Application Note #00131 Rev: 98-06
- Application Description
- Vertical Ovens
- KIC Prophet: Real-Time Process Profiler
- Options For Every Application
- Why You Need the KIC Prophet
- Significant Production Increases
- LIST OF FIGURES
- Figure 1 : Heller Vertical Oven
- Figure 2 : Typical Vertical Oven Process Profile
- Figure 3 : Typical Vertical Oven Virtual Profile
The benefits of the KIC Prophet System in conveyorized forced convection ovens and wave solder machines have been well documented. In over a thousand installations worldwide, the Prophet(tm) Thermal Manager is increasing throughput, reducing defects, and providing users with the ability to monitor their thermal processes in real-time. The Prophet System is now available to users of Vertical Ovens (see Figure 1).
Vertical ovens are used in a variety of applications, the most common being the baking and curing of sensitive electronic components. They are used for extended period thermal processes which would require an unreasonably large conveyorized oven; for the processing of large PCB’s that would suffer warpage and distortion in conventional ovens; and in “chip on board” processing. There are three main benefits in using vertical ovens:
- Automated Vertical Ovens increase productivity by eliminating the need to manually load and unload conventional batch curing ovens.
- Improved process consistency by reducing temperature variations caused by opening and closing batch oven doors.
- More efficient use of factory floorspace. This is especially important when Vertical Ovens are used in clean rooms.
But Vertical Ovens are not without a downside. They generally run product profiles of one to six hours duration. This alone makes conventional product profiling with pass-through thermocouples extremely time-consuming. Even if only one profile is required, it can take close to a full shift to run. And to make things even more complicated, the mechanical structure of the vertical oven makes running conventional profiles difficult for the following reasons:
- Conventional pass-through part profilers, whether data-logging or radio frequency, cannot survive the extended thermal processes without modifications.
- The placement of a modified profiler in the Vertical Oven requires a custom pallet or tray to be loaded, and this pallet combined with the profiler acts as a heat sink, thus giving a potentially distorted and inaccurate product profile.
- Many users of Vertical Ovens have given up on pass-through profilers and returned to the traditional method of using trailing wire thermocouples to profile their process. This method is also troublesome. It is difficult to feed the trailing wires through the oven, especially through the top pass-over or “shuttle” portion of the oven—the result is often damage to the thermocouple cable and sometimes damage to the oven itself. Additionally, the opening and closing of the oven doors required to feed cables through can produce an inaccurate profile.
There is no way to avoid running a profile in the setup of a Vertical Oven, but there is an extremely simple and cost-effective way for users of Vertical Ovens to avoid running the costly and time consuming verification profiles that many contracts, as well as ISO 9000, require.
The KIC Prophet removes the need to run conventional product profiles except to setup the oven. Unlike conventional profilers, which provide a “snapshot” profile, the Prophet is the equivalent of having a video camera running twenty-four hours a day in the oven. The system consists of KICprobes containing up to fifteen internal thermocouples which are mounted in the oven chamber in close proximity to the product; a thermocouple processing unit (TPU) that sends the probe data to a computer; and a completely self contained Windows based software package. The key difference between the Prophet System and conventional product profilers is that the thermocouples in the KICprobes continuously monitor process temperature. Temperatures are continuously displayed as “Process Profiles” on a PC screen and data is permanently recorded on the hard disk (see Figure 2). During production, any temperature drift and its location is instantly visible. Because the KIC Prophet is outside the oven control loop, it can reveal critical temperature deviations in the product profile that are often hidden from the oven control thermocouples. This is especially critical in Vertical Ovens for two reasons:
- Vertical Ovens have a much larger process area than conveyorized ovens. The chamber is generally only heated on one side, and this provides the potential for thermal variations in the chamber that may not be recognized by the control thermocouples.
- Vertical Ovens can have as few as two control thermocouples to monitor the entire process. These thermocouples are located at the heating element rather than in the process chamber, which makes it difficult to monitor the complete process.
KIC resolves this problem by placing up to sixty KICprobe thermocouples in the oven to insure complete process monitoring. KIC probes can be custom configured to fit any Vertical Oven, including retrofits, and address any process concerns. While the KICprobe thermocouples cannot monitor every point inside the oven, they are typically placed in such a way that no point inside the oven can vary significantly without at least one of the KICprobe thermocouples also varying significantly.
