-
- News
- Books
Featured Books
- pcb007 Magazine
Latest Issues
Current IssueThe Growing Industry
In this issue of PCB007 Magazine, we talk with leading economic experts, advocacy specialists in Washington, D.C., and PCB company leadership to get a well-rounded picture of what’s happening in the industry today. Don’t miss it.
The Sustainability Issue
Sustainability is one of the most widely used terms in business today, especially for electronics and manufacturing but what does it mean to you? We explore the environmental, business, and economic impacts.
The Fabricator’s Guide to IPC APEX EXPO
This issue previews many of the important events taking place at this year's show and highlights some changes and opportunities. So, buckle up. We are counting down to IPC APEX EXPO 2024.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - pcb007 Magazine
An Innovation in Horizontal Processing, Part 2
August 13, 2013 |Estimated reading time: 10 minutes
The first paper on this subject covered the theory behind a novel non-contact laminar or streamline flow process chamber that results in a faster and more uniform chemical reaction than obtainable with conventional flood chambers. It also described a number of variations on this chamber to provide a solution to a complete horizontal chemical processing line that reduced the footprint and operating cost over conventional designs. This second paper describes a practical implementation of the design. It further describes how the design has been developed to produce equipment capable of processing material in a variety of chemical applications. Fluid Engine A basic fluid engine is made up of an upper and lower fluid head screwed together to make a complete, easily removed assembly (Figure 1). Each head comprises a base plate machined from a solid piece of plastic and a plastic plenum welded to it. Both base plates have drainage slots to allow any fluid that accumulates on the top head to drain back into the chamber and then to the sump. The complete fluid engine assembly slots into the side frames of the conveyor using two location spigots fitted on a multiple of the conveyor pitch either side of the lower head.A plastic strip screwed into the base plate creates the two fluid discharge slots. This strip can be easily removed for cleaning the heads. Strips fitted to either side of the base plate guide the fluid and stop it flowing over the sides of the head. This ensures laminar flow is constant over the whole width of the head. Fluid is fed into the lower head via a pipe connected to the lower plenum whereas the upper head is fed from pipes that passes through the lower head. The fluid feed is fitted with an “O” ring and is a push fit into the feed pipe from the process pump. This enables the Fluid Head to be easily removed and refitted manually. Figure 2 illustrates these design features. When a heated chemical is used with the fluid engine the upper head is fitted with a pair of condenser plates (Figure 3). The hot chemical vapour condenses on the under side of these plates and runs back into the chamber. The plates are cooled to encourage condensation by drawing ambient air across the top utilising the fume extraction system. The assembly simply slots together and drops over the two nuts that hold the upper and lower heads together. There are no fixings and therefore the plates can be easily lifted off the fluid engine for cleaning. Dual-feed Engine The dual-feed fluid engine is very similar in construction to the basic engine. The difference is in the way that the second fluid is delivered to the base plate and on to the discharge slots. The base plate is exactly the same design, but the liquid plenum is changed to enable the gas to pass through it and into the base plate. The plenum is machined so that a series of tubes pass directly through it. These tubes provide a path for the gas though the liquid plenum. The gas plenum is a hollowed out plastic block with a tapped hole for the gas feed fitting. The two plenums are welded together to give a fluid tight construction and then welded to the base plate. The liquid plenum is positioned such that the tubes align with every other hole in the base plate. The result is that gas and liquid exit the discharge slots from alternate holes spaced at approximately 7 mm across the width of the panel being processed. By adjusting the pressure of the gas at the input port the mix of gas and liquid arriving at the panel can be controlled. Figure 5 shows a cross-section through a dual-fluid engine and shows the paths that the two fluids take to reach the discharge slots. The top head shows the liquid path while the lower head shows the gas path. A membrane is fitted between the two plenums that allows gas to pass through to the discharge slots but prevents liquid from flowing back to the gas plenum. The lower liquid plenum is larger than the upper as liquid feed to both pass through the lower one. Fluid Knife The fluid knife does not have to provide a long contact time between the fluid and the material and so is considerably narrower than the fluid engine. Both upper and lower heads consist of two plastic plates hollowed out to provide a plenum area. These plates are welded together to produce the complete head assembly. The weld line can be seen in Figure 6 running across the length of the heads. The plates are machined to produce a fluid discharge slot running across the width. The plates are further fixed together using plastic screws to overcome the tendency of the plastic to bow over its length. This ensures that the discharge slot width remains constant producing an even flow of fluid. The leading edge of the lower knife has a series of slots machined in it shaped to allow the fluid to rapidly drain into the chamber. This allows the knife to be positioned extremely close to the input roller with the leading edge acting as a guide for thin material. A single location spigot is fitted either side of the lower head to position the knife assembly in the conveyor side frame. Jet Knife Based on similar design concept as the fluid knife with two machined plastic plates welded together, the jet knife has a series of holes tapped in the plenum. These tapped holes can accept standard moulded jets to provide high impingement forces on the panel. Drain holes in the base of the lower head allow fluid to drain away rapidly to prevent it interfering with the spray pattern from the lower jets. Spray Applications Although it has been found that most of the chemicals traditionally sprayed can be used to advantage in the fluid engine it has been anticipated that spray treatment may be required. To meet this requirement a module that can be fitted with either fluid engine or spray manifold has been developed. Figure 8 shows a typical process