Process Trials Procedures. Standard trials are often conducted on reflow ovens by production engineers during product assessment, machine approval or in process set-up. The following trials are also used by machine suppliers during equipment development.
Temperature Uniformity. Measure the surface temperature on an assembly or ideally on a blank laminate test board to obtain any variations across the complete conveyor belt width. This will show any peaks or low points between center or near the edge of the conveyor. Test results ideally achieved to be between 5-10*C
Thermal Loading. First a temperature profile is produced as a reference using six thermocouple probes soldered to the assembly, three on the top and three on the bottom. The oven is then thermally loaded with products. Alternatively copper laminate or steel sheets may be substituted to fully load the oven. During loading a further profile is taken to compare the temperatures in this simulated production test. If only top side heating is being considered on the oven all the probes are placed on the top of the board. Test results achieved ideally less than 10-15*C
Temperature Stability. Measuring surface temperature on an assembly or test board checking variations across the complete belt width. Repeating this trial periodically through out the day in production shows an oven's control system even with a varying environment. The test should be run with one set-up but may be run with different board types. Test results achieved ideally less than 10-15*C
Throughput Speed. Adjustments are made to the conveyor speed for the maximum envisaged circuit board throughput requirements. The preferred temperature profile for the most complex product is then the goal. Reference must be made to the paste or adhesive requirements when considering these tests.
Inerting. Evaluating nitrogen usage must be conducted with discussions on existing users of machines for consumption and maintenance. The use of nitrogen has benefits but needs to be justified. Solderability assessment of surface pads is a good measure of the benefits of nitrogen comparing samples before and after reflow in nitrogen.
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