Engineers at Kemet Electronics Corp. (Greenville, SC) have developed a process over the last 18 months that involves the growing of polymers on a capacitor anode using an electrochemical process. The company is ramping up this new coating method because of the undesirable effects that can be encountered when growing the counter-electrode for tantalum capacitors.
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Engineers at Kemet Electronics Corp. (Greenville, SC) have developed a process over the last 18 months that involves the growing of polymers on a capacitor anode using an electrochemical process. The company is ramping up this new coating method because of the undesirable effects that can be encountered when growing the counter-electrode for tantalum capacitors.
In the process of creating tantalum capacitors, magnesium oxide and other components are created, which can cause the capacitors to fail catastrophically. The reaction of oxygen and magnesium oxide can create a self-sustaining flame that will blow up on the circuit board, thus the motivation to move toward a polymer counter-electrode to prevent such failures. The new process is used specifically for the Kemet Organic line of capacitors designed for use in circuit boards, cell phones, hard drives, and mother boards, as well as automotive electronics.
Concurrent with the deployment of this new coating process, Kemet engineers have developed a new automation structure to replace the older process that involved multiple dips in different polymer types to coat the part. To reduce costs and time involved, in addition to increasing the capacitance of the parts, engineers devised a process of growing the polymer on the part very similar to electroplating, which also provides for better penetration of the polymer into the part. Target production rates using the new process, currently two-thirds complete, is 1 million parts per day.
The new automation system is comprised of four tank modules (containing the chemical used in the polymer growing process), with four tanks on each module; each module is controlled by separate PLCs (Omron CJ1G-H). A bar transfer module moves a set of parts from the lid (the carrier used throughout most of the operations) into a process rack for polymerization. An overhead gantry system, also controlled by a separate Omron PLC, moves the process racks from the loader to the tanks and drops them off. Once the polymerization process is complete—about 30 minutes—the gantry takes the racks to an unloader, then to a cleaning station, then back to the loader for the next batch.
An Omron Open Network Controller (ONC) bridges the system’s ControllerLink and DeviceNet networks to Ethernet, connecting all devices to the Oracle production database, which captures all production parameters and process results. The ONC also stores Web pages, which use embedded Java apps to gather production statistics from PLCs, and publishes them in real time to the company’s intranet. A handheld pendant with touchscreen is used for all operator interface tasks.
Control Engineering editorial director David Greenfield spoke with Joe Jansen, Kemet Electronic’s controls technician, about the development of this automation process.
Q What are the most critical points in the coating process and how has the system been engineered to avoid failure at these points?
Critical parameters are the current and voltage applied to the parts to grow the polymer. Each pan on the module has a separate power supply that typically runs as a current-limited process controlled through an analog output through an Omron PLC that controls voltage on the power supply. Voltage is then read back at the output of the power supply and at the tank where the electrodes enter the solution or attach onto the part so that we can maintain tight control of where the voltage is going. We’re also logging voltage and current levels once per second throughout the entire process so we can chart that into an [Microsoft] Excel spreadsheet and keep it with the batch for tracking purposes.
Q Explain the duties of the PLCs at each module.
There are four tank modules, a cleaning module, and a load/unload module. In the tank module, the PLC controls voltage and current and all the data collection for the one-second logging over 30 minutes for four pans. In the cleaning module, a simple PLC controls a couple of slides with water jets to spray off the part clamps between cycles, because you get residual growth on the clamp itself. The most complex module is the load/unload module—parts move through our processes carried on 12 x 14 x 2.5-inch lids that are basically frames; the parts hanging from the process bars and the bars are lined up in the lids. To perform the electrochemical process, the parts need to be widely spaced so we can get counter-electrodes between each row of parts. So we have a large carrier, called a rack, and we take each process bar out of the lid, opening the clamp and the rack, putting the process bar up into the clamp and then closing the clamp on it, which is done using a series of Robo Cylinder linear actuators [from Intelligent Actuator]. The PLC coordinates the motion between the linear actuators.
The load/unload module is basically divided in half. One side is moving bars from a lid into the rack while the other side is taking them out of the rack and putting them into the lid. Each side has six Robo Cylinder actuators coordinating the motion between moving the lid, moving the rack, opening and closing the clamps on top or opening, and lowering bars to and from the lid. A PLC controls all of this motion.
Q Having had to build this system to interface with the production database, what’s your opinion, as an engineer, about this increasingly common requirement?
I definitely see more and more requests coming to have control data posted into production databases. I’ve found here at Kemet that most of our systems have some sort of PC on them so they can at least talk to the Oracle system. Everything we do runs through the production databases.
Q What was the benefit in opting for the hand-held touchscreen pendant?
By setting registers in the PLCs, each module has a jack for this Omron NT series interface pendant. When you plug the pendant in, the PLC recognizes that the pendant has arrived and it will drive the pendant to the screens appropriate for its module. It configures itself for each module that you plug into. For example, if you plug into a tank module, you can read voltage and current levels, and you can set time values. You can then take it out and plug it into the gantry and teach positions on the gantry arm. That is something we are going to try and incorporate more—the configuration pendant idea. Being able to just plug it in and have that kind of access to each module is really a powerful tool for maintenance and engineers to make setup changes or run experiments.
