27
Measurement error of reflow checker
③
Temperature drop due to heat absorption by memory unit
When the memory unit of reflow checker passes through the reflow oven, a temperature drop occurs
sometimes in the furnace. The memory unit moves at a position several tens of centimeters in the rear
side of the board to be measured. The temperature of the board is not lowered normally by this
arrangement. However, with a reflow oven having smaller thermal capacity, temperature drop of
maximum several percent may occur inside the furnace. In this case, repeat measurement by
determining the set temperature, display value, and positional conditions across the board to be
measured so that good reproducibility of measurement can be obtained.
A 5m long thermocouple is also available. For ensuring precise control of the reflow oven, it may be
necessary to measure the temperature profile without passing the memory unit for comparison purpose.
(Reference drawing) Arrangement of board and memory unit in reflow oven
Measurement with one board: Ordinary measurement
Dummy board
←
Several tens of cm
→
Board to be
measured
→
→
Measurement with multiple boards: Confirmation of temperature drop in mass production
Dummy board
←
Several tens of cm
→
Board to be
measured
←→
→
Board to board distance in mass production
Measurement with board only: Confirmation of temperature drop by memory unit
Board to be
measured
→
Memory unit
Memory unit
Memory unit