Author(s): Dr. Paul Rothe, Creare, Inc., Stephen Dow, Conceptronic, Inc. and Robert Silveri, Conceptronic, Inc.
Thermocouple (TC) usage and operating fundamentals are reviewed. Uncertainty factors associated with the use of thermocouples for device/solder interface temperature profiling are then discussed. Test results are then presented which demonstrate the degree of temperature accuracy possible with the use of various thermocouple types and surface attachment methods. Finally, the many interactive factors associated with product thermal profile derivation in the reflow soldering process are discussed along with strategies for thermal efficiency assessment in SMT reflow ovens.
NOTE: Originally presented at the 1996 Nepcon West Technical Conference
Title: Rework Process for Chip Scale Components
Author: Stanley Kench, Conceptronic, Inc.
The materials and processing issues associated with BGA and Chip Scale packages are discussed. Next, the technical challenges involved with designing semi-automatic single-site soldering/rework stations for this application are discussed. Finally, a soldering/rework process methodology is presented.
Note: Originally presented at the 1996 SMI Trade Conference in San Jose, California
Guidelines for optimum Oven Selection
Author: Stephen Dow
Revision 1, September, 1998
1. Determine the "Baseline" Heating Interval
Using solder paste data sheets, establish the minimum processing interval measured from the beginning of the heating curve to the point where peak temperature is achieved. Typical heating intervals fall between 2.8 and 3.5 minutes. If you are just getting into SMT reflow processing, an interval of "no more than" 3 minutes is recommended. Component heating/cooling requirements should also be considered at this point. Avoid using processing intervals that are longer than 3.5 minutes. They can be misleading.
2. Determine the "Corrected" Conveyor Speed for Various Oven Models
Measure the actual distance from the beginning of the first heating module (i.e., zone) to the end of the last. Divide this by the solder paste processing interval time in minutes and you will get the correct conveyor speed in inches/minute.
Utilization of the correct conveyor speed for all testing is a critical parameter since heat chamber lengths vary tremendously from vendor-to-vendor. Determining a "corrected" value for these differences ensures that you will equally assess heat transfer efficiency, zone profiling capabilities and true production throughput capabilities.
3. Match Customer’s Loading Interval to the Correct Oven Model
Using a "standard" 1 inch/2.54 cm load-spacing between PCB's and the "corrected" conveyor speed from steps #1 and #2, determine which machine model is equal to, or above the actual, board-to-board loading (production) requirements of your process. For example, if a 1-inch spacing cannot be maintained, then the machine is too small for the job. Also, if excessive spacing exists then you may wish to evaluate a smaller model or, enjoy the "excess capacity" you will be purchasing.
4. Compare Actual Heating Efficiency of the Selected Oven Models
Based on the initial screening process described in steps 1-3, your final (and most important) evaluation is to compare actual heating uniformity and repeatability of your finalists. This should be done with, and without load. Also, if a nitrogen will be used then each machines’ thermal capabilities should be studied in both air and nitrogen modes. There should be no difference in performance. Finally, evaluate oxygen level stability under load as well as actual nitrogen consumption.
The optimum oven is the one that possesses the greatest overall performance efficiency in the smallest total length.
Download Reflow Technology Handbook