick to the surface. Therefore, a fluid flowing from a nozzle will follow a nearby curved surface if the curvature of the surface is not too
16、 sharp. Figure 1 Diagrammatic view of the fluid engine showing the laminar flow and the Coanda effect Dual feed engine Some chemical processes associated with the printed circuit industry require a 3 gas (normally oxygen in the form of air) to be introduced at the point of contact of th
17、e chemical with the panel being processed. A dual fluid version of the “Streamline Fluid Engine” that simultaneously feeds gas and liquid to the discharge slots provides this facility, while maintaining the characteristics associated with the standard “Fluid Engine”. The design of this engine is sho
18、wn in Figure 2. The gas is fed under pressure to the outer gas plenum (shown in green) that is separated from the liquid plenum by a permeable membrane. The base plate has a series of closely spaced holes that normally connect the base plate directly to the liquid plenum across the width. In the dua
19、l feed head the liquid plenum has a series of tubes that connect the gas plenum to the base plate. These tubes are pitched such that they line up with every other hole in the base plate and seal the holes from the liquid in the plenum. Therefore, gas and liquid are delivered side by side across the
20、width of the panel through alternate holes. Figure 2 shows how both gas and chemical reach the output jets. The lower head shows the path that the gas takes to reach the jets and the upper head shows how the chemical does. Gas is shown as green and chemical as blue. Figure 2 Dual fluid engine
21、to introduce a gas into the chemical stream Fluid knife Where it is necessary to remove chemicals from the panel by dilution, or where high fluid impingement is required to wet blind features, a shorter version of the fluid engine, known as a fluid knife, is used. Typically, this fluid knife
22、is used for water rinsing after a chemical process or pre-treating prior to a chemical process (Figure 3). The fluid knife considerably reduces both the conveyor length and the power required to pump solution onto the panel. For example, a single fluid knife provides a solution rate of 40L per
23、 minute using a 110W pump, compared to a more conventional spray rinse that delivers 28L per minute from a 750W pump. Similarly, the fluid knife requires only 170mm of conveyor length compared to 240mm for the spray rinse. As with the fluid engine, thin material transport is assisted by the fluid flow characteristics, although the proportionally lower flow rate avoids the need for the overhead fluid deflection, the upper outflow being
