Probe Location - Fluke Datapaq Reflow Tracker User Manual

8. Add any additional information that you wish to have recorded with the
profile data.
After this, Insight can be used to analyze the profile data as required.

Probe Location

Whatever the method of heating, the thermal mass of the PCB, its tracks and
the components attached to them significantly influence the time taken for each
physical element to attain a given temperature. Positioning of probes is thus
crucial in ensuring that all key parts of the PCB follow a specified temperature
profile, usually based on data from the solder-paste manufacturer.
Main Considerations
• Large ground planes absorb
more heat and take longer to
achieve reflow temperatures
than narrow tracks.
• Large quad flat packs and ball-
grid arrays absorb a lot of heat;
they are also more susceptible
to damage by thermal shock
than most other components.
• Large surface-mount devices
can shade the tracks to which
they are to be soldered.
• The edges of the PCB heat
more rapidly than the center.
• Is the track density even? If so, the heating may be more uniform; if not,
there may be localized hot and cold spots.
• Is the board double-sided? If so, it may have to go through the oven twice:
the bottom of the board must be kept below reflow temperatures or solder-
ability could be lost, de-wetting experienced, and components could fall off.
• Is it a multi-layer board? If so, it is likely to have more copper and so require
more heat, but it may heat more evenly.
Typical Probe Locations
• Locations likely to achieve the fastest rate of temperature increase, e.g.
board edges and/or locations of components with low thermal mass.
• Locations having a high thermal mass which may require extra time to
achieve reflow temperature.
20
Reflow Temperature Profiles
Probes attached to the PCB and components.
REFLOW TR ACK ER