REFLOW TRACKER Reflow Temperature Profiles 21
• Locations shaded by large components, i.e. tracks under large quad flat packs
and ball-grid arrays which may require extra time to achieve reflow
temperature. Note that it may be necessary for thermocouple cables to exit
via a hole to the underside of the PCB.
• The underside of double-sided boards.
• Ideally, to ensure profiling is reliable and repeatable, test samples of each
type of PCB with thermocouples permanently attached should be kept
specifically for this purpose.
Due to drying and slight changes in color, the test sample PCB’s thermal
characteristics have a tendency to change slightly each time it passes through the
oven. Any obviously discolored boards should be discarded and replaced.
Probe Attachment
Good thermal contact between probe and product is essential if the probe is to
reflect accurately the product’s temperature. Poor thermal contact will at best
result in slowing the rate at which the product heats the probe, and at worst
prevent the probe achieving the temperature of the element on which it is
mounted.
Good Practice
• Ensure probe tips are clean before attaching them to PCB or component.
• Secure probes along their length to ensure they remain in position, cannot
foul elements in the oven, do not thermally shade the product, and will not
experience excessive temperatures by being too close to heater elements.
• Use glass-fiber insulation when thermocouple cables will be in close proximity
to infrared heating elements or experience temperatures in excess of 260°C.
For further guidance on good practice in thermal profiling – especially
in probe attachment – see the following documents.
• Moisture/Reflow Sensitivity Classification for Nonhermetic Surface Mount
Devices. IPC/JEDEC standard J-STD-020E.
http://www.ipc.org/TOC/IPC-JEDEC-J-STD-020E.pdf
• Guidelines for Temperature Profiling for Mass Soldering (Reflow & Wave)
Processes. IPC-7530A.
http://shop.ipc.org/IPC-7530A-English-D
http://www.ipc.org/TOC/IPC-7530.pdf
• Thermal profiling of electronic assemblies. NPL report MATC(A)50.
http://publications.npl.co.uk/npl_web/pdf/matc50.pdf
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