Maximum rising slopes and peak temperatures were recorded to confirm temperature stability. The test vehicle then was plunged into a 185 oF (85 oC) hot bath. At 32 oF (0 oC), each channel was verified as functioning accurately. Test vehicle accuracy was established by connecting it to a calibrated datalogger, submerging it into an isothermal bath, and recording the data (figure 1). Combined with strain relief on each thermocouple, this provides a test vehicle capable of more than 200 runs through a reflow oven. In order to attach the thermocouples so all are thermally weighted evenly, the 0.011" thermocouple tips were embedded halfway into the fiberglass laminate. The selected laminate responds quickly to variations in the oven but masks noise typically associated with bare thermocouples. The material of choice proved to be 0.062" thick, Class 1 fiberglass laminate. Several types of thermocouple boards, ranging from copper clad and stainless steel to other materials with exposed thermocouple tips, were tested with a wide variety of effects. The acceptance criteria was as follows: Achieve a peak temperature of 422 oF (217 oC) with a change in temperature (gT) of no more than 4 oC, and provide a time above liquidous (TAL) of 70 sec, +/-5 sec. ![]() The K index is the target values of the process. CPK index is a measure of process capability with a K index. With the hardware in place and the initial testing completed, the CPK index was established. Once selected, the data collection device was used to develop a calibrated test board that responds to even the smallest of variations in the oven. ![]() The first step was to select a data collection device. By implementing a certification program, oven manufacturers can prove the stability and calibration of their ovens for ISO 9001 and customer quality requirements as well as reduce or eliminate process variances between manufacturing lines.įor these reasons, one reflow oven manufacturer initiated a statistical process control (SPC) program to certify oven performance. Oven users want to maximize production and throughput, and they demand assurances about the process repeatability for a specific piece of equipment, or consistency between several machines. ![]() One way to address these issues is to implement a statistical process control (SPC) program to certify an oven's temperature stability and repeatability.
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