Once an initial product profile has been run, the Prophet software calculates the relationship between process temperature and product temperature, establishing a “baseline profile.” During production, the software continuously calculates how this profile has changed based on measured changes in process temperature. This calculated profile is referred to as a “virtual profile.” KIC software version 2.2.4 contains an option that allows users to select a Virtual Profile specifically designed for Vertical Ovens (see Figure 3). The virtual profile is updated every thirty seconds and permanently recorded. This can be viewed at any time by entering the date and time in question. If at any point the product profile falls outside user defined limits, an alarm will sound. If a closed loop system is integrated, the alarm feature can be used to shut down the feed conveyor. This capability makes the Prophet an excellent tool for zero defect production, as it eliminates potential product defects due to thermal variation.
The Prophet system is available with options that can be tailored to fit any manufacturer’s needs. These include: Live Data Output, Statistical Process Control, Auto-Predict, Board Sensors, and Barcode Readers. Live Data Output sends process data continuously to other software packages, making data available for Statistical Process Control, ISO 9000 documentation, and other applications. Statistical Process Control can be applied to the thermal process with an integrated Prophet System SPC package: QC-CALC. The Auto-Predict software eliminates guesswork in developing oven profiles, or “recipes.” In seconds, KIC’s Auto-Predict will calculate thousands of combinations of conveyor speed and zone temperature, then rate them to provide an optimal profile. The Board Sensor utilizes optical sensors placed at the entrance and exit of the oven, and will record and display the number of boards in the oven, as well as providing a lost board alarm should a product fail to exit the oven. The Bar Code Reader allows KIC’s software to time and date stamp every product that enters the oven. At any time, the process data on any bar coded product can be reviewed by scanning the barcode. The Board Sensor and Bar Code Reader allow a manufacturer to track and record the thermal profile of every individual product processed in their ovens.
With the addition of one or more of the available options to the KIC Prophet System, it becomes the ultimate Thermal Manager. Zero defect production can be achieved by Real-Time monitoring of all areas that can cause thermal deviations including peak temperature, maximum slope, and time-above specified temperatures. Total process documentation and product traceability simplifies quality control and troubleshooting, helping to determine the origin of any thermal problems that may occur. The KIC Prophet System makes it possible to:
- eliminate the downtime inherent in the use of conventional product profilers
- continuously monitor the thermal process and stop it automatically should a problem arise
- optimize oven recipes and quickly develop new recipes without guesswork
- have total process documentation and product traceability
The most common question manufacturers have about the KIC Prophet System is this: with Vertical Ovens being as efficient and dependable as they have become, what purpose does a thermal manager serve?
- The first benefit is that the Prophet is a valuable tool for troubleshooting the entire production line. The common response to a defect or yield problem is to shut down the line. In many companies, it is mandatory that the oven be profiled whenever there is a production problem, and this can take several hours with a Vertical Oven–production time that is usually wasted because the problem is rarely in the oven. The Prophet System will tell you in a fraction of a second whether there is a problem in the oven.
- The second benefit is ISO 9000 documentation. The Prophet records every aspect of the thermal process and saves it automatically.
- The third benefit is specific to the contract assembly industry, where many companies are using the Prophet System as a sales tool to show their corporate clients they have a commitment to quality and the ability to document everything they do for their customers.
- The fourth benefit is to companies manufacturing a variety of products. The Prophet System facilitates the movement of production between assembly lines. Many companies want to run a variety of products in the same oven using the same recipe, and the Prophet System can find that recipe quickly and without guesswork, optimizing production flexibility.
A major manufacturer of electronic components recently installed the KIC Prophet on their Vertical Ovens. They were producing a high value component and had a very long curing process—close to six hours. Because of the high value of their product, they ran a “confirmation” profile once a week, resulting in the loss of a full shift of production capacity every week. After extensive internal testing of the KIC Prophet System, they concluded that the KIC Virtual Profile was so accurate and reliable they could completely eliminate confirmation profiling. They reduced their down-time required for pass-through profiling from one shift a week to a few set-up profiles a year during scheduled maintenance. This is just one example of the opportunities for increased production that users of the KIC Prophet System experience regularly.