The solder cycle can be influenced by setting a hold time at the highest temperature point.
- The reflow hold time function organizes a guaranteed time (in seconds) that the oven will remain at the highest temperature set in the curve.
- To achieve this, the oven will keep on heating until the highest temperature in the curve is reached and will then remain there for X seconds as set in the “reflow hold time” parameter.
- After this period is ended the oven will resume the solder curve just after the highest temperature point in the curve and will continue from there.
- This function will assure the user that regardless of the theoretical curve, the oven will do X seconds at the highest temperature set in the curve.
- The reflow hold point is triggered by the value measured by the external sensor.
To compensate for any thermal inertia, the point will be triggered at 8°C less than the value set in the reflow hold time parameter.
Fixing the external sensor correctly so any thermal inertia effect is not extra enforced is a must.
For boards with a very high thermal inertia factor (multi layers with heavy copper) it is recommendable to use the temperature correction factor to compensate for the difference between the furnace sensor and the external sensor (usually +/-20°C). Failing to do so in combination with a bad placement of the external sensor may lead to the sitaution that the temperature measured by the external sensor will not reach the reflow hold temperature, what will lead to a very very long solder curve. This should be avoided.
- Using the reflow hold time requires some experience with the oven and could lead to overheating of the PCB when not correctly used.