Ideally, the proximity of a TC to the transport rails should not affect the heating uniformity as compared to one located in the middle of the gap between the rails or at any point in-between. If using the mesh belt, the heating uniformity should not vary across the useable width of the belt. Once the baseline is established, it should not vary between shifts, changes in plant environment, preventative maintenance cycles, etc. Reflow oven profiling can be a slow, costly and painstaking endeavor. Reflow profiles using thermal couples (TCs) can be as useful as ion-chromotography (IC) and strain gauge (SG) testing. However, the incorrect placement of TCs or SGs, or choosing the wrong location to run an IC test, can provide inaccurate results. SG and IC testing will be explored in future blog posts but for now, let's focus on profiling. Reflow is a monolithic process. No matter where a thermal couple (TC) is placed, if the oven is well-constructed, designed, and maintained, the entire assembly will be subjected to the same oven settings. The first step in profiling is to establish a baseline temperature for the oven. At any point of travel within the oven-from entrance to exit-a TC should measure the same temperature from the front of the oven to the back. SiP & Heterogeneous Integration & Assembly (HIA).The Indium Corporation & Macartney Family Foundation.^ a b c d "A Method for Quantifying Thermal Profile Performance"."Taking the Pain Out of Pb-free Reflow" (PDF). ^ Statistical Process Control (SPC) Reference Manual (2 ed.).PWI: Process Optimization Made Simple (PDF). ^ a b c Hall, Jim Zarrow, Phil (February 2002).If the process data plotted on a control chart remains within these specification limits, then the process is considered a capable process, denoted by C ^ p k : External link in |work= ( help) The tolerance values specified by the end-user are known as specification limits – the upper specification limit (USL) and lower specification limit (LSL) respectively. ![]() If the process data plotted on the control chart remains within the control limits over an extended period, then the process is said to be stable. The control limits are set at three standard deviations on either side of the process mean, and are known as the upper control limit (UCL) and lower control limit (LCL) respectively. To help determine the capability of a process, statistically determined upper and lower limits are drawn on either side of a process mean on the control chart. Green blurbs denote that the PWIs are within specification, red depicts out of specification. Process Window Index for a thermal process. To help determine whether a manufacturing or business process is in a state of statistical control, process engineers use control charts, which help to predict the future performance of the process based on the current process. Process capability is the ability of a process to produce output within specified limits. Using PWI values, processes can be accurately measured, analyzed, compared, and tracked at the same level of statistical process control and quality control available to other manufacturing processes. Industrially, these specification limits are known as the process window, and values that a plotted inside or outside this window are known as the process window index. The specification limit is the tolerance allowed for the process and may be statistically determined. PWI measures how well a process fits into a user-defined process limit known as the specification limit. In manufacturing industry, PWI values are used to calibrate the heating and cooling of soldering jobs (known as a thermal profile) while baked in a reflow oven. one which involves heating and cooling, known as a thermal process. Process Window Index ( PWI) is a statistical measure that quantifies the robustness of a manufacturing process, e.g.
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