Fluke Datapaq Reflow Tracker User Manual page 22

Methods of Attachment
The following are the chief methods.
High-melting-point Solder
• Gives best repeatability but difficult to perform.
• Recommended for metal-to-metal attachment.
High-melting-point solder is used to attach thermocouples to the legs of
components and to PCB tracks. It melts far enough above reflow temperature
to ensure that the thermocouple remains in place.
To be successful, any low-melting-point solder must be removed, allowing high-
melting-point solder to be applied directly to the metal to be joined. Use as
little solder as possible, as follows.
1. Remove any low-melting-point solder. Clean the thermocouple then tin it
using high-melting-point solder. Clean the component leg or PCB track to
which the thermocouple will be attached. Tin it using high-melting-point
solder.
2. Solder the thermocouple in place, using as little high-melting-point solder as
is consistent with a satisfactory joint. Ensure the cable lies flat along
the PCB.
SMA Adhesive
• Gives good results.
• Much easier to carry out than soldering, but adhesive needs to be cured.
The best results are obtained as follows.
1. Pre-form the thermocouple cable and hold it in place on the PCB with high-
temperature tape, ensuring that the thermocouple tip is in good contact
with the joint to be measured.
2. Place a small bead of SMA adhesive on the thermocouple tip.
3. Follow the manufacturer's specification to ensure correct curing of the
adhesive: most SMA adhesives are heat-cured and this can be achieved by
running the PCB once through the oven before the first data-collection run.
High-temperature Adhesive Tape
• A temporary means of holding cables in position on the PCB. For one-off
trials only.
• If used in conjunction with aluminum tape, forms a reasonable method of
attachment if high-melting-point solder or SMA adhesive cannot be used.
High-temperature (Kapton) tape is recommended as a means of restraining
thermocouple cables where they run over the PCB (see below) but not of fixing
22
Reflow Temperature Profiles
REFLOW TR ACK ER