section combining fluid engine and spray modules. Both top entry fluid engine and spray module are "plugged in" to their supply manifold and are located in the conveyor side frames. Two single-spray bar manifold assemblies fit the area occupied by one fluid engine and are interchangeable to facilitate testing and development. The design of the spray modules enables standard jets to be fitted providing the facility to generate a variety of spray patterns. Jets are spaced above and below the work to produce the desired fluid coverage. The jets shown in the figure are angled to provide coverage without interfering with fluid flow from adjacent jets. Practical Applications Equipment using the streamline techniques currently in use in, or being developed for, the PCB industry include surface conversion processes such as electroless silver and tin and surface treatment processes that conventionally demand spray application or significantly longer contact time. A low-flow variant of the fluid engine has been developed for nano-coatings and is currently entering the third phase of evaluation. This and the application and capability of the fluid engine as an alternative to complex spray application for etching and similar processes will form the subjects of a further article. By working with specialist manufactures and chemical suppliers Cemco has successfully implemented many aspects of the streamline designs discussed in these two articles into equipment for use outside the PCB industry. These include electroless and electrolytic copper plating and surface treatments for RFID and photo voltaic and are currently being designed into aluminium web anodising equipment. Many of the design concepts illustrated in this article have been protected under the following patents. Copyright reserved. Pat No's: UK.2351458: GR.100 25 619 8: USA.6440215. USA.5155926 GB. 0827800: GR. 697 13 693.0-08; USA 5876499 Pat App No: PCT/GB2008/000062; WO2009/044124 A2.Drying Knife Material drying is achieved using a variation on the fluid knife design. Delivery of air to the discharge slots is the same as liquid delivery in the fluid knife. The path that the air takes however is different than that taken by liquids. Both top and bottom drying knives have extended input sections to help guide the panel into the air stream. The lower knife is shaped to rapidly expand the air leaving the jet to produce a pressure difference between the top and bottom of the panel. This pressure difference sucks fluid from the holes in the panel and also helps to stabilise its position between the knives. To avoid the problem of water left on the trailing edge of panels the knife jets are angled across the width of the conveyor. This causes the air to produce a “wiping” action across the panel driving excess water to the corner where it falls into the lower chamber and to drain. Figure 9 is a view showing the lower air knife and illustrates its angular jet design. Material Transport The conveyor system is housed in a series of wrap around plastic shells the number of shells being dictated by the length of the process. Running along the length of each shell are two side frames with slots cut at the conveyor pitch. A slide in roller bearing block is fitted to every slot where a conveyor roller is located. The lower rollers are fitted with a bevel gear that picks up the drive from another bevel gear fitted to the common shaft that runs the length of the module. Each bevel gear set drives two upper and two lower rollers. A train of spur gears drive the slave roller and upper and lower spur gears provide positive drive to all rollers. Figure 10 shows how the drive is transferred from the main drive shaft to the rollers via the module drive shaft and the bevel gears. One of the design objectives for the conveyor system was to provide the capability of transporting a variety of material with thickness from 0.005 mm to 5.0 mm. The roller diameter has been selected such that the flex strength of 50-micron kapton is sufficient to overcome the capillary attraction of a wet roller and the gap between rollers is sufficient to prevent capillary attraction between them to reduce carry over. The spur gears that transfer the drive from the bottom to top rollers have a special tooth design to achieve positive drive with panels up to 5 mm thick. Figure 11 illustrates how the rollers are coupled via the spur gears on the drive side. The second top roller is driven from the other end of the lower roller immediately below it with spur gears mounted on the opposite end of the rollers. The rollers are fabricated from light, rigid hollow carbon fibre cores, to prevent deflection or damage when dropped and alternative precision ground coatings are available to suit all chemicals. Drag out can be improved by increasing the weight of the upper rollers by inserting weights into the inner core. Bearing blocks fixed directly to the side frames at either end of the module support the module drive shaft. Each module drive shaft picks up its drive from a spur gear on the main drive shaft. The separate drive shaft design enables a long drive train to be assembled without the possibility of potential drive shaft wind up. For longer lines or where composite lines running at multiple speeds are required the drive shaft can be split into two or more sections with a separate motor for each section of shaft. In these cases the motors can either be run from a common speed control where synchronous speeds are required or separate ones where different section speeds are needed. Figure 12 is an exploded view showing how a section of the Streamline process is built up and illustrates its modular construction and ease of maintenance. This particular module shows a single fluid head chemical process followed by a triple water rinse section fitted with fluid knives. The engines and knifes plug into feed ports built into the base of the conveyor chamber--one feeding the upper plenum and the other the lower plenum. The engines can be fed from horizontal or vertical pumps in either remote or integral sumps the former allowing wall mounting to further save space. A typical complete line consists of multiple modules similar to figure 12 with combinations of fluid heads and fluid knives tailored to the complete process. The individual modules would be coupled together and driven from a single drive module. A slave conveyor section is usually fitted to the output end of the line to allow processed panels to be removed. A panel feeder is available for fitting to the input conveyor section while a panel stacker can be included on the output conveyor.Authors' Note: Many of the figures in this paper are from a 3D CAD design software package. They are coloured for clarity and do not represent the colours used in practice.