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September 2023


The Impact of Thermocouple Attachment Methods on Thermal Profiling Accuracy


By Mark Waterman, Mike Hayward, and Oscar Gomez, ECD


parameters are correctly determined and maintained during printed circuit board (PCB) production. Establishing the correct thermal profile


H


to meet solder paste specifications, compo- nent constraints, and equipment capabilities involves the measurement of a product sam- ple. To capture specific temperature meas- urements, thermocouples are attached at strategic points on the PCB and are connect- ed to a thermal profiler that records the data. Measurements are taken, and any required machine setting adjustments are made until satisfactory results are achieved. This may take one profiling operation or several attempts before the specification is reached. Though process control methods for


specification adherence can take many forms, the most common approach is repeat- ed thermal profiling of the product sample used in the initial setup. The product sample is often referred to as the “Golden Sample” or the “Golden Board” and is re-measured peri-


igh-reliability electronics manufactur- ing relies heavily on thermal profiling to ensure reflow soldering process


odically, and results are compared to the baseline profile initially established. Achieving and maintaining accurate


medium that ensures accuracy. Direct sur- face-to-surface contact between the meas- ured solder pad and thermocouple tip is vital. Thermal conductivity should be maximized between the two surfaces and minimized at the mass around the connection. Mechanically, the interface needs to be


strong enough to ensure the thermocouple does not detach throughout the reflow solder- ing process and, in the case of a “Golden Sample,” can withstand storage, handling, and several passes through the process over several months (or even years).


Thermocouple Attachment There are several thermocouple attach-


Figure 1: test vehicle (aluminum tape attachment).


temperature readings is vital at both the ini- tial product profile and subsequent verifica- tion profiles. Precise temperature measure- ments are largely influenced by the method of thermocouple attachment, underscoring the importance of an attachment using a


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ment methods currently used in the electron- ics industry. A recent study set out to better understand the accuracy performance of each of them, draw comparisons, and establish which method performs best against the cri- teria stated above. A set of experiments was designed


specifically to analyze the following thermo- couple attachment methods: high-tempera- ture solder; polyamide (Kapton) tape; alu- minum tape; UV-cured adhesive; and low- temperature cure surface-mount (SMD) adhesive. A PCB was designed and manufactured


with an array of solder pads of differing sizes consistent with a typical SMT product. Holes


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